The effects of the macrolide antibiotic, roxithromycin (RXM) on immunological functions of cultured normal human keratinocytes (NHK) were studied. RXM neither modulated the expression of intercellular adhesion molecule-1 (ICAM-1) and human histocompatibility leukocyte antigen (HLA)-DR nor mobilized intracellular free calcium in NHK that were cultured in medium alone. However, the ICAM-1 and HLA-DR expression induced by cultivation with interferon-gamma (IFN-gamma) was upregulated and suppressed, respectively, by pretreatment of NHK with RXM. Whereas ICAM-1 upregulation was observed with RXM at a concentration as high as 0.1 mM, the inhibition of HLA-DR expression by RXM was virtually dose-dependent at doses ranging from 100 nM to 0.1 mM. Accessory cell function of major histocompatibility complex (MHC) class II-bearing NHK in terms of the T-cell response to staphylococcal enterotoxin B was suppressed by pretreatment of NHK with RXM, indicating the functional consequence of RXM-induced reduction of MHC class II molecules. Furthermore, RXM inhibited IFN-gamma-mediated upregulation of IL-1 alpha secretion by NHK. These results show that RXM suppresses immunological functions of keratinocytes triggered by IFN-gamma and suggest the therapeutic relevance of RXM to T cell-mediated inflammatory skin diseases and T cell malignancies such as atopic dermatitis, psoriasis and cutaneous T cell lymphoma, which can be exacerbated by keratinocytes immunologically modulated by exposure to IFN-gamma.