Control of cell proliferation within the human thymus. A very limited thymocyte subpopulation generates a suppressive activity

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Abstract
It is shown here that a minor subpopulation of the human thymus, representing 2–3% of the whole thymocyte population, can suppress proliferation of syngeneic or allogeneic thymocytes to various stimuli. In contrast, this suppressor cell population has no influence on the proliferative response of peripheral blood lymphocytes. This subpopulation was defined by its cell surface phenotype as CD3+, CD1−, 4−, 8− cells. Its suppressive activity is generated after concanavalin A (Con A) stimulation, but not after stimulation with phytohemagglutinin. In addition, the suppressive activity is not modified by extensive washes of Con A‐stimulated cells with 1‐O‐methyl‐α‐D‐ glucopyranoside, a specific sugar for Con A. This suppressor cell population does not exert any detectable cytotoxic activity, nor does it act by consuming available interleukin 2 (IL2). Rather, it prevents IL2 receptor expression on thymic target cells. Since Con A might activate T cells by binding to molecules physiologicaly involved in T cell activation, particularly the CD3‐T cell receptor complex, these data could be relevant to the regulation of normal thymic differentiation.