THE IMMUNOSUPPRESSORY AND ADHESIVE MINIREGION OF THE HUMAN MAJOR HISTOCOMPATIBILITY PROTEIN, HUMAN-LEUKOCYTE ANTIGEN DQ

Our previous studies showed that the nonapeptide fragment of human leu kocyte antigen DQ with TPQRGDVYT sequence strongly suppresses the immu ne response(1) [Z. Szewczuk, I.Z. Siemion, and Z. Wieczorek (1996) Mol ecular Immunology, 33, 903-908]. The fragment contains the RGDVY seque nce, which is very similar to thymopentin (pentapeptide RKDVY, an acti ve fragment (32-26) of thymopoietin, an immune system activator produc ed in thymi), and at the same time contains the RGD sequence, known as an inhibitor of adhesion processes. In the present study we tested an influence of the nonapeptide and its shorter fragments on binding of activated platelets and K562 cells to fibrinogen and fibronectin, resp ectively. We also designed and synthesized a cyclic thymopentin-like p eptide, CRGDVYC* (where C* indicates Cys participating in disulfide b ridge) to restrict its conformation. The cyclization product strongly suppresses the humoral and cellular immune response and selectively in hibits the adhesion of K562 cells to fibronectin. The results are disc ussed in the light of CD conformational studies. (C) 1997 John Wiley & Sons, Inc.