Question 1

What is the half-life of IgA?

Accepted Answer

Answer reason: Serum IgA has an approximate half-life of about 6 days; commonly cited range is 6–8 days.

Question 2

Passive immunization is achieved by which method?

Accepted Answer

Answer reason: Passive immunization is produced by giving preformed antibodies, such as antiserum or antitoxin. Vaccines induce active immunity; maternal transfer at birth is natural passive, but the standard method given is antisera/antitoxins.

Question 3

Which one of the following vaccines is a live vaccine?

Accepted Answer

Answer reason: BCG is a live attenuated vaccine. IPV is inactivated, and typhoid vaccine is commonly inactivated (injectable Vi polysaccharide).

Question 4

Who made the first successful immunisation against smallpox?

Accepted Answer

Answer reason: Edward Jenner pioneered vaccination by using cowpox inoculation in 1796, leading to the first successful immunization against smallpox.

Question 5

Which type of white blood cell is primarily responsible for phagocytosis?

Accepted Answer

Answer reason: Neutrophils are the most abundant leukocytes and the primary, rapid-response phagocytes that engulf and destroy pathogens, especially in acute bacterial infections.

Question 6

What is the process by which certain cells engulf and destroy foreign particles or microorganisms called?

Accepted Answer

Answer reason: Phagocytosis is the process where immune cells (e.g., macrophages, neutrophils) engulf and digest foreign particles or microbes. Cytolysis is cell rupture and apoptosis is programmed cell death.

Question 7

Which immunobiological substance produces specific protection against disease?

Accepted Answer

Answer reason: A vaccine is an immunobiologic that induces active, specific immunity to protect against a particular disease. 'Immunity' is a state, not a substance, and immunoglobulin provides passive, temporary protection.

Question 8

If a person shows production of interferons in his body, which infection is most likely?

Accepted Answer

Answer reason: Interferons are antiviral cytokines; their increased production indicates a viral infection such as measles.

Question 9

Which type of cell is responsible for phagocytosis?

Accepted Answer

Answer reason: Monocytes differentiate into macrophages, the professional phagocytes of the innate immune system. Eosinophils target parasites, lymphocytes mediate adaptive immunity, and while neutrophils can phagocytose, monocytes/macrophages are classically identified as the principal phagocytic cells.

Question 10

Hepatitis-B vaccine is a?

Accepted Answer

Answer reason: Hepatitis B vaccine contains recombinant HBsAg (a subunit, inactivated) and is not live; it is not a toxoid and antisera refers to passive immunization.

Question 11

Herd immunity is not useful in the prevention of which disease?

Accepted Answer

Answer reason: Herd immunity protects against diseases that spread person-to-person. Tetanus is not transmitted between people; it results from environmental exposure to C. tetani spores, so community immunity does not prevent cases.

Question 12

The protective effects of breast milk are known to be associated with which of the following?

Accepted Answer

Answer reason: Breast milk, especially colostrum, is rich in secretory IgA that coats the infant’s mucosa and provides passive mucosal immunity. IgM is not predominant; mast cells are not the protective factor; lysozyme is present but the hallmark protective component is sIgA.

Question 13

The BCG vaccine is used against which disease?

Accepted Answer

Answer reason: BCG (Bacille Calmette-Guérin) is a vaccine used to prevent tuberculosis, especially severe forms in children.

Question 14

Which cell secretes histamine?

Accepted Answer

Answer reason: Mast cells store histamine in cytoplasmic granules and release it during degranulation, mediating vasodilation and increased vascular permeability.

Question 15

Which of the following is produced in plasma cells?

Accepted Answer

Answer reason: Plasma cells are the effector B cells that synthesize antibodies (immunoglobulins). The other options are leukocyte types not produced within plasma cells.

Question 16

Which immunoglobulin is called the 'Millionaire molecule'?

Accepted Answer

Answer reason: IgM is a large pentamer (~900 kDa, near one million daltons), hence nicknamed the 'millionaire molecule' or macroglobulin.

Question 17

Which antibody is the most abundant in the blood?

Accepted Answer

Answer reason: IgG is the predominant immunoglobulin in serum, comprising about 70–75% of circulating antibodies.

Question 18

Which immunoglobulin can cross the placenta and provide passive immunity to the newborn?

Accepted Answer

Answer reason: IgG is the only immunoglobulin class that crosses the placenta via Fc receptors, providing passive immunity to the newborn.

Question 19

Which vaccine is the most heat sensitive?

Accepted Answer

Answer reason: Oral polio vaccine is the most heat‑sensitive among common vaccines, requiring strict cold‑chain maintenance. Measles and BCG are also heat/light sensitive, while DPT is comparatively more stable.

Question 20

Who first developed the concept of vaccination?

Accepted Answer

Answer reason: Edward Jenner pioneered vaccination by using cowpox to protect against smallpox in 1796; others are known for different contributions (Fleming—penicillin, Koch—germ theory, Hippocrates—ancient medicine).

Question 21

Which of the following is NOT a live vaccine?

Accepted Answer

Answer reason: Tetanus toxoid (TT) is an inactivated toxoid vaccine, not live. OPV, BCG, and measles vaccines are live attenuated.

Question 22

What type of immunity does a vaccine produce?

Accepted Answer

Answer reason: Vaccines introduce antigen to stimulate the host’s immune system to generate antibodies and memory cells, producing active immunity. Passive immunity is from transfer of preformed antibodies (e.g., immunoglobulin), not vaccination.

Question 23

Which cell secretes antibody?

Accepted Answer

Answer reason: Antibodies (immunoglobulins) are produced by plasma cells, which are differentiated B lymphocytes, forming the basis of humoral immunity. Monocytes and neutrophils primarily function in phagocytosis, and eosinophils target parasites and participate in allergic responses. Thus, among the options, lymphocytes are the cells responsible for antibody secretion.

Question 24

Serum for detection of antibodies should be drawn during to ?

Accepted Answer

Answer reason: Serologic diagnosis relies on paired sera drawn during the acute phase and again in the convalescent phase to demonstrate seroconversion or a fourfold rise in antibody titer. A single acute or convalescent specimen cannot reliably distinguish current from past infection. Routine collection 6 months later is not standard for diagnosing the acute illness.

Question 25

What vaccine is designed to protect newborns from severe diarrhea?

Accepted Answer

Answer reason: Rotavirus is the leading cause of severe gastroenteritis and dehydrating diarrhea in infants worldwide. Oral rotavirus vaccines (e.g., RV1, RV5) are specifically designed to prevent severe disease, hospitalization, and death from rotavirus infection. Hepatitis B vaccine prevents hepatitis B virus infection, and the anti-rabies vaccine protects against rabies, not diarrheal illness.

Question 26

Number of domains in IgM is?

Accepted Answer

Answer reason: IgM’s μ heavy chain contains four constant domains (CH1–CH4) plus a variable domain. In contrast, IgG, IgA, and IgD heavy chains have three constant domains. The presence of the extra CH4 domain is characteristic of IgM (and IgE), accounting for the larger size and distinct effector functions. Therefore, the number of domains in IgM is four.

Question 27

Oral polio vaccine was invented by?

Accepted Answer

Answer reason: Albert Sabin developed the oral polio vaccine (OPV) in the 1950s using live attenuated poliovirus strains, administered orally to induce mucosal immunity. In contrast, Jonas Salk created the inactivated injectable polio vaccine (IPV). Pasteur pioneered the rabies vaccine, Jenner introduced smallpox vaccination, and Ross is known for work on malaria transmission. Therefore, the correct inventor of the oral polio vaccine is Albert Sabin.

Question 28

Drug allergy is?

Accepted Answer

Answer reason: A true drug allergy is an immune-mediated hypersensitivity reaction, often IgE-mediated (immediate) or T-cell–mediated (delayed). It is not dose-dependent or predictable from the drug’s pharmacologic action. Idiosyncratic reactions are nonimmune, unpredictable effects, and psychological responses are not allergic mechanisms. Therefore, the best answer is an immunological reaction.

Question 29

First line of defense in human body is...?

Accepted Answer

Answer reason: The first line of defense of the immune system is the physical and chemical barriers, primarily the intact skin and mucous membranes. These barriers prevent pathogen entry through keratinized layers, tight junctions, and antimicrobial secretions. Antibodies are part of the adaptive (third line) response, and WBCs represent internal innate defenses (second line). Platelets are mainly involved in hemostasis, not primary immune defense.

Question 30

Phagocytosis is mainly done by?

Accepted Answer

Answer reason: Phagocytosis is primarily performed by white blood cells, especially neutrophils and macrophages, as part of innate immunity. They ingest and destroy bacteria, cellular debris, and pathogens. Red blood cells do not have this function, platelets are involved in hemostasis, and nephrons are kidney filtration units. Therefore, WBCs are the main phagocytes.

Question 31

Which immune cells are the first responders to infection?

Accepted Answer

Answer reason: Neutrophils are the primary innate immune cells that rapidly migrate to sites of acute infection and inflammation. They arrive within minutes to hours, phagocytose pathogens, and release antimicrobial enzymes and reactive oxygen species. B cells are part of the adaptive response and act later via antibody production. Monocytes become macrophages and typically arrive after neutrophils, while basophils are more involved in allergic and parasitic responses.

Question 32

Who discovered the first vaccine?

Accepted Answer

Answer reason: Edward Jenner pioneered the first vaccine in 1796 by using material from cowpox lesions to confer immunity against smallpox. This was the first documented, systematic vaccination. Louis Pasteur later developed vaccines for diseases like rabies, Alexander Fleming discovered penicillin, and Robert Koch advanced bacteriology, but none discovered the first vaccine.

Question 33

Measles vaccine is?

Accepted Answer

Answer reason: The measles component of the MMR vaccine is a live attenuated virus derived from the Edmonston strain. Live attenuated vaccines replicate minimally and produce robust humoral and cellular immunity, conferring long-lasting protection. Measles is a viral, not bacterial, illness, and there is no inactivated (killed) measles vaccine in routine use. Therefore, the correct classification is a live viral vaccine.

Question 34

An example of a toxoid is the?

Accepted Answer

Answer reason: Toxoid vaccines are inactivated bacterial toxins that retain antigenicity and induce protective antitoxin antibodies. Classic examples are diphtheria and tetanus toxoids. Rabies vaccine is an inactivated or recombinant viral vaccine, and measles is a live-attenuated viral vaccine. Pertussis vaccines are typically acellular subunit formulations containing multiple antigens and are not classically categorized as a pure toxoid vaccine.

Question 35

C-reactive protein is secreted from?

Accepted Answer

Answer reason: Reactive protein (CRP) is an acute-phase reactant synthesized by hepatocytes in the liver, primarily under stimulation by interleukin-6 and other proinflammatory cytokines. It is released into the bloodstream during systemic inflammation, where it opsonizes pathogens and activates complement. The hypothalamus, pancreas, and lungs are not major sources of CRP production.

Question 36

TAB vaccine is useful against ______?

Accepted Answer

Answer reason: The TAB vaccine contains antigens from Salmonella Typhi and Salmonella Paratyphi A and B, providing protection against enteric fever, primarily typhoid. It does not protect against viral illnesses such as polio or dengue, nor the parasitic disease malaria. Modern schedules more often use Vi polysaccharide or Ty21a vaccines, but the classic TAB formulation is specifically for typhoid-paratyphoid prevention.

Question 37

AIDS is caused by a virus that affects?

Accepted Answer

Answer reason: HIV targets CD4+ T lymphocytes, a subset of white blood cells, by binding to the CD4 receptor and coreceptors (CCR5/CXCR4). Progressive depletion and dysfunction of these cells leads to immunodeficiency characteristic of AIDS. Red blood cells and platelets are not primary targets, and while bone marrow may be secondarily affected, it is not the main cellular site of viral infection.

Question 38

Which disease is prevented by BCG vaccine?

Accepted Answer

Answer reason: BCG is a live-attenuated Mycobacterium bovis vaccine that induces cell-mediated immunity against Mycobacterium tuberculosis. It is primarily used to prevent severe childhood forms of TB such as miliary and meningeal tuberculosis. Typhoid, hepatitis, and measles are prevented by different vaccines (Typhoid Vi/Live oral, Hepatitis A/B vaccines, and MMR).

Question 39

ELISA test is used to detect?

Accepted Answer

Answer reason: ELISA is an immunoassay that detects specific antibodies or antigens in serum, and it is the standard high-sensitivity screening test for HIV by detecting anti-HIV antibodies or p24 antigen. Positive screens are confirmed with supplemental assays. Tuberculosis is more commonly screened with Mantoux/IGRA tests, and malaria is diagnosed by smear or rapid antigen tests.

Question 40

Which type of immunity is provided by vaccination?

Accepted Answer

Answer reason: Vaccination introduces antigen by artificial means to stimulate the person’s own immune response, producing antibodies and immunologic memory—this is artificial active immunity. Natural active immunity occurs after actual infection. Artificial passive immunity results from administered antibodies (e.g., immune globulin), and natural passive immunity is from maternal antibodies via placenta or breast milk.

Question 41

The anti-rabies vaccine is called?

Accepted Answer

Answer reason: ARV stands for Anti-Rabies Vaccine, used for pre- and post-exposure prophylaxis against rabies. BCG is a vaccine for tuberculosis, TT is tetanus toxoid, and MMR is measles-mumps-rubella—none relate to rabies. Therefore, the correct term for the anti-rabies vaccine is ARV.

Question 42

Colostrum is rich in?

Accepted Answer

Answer reason: Colostrum contains high concentrations of secretory immunoglobulin A (IgA), which coats the infant’s gastrointestinal mucosa and provides passive immunity. It is relatively lower in lactose (carbohydrates) than mature milk. Colostrum is not a major source of vitamin D or iron. Therefore, the best answer is Immunoglobulin A.

Question 43

Secretory IgA is mainly found in which form?

Accepted Answer

Answer reason: Secretory IgA in mucosal secretions exists predominantly as a dimer linked by a J chain and associated with a secretory component acquired during transcytosis. This dimeric form enhances stability against proteolysis in the gut and other mucosal sites. Serum IgA is mainly monomeric, while pentameric structure is characteristic of IgM.

Question 44

BCG vaccine is given for prevention of...?

Accepted Answer

Answer reason: The BCG (Bacille Calmette–Guérin) vaccine is a live attenuated Mycobacterium bovis vaccine used to prevent tuberculosis, particularly severe forms like miliary TB and TB meningitis in children. It does not protect against hepatitis, tetanus, or polio. Those are prevented by hepatitis B vaccine, tetanus toxoid, and polio vaccines (IPV/OPV), respectively.

Question 45

Which antibody is responsible for indicating a probable recent infection?

Accepted Answer

Answer reason: IgM is the first immunoglobulin produced during the primary immune response and rises early after exposure to a new antigen. Its presence indicates recent or acute infection, before class switching to IgG occurs. IgA is primarily mucosal, IgE mediates allergic and parasitic responses, and IgD functions mainly as a B-cell receptor.

Question 46

Which is the most abundant immunoglobulin in human serum?

Accepted Answer

Answer reason: IgG is the most abundant immunoglobulin in human serum, comprising roughly 70–75% of total immunoglobulins. It provides long-term humoral immunity, mediates opsonization and complement activation, and can cross the placenta. By contrast, IgA predominates in mucosal secretions, IgM is the first antibody produced in primary responses, and IgE is present in very low serum levels and mediates allergic and parasitic responses.

Question 47

Which immunoglobulin is present in highest concentration in blood?

Accepted Answer

Answer reason: IgG is the most abundant immunoglobulin in serum, comprising about 70–80% of total blood immunoglobulins. It provides long-term systemic immunity and can cross the placenta. IgA predominates in mucosal secretions, IgM is the first antibody produced in primary responses but is less abundant in serum, and IgE is present in the lowest concentrations and mediates allergic responses.

Question 48

Which vaccine is most heat sensitive vaccine among followings?

Accepted Answer

Answer reason: Oral polio vaccine (OPV) is the most heat‑labile of common vaccines; it rapidly loses potency when exposed to temperatures above the cold-chain range and is ideally stored at about −20°C. Yellow fever vaccine, though live-attenuated, is freeze‑dried and more stable. Hepatitis B and most influenza vaccines are inactivated or recombinant and are comparatively heat stable. Therefore, polio vaccine is the most heat sensitive among the options.

Question 49

Tuberculosis is controlled by which vaccine?

Accepted Answer

Answer reason: BCG (Bacillus Calmette–Guérin) is a live attenuated vaccine derived from Mycobacterium bovis and provides protection against tuberculosis, particularly severe childhood forms like miliary TB and TB meningitis. Polio vaccine prevents poliomyelitis, MMR targets measles–mumps–rubella, and DPT protects against diphtheria, pertussis, and tetanus. Therefore, BCG is the correct vaccine associated with TB control.

Question 50

Anaphylactic shock is due to?

Accepted Answer

Answer reason: Anaphylactic shock is caused by a systemic severe allergic (type I hypersensitivity) reaction with IgE-mediated mast cell degranulation. This releases histamine and other mediators that trigger profound vasodilation, capillary leak, and bronchospasm, producing distributive shock. Blood loss and dehydration lead to hypovolemic shock, and a heart attack leads to cardiogenic shock, not anaphylaxis.

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