Differentiation changes in cord blood T lymphocytes induced by synthetic C-terminal peptides of thymosin alpha 1

Thymosin fraction 5 and its component thymosin alpha 1 has been reported to play a regulatory role in the later stages of T lymphocyte differentiation. Previous studies from our group have also demonstrated that thymosin fraction 5 can induce changes in purine degradative enzymes and in surface antigenic markers of cord blood lymphocytes, which have been shown to be immature compared with normal adult lymphocytes. Birr et al., have shown that the C-terminal region of thymosin alpha 1 is essential for the biological activity. In this study, the effects of these synthetic peptide fragments on cord blood T lymphocytes were studied. After incubation with different peptide sequences, cord blood lymphocytes were analysed for surface antigenic markers (OKT4/OKT8) and for purine degradative enzymes (PNP, 5 NT). In the range of 1.3 X 10 to 1.3 X 10(-5)M, one of the eleven peptides examined (sequence 13-19) exhibited activity approximately equal to that of the parent peptide thymosin alpha 1: increase in activity of 5'NT (p less than 0.01) and reduction of cells positive for OKT4 (p less than 0.01). Another sequence (20-28) was able to induce an increase in 5'NT only and a third one (20-25) a reduction of cells positive for OKT4. The results obtained in this study confirm that the C-terminal region contains molecular signals for T cell differentiation.