Keratinocitet

Keratinocitet, commonly referred to as keratinocytes in English, are the predominant cell type of the epidermis, the outermost layer of the skin. They make up about 90 percent of epidermal cells and originate in the stratum basale from keratinocyte stem cells. Through proliferation and differentiation, they migrate upward through the spinous and granular layers and are ultimately shed as corneocytes in the stratum corneum. This continuous turnover, usually about 28 days, forms the epidermal barrier that protects against water loss and pathogen entry.

Keratinocytes synthesize keratin intermediate filaments and contribute to the formation of the cornified envelope that strengthens the barrier. In the basal layer they express keratins KRT5 and KRT14, while in the suprabasal layers they switch to KRT1 and KRT10. They also produce lipids and structural proteins such as filaggrin, loricrin, and involucrin, which together with lamellar bodies and intercellular lipids create a lipid-rich, waterproof barrier.

Beyond barrier function, keratinocytes participate in immune defense by secreting cytokines, chemokines, and antimicrobial peptides, and by interacting with resident immune cells of the skin. They influence pigmentation through melanosome transfer from melanocytes and respond to injury by migrating and proliferating to aid wound healing.

Regulation of keratinocyte behavior involves signaling pathways such as Notch, Wnt/β-catenin, and EGFR signaling, as well as transcription factors like p63. Dysregulation can contribute to skin diseases, including psoriasis and ichthyosis, and keratinocytes are the cell of origin for multiple skin cancers, such as squamous cell carcinoma and, in part, basal cell carcinoma.