Immunology and Serology MCQs with Answer and Explanations | Chapter 2

Answer: Lupus erythematosus

Lupus erythematosus is an autoimmune disease where the body attacks its own tissues. This can cause the immune system to produce antibodies that are not specific to syphilis, leading to a false-positive reagin test in syphilis serology.

The other options are incorrect:

• Infectious hepatitis: While some forms of hepatitis can cause false-positive results in some blood tests, they typically don’t affect reagin tests for syphilis.
• Helicobacter pylori: This bacteria is associated with peptic ulcers and doesn’t trigger false-positive reagin tests.
• Pneumonia: While some types of pneumonia can cause a general immune response, they are not known to cause false-positive reagin tests specific to syphilis.

Answer: Confirms the presence of treponemal antibodies

The FTA-AB test detects antibodies specifically against Treponema pallidum, the bacteria that causes syphilis. A reactive test indicates the presence of these antibodies, which suggests current or past infection with syphilis.

The other options are incorrect:

• Indicates the severity of infection: The FTA-AB test is qualitative, meaning it only tells you if antibodies are present, not the severity of the infection.
• Indicates no infection: A reactive FTA-AB test suggests infection.
• Is positive during the chancre stage: While the FTA-AB test can be positive during the chancre stage (the first stage of syphilis with a characteristic sore), it may not always be positive this early. Other tests might be used for initial screening.

Answer: Lupus erythematosus

Lupus erythematosus is an autoimmune disease where the body attacks its own tissues. This can cause the immune system to produce non-specific antibodies that react with the reagin used in syphilis tests, leading to a false-positive result.

The other options are incorrect:

• Infectious hepatitis: While some forms of hepatitis can cause irregularities in some blood tests, they typically don’t affect reagin tests for syphilis.
• Pneumonia: Although some types of pneumonia can trigger a general immune response, they are not known to cause false-positive reagin tests specific to syphilis.
• Helicobacter pylori: This bacteria is associated with stomach ulcers and doesn’t interfere with reagin tests for syphilis.

Answer: Serum protein

Albumin, alpha1, alpha2, beta, and gamma globulin are electrophoretic fractions of serum protein. Electrophoresis is used to separate these protein fractions based on their size and charge, which helps in diagnosing and monitoring various diseases.

The other options are incorrect:

• Serum lipoprotein: Serum lipoproteins are molecules that transport lipids in the blood and are classified into different types such as HDL, LDL, and VLDL, not into albumin or globulin fractions.
• Amino acid: Amino acids are the building blocks of proteins but are not categorized into electrophoretic fractions like albumin and globulins.
• Hemoglobin: Hemoglobin is a protein found in red blood cells that carries oxygen. It has different electrophoretic fractions, such as HbA, HbF, HbS, and HbC, which are distinct from serum protein fractions.

Answer: Alpha-2 globulin and beta globulin

In patients with nephrotic syndrome, there is typically an increase in alpha-2 globulin and beta globulin fractions. This occurs due to the loss of albumin and other low-molecular-weight proteins through the urine, leading to a relative increase in these higher-molecular-weight proteins.

The other options are incorrect:

• Alpha-1 globulin: Alpha-1 globulin is generally not elevated in nephrotic syndrome. Instead, levels of alpha-1 globulin can decrease due to the loss of smaller proteins in the urine.
• Alpha-1 globulin and alpha-2 globulin: While alpha-2 globulin can be elevated, alpha-1 globulin is not typically elevated in nephrotic syndrome. Therefore, this combination is incorrect.
• Beta globulin and gamma globulin: Gamma globulins (immunoglobulins) are generally not elevated in nephrotic syndrome. The increase is more specific to alpha-2 globulin and beta globulin fractions.

Answer: No separation of bound and free antigen is required

Enzyme-multiplied immunoassay techniques (EMIT) differ from other enzyme immunoassays because they do not require a separation step to distinguish between bound and free antigens. This simplifies the assay process and reduces the complexity and time required for testing.

The other options are incorrect:

• Lysozyme is the only enzyme used to label the hapten molecule: This statement is incorrect as various enzymes, not just lysozyme, can be used in enzyme immunoassays, including EMIT.
• Inhibition of the enzyme label is accomplished with polyethyleneglycol: Polyethyleneglycol (PEG) is not specifically used for inhibiting the enzyme label in EMIT. PEG is more commonly associated with other immunoassay techniques for precipitation.
• Antibody absorption to polystyrene tubes precludes competition to labeled and unlabeled antigen: This describes a characteristic of certain solid-phase immunoassays, but it does not specifically pertain to the unique feature of EMIT, which is the lack of a need to separate bound and free antigen.

Answer: B cells

B cells, also known as B lymphocytes, are a type of white blood cell specifically responsible for producing antibodies. These antibodies are proteins designed to recognize and neutralize foreign invaders like bacteria, viruses, and toxins.

The other options are incorrect:

• Killer cells: Killer cells, also known as natural killer (NK) cells, are another type of white blood cell. They directly attack infected cells or cancerous cells but don’t produce antibodies.
• Marrow stem cells: Marrow stem cells are progenitor cells that can differentiate into various types of blood cells, including B cells, but they do not directly secrete antibodies.
• Mast cells: Mast cells are immune system cells involved in allergic reactions and inflammation. They release various inflammatory mediators but not antibodies.

Answer: Constant region of heavy chain

Antibody class and subclass are determined by major physiochemical differences and antigenic variation found primarily in the constant region of the heavy chain. This region defines the type of heavy chain an antibody has (e.g., IgG, IgA, IgM, etc.) and the specific subclass (e.g., IgG1, IgG2).

The other options are incorrect:

• Constant region of light chain: While the constant region of the light chain helps determine the type of light chain (kappa or lambda), it does not determine the antibody class or subclass.
• Variable regions of heavy and light chains: The variable regions of both heavy and light chains are crucial for recognizing and binding to specific antigens. However, they don’t define the antibody class or subclass.
• Constant regions of heavy and light chains: While both heavy and light chains have constant regions, the variations within the heavy chain’s constant region hold more significance for class and subclass determination.

Answer: IgA

The secretory component or transport piece is associated with IgA. This component facilitates the transport of IgA across mucosal surfaces and protects the IgA molecule from degradation in the harsh environment of mucosal secretions.

The other options are incorrect:

• IgD: IgD is not typically associated with a secretory component. It’s found in low concentrations in the bloodstream and plays a role in B cell activation.
• IgE: IgE is involved in allergic reactions and doesn’t require a secretory component.
• IgG: IgG is the most abundant antibody class in the blood and doesn’t have a secretory component. It can move freely throughout the bloodstream and tissues.

Answer: IgE

IgE is the immunoglobulin isotype that binds to mast cells and basophils. When IgE binds to allergens, it triggers these cells to release histamine and other chemicals, leading to allergic reactions.

The other options are incorrect:

• IgG: IgG is the most abundant antibody class in the blood and binds to Fc receptors on various immune cells, but it’s not typically associated with mast cells or basophils.
• IgM: IgM is a large pentameric antibody found in the blood early in the immune response. It doesn’t bind to FcεRI on mast cells or basophils.
• IgD: IgD is found in low concentrations in the blood and plays a role in B cell activation. It’s not known to bind to mast cells or basophils.

Answer: IgE

IgE is the immunoglobulin isotype that is bound to mast cells or basophils. When IgE antibodies encounter allergens, they bind to these cells, triggering the release of histamine and other inflammatory mediators, leading to allergic reactions.

The other options are incorrect:

• IgA:IgA is primarily found in bodily secretions such as saliva, tears, and breast milk, and it plays a role in mucosal immunity. It is not typically associated with mast cells or basophils.
• IgG: IgG, the most abundant antibody class, interacts with various immune cells through Fc receptors, but it’s not typically involved in mast cell or basophil activation through FcεRI binding.
• IgM: IgM is a large pentameric antibody found in the blood early in the immune response. It doesn’t bind to FcεRI on mast cells or basophils.

Answer: All of the above

Phagocytosis is a vital process in the immune system where cells engulf and digest foreign particles, including bacteria, dead cells, and debris. Several cell types are capable of phagocytosis:

• Polymorphonuclear neutrophils: These are the most abundant white blood cells and are the first responders to infections. They are highly phagocytic and play a crucial role in eliminating invading pathogens.
• Monocytes: These monocytes circulate in the blood and then mature into macrophages in tissues. They are actively phagocytic and contribute to inflammatory responses and tissue repair.
• Histiocytes: These are tissue-resident macrophages found in various connective tissues. They play a role in immune surveillance and debris clearance.
• Macrophages: These are mature phagocytic cells derived from monocytes. They are located throughout the body in tissues and organs and are essential for engulfing and digesting foreign material, as well as presenting antigens to activate the adaptive immune response.

Answer: All

IgA is the most abundant antibody found in mucosal secretions and also present in serum. Here’s a breakdown of its presence in the listed options:

• Saliva: IgA is the predominant antibody in saliva, playing a crucial role in protecting the mucosal surfaces of the mouth and throat from pathogens.
• Tears: IgA in tears helps defend the eyes from invading microbes.
• Colostrum: Colostrum, the first milk produced by mothers after childbirth, is rich in IgA antibodies. These antibodies provide essential immune protection for the newborn baby’s developing immune system.
• Serum: While IgA is less concentrated in serum compared to mucosal secretions, it is still present and contributes to the overall humoral immune response.

Answer: IgE

IgE is the immunoglobulin class associated with hypersensitivity or allergic reactions. When an allergen triggers the immune system, IgE antibodies bind to mast cells and basophils, leading to the release of histamine and other inflammatory mediators, which cause the symptoms of allergy.

The other options are incorrect:

• IgA: IgA is another important antibody class but primarily functions in mucosal immunity and isn’t directly involved in triggering allergic reactions.
• IgM: IgM is a large pentameric antibody found in the blood early in the immune response. It’s not associated with allergies.
• IgD: IgD is found in low concentrations and plays a role in B cell activation. It doesn’t participate in allergic reactions.

Answer: IgM

IgM is the most efficient agglutinator among the immunoglobulins. Its pentameric structure allows for the binding of multiple antigens simultaneously, leading to efficient agglutination of pathogens or foreign particles, which enhances their clearance by the immune system.

The other options are incorrect:

• IgG: While IgG antibodies can participate in agglutination, they are not as efficient as IgM due to their monomeric structure.
• IgA: IgA antibodies primarily function in mucosal immunity and are not typically associated with agglutination to the extent seen with IgM.
• IgE: IgE is primarily involved in allergic reactions and has a structure similar to IgG (monomer). It’s not well-suited for agglutination.

Answer: Proteolysis of C4 to C4a and C4b

Proteolysis of C4 to C4a and C4b is mediated only by the classical pathway of the complement system. Both the alternative and classical pathways mediate proteolysis of C3 to C3a and C3b, proteolysis of C5 to C5a and C5b, and the release of anaphylatoxins.

The other options are incorrect:

• Proteolysis of C3 to C3a and C3b Both the alternative and classical pathways mediate the proteolysis of C3 to C3a and C3b, which are essential steps in the complement cascade.
• Proteolysis of C5 to C5a and C5b :Both the alternative and classical pathways mediate the proteolysis of C5 to C5a and C5b, which leads to the formation of the membrane attack complex (MAC) and the release of anaphylatoxins.
• Release of anaphylatoxins: Both the alternative and classical pathways release anaphylatoxins, such as C3a and C5a, which contribute to inflammation and immune responses.

Answer: Neutrophil

Neutrophils are important cellular mediators of immune complex tissue injury. When immune complexes form in tissues, they can trigger the activation of neutrophils, leading to the release of inflammatory mediators and the recruitment of more neutrophils to the site of injury, exacerbating tissue damage.

The other options are incorrect:

• Monocyte: Monocytes can differentiate into macrophages, which phagocytose immune complexes but contribute less directly to tissue injury compared to neutrophils.
• Basophil: Basophils are involved in allergic reactions and contribute to inflammation by releasing histamine. However, they play a minimal role in immune complex-mediated tissue injury.
• Eosinophil: Eosinophils are primarily involved in defense against parasitic infections. While they can be recruited by immune complexes, their role in tissue injury is less significant compared to neutrophils.

Answer: Precipitation

The visible serologic reaction between soluble antigen and its specific antibody is called precipitation. In this reaction, the antigen-antibody complexes form insoluble aggregates that precipitate out of solution, making the reaction visible to the naked eye.

The other options are incorrect:

• Sensitization: Sensitization is the process by which an individual becomes hypersensitive or allergic to a particular antigen upon exposure.
• Agglutination: Agglutination is the clumping together of cells or particles, such as bacteria or red blood cells, due to the binding of antibodies to multiple antigens on their surface.
• Opsonization: Opsonization is the process where antibodies coat a pathogen, making it more recognizable and easier for phagocytes to engulf and destroy. It’s a functional consequence of antigen-antibody binding but not a visible reaction itself.

Answer: Prozone phenomenon

Tubes #1, 2, and 3 showing no reaction while the subsequent tubes show agglutination suggest the prozone phenomenon. In the prozone phenomenon, the antigen-antibody ratio is too high, leading to incomplete lattice formation and inhibiting agglutination. Dilution of the sample would likely resolve this issue.

The other options are incorrect:

• Antigen excess: While antigen excess can cause no agglutination, it would typically be seen in the last few tubes (high dilutions), not the first ones.
• Equivalence: This refers to the ideal antibody:antigen ratio for optimal agglutination, which likely occurred in tubes 4-7 where agglutination was observed.
• Postzone phenomenon: This term is not commonly used in agglutination tests. It’s more relevant in precipitation reactions where very high antibody concentrations can prevent lattice formation necessary for a visible precipitate.

Answer: Indirect fluorescence

The described procedure involves exposing a substrate to the patient’s serum containing antibodies, followed by exposure to a fluorescent antihuman immunoglobulin to detect the presence of specific antibodies. This is known as indirect fluorescence, where the secondary fluorescent antibody binds to the primary antibodies present in the patient’s serum.

The other options are incorrect:

• Fluorescent quenching: This refers to the decrease in fluorescence intensity. It can occur in some scenarios but isn’t the primary purpose of the described procedure.
• Direct fluorescence: Direct fluorescence involves directly labeling the target antigen with a fluorescent tag. In the scenario described, the antigen is not directly labeled with fluorescence.
• Fluorescence inhibition: This technique involves blocking the binding of a fluorescently labelled molecule to its target, leading to a decrease in fluorescence. The described procedure aims to achieve the opposite – visualization of specific binding through fluorescence.

Answer: 1 and 3

The nephelometric determination of immunoglobulin levels involves passing a beam of light through a suspension in a cuvette (Statement 1) and measuring the light that has been scattered as it passes through the suspension (Statement 3). This scattering of light is proportional to the concentration of particles in the suspension, allowing for the quantification of immunoglobulin levels.

The other options are incorrect:

• 2 and 3: Statement 2 (precipitation) is not entirely accurate for nephelometry.
• 4: While nephelometry has a bias towards larger particles, it can detect complexes of varying sizes.
• All: Statement 2 (precipitation) needs clarification as nephelometry measures scattered light by immune complexes, not solely precipitation.

Answer: Indirect

The described rubella enzyme immunoassay uses patient serum, rubella antigen, and an enzyme bound to anti-human gamma globulin. This setup is characteristic of an indirect assay, where the patient’s antibodies (present in the serum) bind to the rubella antigen, and the enzyme-conjugated anti-human gamma globulin is used to detect the bound antibodies.

The other options are incorrect:

• Inhibition: While there’s competition between antibodies, it’s not for inhibiting an enzyme’s activity. It’s for binding sites on the antigen.
• Competitive: This is generally accurate, but indirect ELISAs are a specific type of competitive assay.
• Double antibody: This term can encompass various immunoassay formats, not solely indirect ones.

Answer:

The more specific immunoassay procedure for serum human chorionic gonadotropin (HCG) utilizes antisera against the beta subunit of HCG. The beta subunit is unique to HCG and is used in assays to specifically detect HCG levels in the blood or urine.

The other options are incorrect:

• Alpha: As explained above, the alpha subunit is shared by other hormones and can lead to non-specific binding.
• Gamma: Gamma globulins are a class of antibodies, not a subunit of HCG.
• Chorionic: While “chorionic” refers to the origin of the hormone (placenta), it’s not a specific subunit.

Answer: IgM antibody

The initial immune response following fetal infection with rubella is the production of IgM antibodies. IgM antibodies are the first type of antibodies to be produced in response to a new infection and are typically detected during the acute phase of the illness.

The other options are incorrect:

• IgG antibody: IgG antibodies are produced later in the immune response, during the secondary immune response or after the initial infection has been cleared. They are responsible for long-term immunity.
• IgA antibodies : IgA antibodies are primarily found in mucosal secretions and are not typically the first antibodies produced in response to systemic infections like rubella.
• Both IgG and IgA antibody: While both IgG and IgA antibodies may be produced later in the immune response, IgM antibodies are the first antibodies to be produced during the initial immune response to rubella infection.

Answer: Anamestic response

The rapid rise, elevated level, and prolonged production of antibody following a repeat exposure to antigen is called an anamnestic response. This response occurs due to the memory B cells generated during the primary exposure, leading to a quicker and more robust immune response upon re-exposure to the antigen.

The other options are incorrect:

• Hypersensitivity: Hypersensitivity refers to an exaggerated immune response that can cause tissue damage, not a specific type of antibody production.
• Arthus reaction: This is a localized immune complex-mediated hypersensitivity reaction, not a general term for enhanced antibody production.
• Primary response: The primary response refers to the initial immune response following the first exposure to an antigen. It typically involves a slower and less robust production of antibodies compared to the anamnestic response.

Answer: IgG

Antigenic determinants for the rheumatoid factor (RA factor) are found on the patient’s own IgG antibodies. The RA factor is an autoantibody that binds to the Fc portion of IgG antibodies, forming immune complexes implicated in the pathogenesis of rheumatoid arthritis.

The other options are incorrect:

• IgA: IgA antibodies are not the target antigen for rheumatoid factor.
• IgE: IgE antibodies are primarily involved in allergic reactions, not in RA.
• IgM: IgM antibodies are not the main component targeted by RF in RA.

Answer: Agglutinates gamma globulin coated inert substance

The Rheumatoid Factor (RF) is an autoantibody that agglutinates gamma globulin-coated inert substances. In the context of rheumatoid arthritis, RF specifically reacts with IgG antibodies, forming immune complexes. Detection of RF in serum is a diagnostic marker for rheumatoid arthritis.

The other options are incorrect:

• Agglutinates inert substance: RF doesn’t directly interact with inert substances for agglutination. It requires IgG on the surface.
• Precipitates inert substance: Similar to agglutination, precipitation also wouldn’t occur directly with inert substances.
• Hemolyzes red blood cells: RF doesn’t target red blood cells and wouldn’t cause hemolysis.

Answer: Beef erythrocyte

The heterophile antibody in infectious mononucleosis specifically binds to antigens present on beef red blood cells, but not to those on guinea pig kidney cells. This property is used in differential absorption tests to confirm the diagnosis of mono.

The other options are incorrect:

• Guinea pig kidney: As mentioned above, the heterophile antibody doesn’t bind to guinea pig kidney cells.
• Both: Only beef red blood cells are absorbed by the heterophile antibody.
• Neither: The test relies on the specific absorption of the antibody by beef red blood cells.

Answer: Systemic Lupus Erythematosus

Systemic Lupus Erythematosus (SLE) is associated with autoantibodies to phospholipids, particularly in the form of antiphospholipid antibodies (APLAs). These antibodies can lead to thrombosis, miscarriages, and other complications commonly seen in SLE patients.

The other options are incorrect:

• Rheumatoid Arthritis: While rheumatoid arthritis is an autoimmune disease, the primary target is not phospholipids. It involves autoantibodies targeting components in joints.
• Graves’ Disease: This autoimmune disease affects the thyroid gland and doesn’t involve antibodies against phospholipids.
• Hashimoto’s Disease: Similar to Graves’ disease, Hashimoto’s disease is an autoimmune condition affecting the thyroid, but not phospholipids.

Answer: Cell-mediated immunity

Cell-mediated immunity is the type of immunity mounted against viruses. It involves the activation of cytotoxic T cells, which recognize and destroy virus-infected cells. This response is crucial for clearing viral infections and providing long-term immunity.

The other options are incorrect:

• Innate immunity: While innate immunity plays a role in the initial defense against viruses, it is not specific to viruses and does not involve the activation of lymphocytes like cell-mediated immunity does.
• Second line immunity: “Second line immunity” is not a recognized term in immunology. It is not specific to viruses and does not accurately describe the type of immunity mounted against them.
• General immunity: This is a broad term that doesn’t specify the type of immune response. Both innate and adaptive immunity contribute to general immune function.

Answer: Is absent from the serum

Landsteiner’s law, a cornerstone of the ABO blood group system, states that an individual will not possess antibodies in their plasma (serum) against antigens present on their own red blood cells. This prevents self-agglutination (clumping) of red blood cells.

The other options are incorrect:

• May or may not be present depending on the agglutinogens present: This is incorrect. Landsteiner’s law is a specific principle, not dependent on other factors.
• Is present in the serum: Having antibodies against your own blood cell antigens would lead to agglutination, which is not the case.
• Is present in the blood cells: Antibodies are found in plasma/serum, not within red blood cells.

Answer: Landsteiner

Karl Landsteiner is credited with proposing the most readily acceptable theory of ABO inheritance. His groundbreaking work in the early 20th century led to the discovery of the ABO blood group system, for which he was awarded the Nobel Prize in Physiology or Medicine in 1930.

The other options are incorrect:

• Levine: While Levine made significant contributions to blood group serology, particularly the Rh system, he is not credited with developing the ABO inheritance theory.
• Weiner: Similar to Levine, Weiner also made advancements in blood group identification, especially the Kell system. However, the ABO theory is attributed to Landsteiner.
• Bernstein: Bernstein refined Landsteiner’s ABO inheritance theory by proposing the concept of alleles to explain the observed blood type patterns in offspring. He didn’t propose the initial theory itself.

Answer: Is produced in laboratory animals

Anti-human globulin (AHG) reagent, also known as Coombs’ reagent, is a critical tool in blood bank testing. It’s produced by immunizing animals, typically rabbits, with human antibodies (usually IgG). The animal’s immune system then produces antibodies against these human antibodies.

The other options are incorrect:

• Is produced in humans: Humans wouldn’t develop antibodies against their own antibodies.
• Never detects complement-dependent antibodies: Certain types of AHG reagents can detect antibodies that activate the complement cascade (complement-dependent antibodies).
• Occurs naturally in most humans: AHG does not occur naturally in humans. It’s a laboratory-produced reagent.

Answer: 0.05 mL

A qualitative VDRL (Venereal Disease Research Laboratory) test typically uses a small volume of inactivated serum, around 0.05 mL. This volume is sufficient to react with the VDRL antigen and detect the presence of antibodies against syphilis.

The other options are incorrect:

• 0.10 mL,: This volume is larger than the standard quantity used for the VDRL test, which is 0.05 mL.
• 0.15 mL: This volume is larger than the standard quantity used for the VDRL test, which is 0.05 mL.
• 0.02 mL: This volume is too small and might be insufficient for accurate detection of antibodies.

Answer: Is absent from the serum

Landsteiner’s rule states that an individual will not have antibodies in their plasma (serum) for antigens present on their own red blood cells. This prevents the body from attacking its own cells.

The other options are incorrect:

• May or may not be present depending on the agglutinogens present: This is incorrect because Landsteiner’s rule applies regardless of other agglutinogens (antigens).
• Is present in the serum: This contradicts Landsteiner’s rule and could lead to self-attack by the immune system.
• Is present in the blood cells: Antibodies are found in the blood plasma (serum), not within the red blood cells themselves.

Answer: Confirms the presence of treponemal antibodies

A reactive fluorescent treponemal antibody (FTA-AB) test confirms the presence of treponemal antibodies in the patient’s serum. This test is commonly used to diagnose syphilis by detecting antibodies produced in response to Treponema pallidum, the causative agent of syphilis.

The other options are incorrect:

• Indicates no infection: A reactive test suggests the opposite, a possible current or past infection.
• Is positive during the chancre stage: While often positive during the chancre stage, FTA-ABS may not be positive in the very early stages. Other tests are used for initial screening.
• Indicates the severity of infection: A reactive test doesn’t tell you the severity, only the presence of antibodies. Further evaluation is needed to assess severity.

Answer: High order of specificity

One characteristic of any antigen is its high order of specificity, meaning it can selectively bind to its corresponding antibody or receptor. This specificity allows the immune system to distinguish between self and non-self molecules.

The other options are incorrect:

• Produced by action of antibody: Antigens are not produced by the action of antibodies. Instead, antigens are substances that can stimulate the immune system to produce antibodies.
• High molecular weight: Antigens can have various molecular weights, ranging from small molecules to large proteins. There is no specific requirement for antigens to have a high molecular weight.
• Foreign to animal: While many antigens are foreign to the animal in which they induce an immune response, such as pathogens or non-self molecules, some antigens can be derived from the host’s own tissues (self-antigens). Therefore, being foreign to the animal is not a universal characteristic of antigens.

Answer: Provides humoral immunity

Gamma globulin, also known as immunoglobulin G (IgG), is a major component of the humoral immune response. It plays a crucial role in providing humoral immunity by recognizing and neutralizing pathogens such as bacteria and viruses.

The other options are incorrect:

• Transports glucose: Glucose transport is primarily facilitated by specific transporter proteins in cell membranes, not gamma globulin.
• Regulates body temperature: Body temperature regulation involves complex mechanisms in the hypothalamus, not gamma globulin.
• Performs as fibrinogen for blood coagulation: Fibrinogen is a separate protein essential for blood clotting. It works in a different pathway compared to gamma globulin’s role in immune function.

Answer: Perform a fluorescent treponemal antibody-absorbed (FTA-ABS) test on a specimen of her serum

In a patient with systemic lupus erythematosus (SLE) and a positive serologic test for syphilis (VDRL test), it is important to confirm the diagnosis with a more specific test. The next best step would be to perform a fluorescent treponemal antibody-absorbed (FTA-ABS) test on a specimen of her serum, as it is highly specific for Treponema pallidum, the bacterium that causes syphilis.

The other options are incorrect:

• Reassure her that the test is a false-positive reaction related to her autoimmune disorder: While possible, confirmation with a more specific test is necessary.
• Trace her sexual contacts for serologic testing: This can be considered after a positive FTA-ABS test, but not the first step.
• Treat her with penicillin: Treatment without a definitive diagnosis can be risky.

Answer: The test is rarely positive in primary syphilis.

FTA-ABS is a highly sensitive test for detecting antibodies against Treponema pallidum. While not always positive in the very earliest stages of primary syphilis, it becomes positive relatively soon after infection.

The other options are incorrect:

• The patient’s serum is absorbed with saprophytic treponemes: This is a key step in the FTA-ABS test. Saprophytic treponemes remove non-specific antibodies, increasing the test’s specificity for T. pallidum.
• Once positive, the test remains so despite appropriate therapy: This is true. Even after successful treatment, the body continues to produce antibodies against T. pallidum, resulting in a positive FTA-ABS test.
• The test is specific for Treponema pallidum: This is another advantage of the FTA-ABS test. It has high specificity for T. pallidum, minimizing false positives compared to some other syphilis tests.

Answer: Hepatitis B vaccine

The first vaccine for human use produced using recombinant DNA technology was the Hepatitis B vaccine, specifically the “Recombivax HB” vaccine, approved in 1986. This technology allowed scientists to isolate the specific antigen that triggers an immune response against Hepatitis B without using the whole virus.

The other options are incorrect:

• AIDS vaccine: An effective AIDS vaccine is still under development as of today (May 25, 2024).
• Polio vaccine: The polio vaccine uses a weakened or inactivated form of the poliovirus, not recombinant DNA technology.
• Hepatitis A vaccine: While some Hepatitis A vaccines may use newer technologies, the first ones did not rely on recombinant DNA methods.

Answer: Hepatitis B vaccine

The Hepatitis B vaccine, specifically “Recombivax HB,” was the first vaccine approved for human use in 1986 that was produced using recombinant DNA technology. This technology allowed scientists to isolate the specific antigen that triggers an immune response against Hepatitis B without using the whole virus.

The other options are incorrect:

• Hepatitis A vaccine: While some Hepatitis A vaccines may use newer technologies, the first ones did not rely on recombinant DNA methods.
• Polio vaccine: The polio vaccine uses a weakened or inactivated form of the poliovirus, not recombinant DNA technology.
• AIDS vaccine: An effective AIDS vaccine is still under development as of today (May 25, 2024).

Answer: Corynebacterium diphtheriae

A toxoid vaccine is used to prevent diseases caused by bacteria that produce toxins harmful to the body. Corynebacterium diphtheriae, the bacterium that causes diphtheria, produces a toxin that can lead to severe illness. Vaccination with a diphtheria toxoid vaccine is effective in preventing diphtheria by stimulating the immune system to produce antibodies against the toxin.

The other options are incorrect:

• Haemophilus influenzae: While some strains of Haemophilus influenzae can cause serious illness, there is currently no toxoid vaccine available for this bacteria. Vaccines for Haemophilus influenzae work differently.
• Streptococcus pneumoniae: Similar to Haemophilus influenzae, there is no toxoid vaccine for Streptococcus pneumoniae. Pneumococcal conjugate vaccines are used to prevent infections caused by this bacteria.
• Salmonella typhi: Salmonella typhi causes typhoid fever, and the vaccine for this illness is not a toxoid vaccine. It’s a live attenuated vaccine that uses a weakened form of the bacteria.

Answer: Killed vaccines are safer to give to immunocompromised patients than are live, attenuated vaccines.

Live, attenuated vaccines contain a weakened form of the virus that can replicate slightly in the body. While this mimics a natural infection and often leads to a strong immune response, it can be risky for people with weakened immune systems who might not be able to effectively fight even the weakened virus.

The other options are incorrect:

• Killed vaccines induce a longer-lasting response than do live, attenuated vaccines: In general, live, attenuated vaccines tend to provide longer-lasting immunity compared to killed vaccines.
• Killed vaccines induce a broader range of immune responses than do live, attenuated vaccines: While both types can stimulate an immune response, live attenuated vaccines may trigger a broader immune response because they mimic a natural infection more closely.
• Killed vaccines are no longer used in this country because they do not induce secretory IgA: Killed vaccines are still widely used and offer effective protection against various diseases. They may not induce secretory IgA (an antibody in mucosal secretions) as effectively as some live vaccines, but they still provide valuable immunity.

Answer: Use hyperimmune serum and active immunization

In cases of suspected exposure to rabies virus, such as through animal bites, the recommended approach is to administer both hyperimmune serum (rabies immune globulin, RIG) and active immunization (rabies vaccine). RIG provides immediate passive immunity by delivering pre-formed antibodies against the rabies virus, while the rabies vaccine stimulates the body to produce its own antibodies for long-term protection.

The other options are incorrect:

• Use active immunization only: While vaccination is crucial, it doesn’t provide immediate protection.
• Use hyperimmune serum only: This wouldn’t provide long-term immunity, leaving the person vulnerable if the hyperimmune serum’s effects wear off before they develop their own immunity through vaccination.

Answer: Attenuated

An attenuated vaccine uses a weakened version of a living microbe (virus or bacteria). This weakening process reduces the virulence (ability to cause disease) of the microbe, but it still retains the ability to be recognized by the immune system and stimulate a protective immune response.

The other options are incorrect:

• Denatured: Denaturation refers to the process of altering a protein’s structure, rendering it nonfunctional. While some vaccines may use inactivated components like proteins, these wouldn’t be considered living microbes.
• Dormant: Dormant refers to a state of reduced metabolic activity or temporarily inactive state. Live attenuated vaccines are not dormant; they are actively replicating but with reduced virulence.
• A toxoid: Toxoids are inactivated toxins derived from bacteria. They train the immune system to fight the toxin, not the live bacteria itself.

Answer: gp l20

To prevent the attachment of HIV to helper T lymphocytes, targeting the gp120 molecule would be a logical goal. gp120 is a glycoprotein present on the surface of the HIV envelope. It binds to the CD4 receptor on helper T cells, facilitating viral entry into the cell. By targeting gp120, the goal would be to disrupt this binding interaction and prevent viral attachment and entry into host cells.

The other options are incorrect:

• gp41: While gp41 is another envelope glycoprotein, it plays a role in viral fusion with the host cell membrane after attachment mediated by gp120.
• p24: This is the capsid protein that forms the core of the HIV virion. It wouldn’t be ideal for preventing attachment to T cells.
• Nucleocapsid protein: Similar to p24, the nucleocapsid protein is an internal component of the virus and wouldn’t directly hinder attachment.

Answer: The immunogen in the vaccine is killed rubella virus.

The rubella vaccine uses a weakened (attenuated) form of the rubella virus, not a killed virus. This weakened virus can replicate slightly but is unable to cause disease. It stimulates the immune system to develop immunity without causing illness.

The other options are incorrect:

• The vaccine prevents reinfection, thereby limiting the spread of virulent virus: Vaccination can significantly reduce the risk of reinfection, limiting the spread of the virus in the population.
• The incidence of both childhood rubella and congenital rubella syndrome has decreased significantly since the advent of the vaccine: This statement is true. Rubella vaccination programs have been highly successful in reducing the incidence of both childhood rubella and congenital rubella syndrome.
• The vaccine induces antibodies that prevent dissemination of the virus by neutralizing it during the viremic stage: Vaccination does induce antibodies that neutralize the virus, preventing its spread throughout the body during the viremic stage (when the virus is present in the bloodstream).

Answer: Immunization with tetanus toxoid induces effective protection against tetanus toxin.

Tetanus toxoid is a vaccine that specifically targets the toxin produced by Clostridium tetani, the bacteria that causes tetanus. Vaccination stimulates the immune system to produce antibodies that can neutralize the toxin, preventing the severe muscle spasms and lockjaw characteristic of tetanus.

The other options are incorrect:

• Antitoxin against tetanus protects against botulism as well, because the two toxins share antigenic sites: Tetanus and botulism toxins are different, and antibodies against one won’t necessarily protect against the other.
• The toxoid vaccine against Clostridium difficile infection should be administered to immunocompromised patients: There is currently no commercially available toxoid vaccine for Clostridium difficile infection. Vaccination research for C. difficile is ongoing, but it’s not yet a routine practice.
• Vaccines containing alpha toxin (lecithinase) are effective in protecting against gas gangrene: While alpha toxin (lecithinase) is a component produced by some clostridial species, vaccines for gas gangrene typically target a combination of toxins produced by different clostridia involved in gas gangrene, not just alpha toxin alone.

Answer: 56 C for 30 min

The accepted and recommended time and temperature for heat inactivation of serum is 56°C for 30 minutes. This effectively inactivates complement proteins in the serum that could interfere with downstream applications like cell culture experiments.

The other options are incorrect:

• 25 C for 1 hour: This temperature is too low to effectively inactivate complement proteins.
• 37 C for 30 min: This temperature is closer to physiological body temperature and may not completely inactivate complement.
• 56 C for 10 min: While 56°C is the correct temperature, 10 minutes might not be sufficient for complete inactivation, especially for larger volumes of serum.