Psoriatic leukotactic factor. Further physicochemical characterization and effect on the epidermal cells.

A leukocyte chemotactic factor with a molecular weight of around 12,500 daltons is found in large amounts in psoriatic scales. Except for complement-activated serum none of the extracts prepared from individual contaminants found in psoriatic scales showed an elution pattern similar to that of the psoriatic leukotactic factor (PLF) by Sephadex G-75 chromatography. Checkerboard experiments showed that PLF was highly chemotactic and mildly chemokinetic for polymorphonuclear leukocytes (PMNs). Purification of PLF yielded a cationic peptide fraction similar to that of anaphylatoxin. Intradermal injection of a potent PLF solution into guinea pigs produced degenerative changes in the epidermis within 24 h, particularly in the differentiated cells of the upper epidermis. It increased epidermopoiesis as assessed by incorporation of 3H-thymidine. Planimetric analysis of the epidermis revealed a marked increase in epidermal thickness after 5 days. Since PLF per se did not influence the proliferative capabilities of isolated basal cells or exert any damaging effect on differentiated epidermal cells in human epidermal cell culture, we speculated that PLF induced the advent of PMNs abound with hydrolytic enzymes and toxic substances, which were responsible for the damage of the upper epidermis resulting in the formation of parakeratosis and of acanthosis.