HLA-DR peptide inhibits HIV-induced syncytia

Human Leukocyte Antigen (HLA) and Immune Regulation: How Do Classical and Non-Classical HLA Alleles Modulate Immune Response to Human Immunodeficiency Virus and Hepatitis C Virus Infections?

The genetic factors associated with susceptibility or resistance to viral infections are likely to involve a sophisticated array of immune response. These genetic elements may modulate other biological factors that account for significant influence on the gene expression and/or protein function in the host. Among them, the role of the major histocompatibility complex in viral pathogenesis in particular human immunodeficiency virus (HIV) and hepatitis C virus (HCV), is very well documented. We, recently, added a novel insight into the field by identifying the molecular mechanism associated with the protective role of human leukocyte antigen (HLA)-B27/B57 CD8⁺ T cells in the context of HIV-1 infection and why these alleles act as a double-edged sword protecting against viral infections but predisposing the host to autoimmune diseases. The focus of this review will be reexamining the role of classical and non-classical HLA alleles, including class Ia (HLA-A, -B, -C), class Ib (HLA-E, -F, -G, -H), and class II (HLA-DR, -DQ, -DM, and -DP) in immune regulation and viral pathogenesis (e.g., HIV and HCV). To our knowledge, this is the very first review of its kind to comprehensively analyze the role of these molecules in immune regulation associated with chronic viral infections.

CD4+ T-cell gene expression of healthy donors, HIV-1 and elite controllers: Immunological chaos

OBJECTIVES

T-cell repertoire dysfunction characterizes human immunodeficiency virus type 1 (HIV-1) infection, but the pathogenic mechanisms remain unclear. Disease progression is probably due to a profound dysregulation of Th1, Th2, Th17 and Treg patterns. The aim of this study was to analyze the features of CD4+ T cells in HIV-positive patients with different viroimmunological profile.

METHODS

we used a gene expression dataset of CD4+ T cells from healthy donors, HIV+ naive patients and Elite Controllers (EC), obtained from the NCBI Gene Expression Omnibus (GEO, http://www.ncbi.nlm.nih.gov/geo/, accession number GSE18233).

RESULTS

Principal Component Analysis (PCA) showed an almost complete overlap between the HIV-infected and EC patients, which cannot easily explain the different responses to HIV infection of these two group of patients. We have found that HIV patients and the EC showed an upregulation of the Th1 pro-inflammatory cytokines and chemokines, compared to the controls. Also, we have surprisingly identified IL28B, which resulted downregulated in HIV and EC compared to healthy controls. We focused attention also on genes involved in the constitution of the immunological synapse and we showed that HLA class I and II genes resulted significantly upregulated in HIV and in EC compared to the control. In addition to it, we have found the upregulation of others syncytial molecules, including LAG3, CTLA4, CD28 and CD3, assisting the formation of syncytia with APC cells.

CONCLUSIONS

Understanding the mechanisms of HIV-associated immunological chaos is critical to strategically plan focused interventions.

HIV type 1 envelope glycoprotein 120 carboxy-terminal peptide-induced human T cell lines selectively suppress heterogeneous proliferative T cell responses to soluble antigens

It has been proposed that the highly conserved human immunodeficiency virus type 1 (HIV-1) envelope gp120 carboxy-terminal sequence, TKAKRRVVEREKR (CT120), may represent a functional mimic of the human leukocyte antigen (HLA) class II DR beta-chain third hypervariable region (HVR3) sequence motif located at position 69-81. Presentation of this potentially pathogenic fragment by HLA class I and/or II molecules, in a manner analogous to the indirect pathway of allorecognition, may induce both widespread cellular activation and also break self-tolerance, resulting in the selective and progressive anti-self HLA class II-directed immune suppression, which is a central feature of HIV-1 infection and the associated acquired immune deficiency syndrome (AIDS). To investigate the functional role of the HIV-1 gp120 C-terminal fragment T cell lines (TCLs) were raised from three healthy HIV-1-seronegative subjects at low risk of HIV-1 exposure, by repeated stimulation with a short synthetic 13-mer CT120 peptide in vitro. Graded concentrations (10[3] to 5 x 10[4]) of CT120 TCLs suppressed the primary 6-day proliferation of autologous PBMCs in response to the soluble antigens tetanus toxoid (TT) and purified protein derivative (PPD). In contrast, CT120 TCLs demonstrated no suppressive effect on 3-day phytohemagglutinin (PHA), concanavalin A (ConA), and pokeweed mitogen (PWM) mitogenic responses. Fractionation of CT120 TCLs into highly purified CD4+ and CD8+ T cell subsets demonstrated that the CD8+ T cell fraction mediated the suppressor effector function. HLA restriction analysis revealed a complex pattern as both anti-HLA class II DR and anti-HLA class I (A, B, C) MAbs inhibited proliferation of oligoclonal CD8+ CT120 TCLs. Strategies aimed at specifically inhibiting such putative immunopathogenic HIV-1-encoded T cell epitopes may be an important consideration for development of future HIV-1 immunotherapy.

Genetic predisposition to HIV-1 infection and acquired immune deficiency virus syndrome: a review of the literature examining associations with HLA [corrected]

Researchers have been studying the relationship between host HLA type and the immune response to HIV-1 since early in the AIDS epidemic. Although the literature is replete with suggestions of an association, the exact locus and nature is unclear. This article reviews the current HLA-HIV/AIDS literature, providing a complete summary of all significant associations reported in journal articles (N = 30) between 1982 and 1993. Consistent associations with alleles comprising the haplotype DQ2-DR3-B8-Cw7-A1 and AIDS progression support a genetic component in AIDS progression. DQ1-DR1-B35-Cw4-A11 and DR5 also show consistent associations with HIV/AIDS outcomes, although it is unclear whether they are measuring susceptibility to HIV-1 infection, AIDS progression, or both. The question of whether HLA influences susceptibility to HIV-1 infection remains unanswered, as well-designed studies addressing this topic are lacking. Similarly, further studies are needed to clarify if HLA type is associated with KS. Several issues that complicate across-study comparisons are discussed including heterogeneity of both HLA and AIDS, potential confounding by race or risk group, and other biases which may influence results. In addition, several proposed biologic mechanisms are explored.

Staphylococcal enterotoxin A and toxic shock syndrome toxin compete with CD4 for human major histocompatibility complex class II binding

We have examined the role of the CD4 molecule in primary T-lymphocyte responses to the staphylococcal enterotoxins SEA, SEB, SEC1, and the toxic shock syndrome toxin TSST-1. Proliferating cells were predominantly CD4+; however, the responses to SEA and TSST-1 were most sensitive to inhibition by the anti-CD4 antibody Leu-3a. T-lymphocyte responses to the bacterial superantigens were inhibited by site-directed mutations of residues in the DR beta membrane-proximal domain (DR beta 2) that are also known to be important for interactions with CD4. SEA and TSST-1 binding to DR was reduced by the DR beta 2 mutations and by competition with soluble recombinant CD4. We propose that bacterial superantigens sequentially, or simultaneously with CD4, stabilize complexes of T-cell antigen receptors and major histocompatibility complex class II molecules. The superantigen qualities of these toxins may be due, in part, to a molecular mimicry of CD4 and other adhesion molecules.

Molecular mimicry in the pathogenesis of AIDS: the HIV/MHC/mycoplasma triangle

The immune defects characterizing infection with the human immunodeficiency virus (HIV) and culminating in the acquired immune deficiency syndrome (AIDS) are the result of a multifactorial disease process, components of which are the occurrence of autoimmune phenomena and opportunistic infection. In this discussion, the observation that both the HIV-1 gp 120 envelope and Mycoplasma genitalium adhesin proteins share an area of significant similarity with the CD4-binding site of the class II major histocompatibility complex (MHC) proteins is placed in this perspective and mechanisms by which interaction within this triad could contribute to the T-cell dysfunction, T-cell depletion, Th1-cell-->Th2-cell shift, B-cell proliferation, hyperglobulinemia and antigen-presenting cell dysfunction observed during the development of AIDS are proposed.

Autoreactivity in HIV-infected individuals does not increase during vaccination with envelope rgp160

The HIV-1 envelope protein contains several regions with amino acid homology to HLA class I and class II molecules. We evaluated possible changes in antibody responses to those regions during vaccination with rgp 160 produced in a baculovirus system. Forty asymptomatic HIV-infected patients with CD4 cell counts above 400 were vaccinated with rgp 160. Twenty-one patients were tissue-typed as HLA A2. Sixty-two percent of these patients exhibited cytotoxic lymphocyte antibodies directed to CD8+, HLA A2 cells. This cytotoxicity decreased during HIV gp160 vaccination. In order to further characterize the specificity of these responses, analogues of HLA class I and HLA-DR peptides were chemically synthesized together with their correct HIV-1 gp160 sequences. Enzyme-linked immunosorbent assays (ELISA) with sera from before, during and after immunization were performed with HIV proteins, peptides and their homologues. All patients showed an increase in their previously poor specific T-cell activation to gp160. Fourteen patients developed increased avidities or titres to HIV proteins and/or peptides. Contrarily, serum IgG titers to the HLA homologous peptides were initially low and decreased further during the course of vaccination. This decrease occurred in the majority of patients, 35-40 of the 40 individuals, depending on the antigen. Independent measures of autoantibodies to Ro/SS-A and La/SS-B remained undetectable.

Molecular characterization of the P1-like adhesin gene from Mycoplasma pirum

A DNA fragment has been isolated from the genome of Mycoplasma pirum by use of a genetic probe derived from the conserved region within the genes for the major adhesins of Mycoplasma genitalium and Mycoplasma pneumoniae. A gene encoding an adhesin-like polypeptide was localized, and sequence analysis indicated a G + C content of only 28%, with A- and T-rich codons being preferentially used. A total of 91% of positions 3 were either A or T. The deduced polypeptide is 1,144 amino acids long (126 kDa) and shows 26% identity with the adhesins of M. genitalium and M. pneumoniae. Other features in common with these two membrane proteins include a similar hydropathic profile and a proline-rich C terminus. Antibodies were prepared by using as an immunogen a peptide derived from the C terminus of the M. pirum adhesin-like polypeptide and were found to recognize on immunoblots a 126-kDa polypeptide from an M. pirum cellular extract. The characterization of the adhesin-like gene is a first step toward a better understanding of the mechanisms allowing this human mycoplasma to attach to host cells.

HIV glycoprotein as a superantigen. A mechanism of autoimmunity and implications for a vaccination strategy

The pathogenic effects of HIV may reflect mimicry of several key immunological molecules. The surface glycoprotein of HIV has superantigenic properties responsible for the sequential deletion of T-cell clones. In addition, the glycoprotein has several regions sharing homology with class II MHC products. It can elicit cross-reactive antibodies which block replenishment of these T-cells in the thymus. The usefulness of conventional vaccination strategies in the fight against AIDS has been subject to debate. Based on these considerations, we argue that effective vaccines should avoid viral sequences homologous to class II MHC proteins which might exacerbate this process.

A gp120 HIV peptide with high similarity to HLA class II beta chains enhances PPD-specific and autoreactive T cell activation

The recent report that anti-gp120 antibodies can be induced by allogeneic stimuli in experimental animals in the absence of HIV, has focused attention on the structural similarities between gp120 and MHC. Here we report that some HIV+ individuals develop antibodies which similarly react with the gp120 HIV sequence (aa 254-263) and with the HLA-DR beta chains (aa 142-151). As these two peptides share a high level of similarity, we have investigated the role of this gp120 region on HLA class II mediated T cell recognition. The synthetic peptide corresponding to the gp120 HIV sequence aa 254-263 has been tested on T cell line (TCL) activation. Both the PPD-specific and the self-HLA reactive TCL proliferation increased in the presence of this peptide. Prepulsing experiments indicate that this enhancing effect carried out by HIV peptide is exerted at the level of antigen presentation. Moreover, the specificity of this interaction is supported by the fact that a MoAb specific for this HIV peptide blocked the autoreactive TCL proliferation, similarly to the inhibition carried out by anticlass II antibody. These data support the hypothesis that the functional homology between the HIV peptide and the HLA beta chain described may be involved in the pathogenesis of AIDS.

HIV envelope protein is recognized as an alloantigen by human DR-specific alloreactive T cells

Recent studies from this laboratory reported the mapping of the full profile of T-cell allorecognition regions of HLA-DR2 beta subunit. The results indicated the presence of an allodeterminant within DR2 beta regions 141-156. In another study, we have shown that this allodeterminant is one of five regions of structural homology between the DR2 beta molecule and the HIV-envelope protein gp120 region 254-268. The fact that gp120 peptide 254-268 is homologous to the allodeterminant within the DR2 beta region 141-156 prompted us to investigate whether synthetic gp120 peptide 254-272 is recognized by human DR2-specific alloreactive T-cell lines. Five human alloreactive T-cell lines were prepared that were specific for the DR2 molecule and did not recognize DR1. These lines mounted in vitro proliferative responses to the allodeterminant peptide DR141-156 and also responded to the DR-similar peptide gp254-272. Removal of the residues 262-272 from the gp120 peptide (i.e., peptide 254-263) resulted in essentially complete loss of its proliferative activity. The effect of deletion of three residues of homology (Val-Val-Ser) at the N terminal (i.e., peptides DR145-156 and gp257-272) was examined. Peptide DR2 beta 145-156 exhibited very low stimulating activity, whereas peptide gp 257-272 did not cause T-cell proliferative responses in any of the alloreactive T-cell lines. The T-cell lines did not respond to unrelated peptide controls, thus further confirming the specificity of these responses. These findings indicate that the virus is recognized as an alloantigen by human alloreactive DR2-specific T cells.

Common sequence in HIV 1 GP41 and HLA class II beta chains can generate crossreactive autoantibodies with immunosuppressive potential early in the course of HIV 1 infection

We have previously reported the identification of highly conserved homologous regions located in the carboxy terminus of the HIV 1 gp41 (aa 837-844), and the amino-terminal of the beta chain of all human HLA class II antigens (aa 19-25). Murine monoclonal antibodies raised against synthetic peptides from these homologous regions bound not only to the isolated peptides, but also to "native" HLA class II molecules on cells. Screening of sera from HIV 1 infected individuals revealed high frequency of sera (35%) containing anti-class II crossreactive antibodies (CRAb), not only in AIDS patients, but also in early, asymptomatic patients. The CRAb containing sera caused potent inhibition of normal CD4-bearing cells' proliferative responses to tetanus toxoid in vitro. They could also kill class II bearing cells by ADCC. The possible contribution of these antibodies to the establishment of immunodeficiency state in HIV 1 infected individuals and/or to disease progression, was examined in two clinical studies: I. Asymptomatic patients were tested in parallel for their PBL responses to flu/tetanus, HLA alloantigens, and PHA (proliferation and IL2 production), and for the presence of anti-class II CRAb. About 50% of these patients showed a selective loss of their in vitro responses to recall antigens (flu/tetanus), which depend on CD4+ cells, while still responding to PHA and ALLO. Interestingly, positive correlation was found (P less than 0.001) between patients' lack of responsiveness to flu/tetanus and the presence in their sera of anti-class II CRAb. II. Retrospective study of HIV 1-infected hemophiliacs, suggest that patients with high titers of CRAb early in the disease progressed faster to full blown disease.