C3 nephritic factor and hypocomplementaemia in a clinically healthy individual.

Nephritic factor was detected in an individual whose serum showed a selective decrease in the third component of complement (C3) during and subsequent to an illness resembling disseminated gonococcal infection (DGI). As is characteristic of C3 nephritic factor (C3NeF), its activity was heat stable, was associated with IgG, and enhanced cleavage of normal human serum C3 via the alternative pathway. However, unlike previously reported cases of C3NeF detection in association with glomerulonephritis and/or lipodystrophy, this patient has had no significant disease before or more than 2 years after the apparent DGI. The significance of C3NeF in a healthy individual is unexplained, but this study suggests its occurrence may be more ubiquitous than previously suspected.