Suppressive effect of Escherichia coli on adjuvant-induced arthritis in germ-free rats.

Our previous finding, that germ-free F344 rats develop severe adjuvant-induced arthritis, whereas specific pathogen-free rats develop mild disease, prompted us to investigate the role of bacterial flora in promoting the development of this disease. Germ-free rats given Escherichia coli experienced disease suppression. Germ-free rats treated with 3 strains of Lactobacillus experienced an enhancement of the disease, although it was not significant. Germ-free rats treated with a combination of E coli and lactobacilli had disease suppression similar to that of E coli monoassociated rats. Thus, these findings suggest that E coli may play a dominant role in modulating the development of the disease in this particular strain of F344 rats, possibly through its lipopolysaccharide (as evidenced by positive results on limulus tests). These findings also suggest that microflora play an important role in modifying the development of joint disease.