Age-dependent decline of T-cell cloning potential in mice

Mice spleen cells capable of forming, under stimulation by phytohemagglutinin (PHA), single-cell derived colonies in an in vitro soft-agar system, show with advancing age a progressive reduction of their number, which occurs earlier than the decline of PHA response in fluid phase. In addition to their reduced number, old colony-forming T-cells show the same phenomena recorded in fibroblasts; for example, a decrease of their residual in vitro proliferation potential, as measured by the size of the colonies, reached during the culture period. The reduced number of responding units and the decreased colony size seem to be distinct phenomena, since in the immunodeficiency state of hypopituitary dwarf mice only the first defect is observable, whereas the size distribution is normal. Both the reduced number of T-cell colonies and their decreased proliferative potential in vitro observed in old age, can be restored by transplanting a neonatal FTS ("facteur thymique serique")-producing thymus, but not by injecting isolated thymocytes into old mice. A correlation seems to exist between the decline of T-cell colony potential with advancing age and the progressive deterioration of thymic endocrine activity.