Interactions of eosinophil granule proteins with skin: Limits of detection, persistence, and vasopermeabilization

Background: Eosinophil granule proteins, including eosinophil cationic protein (ECP), eosinophil-derived neurotoxin (EDN), eosinophil peroxidase (EPO), and major basic protein (MBP), are prominently deposited in skin in several cutaneous disorders and likely contribute to disease pathology. Objective: We sought to determine the limit of detection, persistence, and vasopermeabilization activity of the eosinophil granule proteins in skin. Methods: The eosinophil granule proteins were injected intradermally. Their minimum detectable concentrations in human surgical waste skin and their persistence in guinea pig skin were determined by indirect immunofluorescence. Vasopermeabilization activity in the guinea pig without and with H-1 antihistamine (pyrilamine maleate) pretreatment was assessed by extrusion of Evans blue dye-treated plasma. Results: The lowest detectable cutaneous concentrations were 0.05 mumol/L EPO, 0.1 mumol/L MBP, 0.25 mumol/L ECP, and 1 mumol/L EDN. Granule proteins persisted in guinea pig skin in vivo for 1 week (EPO), 2 weeks (ECP), 2.5 weeks (EDN), and 6 weeks (MBP). Each of the eosinophil granule proteins increased cutaneous vasopermeability in a concentration-dependent manner. The potency of vasopermeabilization induced by each granule protein was comparable with that of histamine. Pyrilamine maleate pretreatment of guinea pigs did not alter increased vasopermeability induced by ECP and EDN but significantly inhibited that induced by EPO and MBP. Conclusions: Micromolar concentrations of eosinophil granule proteins are often deposited in skin in eosinophil-associated cutaneous disorders such as atopic dermatitis. These patho-physiologically relevant concentrations of eosinophil granule proteins cause increased cutaneous vasopermeability (both by means of histamine-independent and histamine-dependent mechanisms) and might alter cutaneous function for days to weeks.