Infectious agents have long been suspected of playing a role in the initiation of Crohn's disease. The objective of this study was to search for likely microbial agents in diseased tissues using immunocytochemical techniques. Intestines and mesenteric lymph node specimens of 21 patients from two French families with a high frequency of Crohn's disease and from Connecticut were studied. The microbial agents searched for included Bacteroides vulgatus, Borrelia burgdorferi, Escherichia coil, Listeria monocytogenes, Streptococcus spp., bovine viral diarrhea virus, influenza A virus, measles virus, parainfluenza virus, and respiratory syncytial virus. Seventy-five percent of the patients with Crohn's disease (12 of 16) were positively labeled with the antibody to Listeria. Macrophages and giant cells immunolabeled for this antigen were distributed underneath ulcers, along fissures, around abscesses, within the lamina propria, in granulomas, and in the germinal centers of mesenteric lymph nodes. In addition, 57% (12 of 21) of the cases contained the E. coli antigen, and 44% (7 of 16) contained the streptococcal antigen. The immunolabeling for the latter two agents also occurred within macrophages and giant cells, distributed in a pattern similar to that of Listeria antigen. The results suggest that Listeria spp., E. coli, and streptococci, but not measles virus, play a role in the pathogenesis of Crohn's disease.
