UMLS:C0019693 - FACTA Search

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Query: UMLS:C0019693 (HIV)
170,526 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The development of cytotoxic CD4+ T lymphocytes that can kill target cells in a MHC class II-restricted manner was evaluated by comparing different APCs. B-lymphoblasts (B-LCL) pulsed with the superantigen staphylococcus enterotoxin B or allogeneic B-lymphoblasts induce CD4+ T cells without cytotoxic activity. In contrast, superantigen-pulsed, MHC class II+ T cell blasts or allogeneic T cell blasts preferentially induce the development of specific, MHC class II-restricted CD4+ cytotoxic effector cells. CD4+ T cell clones generated with T or B cell blasts as APCs (T- or B-APCs) differ in their cytolytic potential, but secrete a similar cytokine pattern. Our data implicate that activated T-APCs preferentially induce a cytotoxic, CD8+ and CD4+ T cell response. Because the density of CD80 expression is lower on activated T-APCs than on B-APCs, we studied the involvement of CD28 and CD80 adhesion molecules in the generation of CD4+ CTLs. Partial blockade of the CD80 molecule with a CTLA4-Ig fusion protein and with specific anti-CD80 mAbs on B-APCs enhanced the generation of CD4+ CTLs. Specific anti-CD86 mAbs, on the contrary, had no effect on the generation of CD4+ CTLs. In contrast, stimulation of CD28, the CD80 counter-receptor, with a cross-linked B7-Ig fusion protein or with an anti-CD28 mAb, inhibited the generation of CD4+ CTLs. Thus, a reduced interaction between CD80 and CD28 may be relevant for the induction of CD4+ CTLs. This shows a new and not yet described function of these adhesion molecules. This induction of a cytotoxic immune response by T cells as APCs may be relevant for the anticlonotypic regulation of T cells and for the depletion of CD4+ T cells in HIV infection.
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PMID:Antigen-presenting T cells induce the development of cytotoxic CD4+ T cells. I. Involvement of the CD80-CD28 adhesion molecules. 754 9

CD4+ T cell clones specific for the HIV-1 envelope (env) protein are able to recognize not only uninfected APC that have taken up and processed exogenous env protein, but also virally infected cells expressing the env protein. We have evaluated the hypothesis that endocytosis of endogenously synthesized env protein from the plasma membrane of infected cells permits entry of the protein into the MHC class II-restricted Ag processing pathway. We show here that the env protein of HIV-1 is internalized at a surprisingly high rate through a mechanism that is dependent upon a tyrosine-containing motif located in the cytoplasmic domain of the gp41 subunit. Mutation of a critical cytoplasmic tyrosine residue or truncation of the C-terminal portion of the cytoplasmic domain resulted in forms of the env protein that did not undergo rapid internalization. However, by a variety of assays, these poorly internalized forms of the env protein were processed for class II-restricted Ag presentation as efficiently as wild-type env protein, indicating that internalization by this pathway is not essential for class II-restricted presentation. In addition, a secreted form of the env protein was presented efficiently by class II MHC under conditions that prevented re-uptake by endocytosis. Taken together, these results suggest that although rapid endocytosis from the cell surface is likely to be a major mechanism by which endogenously synthesized env protein is processed for association with class II MHC, an internal pathway may also be used.
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PMID:Endocytosis of endogenously synthesized HIV-1 envelope protein. Mechanism and role in processing for association with class II MHC. 760 19

Periodic infusion of autologous HIV-antigen presenting cells (APCs), that stimulate the cytotoxic (CTL) response, while being incapable of producing virus, should lower viral burden and boost CD4+ count in HIV-seropositive individuals. Viral burden reasserts itself after antiviral therapy ceases or is interrupted for long. Therapy, therefore, would have to continue for life. These are predictions from a computer model of HIV-immune kinetics. The model equations describe the interactive kinetics of viral burden, CD4+ cell decline, neutralization of free virus by antibodies, infection of cells, and killing of infected cells by CTL. The computed trajectories of the kinetic equations reproduce the typical course of an HIV infection and the model yields several predictions that are not intuitively obvious, among them: (a) Persistence of HIV infection (failure of the immune system to clear infection) is an intrinsic property of the kinetics of the HIV-immune interaction. (b) The chronic state of infection is inherently stable, which means that the infection rebounds to the determined steady state, whenever antiviral therapy stops. (c) CTL is chronically activated, and the level correlates inversely with the avidity of neutralizing antibodies. (d) APCs have to be infused at a rate such as to boost and maintain the CTL response above the chronic level. Other therapies include CTL stimulation, via the macrophage route, by erythrocytes, into which MHC binding HIV-CTL epitope polypeptide fragments have been inserted; passive immunization, virion-trapping by CD4 analogs or CD4 expressing erythrocytes; and combination therapies with AZT, IL-2. These are also analyzed. Concerning HIV etiology, the model assumes that cells other than CD4+ cells (such as macrophages/monocytes) become infected, and contribute to the viral burden, and that infectible cells remain available even as CD4+ cells become exhausted. The model further assumes that CD4+ cells decline not only through direct killing by HIV and CTL, but by dysregulation and excess apoptosis caused by the presence of virus. The model predicts that persistence of HIV infection does not depend upon latently infected cells or escape mutants, as has been suggested.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Mechanism of HIV persistence: implications for vaccines and therapy. 762 23

A general method has been developed for measuring the stabilization of class I MHC molecules in extracts of the mutant cell lines .174/T2 and RMA-S. 35S-Met-labeled class I molecules which have been stabilized by peptides in vitro are immunoprecipitated with conformation dependent monoclonal antibodies and electrophoresed on polyacrylamide gels. The heavy and light chains are excised from the dried gel and quantified on a flat bed scintillation counter. The stabilizing effect of peptides on class I molecules in vitro correlates well with peptide binding measured by direct methods and can be therefore used to assess peptide binding affinity. We show that a peptide from HIV-1 gag (which has a high affinity for Db) is a CTL epitope restricted through Db, and also use the assay to analyse the effects of amino acid substitution on peptide affinity. In addition, the effect of a given peptide on a class I molecule within a mixture of human class I molecules can be distinguished by immunoprecipitation with the monomorphic antibody W6/32 and separation by 1-D isoelectric focussing. The technique therefore requires neither labeled peptide ligands nor allele-specific antibodies. It can be used to identify the peptide ligand of any human class I molecule, and gives a measure of peptide binding affinity. The technique should be of value in identifying epitopes recognized by CTL since we have found that these tend to bind with the highest affinities.
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PMID:A method to quantify binding of unlabeled peptides to class I MHC molecules and detect their allele specificity. 767 31

The ability of minigene-encoded viral peptide epitopes to be presented by class I molecules in the absence of MHC-encoded transporters has been evaluated in mutant T2 cells. These cells have a large deletion in the class II MHC region that includes the known transporter protein for antigenic peptides and proteasome genes and they are defective in presenting viral epitopes to CTL. T2 cells that express minigenes encoding the influenza virus matrix peptide 58-66 (GILGFVFTL) and two HTLV 1 Tax peptides 11-19 (LLFGYPVYV) and 12-19 were lysed by HLA-A2-restricted peptide-specific CTL. Minigene expression of a HLA-A2-restricted HIV reverse transcriptase peptide 476-484 (ILKEPVHGV) with three charged residues sensitized T2 cells poorly for lysis by HIV-specific CTL unless the peptide was preceded by an endoplasmic reticulum translocation signal sequence. Expression of an influenza virus nucleoprotein peptide 383-391 (SRYWAIRTR) with three charged arginine residues did sensitize HLA-B27+ T2 cells for lysis by peptide-specific CTL. These and other results with endogenously expressed peptide analogs in which hydrophobic and charged amino acids were interchanged demonstrate that antigenic peptides can be translocated from the cytoplasm into the class I Ag presentation pathway independent of MHC-encoded transporters; and that peptide hydrophobicity appears not to be a major determinant in selecting peptides for this alternate pathway.
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PMID:Presentation of endogenous peptides to MHC class I-restricted cytotoxic T lymphocytes in transport deletion mutant T2 cells. 767 94

Cytotoxic T cells are the main antigen-specific effector cells of the cellular immune system and MHC class I restricted cytotoxic T-lymphocyte (CTL) responses in mice, acting against the HIV-1 envelope protein, are known to be predominantly directed against an amino acid sequence in the third hypervariable domain. We have investigated the epitope specificity of anti-HIV-1 CTL in healthy human volunteers inoculated with a recombinant vaccinia expressing the HIV-1 gp160 envelope gene. Their isolated lymphocytes were stimulated in vitro with autologous HIV-1 infected cells. Our results show that immunization with recombinant virus is able to generate virus-specific CTLs to the HIV-1 gp160 envelope protein and to a 15-residue synthetic peptide corresponding to a highly variable region of the envelope p18(IIIB). The CTL response was restricted by class I MHC molecules HLA-A2 and A3 that commonly occur in the human population.
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PMID:Envelope protein and p18(IIIB) peptide recognized by cytotoxic T lymphocytes from humans immunized with human immunodeficiency virus envelope. 768 70

The T cell response to HIV-1 gp160 is among the most thoroughly studied immune responses to HIV-1 products. In our previous work, the MHC class I molecule Dd as well as H-2u, p, and q, were found to present P18 and HP53, two determinants of HIV-1 gp160, to CD8+ CTL in mice. We have studied the TCR V beta chain expression in CTL lines, either cross-reactive for these two peptides or specific for P18 alone, in these four different MHC haplotypes. The usage of V beta in T cells showing cross-reaction between these two peptides was remarkably conserved (primarily V beta 8 family, with some use of V beta 14) despite the extensive TCR V beta diversity of the non-cross-reactive CTL, which did not use V beta 8 or 14. This correlation of V beta usage with fine specificity was consistent in H-2d, u, and p (p < 0.01), but not in H-2q. The correlation of V beta use with peptide fine specificity independent of MHC restriction was unexpected. The strong predominance of V beta 8 family TCR was all the more surprising in view of the finding that mice bearing a genomic deletion of V beta 8 can still produce T cells with the cross-reactive phenotype, implying that other V beta chains can produce this specificity. We therefore asked whether the complexes of P18 with H-2d, p, and u are recognized as identical, and observed the surprising result that H-2d, p, and u cells mutually cross-present the peptides P18 and HP53 to allogeneic CTL lines and individual clones of each of the other haplotypes, whereas none of these cross-present to H-2q CTL, nor do H-2q targets present to CTL of the other haplotypes. This degeneracy of MHC restriction is novel for class I molecules. Moreover, the observed restriction in V beta usage occurs only in the unique set of CTL that exhibit both peptide-cross-reactive fine specificity and MHC allogeneic cross-presentation. The observation that a strain of mice in which the V beta 8 family is genomically deleted can still make CTL of this phenotype using another V beta demonstrates the plasticity of the class I MHC-restricted repertoire when the dominating receptor is not available.
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PMID:Preferential V beta usage by cytotoxic T cells cross-reactive between two epitopes of HIV-1 gp160 and degenerate in class I MHC restriction. 768 97

The role of natural killer (NK) and lymphokine-activated killer (LAK) cell-mediated cytotoxicity in AIDS has yet to be established. The objective of this study was to determine inducible LAK cell responses at different stages of HIV-1 infection, and specifically to establish the participation of CD8 lymphocytes in these responses. Peripheral blood lymphocytes (PBL) were isolated from healthy seronegative (CDC-0) subjects and HIV-1+ individuals who were clinically asymptomatic (Centre for Disease Control group 2, CDC-2) or symptomatic (CDC-4) with regard to secondary opportunistic infection (OI). LAK cells were generated upon incubation of PBL with IL-2 and their cytolysis of K562 and U-937 targets was determined using chromium release assays. The role of CD8+ lymphocytes as progenitors and effectors of these LAK cell responses was determined by immunomagnetic depletion of CD8+ cells from precursor PBL and LAK cells, respectively. LAK cell-mediated cytotoxicities in HIV-1-infected individuals were reduced compared with seronegative controls without any corresponding changes in the relative proportions of CD56+ (NK) cells among groups. Depletions of CD8+ subsets from either PBL or LAK cells dramatically reduced total LAK cytotoxic responses and LAK activities per unit CD56+ cell in the OI-/CDC-2 seropositive population. No corresponding changes in LAK activities in seronegative control or HIV+/OI+/CDC-4 groups were observed. Levels of LAK activity against K562 targets in CDC-0/HIV- and CDC-4/HIV+ groups correlated with the percentage of CD56+ LAK cells; corresponding LAK activity in the CDC-2/HIV+ group correlated with the percentage of both CD56+ and CD8+ subsets. These findings suggest that adaptive changes in non-MHC restricted cytotoxic responses occur in HIV-1 individuals at early stages post-HIV infection, before the onset of opportunistic infection.
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PMID:Changes in natural immunity during the course of HIV-1 infection. 768 73

After infection with some viruses that tend to persist, neutralizing antibodies are generated rather late, i.e., after 1 to 3 mo. This has been observed for HIV, Hepatitis B infection in man, or after infection with lymphocytic choriomeningitis virus (LCMV) in mice. In contrast, nonneutralizing antibodies to LCMV are generated by day 7 and reach high titers by day 10. This study attempts to evaluate reasons for late and low titered neutralizing antibody responses. After a primary infection with low doses (10(2) plaque forming units) of the poorly cytopathic LCMV-WE, neutralizing antibodies were rarely produced at detectable levels before days 60 to 120. In vivo depletion of CD8+ CTL led to a marked enhancement and acceleration of kinetics of the neutralizing antibody response. In contrast, nonneutralizing antibodies, including those specific for LCMV-GP carrying the neutralizing determinant, were detectable very early, i.e., 4 to 7 days after infection, with maximum titers usually by day 10 irrespective of the presence or absence of CTL. Mice completely lacking CD8+ T cells because of deletion by homologous recombination (CD8-/-) also exhibited neutralizing antibodies early by day 10 to 20, and by day 120 reached very high titers. The neurotropic isolate LCMV-ARMSTRONG induced low but significant titers of neutralizing antibodies relatively early (i.e., by days 7 to 10), whereas the lympho-viscerotrope mutant virus LCMV-ARMSTRONG Cl-13 did not. Early and effective CTL responses causing immunopathology (and immunosuppression) correlated with the absence of neutralizing antibodies. The discrepancy between the CTL-dependent inhibition of neutralizing versus unimpaired anti-GP ELISA responses cannot be explained by different Ag doses alone. Additionally, it may reflect different kinetics of the responses, whereby the later neutralizing responses possibly requiring IgG affinity maturation may be more susceptible to general immunosuppression; also B cells expressing neutralizing receptors, but not those with antibodies binding GP (or NP), may be actively infected, therefore they present viral peptides on class I MHC Ag and may become targets for anti-LCMV-specific CTL.
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PMID:Impairment and delay of neutralizing antiviral antibody responses by virus-specific cytotoxic T cells. 769 11

Complexes of five peptides (from HIV-1, influenza A virus, HTLV-1, and hepatitis B virus proteins) bound to the human class I MHC molecule HLA-A2 have been studied by X-ray crystallography. While the peptide termini and their second and C-terminal anchor side chains are bound similarly in all five cases, the main chain and side chain conformations of each peptide are strikingly different in the center of the binding site, and these differences are accessible to direct TCR recognition. Each of the central peptide residues is seen to point up for some bound peptides, but down or sideways for others. Thus, although fixed at its ends, the structure of an MHC-bound peptide appears to be a highly complex function of its entire sequence, potentially sensitive to even small sequence differences. In contrast, MHC structural variation is relatively limited. These results offer a structural framework for understanding the role of nonanchor peptide side chains in both peptide-MHC binding affinity and TCR recognition.
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PMID:The antigenic identity of peptide-MHC complexes: a comparison of the conformations of five viral peptides presented by HLA-A2. 769 6

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