CHARACTERIZATION OF THE T-CELLS IN AGED RAT BONE-MARROW

In this study, we determined the characteristics of CD3-positive (CD3) T cells existing in rat bone marrow (BM). In contrast to splenic T c ells, BM CD3+ T cells are composed of a higher proportion of CD8+ T ce lls, and the number of both cell types increased with age. Such CD3+ T cells in aged rats showed a similar usage of TCR Vbeta as splenic T c ells, suggesting that BM CD3+ T cells are thymus-dependent and compose d of an ordinary population in view of the expression of the TCR beta- chain. Purified T cells obtained from aged rat BM showed a markedly pr oliferative response by stimulation with immobilized anti-CD3 mAb, as did splenic T cells. However, the addition of BM non-T cells completel y inhibited the response of both BM and splenic T cells in vitro. Thes e results suggest that T cells in rat BM are negatively regulated by B M non-T cells in their response to the TCR-mediated signal not to disr upt the microenvironment of the BM.