**Core Concept:** Rheumatoid Arthritis (RA) is an autoimmune disorder characterized by chronic inflammation, primarily affecting the joints. In RA, the immune system mistakenly attacks the joint lining (synovium), leading to inflammation, pain, and eventual joint damage. The inflammation involves a complex interplay between various immune cells, cytokines, and chemokines.

**Why the Correct Answer is Right:** In RA, the primary cells involved in the inflammatory process are CD4+ T cells, also known as helper T cells or lymphokine-activated killer (LAK) cells. These cells are activated by antigen-presenting cells (APCs) and release cytokines (e.g., interleukin-17, tumour necrosis factor-alpha, etc.) that stimulate the production of other inflammatory cells (e.g., macrophages, neutrophils, and B cells) and amplify the inflammatory response.

**Why Each Wrong Option is Incorrect:**

A. **Monocytes** are not the primary cells involved in RA. Monocytes are part of the mononuclear phagocyte system and contribute to inflammation by differentiating into macrophages and dendritic cells. However, they are not the primary initiators of the inflammatory response in RA.

B. **B cells** are involved in RA, producing antibodies that form immune complexes, leading to joint inflammation. However, the role of B cells is secondary to that of CD4+ T cells.

C. **Macrophages** are part of the mononuclear phagocyte system and contribute to inflammation by releasing cytokines. Similar to monocytes, their involvement in RA is secondary to CD4+ T cells.

D. **Neutrophils** are part of the innate immune response and contribute to inflammation through phagocytosis, degranulation, and release of reactive oxygen species. However, their role in RA is secondary to CD4+ T cells and B cells.

**Clinical Pearl:** Rheumatoid Arthritis is a complex disease involving multiple immune cells, cytokines, and signaling pathways. Understanding the role of each cell type helps in appreciating the chronic inflammatory process and the importance of targeting these cells and their cytokines in RA treatment.

**Correct Answer:** C. Macrophages

**Explanation:** Macrophages are a type of white blood cell (mononuclear phagocyte) that contribute to inflammation in RA. They play a secondary role in the inflammatory process by releasing cytokines, such as tumor necrosis factor-alpha (TNF-alpha), interleukin-1 (IL-1), and interleukin-6 (IL-6), which amplify the inflammatory response.

Macrophages, along with CD4+ T cells and B cells, form part of the inflammatory cascade leading to joint destruction and chronic inflammation in RA. This highlights the complexity of the disease and the importance of targeting multiple immune cells and their cytokines for effective treatment.