Q.1 What is the first line of defense in the innate immune system?
Antibodies
Complement proteins
Physical barriers
T cells
Explanation - The skin and mucous membranes act as physical barriers that prevent pathogens from entering the body.
Correct answer is: Physical barriers
Q.2 Which cells are responsible for producing antibodies?
B cells
T cells
NK cells
Dendritic cells
Explanation - B cells differentiate into plasma cells that secrete antibodies against antigens.
Correct answer is: B cells
Q.3 What type of immune response involves the activation of T cells?
Innate immunity
Cell-mediated immunity
Humoral immunity
Passive immunity
Explanation - Cell-mediated immunity is driven by T cells that directly attack infected cells.
Correct answer is: Cell-mediated immunity
Q.4 Which component of the immune system helps to flag pathogens for destruction by phagocytes?
Cytokines
Complement system
Antibodies
Interferons
Explanation - The complement system forms a complex that opsonizes pathogens, enhancing phagocytosis.
Correct answer is: Complement system
Q.5 What is the primary function of natural killer (NK) cells?
Produce antibodies
Present antigens to T cells
Destroy virus-infected or tumor cells
Release cytokines
Explanation - NK cells recognize and kill abnormal cells without prior sensitization.
Correct answer is: Destroy virus-infected or tumor cells
Q.6 Which lymphoid organ is known as the site where B cells mature?
Spleen
Thymus
Bone marrow
Lymph nodes
Explanation - B cells originate and mature in the bone marrow before migrating to secondary lymphoid organs.
Correct answer is: Bone marrow
Q.7 What role does the thymus play in the immune system?
Produce antibodies
Mature B cells
Mature T cells
Store immune memory
Explanation - The thymus provides an environment for T cells to develop and differentiate.
Correct answer is: Mature T cells
Q.8 Which type of antibody is most abundant in blood and can activate complement?
IgA
IgM
IgD
IgG
Explanation - IgM is the first antibody produced during an immune response and efficiently activates complement.
Correct answer is: IgM
Q.9 What is a primary function of cytokines in the immune response?
Bind to antigens
Signal immune cells
Directly kill pathogens
Serve as antigens
Explanation - Cytokines are signaling molecules that modulate the activity, growth, and differentiation of immune cells.
Correct answer is: Signal immune cells
Q.10 Which of the following is NOT a typical feature of a T helper (Th) cell?
Express CD4
Secrete cytokines
Activate B cells
Directly kill pathogens
Explanation - Th cells support other immune cells but do not directly kill infected cells; that role belongs to cytotoxic T cells.
Correct answer is: Directly kill pathogens
Q.11 What is the primary mechanism by which antibody-dependent cellular cytotoxicity (ADCC) works?
Antibody binds to a pathogen and activates complement
Antibody-coated cells are recognized by NK cells, which then kill them
Antibody binds to T cells to stimulate them
Antibody enhances phagocytosis by macrophages
Explanation - ADCC involves NK cells recognizing antibodies on target cells through Fc receptors, leading to cell death.
Correct answer is: Antibody-coated cells are recognized by NK cells, which then kill them
Q.12 Which cell surface marker is commonly used to identify regulatory T cells?
CD3
CD4
CD25
CD8
Explanation - Regulatory T cells express high levels of CD25 (IL-2 receptor alpha chain) and help maintain immune tolerance.
Correct answer is: CD25
Q.13 What is the main purpose of the complement system?
Produce antibodies
Kill bacteria by forming pores
Activate T cells
Signal for inflammation
Explanation - The complement cascade can form the membrane attack complex (MAC) that perforates bacterial membranes.
Correct answer is: Kill bacteria by forming pores
Q.14 Which of the following best describes immunological memory?
Immediate innate response
Long-lasting adaptive response
Passive transfer of antibodies
Regulation by NK cells
Explanation - Immunological memory refers to the adaptive immune system’s ability to respond more quickly and strongly upon re‑exposure to a pathogen.
Correct answer is: Long-lasting adaptive response
Q.15 What is the primary site where T cell activation occurs?
Spleen
Bone marrow
Lymph nodes
Thymus
Explanation - T cells are activated in secondary lymphoid organs like lymph nodes, where they encounter antigen-presenting cells.
Correct answer is: Lymph nodes
Q.16 Which type of antibody is most effective at neutralizing viruses in the mucosal surfaces?
IgG
IgM
IgA
IgD
Explanation - Secretory IgA is found in mucosal secretions and protects against viral entry at these surfaces.
Correct answer is: IgA
Q.17 Which cytokine is primarily involved in fever and acute phase response?
IL-4
IL-10
IL-6
IL-12
Explanation - IL‑6 is a pro‑inflammatory cytokine that induces fever and the synthesis of acute phase proteins.
Correct answer is: IL-6
Q.18 What is the role of the Fc region of an antibody?
Bind antigen
Recruit complement
Signal T cells
Both B and C
Explanation - The Fc region interacts with Fc receptors on immune cells and activates complement, facilitating effector functions.
Correct answer is: Both B and C
Q.19 Which of the following is a characteristic of a primary immune response?
Rapid onset
High affinity antibodies
Occurs after first exposure
Requires memory cells
Explanation - A primary response is the first reaction to a pathogen; it takes longer and produces lower affinity antibodies.
Correct answer is: Occurs after first exposure
Q.20 What is the main difference between IgG and IgM antibodies?
IgG is larger
IgM is pentameric
IgG is produced first
IgM cannot bind to Fc receptors
Explanation - IgM forms a pentamer with ten antigen-binding sites, whereas IgG is monomeric with two sites.
Correct answer is: IgM is pentameric
Q.21 Which of the following cells is responsible for presenting antigens to T cells?
Neutrophils
Eosinophils
Dendritic cells
Basophils
Explanation - Dendritic cells are professional antigen‑presenting cells that prime T cells in lymph nodes.
Correct answer is: Dendritic cells
Q.22 What is the key feature of T cell receptor (TCR) specificity?
Recognizes free antigens
Recognizes peptides presented on MHC
Binds to antibodies
Recognizes complement proteins
Explanation - TCRs detect peptide fragments displayed by major histocompatibility complex molecules.
Correct answer is: Recognizes peptides presented on MHC
Q.23 Which pathway initiates the complement cascade via antibody binding?
Classical pathway
Alternative pathway
Lectin pathway
Mannose-binding pathway
Explanation - The classical pathway is triggered when C1q binds to antibody-antigen complexes.
Correct answer is: Classical pathway
Q.24 What is the function of the membrane attack complex (MAC)?
Enhances phagocytosis
Stimulates antibody production
Forms pores in target membranes
Signals T cell activation
Explanation - MAC creates transmembrane channels that disrupt cell integrity, leading to lysis of target cells.
Correct answer is: Forms pores in target membranes
Q.25 Which type of T cell is primarily involved in allergic responses?
Th1 cells
Th2 cells
Th17 cells
Regulatory T cells
Explanation - Th2 cells promote IgE production and eosinophil activation, driving allergic inflammation.
Correct answer is: Th2 cells
Q.26 What is the main antigen-presenting molecule on B cells?
MHC I
MHC II
CD8
CD4
Explanation - B cells display peptide fragments on MHC II molecules to help activate CD4+ T helper cells.
Correct answer is: MHC II
Q.27 Which immunoglobulin is known as the first responder during early infection?
IgA
IgM
IgG
IgE
Explanation - IgM is produced rapidly in primary responses and is effective in activating complement.
Correct answer is: IgM
Q.28 Which cell type releases histamine during an allergic reaction?
Macrophages
Basophils
Dendritic cells
Eosinophils
Explanation - Basophils contain histamine granules that are released upon activation, causing vasodilation and inflammation.
Correct answer is: Basophils
Q.29 Which part of the immune system is described as 'non‑specific'?
Adaptive immunity
Innate immunity
Humoral immunity
Cell‑mediated immunity
Explanation - Innate immunity responds the same way to all pathogens, lacking antigen specificity.
Correct answer is: Innate immunity
Q.30 What does the term 'antigen' refer to?
A type of antibody
A molecule that triggers an immune response
A cytokine
A T cell receptor
Explanation - Antigens are foreign molecules that are recognized by the immune system as non‑self.
Correct answer is: A molecule that triggers an immune response
Q.31 Which immune component is directly involved in the adaptive immune response?
Neutrophils
Complement proteins
T and B lymphocytes
Platelets
Explanation - Adaptive immunity is mediated by the specific actions of T and B cells.
Correct answer is: T and B lymphocytes
Q.32 What is the primary function of the spleen?
Filter blood and recycle red cells
Produce T cells
Store platelets
Activate B cells
Explanation - The spleen removes old red blood cells and acts as a site for immune cell interaction.
Correct answer is: Filter blood and recycle red cells
Q.33 Which cytokine is known as a key driver of inflammation and fever?
IL-10
IL-4
IL-6
IL-2
Explanation - IL‑6 stimulates the liver to produce acute phase proteins and raises body temperature.
Correct answer is: IL-6
Q.34 Which immune cell is most abundant in the bloodstream?
Lymphocytes
Granulocytes
Macrophages
Dendritic cells
Explanation - Neutrophils, eosinophils, and basophils make up the majority of circulating white blood cells.
Correct answer is: Granulocytes
Q.35 The 'antigen–antibody complex' is best described as:
A T cell receptor
An immune complex
A complement fragment
A cytokine cascade
Explanation - Antigen–antibody complexes form the basis for immune complex-mediated inflammation.
Correct answer is: An immune complex
Q.36 Which of the following cells is the main mediator of allergic asthma?
Macrophages
Eosinophils
Neutrophils
NK cells
Explanation - Eosinophils release toxic granules and cytokines that damage airway tissues in asthma.
Correct answer is: Eosinophils
Q.37 Which immune cell type releases interferon-gamma during a viral infection?
B cells
Th1 cells
Th2 cells
Regulatory T cells
Explanation - Th1 cells secrete IFN‑γ, which activates macrophages and enhances antiviral defenses.
Correct answer is: Th1 cells
Q.38 The process of an immune cell engulfing a pathogen is called:
Apoptosis
Phagocytosis
Opsonization
Antigen presentation
Explanation - Phagocytosis is the ingestion of particles by phagocytes like macrophages and neutrophils.
Correct answer is: Phagocytosis
Q.39 Which antibody is most important for long‑term immunity?
IgA
IgG
IgM
IgE
Explanation - IgG circulates for months to years and provides durable immune memory.
Correct answer is: IgG
Q.40 What is the main function of regulatory T cells (Tregs)?
Activate B cells
Suppress immune responses
Produce antibodies
Present antigens
Explanation - Tregs maintain self‑tolerance by inhibiting overactive immune cells.
Correct answer is: Suppress immune responses
Q.41 Which of the following is NOT a characteristic of the adaptive immune system?
Memory formation
Specific antigen recognition
Rapid response on first exposure
Clonal expansion
Explanation - Adaptive immunity takes time to develop during the first encounter with an antigen.
Correct answer is: Rapid response on first exposure
Q.42 Which cell type is primarily responsible for the presentation of viral peptides to CD8+ T cells?
B cells
Dendritic cells
Macrophages
NK cells
Explanation - Dendritic cells cross‑present viral antigens via MHC I to activate cytotoxic T cells.
Correct answer is: Dendritic cells
Q.43 Which of the following best describes the 'humoral' arm of the immune system?
Cell-mediated immunity
Antibody‑mediated immunity
Innate immunity
Complement system
Explanation - Humoral immunity involves B cells and antibody production to neutralize pathogens.
Correct answer is: Antibody‑mediated immunity
Q.44 Which cytokine promotes the differentiation of naive T cells into Th2 cells?
IL-2
IL-4
IL-12
IL-17
Explanation - IL‑4 drives Th2 lineage commitment, which aids in humoral immunity.
Correct answer is: IL-4
Q.45 What is the primary role of macrophages in tissue repair?
Secrete collagen
Remove debris and dead cells
Produce antibodies
Activate NK cells
Explanation - Macrophages phagocytose cell debris and release growth factors to aid healing.
Correct answer is: Remove debris and dead cells
Q.46 Which of the following is a feature of immunodeficiency?
Overactive immune responses
Rapid pathogen clearance
Reduced antibody production
Enhanced memory formation
Explanation - Immunodeficiencies often involve decreased antibody levels, leading to increased infections.
Correct answer is: Reduced antibody production
Q.47 Which protein is NOT part of the complement cascade?
C3
C5
C9
C15
Explanation - C15 does not exist in the complement system; the cascade involves C1‑C9.
Correct answer is: C15
Q.48 Which of the following best explains the concept of 'self‑nonself' discrimination?
The immune system only attacks foreign antigens
The immune system attacks any foreign material
The immune system tolerates all antigens
The immune system ignores all antigens
Explanation - 'Self‑nonself' refers to the immune system's ability to recognize and attack only foreign substances.
Correct answer is: The immune system only attacks foreign antigens
Q.49 Which of the following is a function of IgE antibodies?
Neutralize toxins
Activate complement
Trigger allergic reactions
Promote phagocytosis
Explanation - IgE binds to mast cells and basophils, leading to histamine release during allergies.
Correct answer is: Trigger allergic reactions
Q.50 What is the role of B cell receptor (BCR) on immature B cells?
Present antigens
Signal apoptosis if self‑reactive
Activate T cells
Produce antibodies
Explanation - Negative selection removes B cells that bind self‑antigens to prevent autoimmunity.
Correct answer is: Signal apoptosis if self‑reactive
Q.51 Which of the following is a key feature of the innate immune response?
It requires memory cells
It takes several days to develop
It is rapid and non‑specific
It relies on antibodies
Explanation - Innate immunity provides the first, quick, and generic defense against pathogens.
Correct answer is: It is rapid and non‑specific
Q.52 Which of the following is a main function of natural killer (NK) cells?
Produce antibodies
Kill cancer cells
Secrete interferon-alpha
Present antigens
Explanation - NK cells detect altered cells and induce apoptosis without prior sensitization.
Correct answer is: Kill cancer cells
Q.53 What does the 'cytokine storm' refer to?
Overproduction of cytokines during infection
Deficiency of cytokines in immune disorders
Production of cytokines by pathogens
Cytokine production in the brain
Explanation - A cytokine storm is an excessive immune response that can damage host tissues.
Correct answer is: Overproduction of cytokines during infection
Q.54 Which of the following is a hallmark of a secondary immune response?
Slower onset
Lower antibody affinity
Involvement of memory B cells
No memory formation
Explanation - Memory B cells enable a faster, more potent antibody response upon re‑exposure.
Correct answer is: Involvement of memory B cells
Q.55 The process by which a pathogen is coated with antibodies or complement is called:
Phagocytosis
Opsonization
Apoptosis
Antigen presentation
Explanation - Opsonization tags pathogens for ingestion by phagocytes.
Correct answer is: Opsonization
Q.56 Which type of T cell provides help for B cell antibody production?
Cytotoxic T cell
Helper T cell
Regulatory T cell
Thymic epithelial cell
Explanation - Helper T cells secrete cytokines that stimulate B cells to proliferate and produce antibodies.
Correct answer is: Helper T cell
Q.57 What is the primary function of platelets in immune defense?
Secrete antibodies
Engulf pathogens
Release inflammatory mediators
Activate complement
Explanation - Platelets release cytokines and chemokines that recruit immune cells to infection sites.
Correct answer is: Release inflammatory mediators
Q.58 Which of the following is NOT an immunoglobulin class?
IgD
IgF
IgG
IgM
Explanation - IgF is not a recognized class of antibodies; the major classes are IgA, IgD, IgE, IgG, IgM.
Correct answer is: IgF
Q.59 Which component of the immune system is known to directly destroy infected cells?
B cells
NK cells
Platelets
Eosinophils
Explanation - NK cells recognize stressed cells and induce apoptosis via perforin and granzymes.
Correct answer is: NK cells
Q.60 Which cytokine is associated with inflammation and fever?
IL-1
IL-10
IL-2
IL-4
Explanation - IL‑1 promotes fever and stimulates the production of acute-phase proteins.
Correct answer is: IL-1
Q.61 The process of 'class switching' in B cells allows them to produce:
Different antigen receptors
Different antibody isotypes
More cytokines
More T cell receptors
Explanation - Class switching changes the constant region of the antibody heavy chain, altering effector functions.
Correct answer is: Different antibody isotypes
Q.62 Which of the following best describes 'antigen processing'?
Secretion of antibodies
Breaking down antigens for presentation
Transport of antigens across membranes
Synthesis of antigens by pathogens
Explanation - Antigen processing involves degrading proteins into peptides for MHC presentation.
Correct answer is: Breaking down antigens for presentation
Q.63 Which of the following is a primary function of the lymphatic system?
Produce blood cells
Filter toxins from the blood
Return interstitial fluid to circulation
Digest food proteins
Explanation - Lymph collects excess interstitial fluid and returns it to the bloodstream.
Correct answer is: Return interstitial fluid to circulation
Q.64 What is a key role of interferon-alpha?
Activate B cells
Stimulate NK cell activity
Inhibit T cell proliferation
Promote eosinophil migration
Explanation - Interferon‑α enhances the cytotoxic function of NK cells during viral infections.
Correct answer is: Stimulate NK cell activity
Q.65 The 'anaphylactic response' is primarily mediated by:
B cells
IgG antibodies
IgE antibodies
T helper cells
Explanation - IgE binds to mast cells; upon allergen exposure, it triggers a rapid degranulation causing anaphylaxis.
Correct answer is: IgE antibodies
Q.66 Which of the following is a characteristic of the adaptive immune system?
It has a memory component
It responds immediately
It uses the same receptors for all pathogens
It does not involve cytokines
Explanation - Adaptive immunity creates memory cells that enable faster responses upon re‑exposure.
Correct answer is: It has a memory component
Q.67 Which of the following is a function of dendritic cells?
Secrete antibodies
Engulf pathogens
Present antigens to T cells
Produce platelets
Explanation - Dendritic cells capture antigens and present them on MHC molecules to activate T cells.
Correct answer is: Present antigens to T cells
Q.68 Which component of the immune system is responsible for 'tagging' infected cells for destruction by cytotoxic T lymphocytes?
MHC I
MHC II
Cytokines
Complement proteins
Explanation - Cytotoxic T cells recognize peptides presented on MHC I molecules on infected cells.
Correct answer is: MHC I
Q.69 Which of the following best describes the 'phagocytosis' process?
Production of antibodies
Release of cytokines
Engulfment of pathogens by cells
Secretion of interferons
Explanation - Phagocytosis is the process by which cells like macrophages and neutrophils ingest pathogens.
Correct answer is: Engulfment of pathogens by cells
Q.70 Which immune cell type is primarily responsible for the early detection of viral infection?
Neutrophils
Macrophages
NK cells
B cells
Explanation - NK cells recognize stressed or virally infected cells and rapidly kill them.
Correct answer is: NK cells
Q.71 The 'immune checkpoint' molecules such as CTLA‑4 primarily function to:
Activate T cells
Inhibit T cell activation
Present antigens
Secrete antibodies
Explanation - Immune checkpoints regulate T cell responses to prevent autoimmunity.
Correct answer is: Inhibit T cell activation
Q.72 Which of the following best explains 'self‑tolerance'?
Immune system attacks all foreign molecules
Immune system ignores all antigens
Immune system does not attack its own cells
Immune system attacks only pathogens
Explanation - Self‑tolerance prevents the immune system from targeting body tissues.
Correct answer is: Immune system does not attack its own cells
Q.73 What is the main role of 'C3' in the complement system?
Trigger the classical pathway
Act as an opsonin
Form the membrane attack complex
Activate NK cells
Explanation - C3b binds to pathogen surfaces, marking them for phagocytosis.
Correct answer is: Act as an opsonin
Q.74 Which of the following cells produces IL-17?
Th1 cells
Th2 cells
Th17 cells
Regulatory T cells
Explanation - Th17 cells secrete IL‑17, a cytokine involved in neutrophil recruitment.
Correct answer is: Th17 cells
Q.75 The process of 'antigen presentation' requires which of the following molecules?
MHC I only
MHC II only
Both MHC I and MHC II
Cytokines
Explanation - Antigen peptides are presented on MHC I to CD8+ T cells and on MHC II to CD4+ T cells.
Correct answer is: Both MHC I and MHC II
Q.76 Which immune pathway is activated by mannose residues on bacterial surfaces?
Classical pathway
Lectin pathway
Alternative pathway
None of the above
Explanation - Lectins bind mannose on pathogens, initiating the lectin pathway of complement.
Correct answer is: Lectin pathway
Q.77 Which of the following best describes the role of 'helper T cells'?
Kill infected cells directly
Produce antibodies
Assist B cells and other immune cells
Release histamine
Explanation - Helper T cells orchestrate the adaptive immune response by secreting cytokines.
Correct answer is: Assist B cells and other immune cells
Q.78 The 'cytokine' that is critical for the differentiation of naive T cells into Th1 cells is:
IL-4
IL-12
IL-10
IL-2
Explanation - IL‑12 promotes Th1 differentiation, which is essential for cell‑mediated immunity.
Correct answer is: IL-12
Q.79 Which type of antibody is involved in the first line of adaptive immunity?
IgM
IgG
IgA
IgE
Explanation - IgM is the first antibody class produced upon initial exposure to an antigen.
Correct answer is: IgM
Q.80 Which of the following is an example of a 'memory' immune cell?
Neutrophil
Macrophage
Memory B cell
Platelet
Explanation - Memory B cells persist after an infection and quickly produce antibodies on re‑exposure.
Correct answer is: Memory B cell
Q.81 The process by which a T cell recognizes a peptide presented by an MHC molecule is:
Phagocytosis
Cytotoxicity
Antigen recognition
Opsonization
Explanation - TCRs interact with peptide‑MHC complexes to initiate T cell activation.
Correct answer is: Antigen recognition
Q.82 Which of the following is NOT a typical function of neutrophils?
Phagocytose bacteria
Release neutrophil extracellular traps (NETs)
Produce antibodies
Secrete cytokines
Explanation - Neutrophils are innate immune cells that engulf pathogens but do not produce antibodies.
Correct answer is: Produce antibodies
Q.83 Which of the following best describes the 'humoral immune response'?
Cell‑mediated by T cells
Antibody production by B cells
Phagocytosis by macrophages
Activation of NK cells
Explanation - Humoral immunity relies on B cells producing antibodies to neutralize extracellular antigens.
Correct answer is: Antibody production by B cells
Q.84 Which cell surface marker distinguishes naive from memory B cells?
CD27
CD4
CD8
CD19
Explanation - Memory B cells express CD27, whereas naive B cells generally do not.
Correct answer is: CD27
Q.85 The presence of which antibody is an indicator of long‑term immunity after vaccination?
IgM
IgG
IgE
IgA
Explanation - IgG persists for years after vaccination and provides lasting protection.
Correct answer is: IgG
Q.86 Which of the following is a key function of complement protein C4?
Opsonization
Formation of the membrane attack complex
Cleavage of C3
Binding to pathogens in the lectin pathway
Explanation - C4 is cleaved to C4b which participates in the classical pathway, leading to C3 activation.
Correct answer is: Cleavage of C3
Q.87 Which of the following is a hallmark of the secondary immune response?
Lower antibody affinity
Longer time to reach peak response
Involvement of memory cells
Absence of class switching
Explanation - Memory cells enable a faster and more robust secondary immune response.
Correct answer is: Involvement of memory cells
Q.88 The 'Th1/Th2 paradigm' describes:
Two different types of T cells that produce the same cytokines
Two subsets of helper T cells with distinct cytokine profiles
The division of B cells into two lineages
The stages of the complement cascade
Explanation - Th1 cells secrete IFN‑γ for cell‑mediated immunity; Th2 cells secrete IL‑4 for humoral immunity.
Correct answer is: Two subsets of helper T cells with distinct cytokine profiles
Q.89 Which cytokine is essential for the differentiation of regulatory T cells?
IL-2
IL-10
IL-17
IL-4
Explanation - IL‑2 supports the development and maintenance of regulatory T cells.
Correct answer is: IL-2
Q.90 Which of the following is a typical feature of innate immune memory (trained immunity)?
Specific antigen recognition
Rapid response upon re‑exposure to the same pathogen
Production of high‑affinity antibodies
Involvement of T cell receptors
Explanation - Trained immunity is an enhanced innate response to a previously encountered stimulus.
Correct answer is: Rapid response upon re‑exposure to the same pathogen
Q.91 Which of the following is a primary role of T regulatory cells in the immune system?
Activate B cells
Stimulate cytokine production
Suppress autoimmune responses
Directly kill infected cells
Explanation - Tregs maintain self‑tolerance by inhibiting autoreactive immune cells.
Correct answer is: Suppress autoimmune responses
Q.92 Which of the following molecules is a key component of the inflammasome?
Caspase‑1
C5a
IgG
IL‑2
Explanation - Caspase‑1 cleaves pro‑IL‑1β to its active form as part of inflammasome signaling.
Correct answer is: Caspase‑1
Q.93 The term 'immunosurveillance' refers to:
The process of immune cells constantly monitoring for abnormalities
The production of antibodies against self‑antigens
The destruction of all pathogens simultaneously
The suppression of the immune system in tumors
Explanation - Immunosurveillance is the continuous monitoring by immune cells for infected or cancerous cells.
Correct answer is: The process of immune cells constantly monitoring for abnormalities
Q.94 Which of the following is a characteristic of a cytokine storm during severe viral infection?
Decreased immune cell recruitment
Reduced cytokine production
Excessive cytokine release causing tissue damage
Activation of regulatory T cells only
Explanation - A cytokine storm involves uncontrolled cytokine release that can damage host tissues.
Correct answer is: Excessive cytokine release causing tissue damage
Q.95 Which of the following best describes the concept of 'immune evasion' by viruses?
Virus directly destroys immune cells
Virus hides from or suppresses host immune responses
Virus produces more antibodies
Virus does not interact with the immune system
Explanation - Viruses evolve strategies to avoid detection or neutralization by the immune system.
Correct answer is: Virus hides from or suppresses host immune responses
Q.96 Which of the following molecules is a co-stimulatory ligand on antigen-presenting cells?
CD80
CD3
CD8
CD4
Explanation - CD80 binds CD28 on T cells, providing a co‑stimulus essential for activation.
Correct answer is: CD80
Q.97 Which of the following best characterizes the 'adaptive immune system'?
It has no memory component
It responds instantly to any pathogen
It is highly specific and develops memory
It uses innate mechanisms exclusively
Explanation - Adaptive immunity tailors responses to specific antigens and retains memory.
Correct answer is: It is highly specific and develops memory
Q.98 Which of the following is an example of an intracellular pathogen that triggers a cytotoxic T cell response?
Streptococcus pyogenes
Staphylococcus aureus
Herpes simplex virus
Clostridium difficile
Explanation - HSV infects cells, and infected cells present peptides via MHC I to cytotoxic T cells.
Correct answer is: Herpes simplex virus
Q.99 Which of the following best describes 'class switching' in B cells?
Switching of T cell receptor specificity
Switching of antibody constant region while maintaining antigen specificity
Switching from IgE to IgA
Switching from innate to adaptive immunity
Explanation - Class switching changes the Fc region to alter effector functions while keeping the variable region intact.
Correct answer is: Switching of antibody constant region while maintaining antigen specificity
Q.100 Which of the following cells is NOT involved in the clearance of apoptotic cells?
Macrophages
Neutrophils
Dendritic cells
B cells
Explanation - B cells are not major phagocytes for apoptotic cells; macrophages, neutrophils, and dendritic cells handle them.
Correct answer is: B cells
Q.101 Which of the following best describes the 'antibody-dependent cellular phagocytosis' (ADCP) mechanism?
Phagocytes ingest pathogens after being coated with antibodies
T cells kill infected cells directly
NK cells release perforin
Complement forms membrane attack complexes
Explanation - ADCP involves antibodies tagging pathogens, enhancing phagocytosis by cells.
Correct answer is: Phagocytes ingest pathogens after being coated with antibodies
Q.102 Which of the following best describes the 'immunoglobulin class switch recombination' process?
Change of the variable region of antibodies
Recombination of VDJ segments in TCRs
Switching antibody heavy chain constant region gene segments
Production of new B cell receptors
Explanation - Class switching changes the constant region of the heavy chain while preserving antigen specificity.
Correct answer is: Switching antibody heavy chain constant region gene segments
Q.103 Which of the following is the main function of IL-10 in immune regulation?
Promote inflammation
Suppress immune responses
Activate NK cells
Stimulate B cell proliferation
Explanation - IL‑10 is an anti‑inflammatory cytokine that limits immune activation and prevents tissue damage.
Correct answer is: Suppress immune responses
Q.104 Which of the following is a hallmark of T helper 1 (Th1) cell activity?
Secretion of IL-4
Induction of B cell class switching to IgE
Activation of macrophages
Suppression of cytotoxic T cell function
Explanation - Th1 cells produce IFN‑γ, which activates macrophages to kill intracellular pathogens.
Correct answer is: Activation of macrophages
Q.105 Which of the following molecules is a primary marker for NK cell activation?
CD3
CD16
CD28
CD4
Explanation - CD16 (FcγRIII) on NK cells binds antibody Fc regions, facilitating ADCC.
Correct answer is: CD16
Q.106 Which of the following best describes the role of the thymus in T cell development?
Maturation of B cells
Production of antibodies
Negative selection and maturation of T cells
Storage of memory cells
Explanation - The thymus is where T cells mature and undergo positive/negative selection.
Correct answer is: Negative selection and maturation of T cells
Q.107 Which of the following is NOT a typical function of complement?
Opsonization
Direct lysis of pathogens
Recruitment of inflammatory cells
Activation of B cells
Explanation - Complement enhances phagocytosis, forms MAC, and signals inflammation; it does not directly activate B cells.
Correct answer is: Activation of B cells
Q.108 Which of the following best describes 'trained immunity'?
Adaptive memory based on T cell receptors
Innate immune memory-like response after first exposure
Production of memory B cells
Formation of long-lived plasma cells
Explanation - Trained immunity is a form of innate memory that enhances responses to subsequent stimuli.
Correct answer is: Innate immune memory-like response after first exposure
Q.109 Which of the following cytokines is a hallmark of Th17 cells?
IL-17
IL-4
IL-10
IFN-γ
Explanation - IL‑17 is produced by Th17 cells and promotes neutrophil recruitment.
Correct answer is: IL-17
Q.110 Which of the following is an example of a cell surface marker for macrophage activation?
CD69
CD86
CD4
CD8
Explanation - CD86 is up‑regulated on activated antigen‑presenting cells, including macrophages.
Correct answer is: CD86
Q.111 Which of the following best explains the mechanism of 'antigenic drift'?
Large genomic rearrangements in viruses
Small mutations leading to changes in antigenic epitopes
Loss of the antigen altogether
Replication of host DNA
Explanation - Antigenic drift refers to gradual mutations that alter virus antigens, evading immune detection.
Correct answer is: Small mutations leading to changes in antigenic epitopes
Q.112 Which of the following best describes the role of the spleen in immune function?
Filter blood and host innate immune responses
Serve as a site of B cell maturation
Produce T cells
Produce antibodies in large amounts
Explanation - The spleen filters blood, removes old erythrocytes, and supports immune cell interactions.
Correct answer is: Filter blood and host innate immune responses
Q.113 Which of the following molecules is the key for the recognition of antigen by B cell receptors?
MHC II
Antigen
TCR
Cytokine
Explanation - B cell receptors directly bind to antigens on the cell surface or soluble form.
Correct answer is: Antigen
Q.114 Which of the following is an indicator of a robust primary immune response?
High IgG levels after 1 week
Rapid IgM rise within 24 hours
Presence of memory cells
High IL-10 production
Explanation - Primary responses often show a quick rise of IgM before IgG levels increase.
Correct answer is: Rapid IgM rise within 24 hours
Q.115 Which of the following is a feature of the 'innate immune system'?
Memory cells
Specificity to a single antigen
Rapid response within hours
Long‑lasting protection
Explanation - Innate immunity provides an immediate, non‑specific defense.
Correct answer is: Rapid response within hours
Q.116 Which of the following best describes 'immune tolerance'?
Immune system attacks all foreign antigens
Immune system cannot recognize pathogens
Immune system does not attack its own cells
Immune system is permanently suppressed
Explanation - Tolerogenic mechanisms prevent autoimmunity by ignoring self‑antigens.
Correct answer is: Immune system does not attack its own cells
Q.117 Which of the following is an example of a cytokine that promotes Th2 differentiation?
IL-12
IFN-γ
IL-4
TNF-α
Explanation - IL‑4 signals naive CD4+ T cells to become Th2 cells, which aid humoral immunity.
Correct answer is: IL-4
Q.118 Which of the following best explains the term 'adaptive immunity'?
Non‑specific, immediate response
Highly specific, long‑lasting response with memory
Involvement of only innate cells
Only antibody production
Explanation - Adaptive immunity tailors responses to specific antigens and retains memory.
Correct answer is: Highly specific, long‑lasting response with memory
Q.119 Which of the following best describes the role of CD8+ T cells?
Help B cells produce antibodies
Present antigens on MHC II
Directly kill infected or tumor cells
Produce cytokines for allergic reactions
Explanation - CD8+ T cells recognize antigens presented on MHC I and induce target cell death.
Correct answer is: Directly kill infected or tumor cells
Q.120 Which of the following is a hallmark of the secondary immune response?
High IgM levels
Slow antibody production
Memory B cells producing IgG
No class switching
Explanation - Secondary responses are rapid, involve memory cells, and yield high‑affinity IgG.
Correct answer is: Memory B cells producing IgG
Q.121 Which of the following best describes 'phagocytosis'?
Release of cytokines by T cells
Ingestion and destruction of pathogens by immune cells
Secretion of antibodies
Presentation of antigens on MHC I
Explanation - Phagocytosis is performed by macrophages, neutrophils, and dendritic cells.
Correct answer is: Ingestion and destruction of pathogens by immune cells
Q.122 Which of the following is a function of IgA antibodies?
Activate complement system
Neutralize toxins and viruses at mucosal surfaces
Bind to basophils for allergic reactions
Induce cell‑mediated immunity
Explanation - IgA is secreted in mucosal areas, blocking pathogen entry.
Correct answer is: Neutralize toxins and viruses at mucosal surfaces
Q.123 Which of the following is a key mediator of inflammation in the immune response?
IL-10
IL-4
TNF-α
IgM
Explanation - Tumor necrosis factor‑α promotes fever, vasodilation, and chemotaxis of immune cells.
Correct answer is: TNF-α
Q.124 Which of the following best describes the 'classical complement pathway'?
Initiated by mannose binding
Triggered by antibody-antigen complexes
Activated by bacterial lipopolysaccharide
Requires C3 convertase only
Explanation - The classical pathway starts when C1q binds to antibodies bound to antigens.
Correct answer is: Triggered by antibody-antigen complexes
Q.125 Which of the following best describes the role of the MHC class II molecule?
Present peptides to CD8+ T cells
Present peptides to CD4+ T helper cells
Present antigens to NK cells
Present antigens to B cells
Explanation - MHC II presents extracellular-derived peptides to CD4+ T cells.
Correct answer is: Present peptides to CD4+ T helper cells
Q.126 Which of the following is a characteristic of NK cell cytotoxicity?
Requires antigen presentation on MHC II
Relies on perforin and granzymes
Only activated by IL-2
Requires antibody coating
Explanation - NK cells use perforin to create pores and granzymes to trigger apoptosis in target cells.
Correct answer is: Relies on perforin and granzymes
Q.127 Which of the following is an example of a cell that can present antigens via both MHC I and MHC II pathways?
B cells
Macrophages
Erythrocytes
Platelets
Explanation - Macrophages process endogenous and exogenous antigens and present them on both MHC classes.
Correct answer is: Macrophages
Q.128 Which cytokine is primarily involved in the differentiation of Th1 cells?
IL-4
IL-12
IL-10
IL-2
Explanation - IL‑12 drives naive CD4+ T cells toward a Th1 phenotype, promoting cell‑mediated immunity.
Correct answer is: IL-12
Q.129 Which of the following best describes the 'cytokine storm' seen in severe infections?
Under‑production of cytokines
Balanced cytokine release
Excessive cytokine release causing tissue damage
No cytokine involvement
Explanation - A cytokine storm results from uncontrolled cytokine production that can harm host tissues.
Correct answer is: Excessive cytokine release causing tissue damage
Q.130 Which of the following is a hallmark of the innate immune system?
Memory formation
High specificity
Rapid, non‑specific response
Long‑lasting protection
Explanation - Innate immunity responds quickly and non‑specifically to pathogens.
Correct answer is: Rapid, non‑specific response
Q.131 Which of the following molecules is a major component of the membrane attack complex (MAC)?
C3
C4
C5b
C3b
Explanation - C5b initiates MAC formation, creating pores in target membranes.
Correct answer is: C5b
Q.132 Which of the following is the major cytokine responsible for stimulating B cell class switching to IgE?
IL-2
IL-4
IL-6
IL-10
Explanation - IL‑4 promotes class switching from IgM to IgE, which is key in allergic responses.
Correct answer is: IL-4
Q.133 Which of the following best explains the term 'immune checkpoint inhibitors'?
Drugs that enhance T cell activation by blocking inhibitory receptors
Vaccines that block checkpoints
Antibodies that neutralize pathogens
Compounds that suppress innate immunity
Explanation - Checkpoint inhibitors release the brakes on T cells, improving anti‑tumor immunity.
Correct answer is: Drugs that enhance T cell activation by blocking inhibitory receptors
Q.134 Which of the following is a major function of the lymphatic vessels?
Deliver oxygen to tissues
Return interstitial fluid to the bloodstream
Produce immune cells
Filter blood in the liver
Explanation - Lymphatic vessels collect excess fluid from tissues and return it to circulation.
Correct answer is: Return interstitial fluid to the bloodstream
Q.135 Which of the following is NOT a typical feature of an acute inflammatory response?
Redness
Heat
Edema
Permanent tissue necrosis
Explanation - Acute inflammation is reversible; permanent necrosis is a sign of severe damage or chronic inflammation.
Correct answer is: Permanent tissue necrosis
Q.136 Which of the following best describes the function of IgG antibodies?
Activate complement exclusively
Neutralize toxins and pathogens in mucosal surfaces
Provide long‑term immunity and facilitate opsonization
Bind to basophils to cause histamine release
Explanation - IgG circulates for months, mediates opsonization, and neutralizes pathogens.
Correct answer is: Provide long‑term immunity and facilitate opsonization