SIMILAR RATES OF PRODUCTION OF T-LYMPHOCYTES AND B-LYMPHOCYTES IN THEBONE-MARROW

The rate of renewal of T lymphocytes in the bone marrow of euthymic C5 7BL/Ka and athymic nu/nu BALB/c mice was estimated by in vivo labeling with bromodeoxyuridine. T lymphocytes accounted for 16-18% of marrow cells in euthymic mice as judged by immunofluorescent staining with mo noclonal antibodies for Thy-1, CD3, and alpha/beta T cell antigen rece ptor markers. About 70% of marrow cells expressed receptors (Mac-1, Gr -1, B220) for myeloid, macrophage, and B lineage cells. Approximately 13% of cells in the athymic bone marrow expressed alpha/beta T cell re ceptors. Sorted marrow T cells proliferated in response to stimulation with anti-alpha/beta antibodies in vitro and showed functional rearra ngements of V-beta and J(beta) genes. Sorted non-T cells did not respo nd to stimulation in vitro, and all V-beta and J(beta) gene rearrangem ents idetified were nonfunctional. In vivo labeling studies indicated that similar to 17 x 10(6) bone marrow T cells are renewed daily in eu thymic mice and similar to 14 x 10(6) are renewed in athymic mice. App roximately 11 x 10(6) mature B cells (immunoglobulin MC) are renewed d aily in the bone marrow of the latter mice. To determine whether marro w precursors can give rise to T cells directly, marrow cells from euth ymic and athymic mice were depleted of T cells by cell sorting and inc ubated in vitro for 48 h in the absence of exogenous growth factors or thymic stromal cells. Examination of the cells after culture showed t hat 10-12% stained brightly for alpha/beta T cell receptors. Although functional rearrangements of V-beta and J(beta) genes were not detecte d before culture, the majority of rearrangements were functional after culture. The emergence of the bright alpha/beta T cells in culture wa s dependent on depletion T cells from the marrow cells before culture. The results suggest that most marrow T cells are generated in the mar row itself.