An auto immune disease is:
**Core Concept**
Rheumatoid arthritis (RA) is a classic example of an autoimmune disease characterized by the production of autoantibodies against the body's own tissues, leading to chronic inflammation and joint damage. This disease is mediated by T cells and B cells that mistakenly target the body's own collagen and other components of the joints.
**Why the Correct Answer is Right**
The pathogenesis of RA involves the activation of T cells and B cells, which produce autoantibodies against the Fc region of IgG (rheumatoid factor) and against the collagen in the joints. The autoantibodies bind to the collagen, leading to the activation of complement and the recruitment of inflammatory cells, resulting in joint inflammation and destruction. The exact mechanisms are not fully understood, but it is believed that genetic factors, environmental triggers, and hormonal influences all play a role.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify an autoimmune disease. While it may be related to an autoimmune disease, it is not a clear example of one.
**Option B:** This option is incorrect because it is a type of cancer, not an autoimmune disease.
**Option C:** This option is incorrect because it is a type of infection, not an autoimmune disease.
**Clinical Pearl / High-Yield Fact**
The presence of rheumatoid factor (RF) in the blood is a hallmark of RA, but it can also be present in other autoimmune diseases, such as Sjögren's syndrome and systemic lupus erythematosus. The absence of RF does not rule out RA, and patients with RA can also have normal RF levels.
**Correct Answer:** C.