Abnormalities in the alternative pathway of complement in psoriasis

Summary Some of the immunologic aspects of psoriasis suggest that complement may be involved in the pathophysiology of that disease. The purpose of this work was to examine the complement system in more detail in 20 patients with psoriasis. Classical pathway determinations, RCH50 and factor B levels were normal or elevated. Abnormally low properdin levels were seen in 12/20 patients. No patient had a serum properdin value greater than 1 standard deviation above the control mean. Mean C3–C9 consumption after zymosan or cobra venom incubation was also significantly less than normal (P < 0·001). Thus, abnormalities of the complement system are present in psoriasis and seem limited to the alternative pathway.