29. Match the contents of Column I with the most appropriate options in Column II
Column I                                                                              Column II
P. Complement Cl q                                                           i. CD34
Q. L-Selectin                                                                        ii. Complement C 5 b
R. Membrane Attack Complex                                         iii. Fc region of antibody
S. T-Helper cells                                                                 iv. Complement C 5 a
v. CD40L
(A) P-iii ; Q-v; R-iv; S-i
(B) P-i ; Q-ii ; R-iv; S-v
(C) P-iii ; Q-i ; R-ii ; S-v
(D) P-iv; Q-v; R-ii; S-i

Complement C1q binds to the Fc region of antibodies, L-Selectin functions in leukocyte rolling, the Membrane Attack Complex forms from C5b-initiated assembly, and T-Helper cells express CD40L for B-cell activation. The correct matching is option (C).

Correct Answer

Option (C): P-iii; Q-i; R-ii; S-v

This pairing accurately links each Column I term to its primary immunological association in Column II.

Match Explanations

• P. Complement C1q → iii. Fc region of antibody: C1q, the recognition subunit of the C1 complex, binds specifically to the Fc portion of IgG or IgM antibodies in immune complexes, initiating the classical complement pathway. This interaction activates C1r and C1s proteases for downstream cascade progression.

• Q. L-Selectin → i. CD34: L-Selectin (CD62L), expressed on leukocytes, mediates initial tethering and rolling on endothelial cells by binding carbohydrate ligands like CD34 during inflammation-induced leukocyte extravasation. This selectin-ligand interaction slows leukocytes for firm adhesion via integrins.

• R. Membrane Attack Complex → ii. Complement C5b: The MAC (C5b-9) forms when C5b binds the target membrane, recruiting C6, C7, C8, and polymerized C9 to create transmembrane pores that lyse pathogens or cells by osmotic disruption. C5b serves as the nucleating component for this terminal pathway structure.

• S. T-Helper cells → v. CD40L: Activated CD4+ T-helper cells (Th cells) express CD40 ligand (CD40L, CD154), which binds CD40 on B cells, macrophages, and dendritic cells to license antibody class switching, germinal center formation, and cytokine production. This co-stimulatory interaction is essential for humoral immunity.

Option Analysis

Options (A), (B), and (D) mispair key components: C1q does not link to CD34 or C5a, MAC initiation requires C5b over C5a (an anaphylatoxin), and L-Selectin/CD34 is specific to adhesion, not CD40L or hematopoietic markers alone.