THE HUMAN HAIR FOLLICLE - GLYCOPROTEIN-RELATED ANTIGENIC PROFILE OF DISTINCT KERATINOCYTE POPULATIONS IN-VIVO AND THEIR ALTERATIONS IN-VITRO

The cell surface expression of three glycoprotein antigens, as defined by the monoclonal antibodies BT 15, T 43, and MH 99, was investigated in follicular keratinocyte populations in vivo. In addition, the regu lation of glycoprotein synthesis was studied in follicular and interfo llicular keratinocytes cultured in vitro. The BT 15 antigen was strong ly expressed in the inner root sheath and the area above Auber's line of the hair bulb, whereas the T43 antigen was mainly seen in the outer root sheath. Selectively high expression of the MH 99 antigen was fou nd only in outgrowing germ buds of early anagen follicles. Radioimmuno precipitation revealed strong signals with BT 15 in freshly prepared f ollicular keratinocytes, two to three times stronger than those in int erfollicular keratinocytes, but the signals clearly decreased by 80% u nder continuing culture conditions. The T 43 antigen was found by FAGS analysis and radioimmunoprecipitation in initially low amounts in bot h populations, but the signals increased dramatically (up to 50 times) in long-term cultures and in subcultures. The MH 99 antigen was also initially present only in low amounts, in interfollicular rather than in follicular keratinocytes, but its expression increased up to 15-fol d with continuing culture and any differences between the two populati ons disappeared. Our investigation revealed that at least three popula tions of hair follicle keratinocytes are characterized by different su rface glycoprotein antigens, clearly related to their state of differe ntiation and proliferation. The BT 15 antigen seemed in vivo character istic of well-differentiated keratinocytes of the inner root sheath an d the keratogenous zone of the hair bulb, whereas the T 43 antigen app eared to mark a less differentiated keratinocyte population that forme d the outer root sheath, clearly related to the basal epidermal layer. The MH 99 antigen clearly marked an early germ-cell phenotypic cell t ype to be seen only in the embryonal hair germ that showed high prolif erative activity. Quantitative antigenic differences were initially fo und in vitro between follicular and interfollicular keratinocytes, but these differences gradually disappeared with continuing primary cultu re and in subcultures.