Arthritis and enteritis--an interface of protean manifestations.

We live in tenuous proximity to a vast array of microbial agents that inhabit the balanced ecosystem of the gut. When an alteration in that balance occurs our immune system can be challenged abruptly with pathogens expressing microbial antigens that may form immune complexes or that may induce autoimmunity by cross-reactivity with host endogenous antigens. Toxins and proteolytic enzymes, normally limited to bowel lumen, may evade local mucosal defences and effect systemic inflammatory responses. Understanding the pathogenic events behind arthritis related to GI pathology will provide insight not only into this important group of diseases but also into fundamental mechanisms underlying other forms of inflammatory joint disease which remain of unknown origin.