Age-dependent accumulation of thymic hormone-sensitive cells.

T-cell subsets were investigated in the thymus and spleen of BALB/c mice from 1 to 9 mth of age. It was found that in both of these organs, the proportion of T cells with a high surface concentration of Thy 1 antigen increased with age. The intensity of the graft-versus-host reaction induced by spleen and lymph node cells in F1 hybrids also increased with age. On the other hand, the response of thymocytes to Con A measured by migration inhibition decreased with age. All of these parameters could be reversed to the 1-mth-old levels by preincubation of the cells with a thymic hormone preparation. This indicates that in the time span under study, the changes observed could be attributed to an accumulation of thymic hormone-sensitive cells.