Erythema multiforme: direct immunofluorescence studies and detection of circulating immune complexes.

The immunologic parameters of 23 patients with erythema multiforme who were seen by us (17 patients) or who had biopsies sent for immunofluorescence testing (6 cases) are reviewed. Biopsy specimens were sectioned and tested with labeled antisera to human IgG, IgA, IgM, C3 and fibrin. Fourteen biopsies showed IgM deposits in the superficial blood vessels, 13 demonstrated C3, 15 showed fibrin deposition, and 1 biopsy showed IgA deposition. All biopsies were negative for IgG. Eight serum samples tested by indirect IF were negative for skin-reactive antibodies. In addition to IF testing, serum samples from 20 patients were tested for circulating immune complexes with a Clq binding radioassay and a monoclonal rheumatoid factor (mRF) inhibition assay. Immune complexes were not detected by the Clq binding assay, but 6 of 20 serum samples demonstrated low to moderate levels of immune complexes by the mRF inhibition assay. By sucrose density gradient ultracentrifugation in the mRF-reactive material in one serum sample sedimented in high molecular weight fractions and also demonstrated anticomplementary activity. These findings suggest that immune complex formation and subsequent deposition in the cutaneous microvasculature may play a role in the pathogenesis of erythema multiforme.