Eosinophilic cationic protein (ECP) in skin disorders.

Eosinophil cationic protein (ECP) is exclusively secreted only by the eosinophilic leukocyte. In this study the ECP concentration in the serum was measured in patients (n = 155) with various skin disorders and compared with the number of circulating eosinophils. The presence of activated eosinophils in the skin was also studied immunohistochemically using the monoclonal antibody EG-2, which recognizes both the eosinophil protein X (EPX/EDN) and ECP. EG-2 distinctly revealed these proteins in the eosinophils and their granules. Non-activated eosinophils were studied with the monoclonal antibody EG-1. In most cases this did not disclose any more eosinophils and often it was located more diffusely and not seldom on collagen fibers. Elevated serum ECP but normal numbers of circulating eosinophils were found in half of the patients with progressive plaque psoriasis and long-standing daily chronic urticaria. In patients with prurigo nodularis, papular erythematous eruptions, vasculitis, purpura and toxic drug reactions, Wells' syndrome, porphyria cutanea tarda and persistent light reaction the serum ECP was increased, although in some cases the number of circulating eosinophils was normal. In these disorders an increased number of activated eosinophils was found in the skin. Both serum ECP and the number of activated eosinophils normalized when the patients' condition improved. In atopic dermatitis the serum ECP and the number of activated eosinophils in the skin were increased only during exacerbation of the disease. High serum levels of ECP and activated eosinophils in the skin are frequent findings in many skin disorders in spite of often normal blood eosinophil counts.(ABSTRACT TRUNCATED AT 250 WORDS)