Keratinocyte activation following T-lymphocyte binding.

T lymphocytes infiltrate the epidermis and follicular epithelium adhering to keratinocytes within hours following induction of cutaneous inflammation. To determine if the physical binding interaction between a T cell and keratinocyte induces transmission of activation pathways, CD3+ T cells (HUT 78) were allowed to directly bind to non-cytokine-treated cultured keratinocytes. When these T cells bound to keratinocytes, the keratinocytes were activated as evidenced by detection of tumor necrosis factor-alpha, interleukin-6, and intercellular adhesion molecule-1 mRNA. This induction was relatively mRNA specific, as several other mRNA were not found to be altered. This activation process appeared to be one-sided, as no change in HUT cell mRNA levels was detectable. The keratinocyte activation process was confined to cultures that had direct physical binding by HUT cells, because co-culturing the HUT cells immediately above the keratinocyte monolayer (but not in direct contact), resulted in no such mRNA alterations. This direct adhesion-mediated activation of keratinocytes by T lymphocytes may be important in the genesis of cutaneous inflammation by amplifying the original stimulus, as well as contributing to the trafficking pattern of inflammatory cells as they leave the general circulation and enter the skin.