EXPRESSION OF INSULIN-LIKE GROWTH-FACTOR BINDING PROTEIN-3 (IGFBP-3) IN THE PSORIATIC LESION

Epidermal hyper-proliferation is a key feature of psoriasis, and a rol e for IGF-I in this process has previously been proposed. Herein we in vestigated the expression of IGF binding proteins in the psoriatic les ion and compared it with normal skin. With in situ hybridization, we f ound that IGFBP-3 mRNA was expressed in the basal layer of the epiderm is in normal skin, IGFBP-3 was also detected immunohistochemically, ex clusively in the basal layer. In the psoriatic lesion, IGFBP-3 mRNA wa s similarly limited to the basal layer despite the characteristic expa nsion of the basaloid keratinocyte compartment and was detected only i n the suprapapillary epidermis, where IGFBP-3 mRNA was more abundant t han in normal or uninvolved epidermis, and IGFBP-3 protein could be re adily detected with specific antibody. As with IGFBP-3 mRNA, which rep resents the likely site of IGFBP-3 synthesis, IGFBP-3 was strictly lim ited to the basal keratinocytes of the suprapapillary epidermis. By us ing an antibody to the cell cycle antigen Ki67, we also showed that th e suprapapillary epidermis, where IGFBP-3 expression was maximal, cont ained few keratinocytes undergoing mitosis, whereas the tips of the re te pegs, where IGFBP-3 expression was conspicuously absent, contained many keratinocytes undergoing mitosis, We suggest that IGFBP-3 is a gr owth inhibitor in basal keratinocytes and that absence of IGFBP-3 in t he tips of rete pegs may contribute to epidermal hyper-proliferation i n the psoriatic lesion.