Immunology and Serology MCQs with Answer and Explanations | Chapter 4

Answer: All of these

Interferon isn’t produced by just one type of cell in the body. Various cell types, including lymphocytes, lymphoblasts, and fibroblasts, can all be triggered to create interferon in response to viral threats.

• Lymphocytes (While lymphocytes can produce interferon, it’s not the only source.)
• Lymphoblasts (Similar to lymphocytes, lymphoblasts are capable of producing interferon, but not exclusively.)
• Fibroblasts (Fibroblasts are one type of cell that can create interferon, but other cell types can as well.)

Answer: All of these

Virulence-determining antigens, molecules that contribute to a microorganism’s ability to cause disease, can be formed from various types of biomolecules.

• Proteins and polysaccharides: These are the most common types of virulence antigens. Proteins can bind to host cells, aid in invasion, or act as toxins. Polysaccharides can form capsules that shield the microorganism from the immune system.
• Carbohydrate-protein complexes: These combine the properties of both proteins and polysaccharides, offering diverse functions like adhesion and immune evasion.
• Polysaccharide-phospholipid-protein complexes: While less common, these complex structures can contribute to virulence by acting as capsules or facilitating adherence to host cells.

Answer: None of these

Neither Kohler nor Coons were the first to observe fluorescence. Fluorescence is a much older phenomenon with observations dating back to the 1800s.

The other options are incorrect:

• Kohler: Heinrich Kohler was a German physicist who made significant contributions to microscopy, including the development of the Köhler illumination technique. However, he wasn’t the first to observe fluorescence.
• Coons: Albert Coons was an American immunologist who pioneered immunofluorescence microscopy, a technique that uses fluorescence to visualize specific molecules in biological samples. While Coons played a crucial role in developing fluorescence applications, he didn’t discover the phenomenon itself.

Answer: Coons

The fluorescent antibody technique (FAT) utilizes the property of fluorescence to visualize specific antigens or antibodies in a sample. Albert Coons, an American immunologist, is credited with developing this technique in the 1940s.

The other options are incorrect:

• Kohler: As mentioned earlier, Heinrich Kohler was a physicist who made advancements in microscopy but wasn’t involved in the development of FAT.
• Both a and b: Neither Kohler nor Coons were the sole developers of FAT. While Coons played a key role, it wasn’t a collaborative effort with Kohler.
• None of these: Based on historical records, Albert Coons is recognized as the primary developer of the fluorescent antibody technique.

Answer: All of these

Phagocytes are a diverse group of white blood cells that specialize in engulfing and destroying foreign particles, bacteria, and dead or dying cells. Here’s a breakdown of the listed options:

• Monocytes: These are large, immature phagocytes that circulate in the bloodstream before migrating into tissues and maturing into macrophages.
• Macrophages: These are mature phagocytes found in tissues throughout the body. They are highly efficient at engulfing and digesting foreign material.
• Basophils: Unlike monocytes and macrophages, basophils are not primary phagocytes. Their main function is involved in allergic reactions and inflammation.

Answer: Phagosome

When a phagocyte encounters a foreign particle, it engulfs it by extending its cell membrane around it. This creates a membrane-bound sac called a phagosome that holds the engulfed material.

The other options are incorrect:

• Lysosome: Lysosomes are membrane-bound organelles within the phagocyte that contain digestive enzymes. Once the phagosome fuses with a lysosome, it forms a phagolysosome, where the engulfed material is broken down.
• Both a and b: While the engulfed material eventually ends up in a phagolysosome formed by the fusion of a phagosome and lysosome, initially it resides in the separate phagosome.
• None of these: A phagosome is a well-defined stage in the phagocytosis process where the engulfed material is contained within the phagocyte’s membrane.

Answer: All of these

This fusion creates a highly destructive environment to break down foreign particles and pathogens. Here’s why all the options are considered toxic products within a phagolysosome:

• H2SO4 (Sulfuric Acid): While not as concentrated as pure sulfuric acid, lysosomes contain a low pH environment with enzymes that function best in acidic conditions. This acidic environment itself can be detrimental to microorganisms.
• Singlet O2 (Singlet Oxygen): During the respiratory burst, a process triggered by phagocytosis, reactive oxygen species (ROS) like singlet oxygen are produced. These highly reactive molecules can damage proteins, lipids, and nucleic acids of engulfed microbes.
• Superoxide radicals: Similar to singlet oxygen, superoxide radicals are also generated during the respiratory burst. These free radicals contribute to the microbicidal activity within the phagolysosome.

Answer: None of these

During the destruction of antigen particles in the phagolysosome, the primary products formed are reactive oxygen species (ROS) and various enzymes that degrade the antigens. Acetic acid, lactic acid, and citric acid are not typically produced during this process.

The other options are incorrect:

• Acetic acid: This acid is a product of bacterial fermentation. While some bacteria might produce it within a phagolysosome, it’s not the main purpose of the compartment.
• Lactic acid: Similar to acetic acid, lactic acid is produced by some cells during anaerobic respiration. It wouldn’t be a significant breakdown product in a phagolysosome.
• Citric acid: This acid is a key intermediate in the citric acid cycle, a metabolic pathway for energy production. The focus within a phagolysosome is on degradation, not energy generation.

Answer: Opsonisation

Opsonisation is a crucial process in the immune system where specific molecules (opsonins) coat pathogens (like bacteria) to make them more recognizable and easier for phagocytes to engulf. This coating bridges the gap between the negatively charged surfaces of both the phagocyte and the bacteria, allowing for efficient phagocytosis.

The other options are incorrect:

• Agglutination: Agglutination refers to the clumping of particles, such as bacteria, due to the presence of antibodies. While opsonisation can sometimes lead to agglutination, it’s not the primary purpose. The main goal of opsonisation is to enhance phagocytosis.
• CFT: CFT (Complement Fixation Test) is a laboratory test used to detect antibodies or antigens in a sample. It doesn’t directly involve the opsonisation process that occurs within the body.
• None of these: Opsonisation is a well-established concept in immunology, playing a vital role in eliminating pathogens through phagocytosis.

Answer: Serum component

Opsonins are molecules found in the serum that bind to pathogens and enhance their recognition and ingestion by phagocytes. These include antibodies and complement proteins, which are crucial for the opsonization process.

The other options are incorrect:

• Cellwall component: Cell wall components are structural parts of a cell’s outer layer, particularly in bacteria, fungi, and plants. They are not involved in the opsonization process.
• Plasma component: Plasma is the liquid portion of blood that contains various proteins, electrolytes, and other substances. While plasma does contain components involved in immunity, opsonins are specifically part of the serum.
• Cytoplasm component: The cytoplasm is the internal fluid of a cell where metabolic processes occur. Opsonins are not cytoplasmic components; they operate outside cells in the serum.

Answer:6 – 9 months

Cholera vaccination provides protection against cholera for a period ranging from 6 to 9 months. The effectiveness gradually declines after this period, making booster shots necessary for continued immunity.

The other options are incorrect:

• 1 – 3 months: Cholera vaccine protection lasts longer than 1-3 months.
• 3 – 6 months: While some protection may exist after 3 months, the recommended protection window is 6-9 months.
• 9-12 months: While some immunity might last up to 12 months, the optimal protection window is 6-9 months.

Answer: All of these

Cholera is a serious diarrheal illness caused by contaminated water and poor sanitation. A multi-pronged approach is crucial for effective cholera prophylaxis (prevention). This includes:

• Protected water supply: Ensuring access to clean, safe drinking water is essential to prevent cholera transmission.
• Environmental sanitation: Proper sewage disposal and hygiene practices help stop the spread of the bacteria causing cholera.
• Immunisation with oral cholera vaccines: Vaccination offers additional protection, although it’s not 100% effective and should be combined with other preventive measures.

Answer: Indicated delayed hypersensitivity test

The lepromin test is a delayed hypersensitivity skin test used to assess an individual’s immune response to Mycobacterium leprae, the bacterium that causes leprosy. A positive reaction typically indicates a cell-mediated immune response and is used to classify leprosy into different forms.

The other options are incorrect:

• Is negative in tubercular leprosy: In tuberculoid leprosy, the lepromin test usually produces a strong positive reaction due to the individual’s robust cell-mediated immune response against the bacteria.
• Positive in lepromatous type: In lepromatous leprosy, the lepromin test typically produces a negative or weakly positive reaction due to the individual’s impaired cell-mediated immune response.
• Indicates infection: While a positive lepromin test can indicate exposure to M. leprae, it does not necessarily indicate active infection. It primarily reflects the individual’s immune response to the bacterium.

Answer: Brucella

The prozone phenomenon is a specific antigen-antibody reaction where an excess of antibodies can hinder clumping (agglutination) during some diagnostic tests. Brucella is a bacterium well-known to exhibit the prozone phenomenon in agglutination tests used for diagnosis of brucellosis.

The other options are incorrect:

• A typical mycobacteria: Mycobacteria generally don’t exhibit the prozone phenomenon in diagnostic tests.
• Streptococcus: Streptococcus bacteria typically don’t show the prozone effect in agglutination tests.
• Bordetella pertussis: While some studies suggest a possibility, the prozone phenomenon isn’t well-established with Bordetella pertussis. There’s limited evidence for the prozone effect in diagnosing whooping cough caused by this bacterium.

Answer: Reverse transcriptase

Reverse transcriptase is an enzyme used by HIV to convert its RNA genome into DNA, which is then integrated into the host cell’s genome. Detection of reverse transcriptase activity or the presence of HIV RNA or DNA in the blood is indicative of HIV infection.

The other options are incorrect:

• DNA polymerase: While DNA polymerase is an essential enzyme for DNA replication, it’s not specific to HIV. Our own cells also use DNA polymerase for various functions. HIV doesn’t rely on the host cell’s DNA polymerase for its replication.
• RNA polymerase: RNA polymerase is an enzyme involved in RNA synthesis, but it’s not specific to HIV. Human cells use RNA polymerase for various purposes. HIV doesn’t require the host cell’s RNA polymerase for its replication cycle.
• None of these: Among the listed options, reverse transcriptase is the most specific marker for HIV infection.

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Answer: Western blot

The Western blot test is considered the gold standard for confirming HIV infection. It detects antibodies to specific HIV proteins and is highly specific, able to differentiate between HIV-1 and HIV-2, as well as distinguish true positive results from false positives that may occur with screening tests like ELISA.

The other options are incorrect:

• ELISA: While a valuable screening tool, ELISA can have false positives and needs confirmation with a more specific test like Western blot.
• Immunoelectrophoresis: This is not a specific test for HIV diagnosis.
• IHA: IHA has limitations in specificity and sensitivity compared to Western blot for HIV diagnosis.

Answer: Window period

The window period refers to the timeframe between HIV infection and when a blood test can reliably detect the virus. During this period, the body is developing antibodies against HIV, but the levels might not be high enough for a test to pick them up.

The other options are incorrect:

• Intrinsic period: This term isn’t typically used in the context of HIV infection.
• Incubation period: The incubation period refers to the time between exposure to a virus and the development of symptoms. In HIV infection, symptoms may not appear for years, but the window period specifically focuses on antibody development.
• None of these: The window period is a well-established concept in HIV testing.

Answer: ELISA test

ELISA (Enzyme-Linked Immunosorbent Assay) is the primary screening test for HIV/AIDS. It detects the presence of antibodies to HIV in the blood. If the ELISA test is positive, it is usually followed by a confirmatory test like the Western blot to verify the result.

The other options are incorrect:

• Western blot test: While the Western blot test is used to confirm HIV infection, it is not typically used as a screening test due to its higher cost and complexity compared to ELISA.
• Both a and b: This option suggests that both the Western blot and ELISA tests are used as screening tests for AIDS. While both tests are used in HIV diagnosis, ELISA is the primary screening test, and Western blot is the confirmatory test.
• VDRL test: The VDRL (Venereal Disease Research Laboratory) test is used to detect syphilis, not HIV/AIDS. It is not a screening test for AIDS.

Answer: Western blot test

The Western blot test is the confirmatory test for HIV/AIDS. It is used to confirm the presence of antibodies to HIV after a positive result from an initial screening test like ELISA. Western blot is highly specific and helps to rule out false-positive results.

The other options are incorrect:

• ELISA test: As mentioned earlier, ELISA is a screening test, not a confirmatory one for HIV.
• Karpas test: This test is used to diagnose syphilis, a different sexually transmitted infection (STI), and not for HIV confirmation.
• Fujerbio test: This isn’t a recognized standard test for HIV confirmation. There are various rapid tests available, but Western blot remains the most reliable confirmatory method.

Answer: CD4 lymphocytes

During AIDS, HIV primarily infects and destroys CD4 lymphocytes, also known as helper T cells. These cells play a crucial role in coordinating the immune response. HIV targets CD4 lymphocytes, weakening the immune system and making the individual susceptible to opportunistic infections.

The other options are incorrect:

• CD3 lymphocytes: While CD3 proteins are present on the surface of T lymphocytes (including CD4 and CD8 cells), HIV doesn’t directly target CD3. It needs the CD4 receptor for entry into the host cell.
• CD2 lymphocytes: CD2 lymphocytes are a less common type of T cell not specifically targeted by HIV.
• B-lymphocytes: B-lymphocytes are another type of white blood cell that produce antibodies. While HIV can indirectly affect B-cell function, it doesn’t directly infect them.

Answer: BCG

BCG (Bacille Calmette-Guérin) vaccine is used to prevent serious complications of tuberculosis (TB) infection. It contains a weakened (attenuated) form of a live bacterium related to, but not the same as, the one that causes TB.

The other options are incorrect:

• TAB: This vaccine protects against typhoid fever caused by Salmonella typhi bacteria. It’s a heat-killed (inactivated) vaccine, not a live attenuated one.
• Polio: There are two types of polio vaccines: inactivated poliovirus vaccine (IPV) and oral poliovirus vaccine (OPV). IPV is a killed vaccine, while OPV is a live attenuated vaccine. However, due to the risk of rare vaccine-associated polio cases, most countries, including the US, have transitioned to using only IPV.
• Cholera: The cholera vaccine is also an inactivated vaccine, meaning it uses killed cholera bacteria instead of a live attenuated form.

Answer: Acute infection

A rise in anti-HBc immunoglobulin (antibody to hepatitis B core antigen) in a patient typically indicates acute infection with the hepatitis B virus. This antibody becomes detectable during the early stages of infection and persists throughout the course of the infection.

The other options are incorrect:

• Carrier state: The carrier state for hepatitis B refers to individuals who have been infected with the virus for a prolonged period but continue to harbor the virus without symptoms. A rise in anti-HBc immunoglobulin is not typically associated with the carrier state.
• Prodromal phase: The prodromal phase, also known as the pre-icteric phase, occurs before the onset of symptoms in acute hepatitis B infection. A rise in anti-HBc immunoglobulin is typically observed during acute infection but not specifically during the prodromal phase.
• Convalescence: The convalescent phase occurs after the acute phase of illness when the patient begins to recover. During this phase, anti-HBc immunoglobulin levels may start to decline as the infection resolves. Therefore, a rise in anti-HBc immunoglobulin is not characteristic of the convalescent phase.

Answer: The time lapse between the infection and detection of viral antibodies

The window period in HIV infection refers to the time between when someone contracts HIV and when a blood test can reliably detect the virus. During this period, the body is developing antibodies against HIV, but the levels might not be high enough for a test to pick them up. This can range from a few weeks to several months.

The other options are incorrect:

• The time lapse between the infection and development of AIDS: This period can take years, and a blood test can still detect HIV long before a person develops AIDS.
• The time lapse between obtaining the sample and detection of virus in the lab: This is typically a much shorter timeframe, usually a matter of days, not months. Modern HIV tests are very efficient.
• None of the above: The window period is a well-established concept in HIV testing. It’s crucial to consider this window when interpreting negative HIV test

Answer: Rabies

Rabies is a deadly viral infection of the nervous system. Once symptoms develop, the disease is almost invariably fatal. However, there is a highly effective post-exposure prophylaxis (PEP) regimen involving rabies vaccination and sometimes rabies immune globulin (RIG) that can prevent the virus from causing rabies if administered promptly after exposure (bite or scratch from an infected animal).

The other options are incorrect:

• Poliomyelitis: Polio vaccines are administered before exposure to prevent polio infection.
• Influenza: Influenza vaccines are given before the influenza season to provide protection against circulating influenza strains.
• Herpes: There is no vaccine that prevents herpes infection, only medications to manage outbreaks.

Answer: High infectivity

The presence of Hepatitis B e antigen (HBeAg) in patients with hepatitis B infection indicates high viral replication and high infectivity. It suggests that the patient is actively producing and shedding the hepatitis B virus, making them more likely to transmit the infection to others.

The other options are incorrect:

• Simple carriers: Simple carriers typically do not have active viral replication or high levels of infectivity. They may harbor the virus without symptoms but do not exhibit high levels of viral replication.
• Late convalescence: Late convalescence refers to the recovery phase of hepatitis B infection when viral replication decreases and liver function improves. The presence of HBeAg indicates active infection, not late convalescence.
• Carrier status: Carrier status may refer to individuals who harbor the virus without exhibiting symptoms, but the presence of HBeAg suggests active viral replication and high infectivity, rather than carrier status alone.

Answer: HBeAg

Hepatitis B e antigen (HBeAg) is a marker of active viral replication and high infectivity of the hepatitis B virus in humans. Its presence in the blood indicates that the virus is actively replicating and the individual is highly infectious.

The other options are incorrect:

• HBcAg (Hepatitis B core antigen): HBcAg indicates current or past infection with hepatitis B, but it doesn’t necessarily mean the person is infectious. It can be present in both acute infection and chronic carriers.
• Anti-HBc (Antibody to Hepatitis B core antigen): The presence of Anti-HBc indicates past or resolved hepatitis B infection or vaccination. A positive Anti-HBc test doesn’t necessarily mean the person is currently infectious.
• Anti-HBs (Antibody to Hepatitis B surface antigen): A positive Anti-HBs test indicates immunity to hepatitis B infection, either through vaccination or past infection with recovery. This is a good sign and suggests the person is not currently infectious.

Answer: IgM anti – HBc

During the window period of hepatitis B virus (HBV) infection, when HBsAg may not yet be detectable, serologic evidence of recent infection can be seen through the presence of IgM antibodies to hepatitis B core antigen (anti-HBc). IgM anti-HBc typically appears early in acute HBV infection and indicates recent exposure to the virus.

The other options are incorrect:

• HBs Ag (hepatitis B surface antigen): HBsAg is usually detectable during the acute phase of infection but can be negative in the window period.
• Anti-HBs (antibodies against hepatitis B surface antigen): Anti-HBs develop later in the course of infection and are not typically present during the window period.
• None of the above: While the other options may not be present during the window period, IgM anti-HBc is a crucial indicator of recent infection.

Answer: Interferon production

Interferon is a key molecule produced by host cells in response to viral infection. It plays a crucial role in the body’s antiviral defense mechanism by signaling to nearby cells to increase their defenses against viral replication. This mechanism is not typically a significant part of the bacterial response.

The other options are incorrect:

• Toxin production: While both bacteria and viruses can produce toxins, it’s not the defining difference in their actions. Many bacteria produce toxins that contribute to their pathogenic effects, but some viruses can also cause damage through toxins.
• Lymphocytes production: Lymphocytes are white blood cells involved in the adaptive immune response to both viruses and bacteria. While they play a vital role in fighting both types of infections, their production isn’t specific to just viral action.
• Neutrophils production: Neutrophils are phagocytic white blood cells that primarily engulf and destroy bacteria. While they can be involved in the early stages of some viral infections, their role is more prominent in bacterial defense.

Answer: 4 weeks

Seroconversion in HIV infection refers to the period when the body develops antibodies detectable by an HIV antibody test. This process typically takes weeks, not months. While there can be some variation, on average, seroconversion occurs within 4 weeks after exposure to HIV.

The other options are incorrect:

• 2 weeks: While some individuals might develop antibodies sooner, 2 weeks is on the shorter end of the spectrum.
• 9 weeks: This falls within the possible range, but 4 weeks is a more typical timeframe.
• 12 weeks: 12 weeks is on the longer end of the window for seroconversion. It’s important to get tested after a potential exposure, but most people will see seroconversion within a shorter timeframe.

Answer: ELISA

The diagnosis of HIV infection is typically made through serological testing, such as ELISA (Enzyme-Linked Immunosorbent Assay), which detects antibodies to HIV in the blood. ELISA is often used as the initial screening test for HIV infection due to its high sensitivity and specificity.

The other options are incorrect:

• Western blot: Western blot is a confirmatory test used to validate the results of ELISA. It is not typically used as the initial diagnostic test for HIV but rather as a follow-up test to confirm positive ELISA results.
• P24 antigen: The P24 antigen test detects the presence of the HIV-1 capsid protein (p24 antigen) in the blood. While it can be used for early detection of HIV infection, it is not as commonly used as ELISA for initial diagnosis.
• Lymph node biopsy: Lymph node biopsy may be performed to investigate the cause of lymphadenopathy (swollen lymph nodes) in HIV-infected individuals, but it is not a primary diagnostic test for HIV infection. Serological tests like ELISA are used for HIV diagnosis.

Answer: Resistance to hepatitis B

The presence of anti-HBs antibodies (HBsAB) indicates immunity to hepatitis B virus (HBV) infection. These antibodies develop either after successful vaccination against HBV or as a result of past infection. Anti-HBs antibodies provide protection against future HBV infection.

The other options are incorrect:

• Acute infection: This refers to the initial stage of a hepatitis B infection, where the virus is actively replicating in the liver. A positive Anti-HBsAb test would not be present during this stage.
• Good prognosis: While a positive Anti-HBsAb indicates immunity, it doesn’t necessarily predict the outcome of a current illness. Prognosis depends on various factors specific to each case.
• Hepatocellular carcinoma: This is a type of liver cancer and is not directly related to the presence or absence of Hepatitis B surface antibodies.

Answer: High infectivity

The presence of Hepatitis B e antigen (HBeAg) in patients with hepatitis indicates high infectivity. HBeAg is associated with active viral replication, indicating that the individual is highly infectious and capable of transmitting the hepatitis B virus to others.

The other options are incorrect:

• Simple carriers: While HBeAg positivity can be present in carriers, it doesn’t define a “simple” carrier state. Simple carriers typically have low viral loads and are less infectious.
• Late convalescence: This refers to the later stages of recovery from an acute infection. During this phase, HBeAg typically becomes undetectable.
• Carrier status: This is a broader term encompassing various stages of hepatitis B infection, including those with and without HBeAg. A positive HBeAg test helps identify a specific type of carrier with high infectivity.

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Answer: DNA/RNA replication

Interferon interferes with the replication of viruses by inhibiting DNA/RNA replication, which is a crucial step in the viral life cycle. By blocking this process, interferon helps to limit the spread of the virus within the host.

The other options are incorrect:

• Protein synthesis: While some antiviral mechanisms might target protein synthesis, it’s not the primary way interferon disrupts viral replication. Interferon focuses on preventing the virus from making copies of its genetic material, which is essential for protein synthesis to occur later.
• When virus enters the cell: Interferon production is triggered by the detection of viral components or activities inside the cell, not merely by the virus entering.
• Uncoating of the virus proteins capsule: Uncoating is a relatively early stage in the viral lifecycle. Interferon’s action comes into play later, after the virus has entered the cell and begun its replication process.

Answer: Secretory IgA

Secretory IgA is the most abundant antibody found in saliva and plays a crucial role in the body’s first line of defense against pathogens. It works by binding to HIV particles, preventing them from infecting cells in the mouth and throat.

The other options are incorrect:

• Sialoperoxidase: This enzyme has some antimicrobial properties but isn’t specifically known to target HIV.
• Salivary leukocyte proteinase inhibitor (SLPI): While SLPI has antiviral properties, research suggests sIgA plays a more significant role in inhibiting HIV transmission through saliva.
• Histidine rich proteins: These proteins are involved in various functions within saliva but lack specific antiviral activity against HIV.

Answer: Below 200

Kaposi’s sarcoma (KS), a type of cancer caused by human herpesvirus 8 (HHV-8), typically occurs in individuals with severely compromised immune systems, especially when CD4 lymphocyte counts are below 200 cells/mm³. KS is considered an AIDS-defining illness and often manifests in advanced stages of HIV infection.

The other options are incorrect:

• Above 600: CD4 lymphocyte counts above 600 cells/mm³ are generally considered within the normal range. Kaposi’s sarcoma is less likely to occur when CD4 counts are within this range.
• Between 1000-2000: CD4 lymphocyte counts between 1000-2000 cells/mm³ are typically indicative of a well-preserved immune system. Kaposi’s sarcoma is less likely to occur in individuals with CD4 counts within this range.
• Above 2000: CD4 lymphocyte counts above 2000 cells/mm³ are considered high and indicative of a robust immune response. Kaposi’s sarcoma is extremely rare in individuals with such high CD4 counts.

Answer: Surface antigen

The presence of Hepatitis B surface antigen (HBsAg) in the blood indicates current infection with the Hepatitis B virus. This is the most reliable marker for determining the prevalence of active HBV infection in a population.

The other options are incorrect:

• Surface antibody (HBsAb): The presence of HBsAb indicates past infection or vaccination against Hepatitis B, not necessarily current infection.
• Core antigen (HBcAg): HBcAg is rarely used in prevalence studies due to its short-lived presence during acute infection.
• Core antibody (HBcAb): Similar to HBsAb, the presence of HBcAb indicates past infection but doesn’t distinguish between current and resolved cases.

Answer: More sensitive, less specific

The ELISA (Enzyme-Linked Immunosorbent Assay) test is generally more sensitive but less specific compared to the Western blot technique. This means ELISA can detect smaller amounts of the substance or antibodies being tested (higher sensitivity), but it may also produce more false-positive results (lower specificity).

Incorrect Options:

• Less sensitive less specific: This isn’t quite accurate. While ELISA can be less specific, it is generally more sensitive than Western blot.
• More sensitive, more specific: This would be ideal, but ELISA’s simplicity can lead to some cross-reactivity, making it less specific than Western blot.
• Less sensitive, more specific: Western blot can be more specific due to its multi-step process involving protein separation, but its sensitivity is generally lower than ELISA.

Answer: Helper T lymphocytes

HIV specifically targets and infects helper T lymphocytes, also known as CD4+ T cells. These cells play a critical role in coordinating the immune response by helping other immune cells identify and attack pathogens. By progressively destroying CD4+ T cells, HIV weakens the body’s ability to fight off infections and diseases.

The other options are incorrect:

• Natural killer cells: While HIV can indirectly affect natural killer cells, it does not directly target or infect them. Natural killer cells provide a first line of defense against infected cells but rely on signals from helper T cells for optimal function.
• Plasma cells: Plasma cells are responsible for antibody production and are not the primary target of HIV. HIV infection can however, lead to malfunctions in antibody production due to the impaired immune system.
• Macrophages: These cells are involved in phagocytosis and antigen presentation. HIV can infect macrophages, but they are not the main cells affected. The primary impairment of the immune system in HIV is through the depletion of helper T lymphocytes.

Answer: Both are – ve

The window period refers to the time between HIV infection and when an HIV test can reliably detect the virus. During this window period, both the ELISA and Western Blot tests may be negative even though the person is infected.

The other options are incorrect:

• ELISA IS – ve: While this can be true, including “Western Blot is – ve” provides a more complete picture.
• Western Blot is – ve: Similar to ELISA, Western Blot can also be negative during the window period.
• PCR is – ve: PCR detects viral RNA, which can be present even during the window period, making PCR potentially positive.

Answer: HBs AG

Australian antigen is another name for the Hepatitis B surface antigen (HBsAg). It is a protein found on the outer surface of the Hepatitis B virus (HBV). The presence of HBsAg in the blood indicates current infection with HBV.

The other options are incorrect:

• HB Ag: This is not a specific term. “Ag” can refer to any antigen, not just the Hepatitis B surface antigen.
• HBs AG 11: This appears to be a typo or misspelling of HBsAg. There is no standard notation like “HBs AG 11” used in the context of the Hepatitis B surface antigen.
• HBV: HBV refers to the entire Hepatitis B virus, not just the surface antigen. While HBsAg is a part of HBV, it’s not interchangeable with the whole virus.

Answer: LISA followed by western blot technique

The standard method for screening HIV infection involves using an ELISA test for initial screening, which is highly sensitive. If the ELISA test is positive, it is followed by a Western blot test for confirmation due to its high specificity.

The other options are incorrect:

• Virus isolation: This is a complex and time-consuming process not typically used for routine screening due to the difficulty and cost involved.
• Western blot followed by ELISA: This sequence is incorrect. ELISA is used first for screening because it is more sensitive and easier to perform. Western blot is used afterward for confirmation.
• Polymerase Chain Reaction (PCR): PCR is used to detect HIV RNA or DNA, mainly for early detection and monitoring the viral load in infected individuals, but not as the primary screening method.

Answer: Antibody of HBs Ag is associated with resistance to infection

The presence of Hepatitis B surface antibody (HBsAb) indicates immunity against the Hepatitis B virus. People with HBsAb are generally considered protected from future infection.

The other options are incorrect:

• Antibody to HBC is not protective: Antibody to Hepatitis B core antigen (HBcAb) indicates past infection, but it doesn’t necessarily guarantee immunity. However, it can provide some level of protection, especially in combination with HBsAb.
• Highest titres of anti HBC are found in persistent carriers of HBs Ag: While anti-HBc can be found in carriers, the key fact about immune response and protection is related to anti-HBs..
• CMI disappears soon after recovery: CMI (Cell-mediated immunity) plays a crucial role in clearing the Hepatitis B virus and can persist for a long time after recovery, providing long-term protection.

Answer: Hepatitis B surface antigen in acute hepatitis

The Australian antigen is another name for the Hepatitis B surface antigen (HBsAg). The presence of HBsAg in the blood indicates current infection with the Hepatitis B virus (HBV), which can manifest as acute or chronic hepatitis.

The other options are incorrect:

• AIDS: AIDS is the most advanced stage of HIV infection, a different virus altogether.
• Chronic leukemia: This is a type of cancer affecting white blood cells and is not associated with the Australian antigen or Hepatitis B virus.
• Basal cell carcinoma: This is a type of skin cancer and has no connection to the Australian antigen or Hepatitis B virus.

Answer: in a week and reach a peak in 3 weeks

The body starts producing antibodies in response to a new HSV infection within a timeframe. It typically takes around one week for antibodies to HSV (Herpes Simplex Virus) to begin appearing in the bloodstream, and they reach a peak level in about 3 weeks.

The other options are incorrect:

• only after one year: This is too long. While some seroconversion (development of antibodies) can take longer in certain individuals, one year is an excessive timeframe for most cases.
• no antibodies are present in primary HSV: Antibodies are produced by the immune system to fight off the virus. While the initial levels might be low, they will start to develop during a primary HSV infection.
• antibodies are present in recurrent and chronic apthous stomatitis: Aphthous stomatitis (canker sores) is not caused by HSV. Antibodies to HSV are related to herpes infections, not aphthous stomatitis.

Answer: 2:1

The normal ratio of CD4 (T4) to CD8 (T8) cells in a healthy immune system is typically around 2:1. This means that there are generally twice as many CD4 cells as CD8 cells in the blood, which reflects a well-balanced immune response.

The other options are incorrect:

• 1:2: This ratio indicates an inversion, where CD8 cells outnumber CD4 cells, which is abnormal and often seen in conditions like HIV/AIDS.
• 3:1: This ratio is higher than normal and not typical for a healthy immune system.
• 1:3: This is an incorrect ratio and suggests a severe inversion where CD8 cells significantly outnumber CD4 cells, which is not normal and indicative of a compromised immune state.

Answer: 500

In a normal healthy adult, the CD4 count, which reflects the number of CD4 positive T-lymphocytes per microliter of blood, is typically around 500 cells/mm³. This count helps assess the status of the immune system.

The other options are incorrect:

• 200: This count is too low and is often indicative of immune suppression, such as in HIV/AIDS.
• 300: This count is too low and falls below the normal range for a healthy adult, suggesting potential immune compromise.
• 1000: This count is too high for a normal healthy adult. Extremely high CD4 counts can indicate certain conditions like autoimmune diseases or chronic infections.

Answer:

An allo graft refers to a transplant where the organ or tissue comes from a donor who is genetically different from the recipient. In this scenario, the mother and daughter are genetically different, although they share some similarities due to the maternal relation.

The other options are incorrect:

• ISO: An iso graft refers to a transplant between genetically identical individuals, such as identical twins.
• Xeno: A xeno graft refers to a transplant between different species. For example, a pig heart transplant into a human would be considered a xeno graft.
• Auto: An auto graft refers to a transplant where the organ or tissue is taken from one part of the recipient’s body and placed in another. This wouldn’t be the case here as the kidney is coming from the mother, not the daughter.

Answer: Proteins

Proteins are the most potent antigens for stimulating both humoral and cell-mediated immunity. They are highly immunogenic and can activate both B cells (leading to antibody production) and T cells (cell-mediated immunity).

The other options are incorrect:

• Adjuvants: While adjuvants play a crucial role in enhancing the immune response, they are not antigens themselves. They work by amplifying the response to an existing antigen, often a protein.
• Polysaccharides: While polysaccharides can stimulate the humoral immune response (antibody production), they are generally less effective at stimulating cell-mediated immunity compared to proteins.
• Lipids: Lipids are not typically immunogenic and do not stimulate a robust immune response. They are not effective antigens for stimulating either humoral or cell-mediated immunity.

Answer: Typhoid

Typhoid vaccine is not a live attenuated vaccine. It is typically administered as a killed or inactivated vaccine, containing components of the Salmonella typhi bacterium.

The other options are incorrect:

• Tuberculosis (BCG): This is a well-known live attenuated vaccine used to prevent tuberculosis.
• Varicella Zoster virus: The vaccine for chickenpox uses a live attenuated form of the varicella-zoster virus.
• Cholera: There are currently two types of cholera vaccines available in the US, both of which are live attenuated.

Answer: 9 weeks

Seroconversion refers to the period after HIV infection when the body starts producing detectable levels of antibodies against the virus in the bloodstream. This process typically takes time.9 weeks is the most widely accepted timeframe for seroconversion in HIV infection.

The other options are incorrect:

• 3 weeks: This is too short. It takes longer for the body to develop a measurable antibody response.
• 6 weeks: While some seroconversion can occur within this timeframe, 9 weeks is considered a more typical duration.
• 12 weeks: While some cases might take longer, 12 weeks is on the outer edge of the expected window for seroconversion.