Sheep red blood cells enhance T-lymphocyte proliferation

Small numbers of sheep red blood cells (SRBC) markedly augmented the proliferation of T lymphocytes activated by antigens or mitogens. This effect occurred with as few as one SRBC per T lymphocyte and with intact or osmotically lysed red cells. When increasing numbers of SRBC was added to T lymphocyte cultures stimulated with PHA or autologous cells, T lymphocyte proliferation peaked sharply at 10 to 50 SRBC per T cell. The SRBC did not influence resting T-lymphocytes. Rather, the effect occurred after T lymphocyte activation during cell division. There was a detectable increase in interleukin 2 (IL-2) receptor generation but not in IL-2 production by activated T lymphocytes cultured with SRBC versus medium alone. Finally, anti-T11 antibody could inhibit the SRBC enhancing effect on T-lymphocyte function, suggesting that an empty erythrocyte (E) receptor on the T lymphocyte was necessary for the SRBC action.