Anti-CD27 monoclonal antibodies identify two functionally distinct subpopulations within the CD4+ T cell subset

Anti-CD27 monoclonal antibodies react with a cell surface molecule expressed on medullary thymocytes and a large subpopulation (75%) of peripheral blood T lymphocytes. This study was undertaken to analyze the functional capacities of CD27+ and CD27- subpopulations within the CD4+ subset. In addition, we investigated whether CD27 subpopulations belong to two mutually exclusive T cell sublineages. Proliferation upon lectin stimulation by either phytohemagglutinin or pokeweed mitogen (PWM) was found to be consistently higher in CD4+CD27+ cells compared to CD4+CD27- cells. In contrast, CD27+ and CD27- cells did not differ in anti-CD3, soluble antigen or interleukin (IL)2-induced proliferation. In PWM-driven B cell differentiation, CD4+CD27+ cells provided helper activity on IgM production, while CD4+CD27- cells did not. The differences observed between CD4+CD27+ and CD4+CD27- cells in both proliferation and T helper activity on IgM production can, at least in part, be explained by the inadequate production of IL2 by CD27- cells upon lectin stimulation. In contrast, CD27+ and CD27- subpopulations did not differ in the production of interferon-gamma. CD27- cells could be induced to express the CD27 antigen through stimulation of these cells with immobilized anti-CD3 antibodies. After 3 days of culture, approximately 50% of the cells had CD27 membrane expression, whereas after 6 days 80% of the cells express the antigen. We conclude that anti-CD27 antibodies identify two functionally distinct T cell populations within the CD4+ subset. These subpopulations apparently do not belong to two separate T cell sublineages, but may reflect differences in the activation state of CD27+ vs. CD27- peripheral blood T lymphocytes.