A Comparison of the Immunologic Function of Thymus Cells at Varying Stages of Maturation

Injections of mouse thymus cells from fetal, neonatal, 4-week- and 1-year-old syngeneic donors were compared for their ability to potentiate the production of serum antibody to sheep red blood cells in thymectomized, irradiated recipients previously injected with syngeneic bone marrow. Five million fetal thymus cells afforded no restoration of the immunologic response and one-year-old thymus cells gave marginal improvement. The apparent deficiency of the fetal thymus cell inoculum was quantitative since 20 million of these cells proved to be as active as five million neonatal thymus cells. Neonatal and 4-week-old thymus cells induced significant and virtually equal immunologic reactivity in terms of serum antibody titers. Immunologic restoration estimated by the number of spleen direct PFC was insignificant in all the groups given thymus cells. There was no increase in the number of indirect PFC observed in the experimental groups except for the one treated with 4-week-old thymus cells and here the restoration was significant but incomplete. These findings are discussed with reference to the cellular changes in the thymus in the perinatal period.