MORPHOLOGICAL ANALYSIS OF INVITRO HUMAN HAIR-GROWTH

The histological and ultrastructural aspect of normal human hair folli cles maintained ex vivo for 12 days was evaluated. Anagen hair follicl es, dissected free of contaminating connective tissue, were maintained for up to 12 days in a serum-free medium. Macroscopic observations re vealed continued viability for 12 days, at which time some follicles i nvoluted in a manner morphologically similar to catagen. Increased gro wth of maintained follicles was measured from the abrupt ending of the connective tissue sheath (CTS), as no increase in this component was observed from initiation of culture. In general follicles maintained u p to 8 days exhibited little divergence from normal in vivo morphologi es including the persistence of functional hair bulb melanocytes - a m arker of anagen. After this time melanin granules were present in derm al papilla cells, as occurs during impending involution in vivo. Heter otypic cell contact occurred in the middle to upper follicle between o uter root sheath (ORS) keratinocytes and disorganized CTS. Herniation of some ORS cells away from the follicle and the occurrence of loose d esmosomal junctions between ORS keratinocytes reflected loss of normal follicular cell interactions in upper follicles maintained after 8 da ys. Continued follicle growth correlated with the presence of mitotic matrix keratinocytes even at 12 days. After 12 days in culture most fo llicles involuted displaying apoptotic-like keratinocytes and hair bul b melanocytes and the presence of highly keratinized hair 'club' struc tures. While most follicles exhibited this orderly sequence of events, a few follicles involuted after 24 h with synchronous degeneration of all cells, Two follicles exhibited upregulated cortical cell differen tiation at the level of the dermal papilla (DP). Normal cell cytoplasm ic constituents were replaced with ribosomes and keratin bundles. This study reveals for the first time the histology and ultrastructure of normal hair follicles in culture for up to 12 days in serum-free mediu m. Although involuted hair follicles may exhibit some features of cata gen, it is possible that the mechanisms involved are entirely differen t.