[Circulating immune complexes in skin disease patients. Study and literature data (author's transl)].

Circulating immune complexes (C.I.C.) were investigated in 244 patients with various skin diseases and 100 healthy subjects. C.I.C. were detected by the PEG-C4 assay, firstly proposed by Digeon et al. using the precipitation by polyethylene glycol (PEG 3,5 p. 100) and the determination by laser nephelometry of complement component C4 in sera and in precipitates. The percentage of C4 precipitated and of positive subjects were significantly increased in numerous cutaneous diseases: systemic lupus erythematosus, scleroderma, pemphigus, bullous pemphigoid, dermatitis herpetiformis, psoriasis, contact dermatitis and lichen planus. Two cases of dermatomyositis, 3 cases of post herpetic erythema multiformis and 2 cases of Kaposi-Juliusberg syndroma were also positives but no definite conclusion can be given because of the few patients tested. On the contrary, the values of precipitated C4 are normal in most cases of atopic dermatitis (the method does not detect IgE-C.I.C.) scabies, porphyria cutanea tarda, cutaneous epithelioma and discoid lupus. In chronic urticaria and in mycosis fongoides the mean values of precipitated C4 are significantly increased but the number of positive subjects is low and the significance of these results is uncertain because of the wide range of the values. The results of the present study are compared with the literature data. The value of C.I.C. determination in determining the evolutivity of skin diseases and their possible role in pathogenesis are discussed.