Which drug is a B cell modulator?

• A. Rituximab
• B. Abatacept
• C. Tofacitinib
• D. Baricitinib

Answer: (A)

Direct modulation of B cells means targeting the B cell population or their activity. Rituximab is a monoclonal antibody that binds CD20 on mature B cells and depletes them through immune mechanisms like antibody-dependent cellular cytotoxicity and complement activation. This direct B cell depletion reduces B cell–mediated antibody production and antigen presentation, making it a clear B cell modulator.

The other drugs work through different immune pathways. Abatacept blocks T cell activation by interfering with the CD28–CD80/86 costimulatory signal, affecting T cells rather than B cells. Tofacitinib and Baricitinib are JAK inhibitors that dampen cytokine signaling across multiple cell types, influencing both T and B cell functions indirectly but not targeting B cells specifically.