Influence of the bacterial flora on collagen-induced arthritis in susceptible and resistant strains of rats.

Collagen-induced arthritis is an experimental model for rheumatoid arthritis which can be elicited in susceptible strains of rats by intradermal injection of native type II collagen. In order to investigate whether bacterial flora may alter the pathogenic response to type II collagen, we have immunized germ-free (GF) male rats from either highly resistant Fisher (F344) or highly susceptible Dark Agouti (DA) strains. The disease was markedly enhanced in GF DA as compared to conventional (CV) DA rats. The humoral response was also stronger in GF rats of both strains. Neither GF nor CV F344 developed arthritis, although GF F344 exhibited later inflammation of the tail. These data support a suppressive influence of bacterial flora on collagen-induced arthritis.