LFA-1 mediated cell adhesion induces G0-G1 transition of human T lymphocytes in vitro

Proliferation of mature T lymphocytes requires antigenic stimulation of the T cell receptor/CD3 complex (TCR/CD3) and an additional signal provided by different accessory molecules, including the leukocyte adhesion receptor LFA-1. We have used a cytochemical approach to analyse the effect of LFA-1 stimulation, either alone or in association with TCR/CD3 triggering. A dual parameter cytometric analysis of DNA content versus Ki-67 positivity allowed progression throughout the cell cycle to be monitored. Engagement of LFA-I alone was able to initiate the intracellular events necessary for Ki-67 expression (marking G0-G1 transition) in a fraction of the T cell population but was not sufficient to induce the transit into S-phase. Cross-linking of both LFA-1 and CD3 was required for DNA synthesis to occur. These data confirm LFA-1 as an important costimulatory molecule of TCR-mediated T cell activation.