Molecular characterization of retroviral mediated immunosuppression: Human immunodeficiency virus type 1 as a prototype

The molecular mechanism of retroviral mediated immunosuppression was characterized by testing the effect of synthetic, recombinant and native retroviral transmembrane polypeptides on several aspects of immune function. By use of synthetic peptides the minimum amino acid (aa) sequence required for inhibition of lymphoproliferation was determined to be an 8 aa sequence that is highly conserved among retroviruses including gp21 and gp41, the transmembrane proteins of human T lymphotropic virus type I/II (HTLV-I/II) and human immunodeficiency virus type 1 (HIV-1), respectively.; A peptide containing the highly conserved sequence aa581-597 of HIV-1 gp41 inhibited both human and murine lymphoproliferation in vitro in addition to interleukin 2 (IL 2) production and the induction of IL 2 receptor expression. The activity of aa581-597 was dependent upon internalization and was irreversible.; The molecular mechanism was characterized by showing that aa581-597 inhibits the cytoplasmic free Ca{dollar}sp{lcub}2+{rcub}{dollar} influx in T lymphocytes stimulated via the CD3/T cell antigen receptor complex at a site distal to inositol triphosphate production. aa581-597 was shown further to inhibit protein kinase C (pkC)-dependent phosphorylation of the CD3 {dollar}gamma{dollar}-chain in intact cells and to directly inhibit partially purified pkC.; The inhibitory activity was confirmed in vivo; aa581-597 and the recombinant gp41 and p15E proteins inhibited the recruitment of macrophages to sites of delayed inflammatory response in mice after systemic administration of doses that reflected the antigen load present during infection. The immunosuppressive activities observed here for HIV-1 aa581-597 are consistent with the immune defects observed in HIV-1 infected individuals; these results suggest that the transmembrane protein gp41 and HIV-1 may inhibit pkC and thus block pkC-dependent immune function contributing to the immunosuppression of HIV-1 infected individuals.; Studies were also carried out to assess the stability and tumor targeting of radioimmunoconjugates generated by coupling antibody with bifunctional chelating agents into which radioactive bismuth was incorporated.; Furthermore, experiments were performed to correlate the physical characteristics of synthetic peptide proteosome vaccines with their immunogenic potency.