The prevalence of subclinical rejection is lower in patients receiving tacrolimus than in patients treated with cyclosporine. However, it is not known whether this difference is related to the modulation of a specific cell immunophenotype. We perform a two case-one control study in patients treated with tacrolimus (n=44) or cyclosporine (n=22) with a protocol biopsy performed at 4 to 6 months. Immunophenotype of infiltrating cells was evaluated with monoclonal antibodies directed against CD45 (all leukocytes), CD3 (T lymphocytes), CD68 (monocytes/macrophages), and CD20 (B lymphocytes) and expressed as interstitial positive cells/mm(2). The number of interstitial CD45 (290+/-209 vs. 696+/-560; P<0.01), CD3 (121+/-84 vs. 208+/-104; P<0.01), and CD68 (155+/-232 vs. 242+/-280; P<0.05) but not CD20 (137+/-119 vs. 197+/-154) positive cells was lower in tacrolimus-treated patients. T lymphocytes and macrophages interstitial infiltration was reduced in tacrolimus treated patients evaluated with protocol biopsies in comparison to cyclosporine-treated patients.