IMMUNOLOGICAL PROPERTIES OF THE THYMOPENTIN-LIKE FRAGMENTS OF HLA-DQ

Class II human leukocyte antigens (HLA-II) are cell surface alpha beta heterodimers (M(r) approximate to 60 000) that play a pivotal role in the immune response by presenting peptides derived from environmental antigens to the T-cell receptor. A 167-171 fragment of the beta 2-cha in of the HLA-DQ molecule consists of the sequence RGDVY, which is ver y similar to thymopentin (pentapeptide RKDVY, an active fragment (32-3 6) of thymopoietin, an immune system activator produced in thymi), and at the same time contains the RGD sequence, known as an inhibitor of adhesion processes. We synthesized and investigated the immunomodulato ry activity of series of peptide fragments of HLA-DQ containing thymop entin-like sequences. The results indicate that all synthesized peptid es suppress the cellular immune response. However, RGDV, RGDVY and QRG DVY show very weak stimulatory activity in humoral immunological respo nse tests. In contrast to the shorter peptides, the nonapeptide fragme nt of HLA-DQ, TPQRGDVYT, shows significant immunosuppressive activity in all tests. A possible role of these fragments of the polypeptide ch ain of HLA-DQ in the regulation of HLA functions is discussed. Copyrig ht (C) 1996 Elsevier Science Ltd