Functional characterization in vitro of two human T-cell subpopulations with different affinities to sheep erythrocytes.

On the basis of their different abilities to form resettes with unsensitized sheep erythrocytes (SRBC), two subpopulations of human T lymphocytes were separated by the rosette sedimentation technique. In a series of in vitro experiments the T cells carrying high-avidity receptors for SRBC ('active' T cells) were shown to respond significantly better when stimulated with purified protein derivative (PPD) and allogeneic cells than the subpopulation carrying low-avidity receptors ('non-active' T cells). On the other hand, the latter responded better to phytohaemagglutinin, concanavalin A and pokeweed mitogen; it was likewise demonstrated that these cells were better stimulators in a mixed lymphocyte reaction. The role of monocytes in mitogen and PPD responses was investigated by adding such cells to Fe-treated suspensions. These were found to be crucial for an optimal response of both subpopulations. Furthermore, different patterns of activation were observed for the active and non-active cells. Especially interesting was the observation that the Con A response of the active fraction was more monocyte-dependent than that of the non-active one.