Rheumatoid arthritis (RA) is a chronic, autoimmune disease that primarily affects the joints, leading to pain, swelling, stiffness, and joint destruction. The pathophysiology of RA involves a complex interplay of genetic, immunological, and environmental factors.

Genetic Susceptibility:

• Genetic factors play a significant role in the development of RA. Specific genetic variants, particularly those within the human leukocyte antigen (HLA)-DRB1 locus, have been associated with an increased risk of the disease. HLA-DRB1 molecules are involved in presenting antigens to immune cells, and certain variants can present antigens in a way that triggers an immune response against the body's own tissues (1).

Immune Dysregulation:

• RA is characterized by a dysregulated immune response that targets the synovium, the tissue lining the joints. This immune response involves the activation and infiltration of various immune cells, including T cells, B cells, macrophages, and neutrophils (2).

• T cells: Helper T cells (Th cells), particularly Th17 cells, play a key role in the pathogenesis of RA. These cells produce cytokines that promote inflammation and activate other immune cells (3).
• B cells: B cells differentiate into plasma cells that produce autoantibodies, such as rheumatoid factor (RF) and anti-cyclic citrullinated peptide antibodies (anti-CCP). These autoantibodies target components of the synovium and amplify the immune response (4).
• Macrophages: Macrophages are phagocytic cells that engulf and digest foreign particles. In RA, macrophages contribute to inflammation by releasing cytokines and proteases that degrade joint tissues (5).
• Neutrophils: Neutrophils are recruited to the synovium and release reactive oxygen species and enzymes that further damage joint tissues (6).

Cytokine Production:

• The dysregulated immune response in RA leads to the production of various cytokines, including tumor necrosis factor-alpha (TNF-alpha), interleukin-1 (IL-1), interleukin-6 (IL-6), and interleukin-17 (IL-17). These cytokines promote inflammation, joint destruction, and systemic symptoms such as fatigue and malaise (7).

Synovial Hyperplasia and Joint Destruction:

• The chronic inflammation in the synovium leads to synovial hyperplasia, characterized by the proliferation of synovial cells and the formation of a pannus. The pannus invades and erodes the cartilage and bone, resulting in joint damage and deformities (8).

Environmental Triggers:

• While genetic factors predispose an individual to RA, environmental triggers are thought to initiate or exacerbate the disease process. Potential environmental triggers include:
• Smoking: Cigarette smoke contains chemicals that can damage the joints and activate the immune system (9).
• Infections: Certain infections, such as with the Epstein-Barr virus, have been linked to an increased risk of RA development (10).
• Trauma: Physical trauma to a joint may trigger an autoimmune response in susceptible individuals (11).