Immunology and Serology MCQs with Answer and Explanations | Chapter 3

Answer: To neutralize the toxin of the pathogen

Tetanus immunization stimulates the production of antibodies that specifically bind to and neutralize the tetanus toxin, preventing it from binding to nerve cells and causing muscle paralysis.

The other options are incorrect:

• To prevent adherence of the pathogen: Tetanus spores can adhere to tissues, but antibodies do not directly prevent this.
• To prevent growth of the pathogen: Tetanus immunization does not target the growth of the bacteria itself, but rather the toxin it produces.
• To opsonize the pathogen (Clostridium tetani): Opsonization is a process where antibodies tag pathogens for phagocytosis by immune cells. While opsonization may occur with tetanus bacteria, the primary function of the antibodies is to neutralize the toxin.

Answer: The vaccine contains live, attenuated rabies virus.

The rabies vaccine used for pre- or post-exposure prophylaxis is an inactivated vaccine. This means the rabies virus in the vaccine has been killed, making it impossible for it to cause rabies.

The other options are incorrect:

• If your patient is bitten by a wild animal (e.g., a skunk) the rabies vaccine should be given: Wild animals are a major carrier of rabies, and vaccination is crucial after a potential exposure.
• The virus in the vaccine is grown in human cell cultures, thus decreasing the risk of allergic encephalomyelitis: Modern rabies vaccines use human or animal cell cultures to grow the virus, minimizing the risk of allergic reactions compared to older vaccines.
• When the vaccine is used for postexposure prophylaxis, rabies immune globulin should also be given: Rabies immune globulin provides immediate protection by introducing antibodies directly, while the vaccine takes time to stimulate the body’s own antibody production.

Answer: Enzymes released by polymorphonuclear cells

When immune complexes are deposited on the glomerular basement membrane, they activate polymorphonuclear cells (a type of white blood cell). These cells release enzymes and other reactive substances that cause inflammation and damage to the membrane.

Incorrect Options:

• Gamma interferon: This cytokine is involved in cell-mediated immunity but doesn’t directly cause damage to the GBM in this scenario.
• Phagocytosis: While phagocytes might attempt to engulf the immune complexes, their primary role here isn’t causing major damage to the GBM.
• Cytotoxic T cells: These cells target virus-infected or cancerous cells. They are not directly involved in immune complex-mediated damage to the GBM.

Answer: They are found on the surface of both B and T cells.

Class II MHC proteins are primarily expressed on antigen-presenting cells (APCs) like macrophages, dendritic cells, and B cells. They are not typically found on the surface of T cells. T cells, in contrast, express class I MHC proteins.

The other options are incorrect:

• They are involved in the presentation of antigen by macrophages: Macrophages are a type of APC that uses class II MHC proteins to present antigens to CD4+ T helper cells.
• They have a high degree of polymorphism: Class II MHC proteins have a high degree of variability, allowing for diverse antigen presentation and immune response.
• They have a binding site for CD4 proteins: Class II MHC molecules have a binding site for CD4 proteins, which are found on the surface of helper T cells, facilitating the interaction necessary for the immune response.

Answer: IL-1

Macrophages are sentinel cells of the innate immune system and play a crucial role in initiating inflammatory responses. IL-1 (specifically IL-1α and IL-1β) are key pro-inflammatory cytokines produced by macrophages in response to various stimuli, like infection or tissue damage.

The other options are incorrect:

• IL-5: This cytokine is primarily produced by T helper 2 (Th2) cells and is involved in promoting eosinophil development and activation, essential for allergic reactions. While macrophages can produce some IL-5, it’s not their major product.
• IFN (Interferon): Interferons are a family of cytokines with antiviral properties. While macrophages can produce some types of interferon, it’s not their defining characteristic.
• IL-7: This cytokine is crucial for T cell development and is mainly produced by thymic stromal cells. Macrophages do not significantly contribute to IL-7 production.

Answer: Tolerance is not antigen-specific (i.e., paralysis of the immune cellsresults in a failure to produce a response against many antigens).

Immunologic tolerance is very specific. It induces a state of unresponsiveness only to the specific antigen the immune system has encountered before. If tolerance were not antigen-specific, the immune system wouldn’t be able to differentiate between harmless and harmful antigens, leading to a state of generalized immunosuppression.

The other options are incorrect:

• Tolerance is more easily induced in T cells than in B cells: This statement can vary depending on the antigen and the specific mechanism of tolerance induction. Both T and B cells can be tolerized.
• Tolerance is more easily induced by simple molecules than by complex ones: This is generally true. Complex antigens with multiple epitopes might be less efficient in inducing tolerance compared to simpler ones.
• Tolerance is more easily induced in neonates than in adults: This statement is correct. The developing immune system in neonates is more susceptible to tolerance induction, which helps establish self-tolerance.

Answer: Alpha interferon

Alpha interferon (IFN-α) is primarily produced by plasmacytoid dendritic cells and other cells in response to viral infections, not by helper T cells. Helper T cells release various other cytokines to modulate immune responses.

The other options are incorrect:

• Interleukin-2 (IL-2): IL-2 is crucial for T cell proliferation and activation, promoting clonal expansion of antigen-specific T cells.
• Interleukin-4 (IL-4): IL-4 is a key cytokine produced by Th2 cells and is involved in humoral immunity, promoting B cell activation and antibody production.
• Gamma interferon (IFN-γ): IFN-γ is a potent immunomodulatory cytokine produced by Th1 cells and activates macrophages, enhances antigen presentation, and has antiviral and anti-bacterial effects.

Answer: Infected by virus A and identical at class I MHC loci of the cytotoxic T cells

Cytotoxic T cells (CTLs) recognize and kill target cells that present specific viral peptides bound to class I MHC molecules. For CTLs induced by virus A, they will specifically target and kill cells infected with virus A that present the viral antigen in the context of the same class I MHC molecules.

Incorrect Options:

• From the same host infected with any virus: Cytotoxic T cells are highly specific and will not kill cells infected with any virus; they target cells presenting a specific viral peptide (virus A) on the correct MHC class I molecules.
• Infected with a different virus and identical at class II MHC loci of the cytotoxic cells: Cytotoxic T cells recognize antigens presented by class I MHC molecules, not class II. Class II MHC molecules are involved in presenting antigens to helper T cells, not cytotoxic T cells.
• Infected with a different virus and identical at class I MHC loci of the cytotoxic cells: Cytotoxic T cells are specific for the antigen they were activated against. They will not kill cells infected with a different virus, even if those cells have the same class I MHC molecules. The antigen presented must match the original antigen (virus A) that induced the CTL response.

Answer: Class II MHC antigens

Helper T cells recognize antigens presented on Class II MHC molecules on the surface of antigen-presenting cells (APCs). This complex of antigen and MHC molecule triggers the activation of the helper T cell.

The other options are incorrect:

• Class I MHC antigens: These molecules present internal antigens to cytotoxic T cells, not helper T cells.
• Gamma interferon: This is a cytokine secreted by activated T cells, not a molecule expressed on APCs.
• IgE: This immunoglobulin is involved in allergic responses, not in antigen presentation to helper T cells.

Answer: Stem cells originating in the bone marrow

A deficiency in both T and B cells suggests a defect in the hematopoietic stem cells originating in the bone marrow, as these stem cells are the precursors to all blood cells, including T and B lymphocytes.

The other options are incorrect:

• The membrane attack complex of complement: A defect in the membrane attack complex (MAC) would affect the complement system’s ability to lyse pathogens but would not directly affect the development of T and B cells.
• T cell–B cell interaction: Defective T cell-B cell interaction would impair the immune response but would not result in the complete absence of both T and B cells.
• The thymus: A defect in the thymus would primarily affect the maturation of T cells, leading to T cell deficiency but not necessarily affecting B cells.

Answer: Cytotoxic

Hemolytic disease of the newborn caused by Rh incompatibility involves the production of maternal IgG antibodies against fetal Rh antigens, leading to the destruction of fetal red blood cells. This process is a classic example of cytotoxic hypersensitivity, where antibodies directed against specific antigens on host cells cause cell destruction.

The other options are incorrect:

• Immune complex: This type of reaction involves immune complexes (antigen-antibody aggregates) causing tissue damage, not direct cell destruction.
• Atopic or anaphylactic: These hypersensitivity reactions involve IgE antibodies and mast cells, leading to allergic symptoms like rashes or airway constriction, not red blood cell destruction.
• Delayed: This type of hypersensitivity involves T cells taking several days to react to an antigen, not immediate attack by antibodies like in HDN.

Answer: Type I

A wheal and flare reaction is characterized by a raised, itchy bump (wheal) surrounded by redness (flare). This is a classic symptom of an immediate allergic reaction mediated by IgE antibodies, which is a hallmark of type I hypersensitivity.

The other options are incorrect:

• Type II Hypersensitivity: This type involves antibodies directly attacking cells or tissues, often leading to cell death. It doesn’t cause wheal and flare reactions.
• Type III Hypersensitivity: This type involves immune complexes (antigen-antibody) depositing in tissues and triggering inflammation. Symptoms can vary and don’t typically include wheal and flare.
• Type IV Hypersensitivity: This type involves T-cell mediated reactions that take longer to develop. It wouldn’t cause the immediate wheal and flare response.

Answer: Slow-reacting substance A (leukotrienes)

Slow-reacting substance A (leukotrienes) is a potent inflammatory mediator released by various cells, including mast cells and eosinophils, in response to allergen exposure. In asthma, leukotrienes play a crucial role in bronchoconstriction, airway inflammation, and mucus secretion, contributing to the persistence of symptoms. Unlike histamine, which can be blocked by antihistamines, leukotrienes are not effectively controlled by these medications.

The other options are incorrect:

• Interleukin-2: Interleukin-2 (IL-2) is a cytokine primarily involved in T cell proliferation and activation. While it plays a role in immune responses, it is not a major mediator of acute allergic reactions like asthma.
• Bradykinin: Bradykinin is a potent vasodilator and increases vascular permeability, leading to edema and pain. It is involved in inflammatory responses but is not the primary mediator in asthma exacerbations.
• Serotonin: Serotonin (5-hydroxytryptamine) is a neurotransmitter and vasoactive substance, but it is not a major mediator in allergic asthma. While it may contribute to certain aspects of inflammation, it is not the primary cause of symptoms in severe asthma.

Answer: Autoimmune hemolytic anemia

Type I hypersensitivity involves allergic reactions mediated by IgE antibodies. It triggers the release of histamine and other inflammatory chemicals, causing immediate symptoms like hay fever, asthma, and anaphylaxis. Autoimmune hemolytic anemia.

The other options are incorrect:

• Hay fever: This is a classic example of type I hypersensitivity caused by allergens triggering an IgE response.
• Extrinsic asthma: This type of asthma is triggered by allergens in the environment, involving IgE antibodies (type I hypersensitivity).
• Anaphylaxis: This is a severe allergic reaction mediated by IgE antibodies, a hallmark of type I hypersensitivity.

Answer: Potentially lethal graft-versus-host disease

Bone marrow transplantation (BMT) in immunocompromised patients offers a chance to rebuild their immune system. However, a major complication is graft-versus-host disease (GVHD). This occurs when the donor’s immune system (graft) attacks the recipient’s body (host), potentially leading to serious illness or death.

The other options are incorrect:

• Inability to use a live donor: While finding a perfectly matched live donor can be challenging, it’s not the biggest hurdle. BMT can also be performed with stem cells from umbilical cord blood or matched unrelated donors.
• High risk of T-cell leukemia: This is a potential risk, but not the most prominent concern with BMT. The conditioning regimen used before transplant can slightly increase leukemia risk, but GVHD remains the bigger threat.
• Delayed hypersensitivity: This type of immune reaction takes longer to develop and is not a direct consequence of BMT. It wouldn’t be the most concerning issue in this scenario.

Answer: It is caused by sensitized CD4-positive T lymphocytes and macrophages invading the joints.

Rheumatoid arthritis is an autoimmune disease characterized by chronic inflammation of the joints. The most accurate statement regarding its pathogenesis is that it is caused by sensitized CD4-positive T lymphocytes and macrophages invading the joints. These immune cells contribute to the inflammatory response, leading to the destruction of joint tissues.

The other options are incorrect:

• Antibody against human IgG-forming immune complexes: This describes type III hypersensitivity, not directly linked to RA.
• Superantigens inducing lymphokines: Superantigens can trigger a strong immune response, but they are not the primary driver in RA.
• Mast cells and IgE: This describes type I hypersensitivity (allergic reactions) and doesn’t play a central role in RA.

Answer: IgE

Type I hypersensitivity, also known as immediate hypersensitivity or allergic reactions, is mediated by immunoglobulin E (IgE). IgE antibodies are produced in response to allergens and bind to mast cells and basophils, sensitizing them to subsequent exposure to the same allergen. Upon re-exposure, these cells release inflammatory mediators, such as histamine, leading to allergic symptoms.

The other options are incorrect:

• IgG (Immunoglobulin G): IgG is the most abundant antibody and plays a role in various immune responses, but it’s not the primary mediator in type I hypersensitivity.
• IgM (Immunoglobulin M): IgM is the first antibody produced in a primary immune response and helps with complement activation, but it’s not involved in type I hypersensitivity.
• IgA (Immunoglobulin A): IgA is found in mucosal surfaces and secretions, protecting against pathogens, but it’s not a key player in type I hypersensitivity.

Answer: Whether the antibody reacts with the antigen on the cell or reacts with antigen before it interacts with the cell

The principal difference between cytotoxic (Type II) and immune complex (Type III) hypersensitivity is whether the antibody reacts with the antigen on the cell surface (Type II) or reacts with the antigen before it interacts with the cell (Type III). In Type II hypersensitivity, antibodies bind to antigens on the surface of host cells, leading to cell destruction or dysfunction.

The other options are incorrect:

• The class (isotype) of antibody: Both types can involve IgG or IgM antibodies, although type II may also involve IgM.
• The participation of complement: Complement is often involved in both types, although it may play a more prominent role in type II.
• The participation of T cells: T cells are not directly involved in either type II or type III hypersensitivity. They are central players in type IV hypersensitivity (delayed hypersensitivity).

Answer: Sensitized T cells

The child’s rapid onset of respiratory distress and unconsciousness after a bee sting suggests an anaphylactic reaction, which is typically mediated by sensitized T cells triggering the release of inflammatory mediators such as histamine from mast cells and basophils.

The other options are incorrect:

• IgG antibody: IgG is involved in type II and type III hypersensitivity, not type I.
• IgM antibody: IgM plays a role in the early immune response but isn’t the primary mediator in type I hypersensitivity.
• Complement: Complement can be activated in type I reactions but works alongside IgE, not as the sole mediator.

Answer: Allotypes are due to genetic polymorphism within a species.

Immunoglobulin allotypes refer to genetic polymorphisms within a species that result in differences in the amino acid sequences of constant regions of immunoglobulin molecules. These differences can affect various aspects of antibody function and can be inherited.

The other options are incorrect:

• Allotypes are confined to the variable regions: Allotypes are found in the constant regions of immunoglobulin chains, not the variable regions, which are responsible for antigen binding specificity.
• Allotypes are found only on heavy chains: Allotypes can be found on both heavy and light chains of immunoglobulins, depending on the specific allotype system.
• Allotypes are determined by class I MHC genes: Class I MHC genes encode proteins involved in antigen presentation to cytotoxic T cells. Allotypes are determined by genes encoding the immunoglobulin chains themselves, not MHC genes.

Answer: To neutralize the toxin of the pathogen

The most critical protective function of antibodies stimulated by tetanus immunization is to neutralize the toxin produced by the bacterium Clostridium tetani. Tetanus toxoid, which is used in tetanus vaccines, stimulates the production of antibodies that bind to and neutralize the tetanus toxin, preventing it from causing the characteristic symptoms of tetanus infection.

The other options are incorrect:

• To opsonize the pathogen (Clostridium tetani): Opsonization can help target the pathogen for phagocytosis, but the primary function in tetanus is to neutralize the toxin it produces.
• To prevent growth of the pathogen: Tetanus immunization doesn’t directly inhibit bacterial growth; its main focus is on the toxin.
• To prevent adherence of the pathogen: Similar to preventing growth, tetanus immunization is more concerned with the toxin’s effects than bacterial adherence.

Answer: Neutralization

Neutralization refers to the process where an antibody specifically binds to a toxin, rendering it inactive and preventing it from causing harm. When antibodies bind to the toxin’s binding sites, they block its ability to interact with target cells and exert its toxic effects.

The other options are incorrect:

• Opsonization: This process involves antibodies coating a pathogen (bacteria, virus) to enhance its recognition and engulfment by phagocytic cells. While it helps eliminate the pathogen itself, it doesn’t directly inactivate toxins.
• Lyophilization: This is a technique for freeze-drying a substance, not a term related to immune response.
• Lysis: This refers to the destruction of a cell, often by the immune system. While some antibodies can trigger lysis in certain scenarios, it’s not the primary mechanism for inactivating toxins.

Answer: the antigen determinant site

An epitope is the specific region on an antigen molecule (foreign substance) that is recognized and bound by an antibody or T cell receptor. It’s essentially the “target” on the antigen that the immune system interacts with.

The other options are incorrect:

• A B-cell: B-cells are lymphocytes that produce antibodies. They are not the target site themselves, but rather the cells that create the antibodies that bind to epitopes.
• An antibody: Antibodies are proteins produced by B-cells that bind specifically to epitopes on antigens. They are not the target site, but rather the molecules that recognize and bind to epitopes.
• A hapten: A hapten is a small molecule that can bind to an antibody but cannot trigger an immune response on its own. While a hapten can be part of an epitope on a larger antigen molecule, it’s not the same as the epitope itself.

Answer: IgA

IgA antibodies are the predominant type of antibody found in breast milk. These antibodies play a crucial role in providing passive immunity to infants, helping to protect them against infections, especially in the gastrointestinal and respiratory tracts.

The other options are incorrect:

• IgG (Immunoglobulin G): While IgG is the most abundant antibody and can be transferred from mother to baby across the placenta, it’s not as prevalent in breast milk.
• IgM (Immunoglobulin M): IgM is the first antibody produced in a primary immune response but is not a major component of breast milk.
• IgD (Immunoglobulin D): IgD is found in low amounts and its function in the immune system is not fully understood. It’s not a significant player in breast milk’s protective effects.

Answer: heavy chain constant region

Isotypes of antibodies refer to the variations in the constant region of the heavy chain of antibodies. These variations determine the functional properties and distribution of different classes of antibodies within the immune system.

The other options are incorrect:

• Light chain variable region: The light chain variable region contributes to antigen binding specificity, but it doesn’t define the antibody isotype.
• Heavy chain variable region: Similar to the light chain variable region, the heavy chain variable region is involved in antigen binding specificity, not isotype classification.
• Light chain constant region: The light chain constant region plays a role in the overall structure and stability of the antibody, but it doesn’t determine the isotype.

Answer: The amount of IgG made in the secondary response is greater than the amount made in the primary response.

In the secondary antibody response, there is a faster and more robust production of antibodies, particularly IgG, compared to the primary response. This is due to the presence of memory B cells, which can quickly differentiate into plasma cells upon re-exposure to the antigen, leading to a more rapid and heightened antibody response.

The other options are incorrect:

• Lag phase is shorter in the primary response: The lag phase is actually longer in the primary response as the immune system encounters the antigen for the first time.
• Antigen processing not required in secondary response: Even in the secondary response, the antigen needs to be processed and presented by antigen-presenting cells (APCs) to activate memory T cells, which then help B cells produce antibodies.
• Memory T cells not produced in primary response: Both memory B and T cells are generated during the primary response. Memory T cells help with a more robust response in the secondary encounter.

Answer: Simultaneous insertion of VH genes adjacent to each CH gene

Isotype switching, also known as class switching, is a process by which B cells change the class of immunoglobulin they produce while maintaining the same antigen specificity. This process involves the successive insertion of a variable heavy (VH) gene adjacent to different constant heavy (CH) region genes, resulting in the production of antibodies with different effector functions but the same antigen specificity.

The other options are incorrect:

• Simultaneous insertion of VH genes adjacent to each CH gene: This wouldn’t be efficient or create a single functional antibody.
• Activation of homologous genes on chromosome 6: Isotype switching doesn’t involve activating new genes on a different chromosome. It utilizes recombination within the existing heavy chain locus on chromosome 14 (in humans).
• Switching of light chain types (kappa and lambda): Isotype switching specifically targets the heavy chain constant region, not the light chain types (kappa and lambda).

Answer: Facilitation of phagocytosis

The most crucial function of antibodies in host defenses against bacteria is to facilitate phagocytosis. Antibodies can opsonize bacteria, marking them for recognition and ingestion by phagocytic cells such as macrophages and neutrophils. This process enhances the efficiency of bacterial clearance by the immune system.

The other options are incorrect:

• Inhibition of bacterial protein synthesis: While some antibodies can target toxins or neutralize bacteria, directly inhibiting protein synthesis within the bacteria is not a common antibody function.
• Activation of lysozyme that degrades the cell wall: Lysozyme is an enzyme that can break down bacterial cell walls, but antibodies don’t directly activate lysozyme.
• Acceleration of proteolysis of exotoxins: Antibodies can neutralize toxins by binding to them, but they don’t directly accelerate the breakdown (proteolysis) of exotoxins.

Answer: Whole cell/ Soluble molecule

In agglutination reactions, the antigen is typically a whole cell, causing the clumping or aggregation of particles. In precipitation reactions, the antigen is a soluble molecule that forms an insoluble complex with its corresponding antibody, resulting in the formation of a precipitate.

The other options are incorrect:

• Protein/Carbohydrate: While both proteins and carbohydrates can be antigens, this distinction isn’t relevant to the type of antigen used in agglutination vs. precipitation reactions.
• Bacterium/ Virus: These can be antigens in both types of reactions, but the key difference lies in the physical state (whole cell vs. soluble molecule) of the antigen.

Answer: Haptens must be processed by CD8+ cells to become immunogenic.

Haptens are small molecules that are unable to induce an immune response on their own but can bind to a carrier molecule (usually a larger protein) to form a complex that becomes immunogenic. This complex can then stimulate an immune response, leading to the production of antibodies specific to the hapten.

The other options are incorrect:

• Hapten binding to antibody: Haptens can bind to the antigen-binding site of an antibody specific for their structure.
• Hapten requiring a carrier for immunogenicity: Haptens alone are too small to be effectively recognized by the immune system. Binding to a carrier protein makes the complex more immunogenic, allowing B cells to be activated and produce antibodies.
• Haptens in allergies: Penicillin and poison ivy rash involve haptens that bind to carrier proteins on skin or other tissues. The immune system then reacts to the hapten-carrier complex, leading to allergic reactions.

Answer: An IgM antibody produced by the same plasma cell that produced the IgG

Idiotypic determinants are unique antigenic determinants present on the variable region of an antibody. An antibody directed against the idiotypic determinants of a human IgG antibody would react with the variable region of an IgM antibody produced by the same plasma cell that produced the IgG antibody. This is because IgM and IgG antibodies produced by the same plasma cell share similar idiotypic determinants due to their common origin.

The other options are incorrect:

• The Fc part of the IgG: The Fc region is the constant region of the antibody and doesn’t contain the idiotypic determinants.
• All human kappa chains: Idiotypic determinants are specific to a particular B cell clone, not all kappa light chains.
• All human gamma chains: Similar to kappa chains, idiotypes are specific and wouldn’t target all human gamma heavy chains.
• An IgM antibody from a different plasma cell: Idiotypic determinants are unique to a B cell clone. An IgM from a different plasma cell wouldn’t share the same idiotype.

Answer: glycoprotein

Immunoglobulins, also known as antibodies, are molecules produced by the immune system that help fight infection. They are complex molecules with both protein and carbohydrate components, making them glycoproteins.

The other options are incorrect:

• Fatty Acid: Fatty acids are simple building blocks of fats and oils. They don’t have the complex structure or function of immunoglobulins.
• Protein: While immunoglobulins are primarily proteins, they also have attached carbohydrates, qualifying them as glycoproteins.
• Carbohydrate: Carbohydrates are sugars and starches. They lack the specific structure and function required of immunoglobulins.

Answer: Super antigen

A super antigen is a type of antigen that binds to a large number of T-cell receptors (TCRs) non-specifically, bypassing the normal antigen presentation process. This overstimulates the immune system, leading to a massive release of inflammatory cytokines and potentially life-threatening conditions.

The other options are incorrect:

• Non-specific antigen: This is a general term for any antigen that doesn’t bind specifically to a single type of immune receptor. Super antigens are a specific type of non-specific antigen with a particularly strong and harmful effect.
• Toxic shock syndrome: This is a severe illness caused by toxins produced by certain bacteria, not by super antigens themselves. Super antigen activation can contribute to toxic shock syndrome in some cases.
• Super necrotic: This term is not commonly used in immunology. It’s possible you might be thinking of “necrotizing fasciitis,” a serious bacterial infection that causes tissue death. Super antigens are not directly related to this condition.

Answer: Are identical except for their CH regions

Both membrane IgM and IgD on a B cell share the same antigen-binding region (variable region, composed of VH and VL domains). This allows them to recognize the same antigen. However, they differ in their constant regions (CH regions), which are responsible for different functions like complement activation (IgM) and B cell signaling (IgD).

The other options are incorrect:

• Have identical heavy chains but different light chains: While immunoglobulins have both heavy and light chains, both IgM and IgD on the same B cell will have identical heavy and light chains responsible for antigen recognition.
• Are identical except for their VH regions: As mentioned above, the variable regions (including VH) are identical between IgM and IgD on the same B cell.
• Have different VH and VL regions: This would result in the B cell recognizing different antigens with its IgM and IgD receptors, which is not the case.

Answer: IgA

IgA, specifically secretory IgA (sIgA), is the most abundant antibody found in body secretions like tears, milk, saliva, and mucus. It plays a crucial role in mucosal immunity, protecting these surfaces from pathogens.

The other options are incorrect:

• IgG: IgG is the most common antibody in the blood, but it’s less prevalent in secretions due to its large size.
• IgE: IgE is primarily involved in allergic reactions and is not typically found in high amounts in secretions.
• IgM: IgM is the first antibody produced in response to infection but is not well-suited for mucosal immunity due to its size and structure.

Answer: Both A V segment and a J segment are preselected by an antigen to make up the and variable-region portion of the gene.

Gene segments encoding the variable region of heavy chains undergo somatic recombination during B cell development to generate a diverse repertoire of antibodies. The selection of V (variable) segments, D (diversity) segments, and J (joining) segments is not antigen-dependent; rather, it is a random process that occurs during B cell maturation in the bone marrow.

The other options are incorrect:

Several J segments and several D segments are available: This is also true. The heavy chain locus contains multiple J and D segments that can be recombined with V segments during B cell development.

Answer: IgG and IgM antibodies

IgG and IgM antibodies are the main host defense against bacterial exotoxins because they can directly neutralize the toxins by binding to them. This prevents the toxins from reaching and damaging host cells.

The other options are incorrect:

• Modulation of host cell receptors in response to the toxin: While some cells can downregulate receptors in response to toxins, this is not the primary defense mechanism.
• Activated macrophages secreting proteases: Macrophages can play a role in engulfing bacteria and clearing debris, but they don’t directly neutralize exotoxins with proteases.
• Helper T cells: Helper T cells are important for coordinating the immune response, but they don’t directly neutralize exotoxins themselves. They can activate B cells to produce antibodies, which are the key to neutralizing exotoxins.

Answer: IL-3

IL-3 (Interleukin-3) is a multilineage cytokine that acts on various hematopoietic cells to stimulate their proliferation, differentiation, and survival. It can influence the development of multiple blood cell lineages, including granulocytes, monocytes, erythrocytes, and megakaryocytes.

The other options are incorrect:

• IL-1: While IL-1 is involved in inflammation and immune response, it primarily affects cells involved in the innate immune system and doesn’t have the same broad effect on multiple hematopoietic lineages like IL-3.
• IL-2: IL-2 is crucial for T cell activation and proliferation, but it doesn’t directly stimulate the development of various blood cell types like IL-3.
• IL-4: IL-4 plays a key role in B cell differentiation and antibody production, but its influence is more specific to the B cell lineage compared to the multilineage effects of IL-3.

Answer: Kohler and Milstein

Georges Köhler and César Milstein are credited with discovering the hybridoma technique in 1975. This technique paved the way for the production of monoclonal antibodies, which have revolutionized various fields of medicine and research.

The other options are incorrect:

• Robert Koch: Robert Koch was a prominent microbiologist known for his work on identifying causative agents of infectious diseases. He did not discover the hybridoma technique.
• ‘D’ Herelle: Félix d’Herelle was a microbiologist who made significant contributions to the field of bacteriophages (viruses that infect bacteria). While his work played a role in the early understanding of immunity, he is not associated with the hybridoma technique.
• Landsteiner: Karl Landsteiner was a pioneering immunologist who discovered the ABO blood group system. He did not discover the hybridoma technique.

Answer: Milstein kohler

Georges Köhler and César Milstein are credited with developing the hybridoma technique in 1975, which revolutionized the field by enabling the production of monoclonal antibodies. These antibodies have become a cornerstone of various medical applications and research.

Incorrect Options:

• Burnet: Sir Macfarlane Burnet was an immunologist who made significant contributions to our understanding of immunological tolerance. While his work is important in immunology, he is not directly associated with the development of monoclonal antibodies.
• Medawar: Sir Peter Medawar was an immunologist who conducted pioneering research on skin grafting and immunological tolerance. Similar to Burnet, his work is relevant to immunology, but not directly tied to the invention of monoclonal antibodies.
• Owen: R.D. Owen is known for his work on discovering immunological tolerance. While relevant to the field, he is not directly associated with the development of the hybridoma technique.

Answer: Edward Jenner

Edward Jenner, a pioneer in the field of immunology, is credited with coining the term “vaccine” in 1798. He derived it from the Latin word “vacca” meaning cow, referencing his work with cowpox to develop the first successful vaccine against smallpox.pen_spark

The other options are incorrect:

• Robert Koch: Robert Koch was a pioneering microbiologist known for his work on bacteriology and the development of Koch’s postulates, which are criteria for establishing the causative relationship between a microorganism and a disease. However, he did not coin the term “vaccine.”
• Pasteur: Louis Pasteur was a French microbiologist renowned for his discoveries in microbiology, immunology, and vaccination. He developed vaccines against diseases such as rabies and anthrax. Pasteur’s work significantly advanced the field of vaccination, but he did not coin the term “vaccine.”
• Needham: John Needham was an English biologist known for his experiments on spontaneous generation and his contributions to cell theory. However, he did not coin the term “vaccine.”

Answer: Elie Metchikoff

Elie Metchnikoff, a Russian zoologist and microbiologist, is credited with discovering the process of phagocytosis in 1882. He observed mobile cells in starfish larvae engulfing foreign material and recognized their role in defending the organism.

The other options are incorrect:

• Paul Ehrlich: Paul Ehrlich was a renowned microbiologist who made significant contributions to immunology, particularly with his work on staining techniques and developing chemotherapy for syphilis. However, he is not associated with the discovery of phagocytosis.
• Joseph Lister: Joseph Lister was a pioneering surgeon who championed the use of antiseptic techniques to prevent surgical infections. While his work is crucial in hygiene and infection control, he is not credited with discovering phagocytosis, a cellular process.
• Louis Pasteur: Louis Pasteur, another prominent figure in microbiology, made significant contributions to vaccines and our understanding of pathogens. However, he is not associated with the specific discovery of phagocytosis.

Answer: Elie Metchnikoff

Elie Metchnikoff, a prominent figure in immunology, proposed the phagocytic theory in 1882. This theory highlighted the role of phagocytes, white blood cells that engulf and destroy foreign invaders like bacteria, as a fundamental defense mechanism in the immune system.

The other options are incorrect:

• Louis Pasteur: Louis Pasteur, a renowned microbiologist, made significant contributions to vaccines and understanding pathogens. While his work is related to immunity, he is not associated with proposing the phagocytic theory.
• Behring: Emil von Behring was a German physician and bacteriologist who shared the Nobel Prize with Metchnikoff in 1908 for their work on immunity. However, Behring’s specific contributions focused on antitoxins and humoral immunity, not the phagocytic theory.
• Widal: Georges-Fernand Widal was a French physician and microbiologist known for developing the Widal test for typhoid fever. While his work is relevant to immunology, he is not credited with proposing the phagocytic theory.

Answer: Parter & Richet

Parter & Richet first observed anaphylaxis during their experiments with sea anemone toxin in 1902.

The other options are incorrect:

• Coombs: Coombs is known for developing the Coombs test, used in blood typing and diagnosing autoimmune hemolytic anemia.
• Gell: Gell is known for the Gell and Coombs classification of hypersensitivity reactions.

Answer: All of these

Histamine, serotonin, and heparin are all primary mediators involved in anaphylaxis. They are released from mast cells and basophils upon exposure to an allergen and contribute to the characteristic symptoms of anaphylaxis, such as vasodilation, bronchoconstriction, and increased vascular permeability.

• Histamine: Histamine is indeed a primary mediator in anaphylaxis, contributing to vasodilation, increased vascular permeability, and bronchoconstriction.
• Serotonin: Serotonin, also known as 5-hydroxytryptamine (5-HT), is released from mast cells and platelets during anaphylaxis, contributing to vasodilation and smooth muscle contraction.
• Heparin: Heparin, an anticoagulant, is released during anaphylaxis and contributes to increased vascular permeability.

Answer: Marrice Arthus

The Arthus reaction is named after French physiologist Maurice Arthus. He discovered this phenomenon in 1903 through experiments where he repeatedly injected rabbits with horse serum.

The other options are incorrect:

• Von Pirquet: Clemens von Pirquet was an Austrian pediatrician known for developing the Pirquet skin test for tuberculosis.
• Richet: Charles Richet was a French physiologist who, along with Paul Portier, discovered anaphylaxis.
• Porter: Paul Portier, alongside Charles Richet, discovered anaphylaxis.

Answer: Von perquit

Serum sickness was first characterized in 1906 by Clemens von Pirquet and Béla Schick, two Austrian pediatricians. They described the reaction in patients who received antisera (blood serum containing antibodies) derived from animals.

The other options are incorrect:

• Maurice Arthus: While Maurice Arthus discovered the Arthus reaction, a localized immune response, it’s different from serum sickness.
• Richet: Charles Richet, along with Paul Portier, discovered anaphylaxis, a different type of hypersensitivity reaction.
• Porter: Paul Portier, alongside Charles Richet, discovered anaphylaxis.

Answer: Both a and b

The hybridoma technique was a groundbreaking discovery in immunology, credited to César Milstein and Georges Köhler. Their research in 1975 established the method for producing monoclonal antibodies.

The other options are incorrect:

• Niel’s Jerne: While Niels Jerne made significant contributions to immunology, particularly the theory of the immune network, he wasn’t directly involved in developing the hybridoma technique.
• None of these: This is incorrect as Köhler and Milstein are acknowledged for this invention.

Answer: Pasteur

The term “vaccine” was coined by Edward Jenner, an English physician, in the late 18th century. It was later popularized by Louis Pasteur, a French microbiologist, who developed vaccines for rabies and anthrax. Pasteur’s work significantly advanced the field of vaccination.

The other options are incorrect:

• Robert Koch: While Robert Koch made significant contributions to microbiology and bacteriology, he did not coin the term “vaccine.”
• Needham: John Needham was an English biologist known for his work on spontaneous generation and cell theory, but he did not coin the term “vaccine.”

Answer: Elie Metchikoff

Élie Metchnikoff (also known as Ilya Ilyich Mechnikov) is credited with discovering the role of phagocytosis in the immune system. In 1882, through his observations of starfish larvae, he identified mobile cells engulfing foreign particles, a process he termed phagocytosis. Metchnikoff’s work laid the foundation for understanding how our bodies defend against invading pathogens.

The other options are incorrect:

• Paul Ehrlich: Paul Ehrlich was a renowned German physician who made significant contributions to immunology, particularly developing staining techniques for blood cells and proposing the “side-chain theory” of antibody function. However, he wasn’t directly involved in discovering the role of phagocytosis.
• Joseph Lister: Joseph Lister was a British surgeon known for his pioneering work in antiseptic surgery. While his discoveries played a crucial role in preventing infections, he didn’t focus on the specific immune response mechanisms like phagocytosis.
• Louis Pasteur: Louis Pasteur was a French microbiologist who made significant contributions to microbiology, immunology, and vaccination. While he developed vaccines and proposed the germ theory of disease, he did not discover the role of phagocytosis.