**Core Concept:** Rituximab is a monoclonal antibody used in the treatment of certain B cell malignancies and autoimmune disorders. It targets the CD20 antigen expressed on the surface of mature B cells.

**Why the Correct Answer is Right:** Rituximab is a monoclonal antibody that specifically binds to the CD20 antigen found on the surface of mature B cells. By binding to CD20, Rituximab triggers a cascade of events leading to B cell death through apoptosis. In the context of B cell malignancies, this therapeutic effect is used to target and eliminate cancerous B cells, as in Non-Hodgkin's lymphoma (NHL) and chronic lymphocytic leukemia (CLL). This targeted therapy reduces the overall disease burden and improves clinical outcomes.

**Why Each Wrong Option is Incorrect:**

A. Rituximab is not used in treating acute lymphoblastic leukemia (ALL), which is a different type of leukemia involving T cells rather than B cells.

B. Although Rituximab can cause B cell depletion, it is not the primary treatment for autoimmune disorders like systemic lupus erythematosus (SLE) or rheumatoid arthritis (RA), where immunosuppressive therapy is usually used.

C. Rituximab is not used for treating multiple myeloma, a plasma cell malignancy, as it primarily targets B cells.

D. Rituximab is not used in the treatment of acute myeloid leukemia (AML), which is a type of leukemia involving myeloid cells rather than B cells.

**Clinical Pearl:** Rituximab is a crucial agent in the treatment of B cell malignancies and certain autoimmune disorders, demonstrating the importance of understanding the target cell and disease context when choosing appropriate therapies.