Generation of terminal complement complexes in psoriatic lesional skin.

The complement system is thought to play an important role in the recruitment of neutrophils within the epidermis. In the present study we examined whether or not complement activation in psoriatic lesional skin results in the deposition of terminal complement complexes within the epidermis by measuring levels of SC5b-9 in the plasma and horny tissues of psoriatic patients. The levels of SC5b-9 in psoriatic plasma were significantly higher than those of controls or those of patients with atopic dermatitis. However, when the levels of SC5b-9 in the psoriatic plasma were compared before and after successful treatment of psoriasis, a significant reduction was observed after treatment. Studies of total protein extracts from lesional skin showed that, while no SC5b-9 was detected in the noninflammatory horny tissues, there were high levels of SC5b-9 in lesional horny tissues of psoriasis. By immunofluorescence using a monoclonal antibody to the C5b-9 neoantigen, deposition of C5b-9 was observed only in the stratum corneum of psoriatic skin. Thus the results of the present study suggests that in psoriatic lesional skin, the complement system is activated and that this complement activation proceeds all the way to the terminal step, generating membrane attack complex.