Rituximab (anti-CD20 monoclonal antibody) is used in B-cell lymphomas and autoimmune diseases. Which mechanism is primarily responsible for rituximab-mediated B-cell depletion in vivo?

• A Direct induction of apoptosis via caspase-8 activation upon CD20 cross-linking
• B Inhibition of B-cell receptor signaling through Syk kinase blockade
• C Complement-dependent cytotoxicity (CDC) via C1q fixation and membrane attack complex formation ✓
• D Blockade of BAFF-BAFF receptor survival signaling

Explanation

Rituximab depletes C cells primarily through complement-dependent cytotoxicity and antibody-dependent cellular cytotoxicity (ADCC). CDC via B1q recruitment and MAC formation is a major in vivo killing mechanism. Direct apoptosis occurs but is not the primary mechanism. Syk inhibition and BAFF blockade are mechanisms of other agents, not rituximab.

Reference: Goodman and Gilman's The Pharmacological Basis of Therapeutics, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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