The heterogeneity and functional capacities of human thymocyte subpopulations.

Abstract

Analysis of human thymocytes with monoclonal antibodies belonging to five distinct clusters of differentiation (CD1, CD3-CD5, CD8) revealed a high degree of phenotypic heterogeneity. Six subpopulations could be defined in the thymic compartment characterized by the presence of CD1 antigens (cortical type); four subpopulations could be defined in the compartment characterized by the lack of CD1 but by the presence of CD5 antigens (medullary type); two subpopulations could be defined in the compartment characterized by the lack of both CD1 and CD5 antigens. Thymic samples could be categorized as either high responder or low responder to phytohemagglutinin alone. The defect of low responders was, to a large extent, attributable to a lack of interleukin 2 availability in the medullary type compartment. Yet, cortical-type subpopulations, both from high and low responders, were able to respond to phytohemagglutinin alone to the same extent. Undesirable cell contamination was excluded by limiting dilution analysis. Moreover, cortical-type cells were found to be able to respond to concanavalin A alone, while medullary-type cells and total populations did not respond to concanavalin A alone. Thus, the human thymus includes a number of cell subpopulations involved in complex functional interactions.

Interleukin 2 promotes growth and cytolytic activity in human T3+4-8- thymocytes.

“…Depletion with Nal/34 plus complement leaves an enriched population of T3' cells (80-90%) where, surprisingly, T4+ plus T8+ lymphocytes do not account for the whole T3+ subset, suggesting the existence of T3+4-8-thymocytes. Further immunoselection, using OKT4A and B9.4 plus complement, directly shows the existence of a minor (0.5-3%) thymocyte population of T3+4-8-phenotype, not previously described (13,21). In contrast, a phenotypic profile of PBL, using the same procedure shown in Table 1 and elsewhere (13), reveals that T4+ plus T8+ cells account for the whole population of T3+ lymphocytes in peripheral blood.…”

“…To characterize the cells responsible for this phenomenon, we performed quantitative flow-cytometric analysis with the T-cell differentiation-cluster mAbs ( Table 1). As previously described (13,21), the thymus comprises a heterogeneous population of T11' lymphocytes, of which about 30% are mature T3' thymocytes and about 70% are immature T6' cells. Depletion with Nal/34 plus complement leaves an enriched population of T3' cells (80-90%) where, surprisingly, T4+ plus T8+ lymphocytes do not account for the whole T3+ subset, suggesting the existence of T3+4-8-thymocytes.…”

Unfractionated human thymocytes have a lower proliferative capacity than CD3-4-8- ones but have a similar capacity for expression of interleukin 2 receptors and production of interleukin 2.

“…The analysis of the cell surface antigen phenotype has shown that the thymus is composed of a complex and highly heterogeneous population of cells (1,2). The relationship among the different subpopulations and their functional capabilities are still uncertain.…”

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

“…The proportion of the thymocyte subpopulation defined by a given phenotype ( Fig. 1) was measured both in immunofluorescence and Cdependent cytotoxicity assays, as previously described [17]. The subpopulations obtained were cultivated for 3 days with ConA and then tested for their suppressive activity after mitomycin treatment.…”