Q.1 Which immunoglobulin is predominantly found in mucosal secretions?
IgG
IgA
IgM
IgE
Explanation - IgA is the main antibody in mucosal secretions like saliva, tears, and intestinal fluids, providing immune protection at mucosal surfaces.
Correct answer is: IgA
Q.2 M cells in the Peyer's patches are primarily responsible for:
Producing antibodies
Antigen uptake and transport
Secreting cytokines
Activating T cells directly
Explanation - M cells are specialized epithelial cells in Peyer's patches that sample antigens from the gut lumen and transport them to underlying immune cells.
Correct answer is: Antigen uptake and transport
Q.3 Which of the following is a key cytokine involved in IgA class switching?
IL-2
IL-4
TGF-β
IFN-γ
Explanation - TGF-β (Transforming Growth Factor-beta) promotes class switching to IgA in B cells, which is critical for mucosal immunity.
Correct answer is: TGF-β
Q.4 Secretory IgA (sIgA) protects mucosal surfaces primarily by:
Opsonization for phagocytosis
Neutralizing pathogens and toxins
Activating complement
Inducing apoptosis in infected cells
Explanation - sIgA binds pathogens and toxins, preventing their attachment and entry into epithelial cells without causing inflammation.
Correct answer is: Neutralizing pathogens and toxins
Q.5 Which cells in the gut epithelium produce antimicrobial peptides such as defensins?
Goblet cells
Paneth cells
Enterocytes
M cells
Explanation - Paneth cells, located at the base of intestinal crypts, secrete antimicrobial peptides to maintain gut microbial balance and prevent infections.
Correct answer is: Paneth cells
Q.6 The gut-associated lymphoid tissue (GALT) includes all EXCEPT:
Peyer's patches
Tonsils
Spleen
Appendix
Explanation - GALT consists of mucosal lymphoid tissues such as Peyer's patches, tonsils, and appendix, while the spleen is a systemic lymphoid organ.
Correct answer is: Spleen
Q.7 Which of the following best describes oral tolerance?
Activation of T cells by oral antigens
Suppression of immune responses to ingested antigens
Production of IgE against food antigens
Enhanced inflammation in gut mucosa
Explanation - Oral tolerance is a mechanism by which the immune system avoids overreacting to harmless antigens in food or commensal bacteria.
Correct answer is: Suppression of immune responses to ingested antigens
Q.8 Which chemokine is important for the homing of IgA-secreting plasma cells to the gut?
CCL25
CXCL8
CCL19
CXCL10
Explanation - CCL25 interacts with CCR9 on IgA-secreting plasma cells, guiding their migration to the small intestine for mucosal immunity.
Correct answer is: CCL25
Q.9 In mucosal immunity, dendritic cells can extend processes through epithelial tight junctions to:
Secrete antibodies
Capture antigens from the lumen
Kill infected cells
Produce mucus
Explanation - Mucosal dendritic cells sample antigens directly from the lumen to initiate adaptive immune responses without disrupting the epithelium.
Correct answer is: Capture antigens from the lumen
Q.10 Which molecule is essential for transporting dimeric IgA across epithelial cells into secretions?
J chain
CD28
FcRn
Poly-Ig receptor
Explanation - The poly-Ig receptor binds dimeric IgA (linked by the J chain) and transports it across epithelial cells to form secretory IgA.
Correct answer is: Poly-Ig receptor
Q.11 Which mucosal site contains the largest number of lymphocytes in the body?
Spleen
Bone marrow
Gut
Lymph nodes
Explanation - The gut harbors the largest lymphocyte population in the body due to its constant exposure to food antigens and microbes.
Correct answer is: Gut
Q.12 Commensal bacteria in the gut contribute to mucosal immunity by:
Directly producing IgA
Stimulating immune system maturation
Causing inflammation
Blocking all immune responses
Explanation - Commensal microbiota interact with the immune system, promoting the development of mucosal lymphoid tissues and regulatory mechanisms.
Correct answer is: Stimulating immune system maturation
Q.13 Which cytokine is primarily involved in the differentiation of Th17 cells in the mucosa?
IL-6
IL-2
IL-10
IFN-γ
Explanation - IL-6, along with TGF-β, drives differentiation of naïve T cells into Th17 cells, which protect mucosal surfaces against extracellular pathogens.
Correct answer is: IL-6
Q.14 Secretory IgA can prevent pathogen attachment by:
Neutralizing cytokines
Immune exclusion
Complement activation
Phagocytosis
Explanation - sIgA binds antigens and pathogens in the lumen, preventing their adherence to epithelial cells, a process called immune exclusion.
Correct answer is: Immune exclusion
Q.15 Which enzyme is critical for IgA production in B cells?
Activation-induced cytidine deaminase (AID)
RNA polymerase II
DNA ligase
Topoisomerase II
Explanation - AID mediates class switch recombination and somatic hypermutation, allowing B cells to produce IgA and other antibody classes.
Correct answer is: Activation-induced cytidine deaminase (AID)
Q.16 Peyer's patches are most abundant in which part of the gastrointestinal tract?
Stomach
Jejunum
Ileum
Colon
Explanation - Peyer's patches, organized lymphoid follicles, are concentrated in the ileum and are essential for sampling gut antigens.
Correct answer is: Ileum
Q.17 Which type of T cell is crucial for helping B cells produce IgA at mucosal sites?
Cytotoxic T cells
Treg cells
Th2 cells
Follicular helper T cells
Explanation - Follicular helper T (Tfh) cells provide signals via cytokines and CD40L to promote B cell class switching to IgA in mucosal tissues.
Correct answer is: Follicular helper T cells
Q.18 Which mucosal immune mechanism helps control commensal bacteria while limiting inflammation?
Inflammatory cytokine release
Regulatory T cell induction
Complement activation
Phagocytosis by neutrophils
Explanation - Regulatory T cells suppress excessive immune responses to commensal bacteria, maintaining mucosal tolerance.
Correct answer is: Regulatory T cell induction
Q.19 The main role of goblet cells in mucosal immunity is to:
Secrete antibodies
Produce mucus
Phagocytose bacteria
Present antigens
Explanation - Goblet cells secrete mucus that forms a protective barrier on mucosal surfaces, trapping pathogens and preventing direct contact with epithelial cells.
Correct answer is: Produce mucus
Q.20 Which receptor on dendritic cells recognizes microbial components in the gut?
Toll-like receptor (TLR)
B cell receptor (BCR)
Fc receptor
Complement receptor
Explanation - TLRs on dendritic cells detect pathogen-associated molecular patterns (PAMPs), initiating immune responses in the mucosa.
Correct answer is: Toll-like receptor (TLR)
Q.21 Which component of secretory IgA protects it from proteolytic degradation in the gut?
J chain
Secretory component
Fc portion
Hinge region
Explanation - The secretory component, derived from the poly-Ig receptor, shields sIgA from enzymatic degradation in mucosal secretions.
Correct answer is: Secretory component
Q.22 In mucosal immunity, which cells are primarily responsible for antigen presentation to T cells?
B cells
Epithelial cells
Dendritic cells
Goblet cells
Explanation - Dendritic cells capture antigens at mucosal surfaces and present them to T cells, initiating adaptive immune responses.
Correct answer is: Dendritic cells
Q.23 Which of the following is an example of a mucosal-associated lymphoid tissue (MALT)?
Thymus
Bone marrow
Tonsils
Spleen
Explanation - Tonsils are part of MALT, specialized for immune responses at mucosal surfaces in the oropharyngeal region.
Correct answer is: Tonsils
Q.24 Which signaling molecule is essential for IgA class switching in B cells located in Peyer's patches?
CD40-CD40L interaction
TCR-MHC I interaction
IL-2 receptor signaling
Fas-FasL interaction
Explanation - CD40 on B cells interacts with CD40L on T helper cells, providing critical signals for class switch recombination to IgA in mucosal lymphoid tissues.
Correct answer is: CD40-CD40L interaction