In vitro induction of Lyt surface markers on precursor cells incubated with thymosin polypeptides.

Induction of precursor T cells by thymosin fraction 5 was found to generate a population of cells bearing the Lyt 1+, 2+, and 3+ phenotype and functionally capable of providing T-cell helper activity in vitro. However, when the component polypeptides of thymosin fraction 5 were similarly analyzed, several displayed inductive activities quite different from those of the parent preparation. These results suggest that variations in the polypeptide composition determine, to a large part, the inductive properties of a thymosin preparation and that such variations in vivo may serve as a regulatory system for T-cell maturation.