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5.3 Class Switching & Isotype Regulation — Test 1
Q1. Class (isotype) switching changes the antibody's:✓ Heavy-chain constant region (and thus effector function)
Q2. Class-switch recombination is initiated by the enzyme:✓ Activation-induced cytidine deaminase (AID)
Q3. Switch (S) regions involved in class switching are located:✓ Upstream of each constant-region gene (except Cδ)
Q4. IL-4 directs class switching toward which isotype(s)?✓ IgE (and IgG1 in mice)
Q5. TGF-β is an important cytokine for switching to:✓ IgA
Q6. IFN-γ promotes switching toward isotypes that are good at:✓ Opsonisation and complement fixation (e.g. IgG subclasses)
Q7. The contact signal essential for T-dependent class switching is:✓ CD40L (on the T cell) engaging CD40 (on the B cell)
Q8. Hyper-IgM syndrome is characterised by:✓ High IgM but low IgG, IgA and IgE due to failed switching
Q9. Class switching, unlike V(D)J recombination, does NOT change:✓ The antigen specificity of the antibody
Q10. Germline (sterile) transcription of a switch region serves to:✓ Make the S region accessible to AID for targeted switching
Q11. Switching to IgA is especially important at:✓ Mucosal surfaces
Q12. The DNA deleted during class-switch recombination is:✓ Excised as a switch (circular) DNA and lost
Q13. Because switching deletes upstream constant genes, a B cell that has switched to IgG can no longer make:✓ IgM
Q14. Antibody affinity and isotype together determine an antibody's:✓ Effectiveness and the effector mechanisms it can recruit
Q15. Class switching most commonly takes place in the:✓ Germinal centres of secondary lymphoid organs
Q16. T-independent antigens generally produce little class switching because they:✓ Lack the T-cell help (CD40L, cytokines) needed for switching
Q17. A key clinical consequence of CD40L deficiency (X-linked hyper-IgM) is:✓ Susceptibility to pyogenic and opportunistic infections with poor germinal centres
Q18. The order in which isotypes can be produced from a single VDJ is constrained because:✓ Switching deletes upstream constant genes, allowing only downstream isotypes thereafter
Q19. Cytokine control of isotype switching is important because it:✓ Matches the antibody isotype to the type of pathogen/response
Q20. Antibody class switching results from:✓ Shuffling exons from one constant-region type to another, joined to the V(D)J unit
Q21. How do affinity maturation and isotype (class) switching differ?✓ Affinity maturation raises antibody affinity; class switching changes the antibody class
Q22. Match each cytokine/signal with the switching outcome it favours and select the correct option.✓ A-ii, B-i, C-iv, D-iii