THE DISTRIBUTION OF ALPHA-2-BETA-1, ALPHA-3-BETA-1 AND ALPHA-6-BETA-4INTEGRINS IDENTIFIES DISTINCT SUBPOPULATIONS OF BASAL KERATINOCYTES IN THE OUTER ROOT SHEATH OF THE HUMAN ANAGEN HAIR FOLLICLE

The human hair follicle is composed of different concentric compartmen ts, which reflect different programmes of differentiation. Using monoc lonal antibodies against alpha 2 beta 1 and alpha 3 beta 1 integrins w e demonstrated a shift in their expression, from a basolateral distrib ution in the basal cells of the lower outer root sheath, to an apicola teral expression in the upper outer root sheath, as in epidermis. This shift takes place in a transition zone, localized to the midpart of t he follicle. The distinct basolateral distribution of alpha 2 beta 1 a nd alpha 3 beta 1 integrins in the lower portion of the outer root she ath coincides with the presence of basal cell protrusions and is proba bly linked to the presence of the vitreous membrane which surrounds th e bottom part of the anagen human hair follicle. Moreover, we showed t hat the expression of alpha 6 beta 4 integrin is discontinuous along t he hair follicle and coincides with that of laminin 5. Together these results establish that within a given compartment - namely the outer r oot sheath - several domains can be clearly identified, which probably reflect the onset of successive differentiation pathways along the ha ir follicle.