A Subpopulation of Human Basal Keratinocytes Has a Low/Negative MHC Class I Expression

Abstract

By means of flow cytometry, we demonstrate that a subpopulation of cells in the basal layer of the human epidermis has undetectable levels of major histocompatibility complex (MHC) class I molecule. The percentage of MHC class I–negative cells in the basal layer ranged 0.5%–2%. MHC class I–negative cells were characterized by small size (low forward scatter) and low granularity (low side scatter). Upon culturing of MHC class I–negative cells, increase of MHC class I expression was observed. This expression was lower than the expression of MHC class I molecule both in cultured MHC class I–positive cells and in ex vivo keratinocytes. Furthermore, stimulation of MHC class I–negative keratinocytes with interferon gamma (IFN-γ) did not bring about further increase in MHC class I expression. MHC class I–negative cells were identified as keratinocytes as they expressed keratin 14 and formed keratinocyte colonies in vitro.