An HIV p24 heptapeptide down-regulates antigen-specific responses in vitro interfering at the level of the T3-Ti complex

Possible role of the plasminogen receptor as a site of interaction of the human immunodeficiency virus p24 immunosuppressive heptapeptide Ch7 with the host immune system

Previous work from our laboratory demonstrated that a synthetic heptapeptide (Ch7: RGSDIAG), corresponding to a conserved sequence of human immunodeficiency virus (HIV) core protein p24 (amino acids 232- 238), was able to specifically abrogate antigen-induced responses in cultures of normal human peripheral blood mononuclear cells (PBMC), probably acting at the level of monocytes. The Ch7 peptide displays sequence homology to human plasminogen. In the present report we show that a compound (6-aminoexanoic acid), known to prevent plasminogen binding to monocyte-like cells, greatly reduced the immunosuppressive capacity of Ch7. We suggest that the plasminogen receptor may represent a target structure on human monocytes for the immunosuppressive p24 sequence.

Increased PGE2 production mediates the in vitro inhibitory effect of the human immunodeficiency virus P24 immunosuppressive heptapeptide Ch7

Previous work from our laboratory demonstrated that a synthetic heptapeptide (Ch7), corresponding to a conserved sequence of human immunodeficiency virus (HIV) core protein p24 (amino acids 232-238), was able to specifically abrogate antigen-induced responses in cultures of normal human peripheral blood lymphocytes (PBL). Addition of recombinant human interferon-gamma (IFN-gamma) to Ch7-suppressed cultures restored the capacity to mount an antigen-specific antibody response, suggesting that a cytokine imbalance may be at the basis of the Ch7 immunosuppressive activity. In the present paper we show that the Ch7-dependent in vitro immunosuppression was accompanied by a significant up-regulation of prostaglandin E2 (PGE2) production and induction of interleukin-10 (IL-10)-secreting cells. In the presence of the PGE2 inhibitor indomethacin, IL-10 up-regulation was prevented and the induction of a specific antibody response was partially restored. PGE2 is indeed an important regulator of immune responses with the ability to differentially affect cytokine production. Thus, our results demonstrate that the Ch7 immunosuppressive epitope may primarily act by up-regulating PGE2 production and, through this mediator, by causing a cytokine dysregulation, finally responsible for immune response suppression.

Enhancement of monocyte migration and phagocytosis by the bovine immunodeficiency-like virus Gag proteins

Supernatants from bovine immunodeficiency-like virus (BIV)-infected cells have been previously shown to affect monocyte random migration, chemotaxis, phagocytosis, and antibody-dependent cell-mediated cytotoxicity (ADCC) in vitro. The experiments in this report demonstrate that the BIV Gag (core) proteins can enhance monocyte random migration, chemotaxis, and phagocytosis. Supernatants from BIV-infected cells contained 10-30 and 30-50 kDa proteins, which significantly (p < 0.05) increased monocyte chemotaxis. The 30-50 kDa protein(s) could be cleaved by limited proteolysis into 10-30 kDa active components. Affinity purification with monoclonal anti-p26 (capsid) antibodies yielded preparations that were active in the random migration, chemotaxis, and phagocytosis assays, but did not affect ADCC. Furthermore, activity of the affinity purified preparation could be specifically neutralized by hyperimmune rabbit serum against BIV Gag proteins. A recombinant Gag protein, consisting primarily of BIV p26, also enhanced monocyte random and chemotactic migration. It appears, therefore, that direct treatment with affinity-purified BIV Gag proteins or a recombinant Gag protein, is able to significantly affect the function of normal monocytes in vitro. Factors affecting monocyte migration and phagocytosis appear to be one or more breakdown products of the BIV Gag precursor, particularly those containing the p26 (capsid) protein.

T-helper reactivity to simian immunodeficiency virus gag synthetic peptides in human immunodeficiency virus type 2 infected individuals

West African populations are infected with divergent strains of human immunodeficiency virus type 2 (HIV2), some of which are closely related to simian immunodeficiency virus (SIV) and it has been postulated that the HIV2 epidemic might have arisen by cross-species spread of SIV into the human population in West Africa. To gain some insight into the possible basis for cross protection between these two closely related viruses, the T-helper responses to 15 synthetic peptides from SIV gag synthetic peptides were investigated in seven HIV2-infected subjects and in seven healthy controls. Significant reactivity to at least one of the synthetic peptides tested was found in all patients and a statistically significant correlation between CD4+ lymphocyte absolute numbers and the number of reacting peptides was observed. A marginal lymphocyte reactivity was found in two of the healthy controls studied. In conclusion, this preliminary evidence that HIV2-infected patients exhibit T-cell responses to SIV gag peptides suggests that both viruses share t-helper epitopes in the gag viral region and raises the possibility of cross protection between SIV and HIV2 which may be relevant for HIV2 vaccine research based on closely related retroviruses.

Evaluation of the Immunotoxicity of Antiretroviral Drugs Using an In Vitro Method for the Induction and Measurement of a Specific Antibody Response in Human Peripheral Blood Lymphocytes

We studied the effects of the antiretroviral drugs 3’-azido-3’-deoxythymidine (AZT) and 2’,3’-dideoxycytidine (DDC) on the induction of a specific primary antibody response to the antigen SRC and on Pokeweed mitogen-induced polyclonal immunoglobulin (Ig) production in cultures of normal human peripheral blood lymphocytes.

The results presented here show that AZT and DDC inhibited both systems in a dose-dependent way. However, inhibition of the antigen-specific antibody response occurred at drug concentrations significantly lower than those effective on the mitogen-driven polyclonal response. This was particularly striking for DDC, which was approximately 100 times more powerful, on a molar basis, on the specific antibody response than on polyclonal Ig production. Thus, in vitro systems for the induction of antigen-specific antibody responses in human lymphocytes may be important, sensitive tools for preclinical studies of the immunotoxicity of antiretroviral drugs.

Serum reactivity against an immunoregulatory sequence of HIV p24 in HIV-1-infected subjects

The aim of this study was to assess the antibody reactivity in HIV-infected subjects against an HIV-1 p24 sequence, p226 (aa226-237), including a seven amino acid epitope showing immunosuppressive activity in vitro and to evaluate the relationship between anti-peptide antibody levels and disease progression. Sera of HIV-infected subjects, at different stages of disease, were compared to control sera in a retrospective evaluation. Recombinant HIV-1 p24 and p24- and control-peptides were used in an enzyme immunoassay as targets for antibodies present in the sera. Antibodies directed against the whole p24 protein and its peptides were found in all the sera studied but at different levels. The anti-p226 reactivity was not significantly different at different clinical stages. Nevertheless, it was inversely correlated to the reactivity directed against the whole protein, that was lower in subjects characterized by low CD4 cell numbers.