Functional Relationship of Human T Lymphocytes, Monocytes and Interleukins

Abstract

The different requirements of human T lymphocytes of different densities for accessory cells and helper factors (Interleukin 1 (Il-1) and Interleukin 2 (Il-2)) in the response to phytohacmagglutinin (PHA) were investigated. Humun T lymphocytes were subfractionated by discontinuous density gradient centrifugation. The various T-cell subsets were stimulated by PHA to form colonies in an agar micro-culture in the presence or absence of additional adherent cells or crude preparations of Il-1 or Il-2. The results show that the higher the density of the fractionated T lymphocytes and the lower the number of cells cultured, the greater is the number of adherent cells or the amount of helper factors required for the stimulation of colony-forming T lymphocytes. The results are consistent with the assumption that monocytes provide positive modulating activity during mitogenic stimulation of colony-forming T lymphocytes. The number of monocytes necessary for exerting an optimal modulating activity depends on the number of T cells cultured and the density of the T-cell fraction. This may reflect a distinct susceptibility of T cells of different densities to monocyte-mediated helper effects.