**Core Concept**
Rituximab is a monoclonal antibody used in the treatment of various B-cell lymphomas and autoimmune diseases. It targets a specific protein on the surface of B cells, leading to their depletion and subsequent therapeutic effect.

**Why the Correct Answer is Right**
Rituximab specifically binds to the CD20 antigen on mature B cells, but not on pro-B or stem cells, plasma cells, or other cell types. This binding leads to the activation of complement-dependent cytotoxicity, antibody-dependent cellular cytotoxicity, and direct cell death pathways, ultimately resulting in the reduction of B-cell populations.

**Why Each Wrong Option is Incorrect**
* **Option A:** Incorrect because Rituximab is not an antibody against CD3, which is a component of the T-cell receptor complex.
* **Option B:** Incorrect because Rituximab is not an antibody against CD52, which is a protein found on mature lymphocytes but is targeted by Alemtuzumab, another monoclonal antibody.
* **Option C:** Incorrect because Rituximab is not an antibody against CD25, which is the alpha chain of the IL-2 receptor and is targeted by Daclizumab.

**Clinical Pearl / High-Yield Fact**
Rituximab's mechanism of action is unique in that it can induce long-term depletion of B cells, which can lead to a reduced risk of autoimmune complications in patients with autoimmune diseases such as rheumatoid arthritis.

**Correct Answer: D. CD20**