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7.4 Complement Activation Pathways — Test 1
Q1. The three pathways of complement activation are the:✓ Classical, lectin and alternative pathways
Q2. The classical pathway is initiated when C1q binds to:✓ Antibody (IgG or IgM) bound to antigen
Q3. The lectin pathway is initiated by:✓ Mannose-binding lectin (MBL) binding microbial carbohydrates
Q4. The alternative pathway is initiated by:✓ Spontaneous low-level C3 hydrolysis that is stabilised on microbial surfaces
Q5. All three pathways converge on the formation of:✓ A C3 convertase that cleaves C3
Q6. The C3 convertase of the classical and lectin pathways is:✓ C4b2a
Q7. The C3 convertase of the alternative pathway is:✓ C3bBb
Q8. After C3 is cleaved, the C5 convertase cleaves C5 to generate:✓ C5a (anaphylatoxin) and C5b (which nucleates the MAC)
Q9. The terminal (lytic) pathway, common to all three, assembles the:✓ Membrane attack complex (C5b–C9)
Q10. Which immunoglobulin is the most efficient activator of the classical pathway?✓ IgM (a single bound pentamer can activate C1q)
Q11. The lectin pathway differs from the classical pathway mainly in that it:✓ Is antibody-independent, recognising microbial carbohydrates directly
Q12. The alternative pathway provides immediate defence because it:✓ Operates continuously and is amplified on any unprotected (microbial) surface
Q13. Factor D in the alternative pathway functions to:✓ Cleave factor B (when bound to C3b) to form the convertase
Q14. Properdin stabilises the alternative-pathway convertase, thereby:✓ Prolonging C3bBb activity and amplifying complement activation
Q15. C1 inhibitor (C1-INH) regulates the classical pathway by:✓ Inactivating C1r/C1s (and limiting early activation)
Q16. On host cell surfaces, the alternative pathway is kept in check by regulators such as:✓ Factor H and DAF (CD55)
Q17. A key advantage of having three pathways is that complement can be activated:✓ By antibody-dependent and antibody-independent (innate) triggers
Q18. The amplification loop of complement is driven largely by:✓ Newly generated C3b feeding back into more convertase formation
Q19. Mannose-binding lectin (MBL) deficiency predisposes individuals to:✓ Increased susceptibility to certain infections, especially in early childhood
Q20. The classical complement pathway is activated by:✓ Antigen–antibody (immune) complexes
Q21. The alternative complement pathway is activated by:✓ Microbial surfaces or their products (antibody-independently)
Q22. The classical pathway of complement is most closely linked to:✓ Adaptive immunity (it is antibody-triggered)
Q23. The C3 convertase of the classical pathway is:✓ C4b2a
Q24. The C3 convertase of the alternative pathway is:✓ C3bBb
Q25. The C5 convertase of the alternative pathway is:✓ C3bBb3b
Q26. The C5 convertase of the classical pathway is:✓ C4b2a3b
Q27. The alternative-pathway C3 convertase is stabilised by:✓ Properdin
Q28. Activation of the first complement component C1 requires which element?✓ Calcium (Ca)
Q29. Which factors are involved in the alternative pathway?✓ Both factor B and factor D
Q30. In the alternative pathway, complement component C3 is cleaved by:✓ C3bBb
Q31. The first complement component bound by IgG in the classical pathway is:✓ C1q
Q32. The complement component common to (the convergence point of) all activation pathways is:✓ C3
Q33. The lectin pathway is activated by mannose-binding lectin (MBL) binding microbial sugars, and its steps then resemble the:✓ Classical pathway
Q34. Match each pathway/component with its description and select the correct option.✓ A-ii, B-i, C-iv, D-iii