[Immunohistochemical localization of interleukin-1 and lipopolysaccharide (LPS) of experimental arthritis in the ankles of rats immunized with LPS extracted from Escherichia coli].

Sprague Dawley (SD) rats were immunized by subcutaneous injections with heat-killed E. coli 0:14 and lipopolysaccharide (LPS) extracted from E. coli for 15, 29 and 39 weeks which induced arthritis in the ankle. Localization of interleukin-1 (IL-1) and LPS in the ankle joints were investigated immunohistochemically. Serum IgM rheumatoid factor-like substance (RFLS) and anti-LPS IgM were detected by enzyme-linked immunosorbent assay (ELISA). Rats immunized with LPS for 39 weeks developed synovial lining cell hyperplasia in 25 of 40 ankles and lymphoid cell infiltration in 25 and pannus formation in 23, the rates of which were significantly higher than those of control and rats immunized with LPS for 15 and 29 weeks. The induction rate of arthritis in rats immunized with LPS was the same as that in rats immunized with E. coli. LPS and IL-1 were located in synovial cells and pannus in arthritic joints. Changes of RFLS level in rats immunized with LPS were elevated more gradually than those in rats immunized with E. coli. These findings suggest that LPS could stimulate IL-1 and RFLS production and may induce arthritis in rats resembling rheumatoid arthritis.