Immunological study of lupus nephritis: Demonstration of nuclear ribonucleoprotein(RNP) in diseased kidney from patients with systemic lupus erythematosus.

Renal tissue from 50 patients with systemic lupus erythematosus (SLE) and 25 with primary glomerulonephritis were tested for the presence of nuclear ribonucleoprotein (RNP) by an immunofluorescent technique. Antibody to RNP was obtained from a patient with mixed connective tissue disease. Fluorescent isothiothianate (FITC) was labelled on purified IgG from the serum. Bright speckled nuclear staining was obtained when the tissue section of mouse kidney was incubated with this conjugate. The staining was completely inhibited when the section was preincubated with non labelled antibody to RNP eluted from RNP immune complex formed in vitro. Granular deposition of RNP antigen in glomeruli was found in 7 of 50 SLE kidneys. The antigen was distributed mainly in the subendothelial site of the glomerular basement membrane and mesangium. The staining was completely inhibited by preincubation of the section with non-labelled antibody to RNP. Deposition of RNP was also found along the tubular basement membrane in 3 of 7 SLE. None of the kidneys from primary glomerulonephritis patients showed positive staining of RNP irrespective of the presence of immunoglobulins and complements in glomeruli. The present observations support the hypothesis that antibody to RNP besides antibody to double stranded DNA might also be of importance in the pathogenesis of renal disease in SLE.