Immune complexes in erythema multiforme and the Stevens-Johnson syndrome

Early cutaneous lesions of erythema multiforme or mucosal lesions of the Stevens-Johnson syndrome contain delicate granular deposits of immune reactants and/or complement components lodged in the walls of vessels of the papillary dermis. Such deposits are not present in normal, unaffected skin although they can be caused to occur there by injection of substances which increase vascular permeability. Factors which cause accumulation of mononuclear cells in the papillary dermis have not been elucidated but we suggest that receptors for the C3d fragment of the third component of complement could be responsible. Factors which cause intercellular edema in the epidermis, epidermal-dermal separation, or necrotic keratinocytes are unknown. We, and others, may now measured immune complexes in the serum of patients experiencing these reaction patterns by means of Raji cell radioimmunoassay, C1q precipitation, 125I-C1q binding, cryoprecipitation and with monoclonal rheumatoid factor. Cryoimmunoglobulins have also been described and antigens of Herpesvirus hominus have been measured in the cryoprecipitate of 2 patients who experienced erythema multiforme following recurrent herpesvirus infection. Erythema multiforme commonly accompanied serum sickness reactions which occurred following injection of immune horse serum in the 1980s (von Pirquet and Schick). Such reactions are now well established as due to circulating immune complexes in antigen excess.