Q.1 Which immune cells are primarily responsible for killing virus-infected cells?
B cells
Cytotoxic T lymphocytes
Neutrophils
Eosinophils
Explanation - Cytotoxic T lymphocytes (CD8+ T cells) recognize viral antigens presented on MHC I molecules and induce apoptosis of infected cells.
Correct answer is: Cytotoxic T lymphocytes
Q.2 Which cytokine is mainly responsible for inducing fever during an infection?
Interleukin-1 (IL-1)
Interferon-gamma (IFN-γ)
Tumor necrosis factor-beta (TNF-β)
IL-10
Explanation - IL-1 is a pyrogenic cytokine that acts on the hypothalamus to raise body temperature in response to infection.
Correct answer is: Interleukin-1 (IL-1)
Q.3 Which antibody is most abundant in mucosal surfaces and protects against respiratory and gastrointestinal pathogens?
IgG
IgA
IgM
IgE
Explanation - IgA is secreted in mucosal areas, such as the respiratory and gastrointestinal tracts, preventing pathogen adherence.
Correct answer is: IgA
Q.4 Which component of the innate immune system acts as the first line of defense against bacterial infections?
Complement system
Cytotoxic T cells
B cells
Plasma cells
Explanation - The complement system can directly lyse bacteria and enhance phagocytosis as an immediate defense mechanism.
Correct answer is: Complement system
Q.5 Which pathogen-associated molecular patterns (PAMPs) are recognized by Toll-like receptors (TLRs) on immune cells?
Self-antigens
Bacterial DNA, LPS, viral RNA
Hormones
Neurotransmitters
Explanation - TLRs recognize conserved molecular structures from pathogens, including lipopolysaccharide (LPS), viral RNA, and unmethylated CpG DNA.
Correct answer is: Bacterial DNA, LPS, viral RNA
Q.6 Which type of hypersensitivity reaction is mainly involved in response to extracellular bacteria?
Type I
Type II
Type III
Type IV
Explanation - Type III hypersensitivity involves immune complex formation with antigens and antibodies, often triggered by extracellular pathogens.
Correct answer is: Type III
Q.7 Which immune cells produce large amounts of interferons in response to viral infections?
NK cells
Plasma cells
Macrophages
B cells
Explanation - Natural Killer (NK) cells respond to virally infected cells and produce interferon-gamma to activate other immune cells.
Correct answer is: NK cells
Q.8 Which of the following is a key feature of adaptive immunity in response to infection?
Immediate response
Memory formation
Non-specific recognition
Barrier protection
Explanation - Adaptive immunity is characterized by antigen-specific responses and the formation of immunological memory for faster future responses.
Correct answer is: Memory formation
Q.9 Which T helper cell subset is most important for defense against intracellular pathogens like Mycobacterium tuberculosis?
Th1
Th2
Th17
Treg
Explanation - Th1 cells produce IFN-γ, which activates macrophages to kill intracellular pathogens.
Correct answer is: Th1
Q.10 Which innate immune cell is primarily responsible for phagocytosis of bacteria?
Neutrophils
B cells
Eosinophils
T cells
Explanation - Neutrophils are the first responders to bacterial infection and engulf pathogens through phagocytosis.
Correct answer is: Neutrophils
Q.11 Which immune component is primarily responsible for opsonization of pathogens?
Complement C3b
IgE
Cytokines
Histamines
Explanation - C3b binds to pathogen surfaces and enhances their uptake by phagocytes, a process called opsonization.
Correct answer is: Complement C3b
Q.12 Which type of vaccine uses live attenuated organisms to stimulate immunity?
Subunit vaccine
Inactivated vaccine
Live attenuated vaccine
Toxoid vaccine
Explanation - Live attenuated vaccines contain weakened forms of pathogens that elicit strong, long-lasting immune responses.
Correct answer is: Live attenuated vaccine
Q.13 Which antibody class is first produced during the primary immune response?
IgG
IgA
IgM
IgE
Explanation - IgM is the first antibody produced in response to an initial infection and is effective at forming antigen-antibody complexes.
Correct answer is: IgM
Q.14 Which immune cells form the basis of immunological memory after infection or vaccination?
Naive B and T cells
Memory B and T cells
Macrophages
Neutrophils
Explanation - Memory cells remain in circulation after an initial infection, enabling a rapid and strong response upon re-exposure to the pathogen.
Correct answer is: Memory B and T cells
Q.15 Which pathogen type is primarily targeted by Th2 immune responses?
Viruses
Intracellular bacteria
Parasites
Fungi
Explanation - Th2 cells secrete IL-4, IL-5, and IL-13, promoting antibody-mediated responses effective against extracellular parasites.
Correct answer is: Parasites
Q.16 Which component of the innate immune system can recognize fungal β-glucans?
TLR4
Dectin-1
CD8 receptor
B cell receptor
Explanation - Dectin-1 is a pattern recognition receptor that binds β-glucans on fungal cell walls, activating innate immune responses.
Correct answer is: Dectin-1
Q.17 Which cytokine is central to the differentiation of naive T cells into Th17 cells?
IL-12
IL-4
TGF-β and IL-6
IFN-γ
Explanation - The combination of TGF-β and IL-6 promotes differentiation of naive T cells into Th17 cells, important in defense against extracellular bacteria and fungi.
Correct answer is: TGF-β and IL-6
Q.18 Which viral component is most likely to activate plasmacytoid dendritic cells to produce interferon-alpha?
Viral envelope proteins
Viral RNA
Viral DNA only
Viral lipids
Explanation - Plasmacytoid dendritic cells detect viral RNA via TLR7 and TLR9, leading to production of type I interferons.
Correct answer is: Viral RNA
Q.19 Which type of hypersensitivity reaction is responsible for tuberculin skin test response?
Type I
Type II
Type III
Type IV
Explanation - Type IV hypersensitivity is cell-mediated, involving Th1 cells and macrophages, which is the mechanism behind the tuberculin skin test.
Correct answer is: Type IV
Q.20 Which component of the immune system is primarily involved in clearing extracellular bacteria from the bloodstream?
Complement system
Cytotoxic T cells
NK cells
Helper T cells
Explanation - The complement system opsonizes and lyses extracellular bacteria, playing a critical role in bloodborne infections.
Correct answer is: Complement system
Q.21 Which immune receptor recognizes bacterial lipopolysaccharide (LPS)?
TLR4
TLR3
CD4
BCR
Explanation - TLR4 on macrophages and dendritic cells recognizes LPS, triggering innate immune activation.
Correct answer is: TLR4
Q.22 Which immunoglobulin is responsible for allergic reactions against environmental antigens?
IgG
IgA
IgM
IgE
Explanation - IgE binds to allergens and triggers degranulation of mast cells and basophils, causing allergy symptoms.
Correct answer is: IgE
Q.23 Which process allows phagocytes to move toward infection sites in response to chemokines?
Diapedesis
Chemotaxis
Opsonization
Endocytosis
Explanation - Chemotaxis is the directed movement of immune cells toward chemical signals such as chemokines at infection sites.
Correct answer is: Chemotaxis
Q.24 Which immune mechanism is responsible for neutralizing bacterial toxins?
Phagocytosis
Antibody binding
Complement lysis
Cytotoxic T cell killing
Explanation - Antibodies, especially IgG and IgA, can bind bacterial toxins and prevent them from interacting with host cells, neutralizing their effect.
Correct answer is: Antibody binding
Q.25 Which type of immune response is most effective against helminth infections?
Th1-mediated
Th2-mediated
Cytotoxic T cell-mediated
Type IV hypersensitivity
Explanation - Th2 responses stimulate IgE production and eosinophil activation, which are crucial for defense against helminths.
Correct answer is: Th2-mediated