Serial complement component alterations in acute glomerulonephritis and systemic lupus erythematosus

Abstract

Serial determinations of whole serum complement (C') and absolute weight concentrations of the C'1q (11S) portion of the first and the third (C'3), fourth (C'4) and fifth (C'5) components of human complement were carried out in patients with post-streptococcal acute glomerulonephritis, systemic lupus erythematosus and other types of nephritis including Henoch–Schönlein (anaphylactoid purpura), Goodpasture's syndrome and chronic glomerulonephritis.

Total haemolytic complement was decreased in patients with acute glomerulonephritis and active systemic lupus erythematosus, but distinctly different component patterns occurred which were characteristic for each disease. In acute glomerulonephritis the concentration of C'1q was normal and C'4 was decreased only during the initial phase of illness. More prolonged depressions of C'3 and C'5 occurred which paralleled the whole complement titres. In contrast subjects with active systemic lupus erythematosus had normal C'5 concentrations and decreases in C'1q, C'4 and C'3 with prolonged depression of C'4 being the most consistent finding. Recent evidence has suggested that both post-streptococcal acute glomerulonephritis and systemic lupus erythematosus share a similar immunopathogenic mechanism involving the deposition in renal glomeruli of immune complexes formed by non-glomerular antigen and specific antibody. If so, the physico-chemical characteristics of the immune complexes differ enough to cause distinctive component alterations. Entirely normal whole complement and component levels were observed in patients with other types of nephritis.

In post-streptococcal acute glomerulonephritis the early return to normal of fourth component concentrations may be a favourable prognostic sign while the persistent depression of this component in systemic lupus erythematosus may be an indication of occult disease activity.