In renal transplant, patients, the number of T cells expressing high levels of LFA-1 (LFA-1-bright) and of T cells expressing CD57 increases in response to viral infection, even if the latter is asymptomatic. Their role in long-term renal transplant patients with cytomegalovirus (CMV) antigenemia and concomitant transplant dysfunction was investigated. For this purpose, this study used triple-color flow cytometry, fluorescence-activated cell sorting of peripheral blood T cells (CD3+/LFA-1-dim or -bright and CD8+/CD57+ or CD57- subsets), and subsequent semiquantitative reverse transcription-polymerase chain reaction. Cytokine mRNA levels for interleukin (IL)-1 beta, IL-2, IL-4, IL-8, IL-10, tumor necrosis factor alpha, and interferon-gamma, as well as Granzyme A and IL-2R p55 and p75 transcripts were determined and compared in peripheral blood mononuclear cells and in separated T cell subsets. Although in patients with CMV infection and/or rejection, cytokine transcripts were readily detected and the levels in the CD3+/LFA-1-bright subsets were, by orders of magnitudes, higher than in the LFA-1-dim subset, hardly any cytokine message was found in patients without CMV infection or rejection episodes or in control subjects. The expression of Granzyme A, which is involved in cytotoxic T lymphocyte-mediated cytotoxicity, was not upregulated in LFA-1-bright T cells, which is in discordance with cytokine levels. Differences between CD57+ and CD57- T cells were limited to the IL-2R p55 mRNA, of which the former expressed significantly less than the latter. It is concluded that upon virus-induced activation of peripheral blood T cells, an effector type that is marked by high inflammatory but small cytotoxic potential is produced. The results of this study propose that these cells represent a correlate of persistent immune activation and are liable to produce graft dysfunction, although they are unable to clear the organism from virus infection because of their lack of cytotoxic potential.