What is the third step in the proposed pathophysiology of enteropathic arthritis?

• A. Gut inflammation damages the intestinal barrier
• B. Bacterial antigens travel to joints
• C. Molecular mimicry (Autoimmune reaction)
• D. Autoimmune joint degeneration

Answer: (C)

In enteropathic arthritis, the third step is when the immune system launches an autoimmune reaction driven by molecular mimicry. Once gut inflammation damages the intestinal barrier, bacterial antigens leak out and can reach the joints. Some of these antigens resemble components of joint tissue closely enough that the immune response against the microbes also targets the joints. This cross-reactive attack causes autoimmune inflammation in the synovium. Over time, this persistent autoimmune inflammation leads to joint damage and degeneration. The first step is barrier disruption, the second is antigens traveling to the joints, and the third is the autoimmune response triggered by mimicry, with degeneration as the downstream consequence.