Rheumatoid factor isotypes and renal disease in systemic lupus erythematosus.

There is no agreement on whether rheumatoid factor (RF) exerts protection, injury, or is an epiphenomenon with regard to kidney disease in systemic lupus erythematosus (SLE). In this study we examined the occurrence and isotype distribution of rheumatoid factor in SLE in relation to some clinical parameters, including renal function and arthritis. A highly significant correlation (p less than 0.001) was noted between the presence of IgG RF and absence of kidney disease. The IgG RF also seemed to protect SLE patients from developing arthritis (p less than 0.01). On the other hand, elevated IgM RF levels indicated active SLE disease. The results obtained are discussed in relation to the ability of RF to interact with immune complexes in vitro and in vivo.