Which sequence correctly describes the pathophysiology steps?

• A. Gut inflammation damages barrier → Bacterial antigens travel to joints → Molecular mimicry
• B. Molecular mimicry → Bacterial travel → Gut inflammation
• C. Bacterial travel → Molecular mimicry → Gut inflammation
• D. Molecular mimicry → Gut inflammation → Bacterial travel

Answer: (A)

Gut barrier integrity is the starting point. When gut inflammation damages the barrier, more bacterial antigens leak into the circulation and can reach sites like the joints. Once these antigens are in the body, the immune system may mistake joint tissues for the invaders because some bacterial proteins resemble self proteins. That cross-reactivity is molecular mimicry, which then drives autoimmune attack on the joints. So starting with barrier damage, followed by antigen exposure in the joints, and then molecular mimicry leading to autoimmunity is the logical, supported sequence.

This order wouldn’t fit if the immune cross-reactivity occurred before any antigen exposure, or if bacteria were assumed to reach the joints directly without a prior breach in gut barrier function.