**Core Concept**
Rheumatoid arthritis (RA) is a chronic autoimmune disorder characterized by inflammation and destruction of joints, leading to pain, stiffness, and deformity. It is a classic example of an autoimmune disease, where the immune system mistakenly attacks the body's own tissues.

**Why the Correct Answer is Right**
Rheumatoid arthritis is a disease of the synovium, the lining of the joints, where an abnormal immune response leads to the production of various cytokines and chemokines, such as TNF-alpha, IL-1, and IL-6. These inflammatory mediators cause the synovium to become inflamed, leading to joint damage and destruction. The hallmark features of RA include symmetrical joint involvement, morning stiffness, and the presence of rheumatoid factor (RF) or anti-CCP antibodies.

**Why Each Wrong Option is Incorrect**
**Option A:**
* This is a feature of rheumatoid arthritis, characterized by inflammation of the synovium and joint destruction.

**Option B:**
* This is a feature of rheumatoid arthritis, often seen in advanced cases where the joint destruction leads to deformity and loss of function.

**Option C:**
* This is a feature of rheumatoid arthritis, where the abnormal immune response leads to the production of various inflammatory mediators.

**Clinical Pearl / High-Yield Fact**
One key feature of rheumatoid arthritis that differentiates it from other forms of arthritis is its symmetrical joint involvement, where both sides of the body are affected equally.

**Correct Answer: C. Osteoarthritis**