Mechanism of action of Rituximab?
**Core Concept**
Rituximab is a monoclonal antibody that targets the CD20 antigen present on the surface of B cells, leading to their depletion and subsequent immunosuppression.
**Why the Correct Answer is Right**
Rituximab binds to the CD20 antigen on B cells, leading to their activation-induced cell death (AICD) and apoptosis. This is achieved through several mechanisms, including:
* Antibody-dependent cellular cytotoxicity (ADCC), where natural killer cells and macrophages recognize the Rituximab-bound CD20 antigen and destroy the B cells.
* Complement-dependent cytotoxicity (CDC), where the Rituximab-bound CD20 antigen activates the complement system, leading to the formation of the membrane attack complex and B cell lysis.
* Inhibition of B cell proliferation and differentiation, by preventing the interaction between B cells and their growth factors.
**Why Each Wrong Option is Incorrect**
**Option A:** Rituximab's mechanism of action is not primarily through the inhibition of calcineurin, which is involved in T cell activation.
**Option B:** Rituximab does not work by inhibiting the enzyme Janus kinase (JAK), which is involved in cytokine signaling.
**Option C:** Rituximab's action is not limited to the depletion of plasma cells, as it also targets mature B cells.
**Clinical Pearl / High-Yield Fact**
Rituximab is most effective in diseases where B cells play a central role, such as non-Hodgkin's lymphoma, rheumatoid arthritis, and autoimmune hemolytic anemia.
**Correct Answer:** A. Rituximab binds to the CD20 antigen on B cells, leading to their activation-induced cell death and apoptosis.