Regulation of the intercellular adhesion molecule-1 (ICAM-1) expression on human renal tubular epithelial cells in culture (hKEC-1) was investigated. A large proportion of hKEC-1 cells from the primary cultures expressed the ICAM-1 antigen. Supernatants from mixed lymphocyte reaction (MLR) of both specific and third-party combinations augmented the expression of the ICAM-1 antigen, in a dose-dependent manner. A kinetic study revealed maximal augmentation by MLR supernatant on the first day, with a gradual decrease thereafter. Among several recombinant human cytokines tested, i.e., interferon-gamma, tumor necrosis factor-alpha, interleukin 1 alpha and beta, and IL-4, IFN-γ, TNF-α, and IL-1α/β were shown to augment the expression of ICAM-1. MLR supernatants and IFN-γ were more effective in augmenting ICAM expression than TNF-α and IL-1α/β. IFN-γ upregulated ICAM-1 expression in a dose-dependent manner, and maximal augmentation was achieved on the first day. The MLR supernatants were shown to contain IFN-γ and TNF-α, and the activity of the MLR supernatant was partially inhibited by neutralizing antibody against IFN-γ. These data suggest that cytokines, especially IFN-γ, TNF-α, and IL-1α/β, released by T cells and antigen-presenting cells upon recognition of alloantigens upregulate ICAM-1 expression on renal tubular epithelial cells. This may result in an increase in the attachment of graft-infiltrating T cells to the renal tubular cells, by the ICAM-1-LFA-1 interaction.