**Core Concept**
Infliximab is a biologic medication that targets the tumor necrosis factor-alpha (TNF-alpha) pathway, which plays a crucial role in inflammation and immune response. TNF-alpha is a pro-inflammatory cytokine involved in the pathogenesis of various autoimmune diseases.

**Why the Correct Answer is Right**
Infliximab is a chimeric monoclonal antibody that specifically binds to TNF-alpha, preventing its interaction with TNF receptors on cell surfaces. This mechanism of action reduces inflammation and immune cell activation, leading to therapeutic effects in conditions such as rheumatoid arthritis, psoriasis, and Crohn's disease. The chimeric structure of infliximab consists of human constant regions and murine variable regions, allowing for efficient targeting of TNF-alpha while minimizing immunogenicity.

**Why Each Wrong Option is Incorrect**
**Option A:** CD20 is a surface antigen found on mature B cells, and CD20 antagonists, such as rituximab, target B cell proliferation and activation. Infliximab does not target CD20 or B cells.
**Option B:** IL-6 (interleukin-6) antagonists, such as tocilizumab, target the IL-6 receptor and inhibit inflammation. Infliximab targets TNF-alpha, not IL-6.
**Option D:** Her2-neu is a receptor tyrosine kinase overexpressed in certain types of cancer, and trastuzumab is a monoclonal antibody that targets Her2-neu. Infliximab does not target Her2-neu or cancer cells.

**Clinical Pearl / High-Yield Fact**
Infliximab is a first-generation TNF-alpha inhibitor, and its use is associated with an increased risk of infections, particularly reactivation of latent tuberculosis. Regular screening for tuberculosis and other infections is essential before initiating infliximab therapy.

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