The proliferative capacity of human T lymphocyte subpopulations in a continuous culture system

The continuous growth of subpopulations of human T lymphocytes was investigated using a culture system containing conditioning factors from mitogen-stimulated lymphocytes. Cultures of purified peripheral blood lymphocytes rapidly became enriched for T lymphocytes, detected as sheep erythrocyte rosette-forming cells, and could be maintained for up to a month in an actively growing state. Subpopulations of T lymphocytes bearing Fc receptors for IgM(T.M) or IgG(T.G) could not be detected in these cultures unless the cells were first washed and cultured for 3 days in medium devoid of conditioning factors. During this second culture step, many of the cells reverted from a large, blast-like state to a small lymphocyte morphology and proportion of the T lymphocytes re-expressed Fc receptors. The proportions of T.M and T.G lymphocytes so detected remained constant throughout the continuous culture period indicating that the system permitted the proliferation of all T lymphocytes. Fractionation studies supported this conclusion by demonstrating that purified T, T.M and T.G but not B lymphocyte populations proliferated when cultured in the presence of conditioned medium. The majority of cells in cultures of purified T.M lymphocytes re-expressed IgM Fc receptors following reculture in unconditioned medium. However, the re-expression of IgG Fc receptors by cultured T.G lymphocytes could not be achieved.