Multiple immune complexes and hypocomplementaemia in dermatitis herpetiformis and coeliac disease.

Circulating immune complexes have been detected in 100% of 59 patients with dermatitis herpetiformis (D.H.), and in 100% of 27 patients with coeliac disease (C.D.). Three methods for detecting immune complexes were employed: radiobioassay, which gave an incidence of 77% in D.H. and 81% in C.D.; C1q binding activity, with which the incidence was 83% and 96%, respectively; and precipitation with 4% polyethylene glycol (69% positivity in D.H., 100% in C.D.). The immune complexes in D.H. and C.D. were compared with those in sera from 23 patients with systemic lupus erythematosus (S.L.E.). Multiple complexes of differing properties were found in D.H. and C.D. but not in S.L.E. The varying nature of the complexes in D.H. and C.D. may account for the damage to different tissues (skin, small intestine, reticuloendothelial system). Low third component of complement was found in 49% and low C4 in 20% of D.H. patients. C3 hypocomplementaemia was found in 26% of patients with C.D.