Understanding the structure and function of immunoglobulins is essential for B. Pharm students studying immunology and pharmacology. Immunoglobulins (antibodies) are glycoproteins composed of two heavy and two light chains with variable and constant regions that determine antigen-binding and effector functions. Key concepts include isotypes (IgG, IgM, IgA, IgD, IgE), subclasses, hinge regions, disulfide bonds, complement activation, opsonization, neutralization, and Fc receptor interactions such as neonatal FcRn-mediated recycling. Molecular details—CDRs, somatic hypermutation, class switch recombination, glycosylation, and fragmentation (Fab, Fc, F(ab’)2)—underpin therapeutic antibody design and vaccine responses. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which polypeptide chain composition forms a typical immunoglobulin molecule?
- Two heavy chains and two light chains
- One heavy chain and one light chain
- Three heavy chains and one light chain
- Four light chains
Correct Answer: Two heavy chains and two light chains
Q2. The antigen-binding site of an antibody is primarily formed by which regions?
- Constant regions (CH and CL)
- Hinge region
- Complementarity-determining regions (CDRs) of variable domains
- Fc glycosylation sites
Correct Answer: Complementarity-determining regions (CDRs) of variable domains
Q3. Which immunoglobulin is the first to appear in the primary immune response?
- IgG
- IgM
- IgA
- IgE
Correct Answer: IgM
Q4. Which fragment is produced by papain digestion of an IgG molecule?
- One Fc fragment and one F(ab’)2 fragment
- Two Fab fragments and one Fc fragment
- Only Fc fragments
- Polypeptide fragments without antigen-binding sites
Correct Answer: Two Fab fragments and one Fc fragment
Q5. The neonatal Fc receptor (FcRn) primarily contributes to which property of IgG?
- Mucosal secretion of IgG
- Short plasma half-life of IgG
- Placental transfer and prolonged half-life of IgG
- Activation of classical complement pathway
Correct Answer: Placental transfer and prolonged half-life of IgG
Q6. Which Ig isotype is predominantly found in mucosal secretions and exists as a dimer with a secretory component?
- IgG
- IgM
- IgA
- IgE
Correct Answer: IgA
Q7. Class switch recombination in B cells changes which of the following?
- Antigen specificity determined by V(D)J region
- Heavy chain constant region (isotype) while preserving antigen specificity
- Light chain variable region sequence
- CDR length in light chains only
Correct Answer: Heavy chain constant region (isotype) while preserving antigen specificity
Q8. Which immunoglobulin is most efficient at activating the classical complement pathway?
- IgE
- IgA monomer
- IgM pentamer
- IgD
Correct Answer: IgM pentamer
Q9. Opsonization by antibodies enhances which process?
- Antibody glycosylation
- Phagocytosis of microbes by macrophages and neutrophils
- Class switch recombination
- Somatic hypermutation
Correct Answer: Phagocytosis of microbes by macrophages and neutrophils
Q10. The hinge region of an antibody contributes primarily to which property?
- Antigen specificity
- Flexibility between Fab and Fc for antigen binding and effector function
- Binding to Fc receptors exclusively
- Glycosylation site for complement activation
Correct Answer: Flexibility between Fab and Fc for antigen binding and effector function
Q11. Somatic hypermutation occurs in which region and contributes to what?
- Constant region causing isotype change
- Variable region increasing antibody affinity during affinity maturation
- Fc region altering receptor binding
- J chain sequence altering secretory transport
Correct Answer: Variable region increasing antibody affinity during affinity maturation
Q12. Which enzyme classically mediates the joining of V, D, and J gene segments during B-cell development?
- Activation-induced cytidine deaminase (AID)
- RAG1/RAG2 recombinase
- DNA polymerase I
- Restriction endonuclease
Correct Answer: RAG1/RAG2 recombinase
Q13. Which IgG subclass is least effective at complement activation?
- IgG1
- IgG2
- IgG3
- IgG4
Correct Answer: IgG4
Q14. The J chain is important for which immunoglobulin property?
- Monomerization of IgG
- Pentamerization of IgM and dimerization of IgA for secretion
- Glycosylation of Fc region
- Binding to neonatal Fc receptor
Correct Answer: Pentamerization of IgM and dimerization of IgA for secretion
Q15. Affinity and avidity differ in that affinity refers to ___ and avidity refers to ___?
- Strength of single antigen–antibody bond; overall strength of multivalent interactions
- Overall strength of multivalent interactions; strength of single bond
- Fc–receptor binding; complement binding
- Isotype switching; somatic hypermutation
Correct Answer: Strength of single antigen–antibody bond; overall strength of multivalent interactions
Q16. Which fragment retains the Fc-mediated effector functions such as complement activation?
- Fab fragment
- F(ab’)2 fragment
- Fc fragment
- Light chain only
Correct Answer: Fc fragment
Q17. Glycosylation of the Fc region most directly affects which of the following?
- Antigen specificity of the Fab
- Fc receptor binding and effector functions
- V(D)J recombination frequency
- B cell receptor expression on naïve B cells
Correct Answer: Fc receptor binding and effector functions
Q18. Which technique is commonly used to measure antigen-antibody binding affinity in the lab?
- Southern blotting
- ELISA or surface plasmon resonance (SPR)
- Gram staining
- Flow cytometric karyotyping
Correct Answer: ELISA or surface plasmon resonance (SPR)
Q19. IgE-mediated functions are primarily associated with which physiological response?
- Neutralization of toxins in blood
- Allergic reactions and defense against helminths
- Classical complement activation in serum bactericidal activity
- Mucosal transport across epithelium
Correct Answer: Allergic reactions and defense against helminths
Q20. Which statement best describes an idiotype?
- Genetically determined constant-region polymorphism between individuals
- Unique set of antigenic determinants in the variable region of a specific antibody
- A conserved Fc receptor on macrophages
- A type of complement protein
Correct Answer: Unique set of antigenic determinants in the variable region of a specific antibody
Q21. In therapeutic monoclonal antibody design, humanization primarily aims to reduce what?
- Antigen-binding affinity
- Immunogenicity of non-human sequences while retaining antigen specificity
- Fc-mediated effector functions
- Half-life via FcRn interactions
Correct Answer: Immunogenicity of non-human sequences while retaining antigen specificity
Q22. Which immunoglobulin is mainly present on the surface of mature naïve B cells as a B-cell receptor?
- Secreted IgA
- Membrane-bound IgM and IgD
- Circulating IgG only
- Free light chains
Correct Answer: Membrane-bound IgM and IgD
Q23. Pepsin digestion of an IgG molecule yields which major fragments?
- Two Fab fragments and one Fc fragment
- F(ab’)2 fragment and degraded Fc fragments
- Only light chains
- Intact IgG without fragmentation
Correct Answer: F(ab’)2 fragment and degraded Fc fragments
Q24. Complement activation by antibodies via the classical pathway is initiated by which antibody feature?
- Binding of monomeric IgA to antigen
- Binding of complement component C1q to Fc regions of IgM or clustered IgG
- Interaction of Fab with bacterial capsule
- Glycosylation of light chains
Correct Answer: Binding of complement component C1q to Fc regions of IgM or clustered IgG
Q25. Allotype refers to which characteristic of immunoglobulins?
- Antigen-binding site variation within an individual
- Allelic variation in constant region sequences among individuals of the same species
- Pathogen-specific idiotype diversity
- Glycosylation pattern unique to each antigen
Correct Answer: Allelic variation in constant region sequences among individuals of the same species
Q26. Which statement about IgM is correct?
- IgM is primarily monomeric in serum and crosses the placenta
- Secreted IgM is pentameric, efficient at complement activation, and is early in immune response
- IgM has the longest half-life among isotypes due to FcRn
- IgM is the main isotype for mucosal immunity
Correct Answer: Secreted IgM is pentameric, efficient at complement activation, and is early in immune response
Q27. The major role of the constant (C) region of the heavy chain is to:
- Determine antigen specificity
- Mediate effector functions such as complement activation and Fc receptor binding
- Create CDR loops
- Undergo V(D)J recombination
Correct Answer: Mediate effector functions such as complement activation and Fc receptor binding
Q28. Which immunoglobulin is primarily involved in allergic hypersensitivity and immediate-type reactions?
- IgG
- IgD
- IgE
- IgM
Correct Answer: IgE
Q29. Which process creates diversity in the light and heavy chain variable regions during early B-cell development?
- Class switch recombination
- Somatic hypermutation in germinal centers
- V(D)J recombination involving RAG enzymes
- Fc glycosylation changes
Correct Answer: V(D)J recombination involving RAG enzymes
Q30. Secretory IgA protects mucosal surfaces mainly by which mechanism?
- Fixing complement in mucosal secretions to lyse bacteria
- Neutralizing pathogens and toxins and preventing attachment to epithelium
- Activating NK cells via Fc receptors in the gut lumen
- Increasing systemic opsonization in blood
Correct Answer: Neutralizing pathogens and toxins and preventing attachment to epithelium
I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.
Mail- Sachin@pharmacyfreak.com