CO-LOCALIZED OVEREXPRESSION OF GRO-ALPHA AND IL-8 MESSENGER-RNA IS RESTRICTED TO THE SUPRAPAPILLARY LAYERS OF PSORIATIC LESIONS

Epidermal infiltration by polymorphonuclear cells is a prominent featu re in psoriatic lesions, Expression of neutrophil-specific chemoattrac tants by lesional keratinocytes could play an important role in the re gulation of this infiltration process. We therefore examined the mRNA expression of GRO-alpha, a well-characterized peptide with neutrophil- specific activation profile in psoriatic lesions by in situ hybridizat ion, Clusters of clearly detectable and in some cases highly abundant GRO-alpha hybridization signals could be demonstrated in the different iated layers of psoriatic epidermis, The signals were clearly associat ed with keratinocytes, with no nearby neutrophils detectable by micros copic examination, When additional tissue sections of GRO-alpha-expres sing lesions were examined with an interleukin-8/neutrophil-activating peptide-8 (IL-8)-specific anti-sense probe, IL-8 expression was detec table and confined to areas also expressing GRO-alpha. Expression of b oth GRO-alpha and IL-8 is focally upregulated by an as yet unknown mec hanism in lesional psoriatic keratinocytes, ultimately leading to neut rophil tissue infiltration. We suggest that the focal expression of GR O-alpha and IL-8 in the epidermal layers above the dermal papillae may be involved in the ''squirting papilla'' reaction described as a char acteristic feature of psoriatic plaque-type lesions.