944 ABNORMALITIES IN THE ALTERNATIVE PATHWAY OF COMPLEMENT IN PSORIASIS

Abstract

The complement system of twenty-four patients with psoriasis was studied in detail. Quantitation of classical pathway components (C4, C3, C3-C9) and the ability of the patient's serum to support lysis of antibody-coated target cells and C3-C9 consumption after incubation with a preformed immune precipitate were either normal or elevated. Alternative pathway evaluation involved quantitation of serum levels of factor B and properdin by radial immunodiffusion; in addition, the ability of the patient's serum to support C3-C9 activation with zymosan and cobra venom factor as well as lysis of unsensitized rabbit erythrocytes was also ascertained. Rabbit CH50 titers and factor B levels were normal or elevated in 23/24 and 24/24 patients respectively. Abnormally low properdin levels more than 2 standard deviations below the normal mean were seen in 14/24 patients. Mean C3-C9 consumption after zymosan or cobra venom factor incubation was significantly less than normal (p < .001 and 0.025); in 11/24 sera incubated with zymosan, the extent of C3-C9 activation was more than 2 S.D. below the normal mean. Thus, abnormalities of the complement system are clearly present in patients with psoriasis and seem limited to the alternative pathway. Further, these abnormalities suggest that this pathway may be involved in the genesis of this disorder.