What is the mechanism of action of rituximab in autoimmune diseases?

• A. Anti-CD20 monoclonal antibody that depletes B cells
• B. Inhibits TNF-alpha
• C. Inhibits JAK-STAT signaling
• D. Stimulates T-cell activation

Answer: (B)

Rituximab works by targeting CD20 on B cells and causing their depletion. This happens mainly through antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity, with some direct induction of B-cell apoptosis. By removing B cells, autoantibody production drops and B cells’ role in presenting antigen and supporting inflammatory signals decreases, which helps in autoimmune diseases driven by B cells. The alternative options describe other types of immunomodulators: inhibiting TNF-α is the action of TNF inhibitors, inhibiting JAK-STAT signaling is the action of JAK inhibitors, and stimulating T-cell activation would amplify immune responses rather than dampen them.