Immunoregulatory effects of a peptide derived from the α₁ domain of an HLA class II molecule

We have shown tolerogenic effects, in vitro and in vivo, of synthetic peptides corresponding to regions of class IHLA molecules. To test if HLA class II molecules had these properties, a panel of peptides were made from the α₁ α helix. One peptide inhibited proliferation of human PBL and lysis of target cells by CTL in an allele non-specific way. It could inhibit proliferation when added 0-24 hrs after stimulation. It had no effect on early mRNA expression, nor did it decrease cell surface molecules expression. Restimulation experiments showed that the peptide induced a long-term unresponsiveness that was not reversible with IL-2. These data indicated that the peptide functioned more like the immunosuppressant rapamycin than cyclosporin. Both delayed cell cycle progression through prolonging the presence of the inhibitor protein p27. Both also inhibited S6 kinase activity. The two did differ: the peptide did not inhibit yeast cell proliferation, nor did it bind FKBP, whereas rapamycin did not inhibit CTL killing.