Biological activities of a synthetic peptide composed of two unlinked domains from a retroviral transmembrane protein sequence

The immunosuppressive peptide of HIV-1 inhibits T and B lymphocyte stimulation

The transmembrane glycoproteins of all retroviruses contain a conserved region composed of a leucine zipper, an immunosuppressive domain, and an immunodominant Cys-Cys loop. The amino acid sequence of the immunosuppressive domain of gp41 of human immunodeficiency virus type 1 (HIV-1; amino acids 583-599) is closely related, but not identical, to the immunosuppressive domains of type C and D retroviruses. A synthetic peptide corresponding to the immunosuppressive domain of HIV-1 (immunosuppressive peptide, ISU-peptide) inhibits mitogen and lymphokine stimulation of T lymphocytes. It is interspecies reactive and inhibits both human and mouse lymphocytes. The inhibitory effect is not based on direct cytotoxicity and the peptide is immunosuppressive only when conjugated to a carrier protein. The ISU-peptide of HIV-1 also inhibits B lymphocyte stimulation by the B cell mitogen lipopolysaccharide and by specific antibodies against delta and mu chains of cell surface immunoglobulins. These data suggest that the immunosuppressive domain of gp41 may play an important role in the immunopathogenesis of AIDS.

Retrovirus and filovirus "immunosuppressive motif" and the evolution of virus pathogenicity in HIV-1, HIV-2, and Ebola viruses

The "immunosuppressive motif" was found to be present in the glycoproteins of retroviruses and filoviruses. This sequence is also conserved in the pathogenic lentiviruses, HIV-1 and SIV, and is absent from HIV-2 gp41 and from an apathogenic simian retrovirus. The present analysis deals with the possible involvement of the "immunosuppresessive motif" in the pathogenicity of retroviruses and filoviruses, and the reasons for the conservation of this motif. The ancestral gene from which the "immunosuppressive motif" originated is not known.

HIV: virology and mechanisms of disease

HIV is the etiologic agent of AIDS. AIDS results from the loss of cells that are central to immune responses, T lymphocytes that express the CD4 protein on their surface. This paper relates HIV structure and replication to the clinical course of HIV infection. The virology of HIV replication is discussed first at the cellular and molecular levels. The course of HIV infection in vivo then is discussed and related to HIV replication. Finally, models that have been proposed to explain the mechanism whereby HIV causes immunodeficiency are considered. Although much is known about the growth of the virus both in vitro and in vivo, many questions remain about how HIV can deplete CD4-positive T lymphocytes and cause AIDS.

Comparison of retroviral p15E-related factors and interferon alpha in head and neck cancer

Head and neck squamous cell carcinomas (HNscc) produce low-molecular-mass factors (low-M(r) factors, M(r) < or = 25,000), which are antigenically related to the immunosuppressive retroviral transmembrane envelope protein p15E. These P15E-related tumour factors are thought to be responsible for some immunological impairments found in these patients (particularly the defective monocyte chemotaxis). A sequential and functional homology has been reported to exist between a bioactive fragment of interferon alpha (IFN alpha) and the putative immunosuppressive region of retroviral p15E (CKS-17). In this study we investigated (a) a possible functional and structural relationship between p15E and IFN alpha, and (b) the presence of and the relationship between p15E-related low-M(r) factors and IFN alpha in HNscc patients. We report the following results. (a) Recombinant human (rhu) IFN alpha was able to inhibit monocyte chemotaxis. (b) The anti-p15E antibodies crossreacted with rhuIFN alpha in a dot-blot technique; however, the anti-IFN alpha antibodies did not crossreact with disrupted murine leukaemia virus (p15E source). (c) Low-M(r) factors (n = 8-11) prepared from the sera of HNscc patients, which inhibit the monocyte chemotactic responsiveness, could be adsorbed by the anti-p15E antibodies as well as by the anti-IFN alpha antibodies. However, the abilities of the factors to adsorb to the two categories of antibodies (namely, anti-p15E and anti-IFN alpha) did not correlate. (d) Immunohistochemically we found IFN alpha-related epitopes, in almost all HNscc specimens studied (17/18), in locations distinctive from those of p15E-related factors. The anti-IFN alpha antibodies used in this study mainly reacted with basal epithelial cells close to the basal membrane, the prickle and granular cells of the squamous cell carcinomas. The anti-p15E antibodies mainly reacted with corneal layers, the granular and prickle cells, and did not react with basal epithelial cells. Our findings suggest that the immunosuppressive factors produced by HNscc cells are heterogeneous and p15E- and/or IFN alpha-related.

CD4-independent inhibition of lymphocyte proliferation mediated by HIV-1 envelope glycoproteins

The cytopathic effects of HIV-1 produced by direct infection of human T cells do not account for the disproportionate loss of CD4-positive lymphocytes during the course of HIV infection. Previous studies have demonstrated the inhibition of uninfected human T cell activation and proliferation by the HIV-1 envelope glycoproteins, presumably due to gp120-CD4 interactions. To examine the ability of HIV-1 to inhibit T cell proliferation in the absence of both direct infection and gp120-CD4 interactions, we tested the effect of HIV-1 on mouse T cell proliferation. Culture media containing HIV-1 released from infected cells inhibited T lymphocyte proliferation in response to interleukin-2 (IL-2). Studies to explore the mechanism of this inhibition suggested that the decrease in proliferation resulted from interactions between HIV-1 and the mouse cells, but did not involve IL-2/IL-2 receptor interactions. We used monoclonal antibodies to demonstrate that the HIV-1 envelope glycoproteins were required for the inhibition of murine T cell proliferation. Anti-gp120 antibodies completely restored proliferation, indicating that the surface protein gp120 was primarily required for the inhibition of proliferation. However, antibodies directed against the transmembrane protein of HIV-1 (gp41) also partially restored lymphocyte proliferation. The functional significance of the HIV-1 envelope protein epitopes recognized by the monoclonal antibodies is discussed.

Elevated antibodies to synthetic peptides of HTLV-1 envelope transmembrane glycoproteins in patients with HAM/TSP

We studied the antibody response to various kinds of well-characterized synthetic peptides of human T lymphotropic virus type 1 (HTLV-1) envelope glycoproteins in patients with HTLV-1 associated myelopathy (HAM)/tropical spastic paraparesis (TSP) and non-HAM/TSP HTLV-1 carriers. The serum antibody titers to most of the synthetic peptides were significantly higher in patients with HAM/TSP than those in non-HAM/TSP HTLV-1 carriers. However, the degree of the increase of antibody titers to the synthetic peptides corresponding to the transmembrane portions of HTLV-1 envelope glycoproteins (env-p20E), such as p20E 332-352, 374-392, 426-448 and 458-488, was greater than those to synthetic peptides of exterior portions of HTLV-1 envelope glycoproteins (env-gp46) in sera from patients with HAM/TSP. Antibodies to env-p20E 332-352 and 374-392 were elevated in the cerebrospinal fluid (CSF) only from patients with HAM/TSP but not from non-HAM/TSP HTLV-1 carriers. These data indicate that the increase of antibody titers to transmembrane portions of HTLV-1 envelope glycoproteins in sera and CSF is a characteristic feature of antibody response in patients with HAM/TSP and may be closely associated with the development of HAM/TSP from non-HAM/TSP HTLV-1 carriers.

Identification of a decapeptide region of human interferon-alpha with antiproliferative activity and homology to an immunosuppressive sequence of the retroviral transmembrane protein P15E

We have identified a 10-amino acid sequence (amino acid, 9-18) from interferon-alpha (IFN-alpha) that when presented as a synthetic peptide inhibits both the proliferation of the Daudi lymphoblastoid cell line and the antigen receptor-stimulated proliferation of fresh human T lymphocytes. This sequence, which was identified by virtue of its sequence similarity (70% identity) to the immunosuppressive sequence of the retroviral transmembrane protein p15E, represents the smallest fragment of IFN-alpha that has been shown to date to be biologically active.