IgA immune complexes in patients with dermatitis herpetiformis occur in the absence of IgA rheumatoid factor.

Thirty to forty percent of patients with dermatitis herpetiformis (DH) have IgA-containing circulating immune complexes (IgA-CIC); however, the antigenic composition of these complexes as well as the role they play in the pathogenesis of DH are unknown. The failure to detect wheat protein in these IgA-CIC, despite the association of DH with gluten-sensitive enteropathy, suggests that the IgA-CIC in DH may be similar to those seen in the IgA nephropathies and represent IgA rheumatoid factor (RF)-IgG complexes. We have examined the sera of 32 patients with DH, 16 non-DH patients positive for RF by latex fixation, and 15 normal subjects for IgA and IgM RF using enzyme-linked immunosorbent assays (ELISAs) and for IgA-CIC using an anti-C3 ELISA. Thirteen of 16 (81%) latex fixation test-positive patients had IgA RF by ELISA and 15/16 (94%) had IgM RF by ELISA. The total amount of RF detected by the ELISA (IgA + IgM RF) correlated with the latex fixation titer (r = 0.678, p = 0.004) in these latex fixation-positive patients. Six of the 16 (38%) latex fixation-positive patients also were found to have IgA-CIC. Solid phase absorption using goat antihuman C3 decreased the levels of immune complexes but not the level of IgA RF, suggesting the IgA-CIC detected do not represent uncomplexed IgA RF. In contrast, although 12 of 31 (39%) patients with DH had IgA-CIC ranging in amount from 0.331-26.0 micrograms IgA/ml (nl less than 0.150 microgram IgA/ml), only 1 of 32 (3%) DH patients had detectable levels of IgA RF (7.0 micrograms IgA/ml, nl less than 2.0 micrograms IgA/ml). Low levels of IgM RF were found in 8/32 (25%) of patients with DH (1.1-1.6 micrograms IgM/ml, nl less than 1.0 microgram IgM/ml). These data document that IgA RF is not present in the sera of patients with DH independent of the presence or absence of IgA-CIC and that it is unlikely that the IgA-CIC present are IgA RF complexed with autologous IgG.