BACKGROUND/AIMS: Heat-shock protein (Hsp) 60 is an immunodominant antigen of mycobacteria and other microorganisms that is highly homologous to its human counterpart. Hsp60 may provide a link between immunity to invading microorganisms and autoimmune diseases. METHODS: Expression of Hsp60 was studied by immunohistochemistry in gut resection specimens of patients with Crohn's disease (n = 14), ulcerative colitis (n = 7), acute self-limited colitis (infective type) (n = 5), and controls (n = 9) using the monoclonal antibodies LK1 and LK2. RESULTS: A strong staining positivity for Hsp60 was observed in numerous mononuclear cells of the mucosa and submucosa in ileum and colon tissue biopsy specimens of patients with Crohn's disease from inflamed and healthy areas. In ulcerative colitis, Hsp60 expression was limited to the mucosa. In biopsy specimens from patients with acute self-limited colitis and controls, Hsp60-positive cells were absent or only present in low numbers and staining intensity was weak. Differentiation between mammalian and bacterial Hsp60 showed expression of the human homologue. Double staining for B7 and Hsp60 showed that Hsp60 was expressed by B7-positive cells. CONCLUSIONS: Human Hsp60 is strongly expressed by B7-positive antigen-presenting mononuclear cells in the mucosa of patients with inflammatory bowel disease and might play a role in the initiation or maintenance of the inflammatory process.