**Core Concept**
Infliximab is a biologic medication used to treat autoimmune diseases by targeting the tumor necrosis factor-alpha (TNF-alpha) pathway. TNF-alpha is a pro-inflammatory cytokine involved in systemic inflammation and plays a key role in the pathogenesis of various conditions, including rheumatoid arthritis, psoriatic arthritis, and Crohn's disease.

**Why the Correct Answer is Right**
Infliximab is a chimeric monoclonal antibody that specifically binds to TNF-alpha, preventing its interaction with cell surface receptors on immune cells. By blocking TNF-alpha, infliximab reduces inflammation and halts disease progression in conditions where TNF-alpha is overexpressed. Infliximab's mechanism of action involves binding to the soluble form of TNF-alpha, preventing its interaction with the p55 and p75 receptors on immune cells, and also inducing apoptosis in TNF-alpha-producing cells.

**Why Each Wrong Option is Incorrect**
**Option A:** CD20 is a surface antigen expressed on B cells, and CD20 antagonists, such as rituximab, are used to treat B cell lymphomas and autoimmune diseases by depleting B cells. Infliximab does not target CD20.

**Option B:** IL-6 (Interleukin-6) is another pro-inflammatory cytokine involved in inflammation, but infliximab does not target IL-6. Tocilizumab is a monoclonal antibody that targets IL-6 and is used to treat rheumatoid arthritis.

**Option D:** Her2-neu is a receptor tyrosine kinase overexpressed in certain breast cancers, and trastuzumab is a monoclonal antibody that targets Her2-neu. Infliximab is not used to treat breast cancer or target Her2-neu.

**Clinical Pearl / High-Yield Fact**
Infliximab is a chimeric antibody, meaning it is composed of both human and murine (mouse) antibody sequences. This chimeric structure can lead to the formation of human anti-chimeric antibodies (HACA), which may reduce the efficacy of infliximab over time.

**✓ Correct Answer: C. Chimeric antibody against TNF alpha**