Activity of synthetic thymosin alpha 1 C-terminal peptides in the azathioprine E-rosette inhibition assay.

The helical C-terminal portion of the thymic hormone thymosin alpha 1 exhibits immunological activities in several in vitro assays. The C-terminal region spanning positions 17-28 was subdivided into 11 overlapping peptide segments to collect further information on the molecular signal hypothesis for T lymphocyte differentiation by thymosin alpha 1 derived peptides. All peptides were synthesized by classical means and tested in the azathioprine E-rosette inhibition assay. The results provided additional evidence that a basic-acidic-lipophilic sequence character is a possibly essential feature of a molecular signal for T cell differentiation. Five to seven structures beginning N terminally with lysine fitted this functional key. They showed immunological in vitro activities similar to and even better than the parent hormone thymosin alpha 1 in the ability to express in immature spleen cells from adult thymectomized mice the E-receptor sensitive to azathioprine inhibition.