Reactivation of antigen-induced arthritis in mice by oral administration of lipopolysaccharide.

We examined whether oral administration of lipopolysaccharide (LPS) from Escherichia coli reactivated antigen-induced arthritis (AIA) in mice that is one of models of human rheumatoid arthritis. To induce AIA, mice were immunized by subcutaneous injection of ovalbumin (OVA) emulsified with complete Freund's adjuvant into the base of the tail (day 0) followed by intraarticular injection of OVA on day 21. To investigate the ability of LPS to reactivate AIA, varying doses of LPS were p.o. administered 48 h after the challenge injection. The results showed that administration of LPS was followed by reactivation of AIA in a dose-related fashion. The reactivation of AIA by LPS was associated with increases in interferon-gamma, interleukin-1beta and tumour necrosis factor-alpha. Polymyxin B sulfate given immediately before administration of LPS suppressed the reactivation of AIA. These findings suggest that LPS from intestinal bacteria may play a role in the reactivation of joint inflammation in which immune responses to pathogenic antigens are involved.