Marked synergism between tumor necrosis factor-alpha and interferon-gamma in regulation of keratinocyte-derived adhesion molecules and chemotactic factors.

T lymphocytes and mononuclear cells preferentially accumulate in the epidermis in inflammatory skin disease. To determine the role of keratinocytes in both the chemotaxis and adhesion of these cells to the epidermis, cultured keratinocytes were incubated with IFN-gamma and tumor necrosis factor-alpha (TNF-alpha), and mRNA detected and quantitated for IL-8, monocyte chemotaxis and activating factor, and intercellular adhesion molecule-1. Whereas induction of these mRNAs was either absent, or relatively weak and transient, to either IFN-gamma or TNF-alpha alone, when administered in combination there was a dramatic increase and persistence in the induction of all three genes. Pretreatment of the keratinocytes with cycloheximide failed to eliminate transcription, implying that all three are primary response genes. Transforming growth factor-beta, which modulates other keratinocyte functions (not related to adhesion or chemotaxis of inflammatory cells) failed to induce any of the genes. These novel findings potentially explain the selective recruitment of T cells and monocytes observed in inflammatory skin disease, because IFN-gamma and TNF-alpha can co-ordinately regulate keratinocyte-derived chemoattractants and adhesion molecule production.