The distribution of alpha 2 beta 1, alpha 3 beta 1 and alpha 6 beta 4 integrins 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 compartments, which reflect different programmes of differentiation. Using monoclonal antibodies against alpha 2 beta 1 and alpha 3 beta 1 integrins we demonstrated a shift in their expression, from a basolateral distribution in the basal cells of the lower outer root sheath, to an apicolateral expression in the upper outer root sheath, as in epidermis. This shift takes place in a transition zone, localized to the midpart of the follicle. The distinct basolateral distribution of alpha 2 beta 1 and alpha 3 beta 1 integrins in the lower portion of the outer root sheath coincides with the presence of basal cell protrusions and is probably linked to the presence of the vitreous membrane which surrounds the bottom part of the anagen human hair follicle. Moreover, we showed that the expression of alpha 6 beta 4 integrin is discontinuous along the hair follicle and coincides with that of laminin 5. Together these results establish that within a given compartment-namely the outer root sheath-several domains can be clearly identified, which probably reflect the onset of successive differentiation pathways along the hair follicle.