The potentiating effect of rheumatoid arthritis serum in the immediate phase of nephrotoxic nephritis.

Nephrotoxic nephritis induced in rats was employed as an experimental model to investigate the possible effects of rheumatoid factor on antigen–antibody reactions. Rats injected simultaneously with rheumatoid arthritis serum and rabbit nephrotoxic globulin showed a three-fold increase in immediate proteinuria compared with rats injected with nephrotoxic globulin alone. This potentiating effect of rheumatoid arthritis serum was evident even when the serum was injected 48 hr after the nephrotoxic globulin and was also apparent to a lesser extent in rats decomplemented by a prior injection of aggregated human IgG. Normal human serum had no effect on the proteinuria produced by a standard dose of nephrotoxic globulin while rheumatoid arthritis serum injected with normal rabbit globulin did not increase urinary protein excretion above baseline levels. In rats injected with rheumatoid arthritis serum and nephrotoxic globulin, human IgM (presumably rheumatoid factor) was detected by immunofluorescence on the glomerular basement membrane along with the nephrotoxic globulin and rat complement and persisted at this site for as long as 42 days after the initial injections. Rheumatoid factor activity was also recovered by elution from glomeruli isolated from rat kidneys 24 hr after the injection of rheumatoid arthritis serum and nephrotoxic globulin.