T lymphocyte-mediated bone marrow failure is a recently recognized clinical disorder, but the T lymphocyte subsets responsible for mediating the inhibitory effect have not been identified. We obtained T lymphocytes from the bone marrow of two patients with T lymphocyte-mediated granulopoietic failure, exposed them to monoclonal antibodies (OKT3, OKT4, and OKT8) in cytotoxicity assays, then recombined the treated T cells with autologous T-depleted marrow cells in clonal assays for granulocyte/macrophage progenitors (CFU-GM). Treatment of T cells with OKT3 and OKT8 abrogated their granulopoietic inhibitory effect but treatment with OKT4 did not. Therefore, in these two patients, the lymphocytes that played a role in the inhibition of granulopoiesis were of the cytotoxic/suppressor subset.
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