The immunogenicity of allogeneic cultured human epidermal keratinocytes (cHEKs) has been studied in several models with contradictory results. We studied human T-cell activation in an in vitro assay by incubating, for 4 and 24 hr, cHEK confluent sheets with human peripheral blood mononuclear cells (PBMC); parallel HEK cultures were incubated with interferon (IFN)-gamma to induce the expression of major histocompatibility complex (MHC) molecules before their interaction with PBMC. T-cell activation was evaluated by flow cytometry. T cells neither expressed the early and late activation markers CD69 and CD25, respectively, nor proliferated after incubation with the epidermal sheets, despite the IFN-gamma-induced expression of MHC and adhesion molecules in cHEKs. Interleukin (IL)-10 was detected in the medium from the co-cultured PBMC and HEK sheets, but not from HEK alone. The results suggest that HEKs are unable to stimulate T lymphocytes through secretion of cytokines that might contribute to the immunosuppressive effect in this in vitro model.