The epidermal layer of the skin provides an essential function as a protective barrier against insults from the external environment. The predominant cell type in the epidermis is keratinocytes and they are located in the stratified squamous epithelia. Keratinocytes are named after keratin, which is the most abundant protein in this cell. Progenitors of keratinocytes reside and divide in the basal layer of the epidermis. They then differentiate, migrate towards the surface of epidermis, and eventually withdraw from the cell cycle permanently. Keratinocyte proliferation, differentiation, and programmed cell death are complex and carefully choreographed processes. Apart from their protective functions, keratinocytes express adhesion molecules and cytokines, further suggesting an implication in skin innate immunity, tissue homeostasis, wound healing, cancer development, and skin-based gene-therapy. HEK-a from ScienCell Research Laboratories are isolated from adult human skin. HEK-a are cryopreserved at passage one and delivered frozen. Each vial contains >5 x 105 cells in 1 ml volume. HEK-a are characterized by immunofluorescence with antibodies specific to cytokeratin-18 and/or cytokeratin-19. HEK-a are negative for HIV-1, HBV, HCV, mycoplasma, bacteria, yeast, and fungi. HEK-a are guaranteed to further expand for 10 population doublings under the conditions provided by ScienCell Research Laboratories. Recommended Medium It is recommended to use Keratinocyte Medium (KM, Cat. #2101) for culturing HEK-a in vitro.