Stimulation and inhibition of human granulopoiesis in vitro by normal and malignant T4- or T8-lymphocyte subpopulations

: We studied the role of total peripheral blood T-lymphocytes and separated subpopulations of OKT4+ and OKT8+ cells stimulated with concanavalin A in the regulation of human granulopoiesis. Unfractionated total T cells depleted of monocytes are capable of producing colony-stimulating activity (CSA) and colony-forming unit-clone (CFU-C) suppressor activity simultaneously. After positive selection of cell subsets using a fluorescence-activated cell sorter, these two activities were produced by OKT4+ lymphocytes, whereas OKT8+ cells displayed small amounts of CSA and were incapable of releasing suppressor activity. On the other hand, total human thymocytes and subsets defined by monoclonal antibodies Leu2a/Leu3a failed to express any detectable CSA or CFU-C suppressor activity. A total of 14 cases of phenotyped lymphoid malignancies were also studied: the results showed that the production of stimulating and/or inhibiting factors is neither clearly related to a discrete stage of differentiation nor to the OKT4/OKT8 phenotype. Moreover, three monoclonal T leukemias, OKT4+OKT8-, OKT4-OKT8-, and OKT4-OKT8+ have been able in each case to produce simultaneously CSA and CFU-C suppressor activity. Finally, these studies strongly suggest that the activities of T-lymphocytes involved in the regulation of granulopoiesis are not closely linked with OKT4/OKT8 phenotype.