Rituximab is used in :
**Core Concept**
Rituximab is a monoclonal antibody that targets the CD20 antigen on the surface of B lymphocytes, leading to their depletion and subsequent immunosuppression. This mechanism is primarily used in the treatment of autoimmune diseases and certain types of cancer.
**Why the Correct Answer is Right**
Rituximab works by binding to the CD20 antigen, which is expressed on the surface of mature B cells but not on stem cells or plasma cells. This binding leads to the activation of complement-dependent cytotoxicity (CDC) and antibody-dependent cellular cytotoxicity (ADCC), ultimately resulting in the depletion of B cells. Rituximab is used in the treatment of conditions such as rheumatoid arthritis, Wegener's granulomatosis, and non-Hodgkin's lymphoma.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Rituximab is not primarily used as an immunosuppressant in organ transplantation.
**Option B:** This option is incorrect because Rituximab is not a chemotherapeutic agent, although it is used in the treatment of certain types of cancer.
**Option C:** This option is incorrect because Rituximab is not used in the treatment of multiple sclerosis, although it is used in some autoimmune disorders.
**Clinical Pearl / High-Yield Fact**
It is essential to note that Rituximab can cause severe infusion reactions, particularly in patients with pre-existing cardiovascular disease, and patients should be closely monitored during and after administration.
**Correct Answer:** C. Non-Hodgkin's lymphoma.