Dermatitis herpetiformis: immune complex detection with C1q and monoclonal rheumatoid factor.

To determine the significance of circulating immune complexes in dermatitis herpetiformis, serum samples from thirty patients with active disease were tested by a C1q binding radioassay, while serum samples from twenty-one of these patients were tested by a monoclonal rheumatoid factor (mRF) inhibition radioassay. By direct immunofluorescence, all patients demonstrated typical IgA deposition in dermal papillae. Using the C1q binding assay, only seven of forty-two serum samples had elevated C1q binding activity, while by the mRF inhibition assay, thirteen of twenty-five samples had elevated immune complex levels. Nine of these latter thirteen positive serum samples, however, were minimally elevated. Thus, IgG and/or IgM containing immune complexes are infrequently present, or at very low levels, in sera of patients with active dermatitis herpetiformis.