HIV-1-infected T cells show a selective signaling defect after perturbation of CD3/antigen receptor

T-Cell Receptor/CD3 Downregulation and Impaired Signaling in HTLV-1-Infected CD4+ T Cells of HAM Patients

Human T-cell leukemia virus type 1 (HTLV-1) is a retrovirus associated with adult T-cell leukemia (ATL), a hematological malignancy, and HTLV-1-associated myelopathy (HAM), a progressive neurological disorder. HTLV-1 predominantly infects CD4+ T cells in vivo. The T-cell receptor (TCR)/CD3 complex on CD4+ helper T cells plays a pivotal role in immune responses by recognizing antigens and facilitating coordination with other immune cells. Dysfunction of the TCR/CD3 complex may impair immune function. Although CD3 downregulation has been identified as a characteristic of ATL cells, it remains uncertain whether a similar downregulation occurs in HTLV-1-infected cells from HAM patients. We hypothesized that HTLV-1 infection leads to TCR and CD3 downregulation, contributing to immune dysfunction in HAM patients. To test this hypothesis, we analyzed TCR/CD3 expression, TCR signaling, and immune responses in HTLV-1-infected cells from HAM patients. Intracellular HTLV-1 Tax detection revealed that HTLV-1 preferentially targets CD4+ over CD8+ T cells. CD3 and TCR expression levels were significantly lower in CD4+ T cells from HAM patients compared to healthy controls. Furthermore, HTLV-1-infected cells exhibited markedly reduced CD3 and TCR expression compared to uninfected cells. Impairments in TCR signaling, assessed through Lck and ZAP70 phosphorylation upon CD3 stimulation, were observed in CD4+ T cells from HAM patients compared to those from healthy controls. Notably, this reduction in TCR signaling was more pronounced in HTLV-1-infected CD4+ T cells than in uninfected CD4+ T cells in HAM patients. Additionally, cytomegalovirus (CMV)-specific CD4+ T cells detected by an addition of CMV antigens demonstrated reduced interferon-γ production in HTLV-1-infected cells compared to their uninfected counterparts. These findings suggest that TCR/CD3 downregulation and impaired TCR signaling contribute to immune dysfunction in HTLV-1-infected CD4+ T cells. As CD4+ T cells play a central role in immune responses, this mechanism may partially explain the cellular immune dysfunction to other pathogens observed in HAM patients.

T cell receptor signaling pathway is overexpressed in CD4(+) T cells from HAM/TSP individuals

Human T-lymphotropic virus type 1 (HTLV-1) is a human retrovirus related to the chronic neuroinflammatory disease HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). CD4⁺ T cells activation appears to play a key role on HTLV-1 infection. Here we investigated the expression of genes associated to T cell activation CD3e molecule, epsilon (CD3ɛ), lymphocyte-specific protein tyrosine kinase (LCK), vav 1 guanine nucleotide exchange factor (VAV1), and zeta-chain (TCR) associated protein kinase 70 kDa (ZAP70) on T lymphocytes of HTLV-1-infected individuals and compared to healthy uninfected individuals (CT). We observed that CD3ɛ, LCK, ZAP70, and VAV1 gene expression were increased in CD4⁺ T cells from HAM/TSP group compared to HTLV-1 asymptomatic patients (HAC). Moreover, ZAP70 and VAV1 were also upregulated in HAM/TSP compared to CT group. We detected a positive correlation among all these genes. We also observed that CD3ɛ, LCK, and VAV1 genes had a positive correlation with the proviral load (PVL) and Tax expression. These results suggest that PVL and Tax protein could drive CD3ɛ, LCK, and VAV1 gene expression in CD4⁺ T cells, and these genes function on a synchronized way on the CD4⁺ T cell activation. The elucidation of the mechanisms underlying T cell receptor signaling pathway is of considerable interest and might lead to new insights into the mechanism of HAM/TSP.

HIV, 'an evolving species'. Roles of cellular activation and co-infections

Each small variation of the genome of a species can be preserved if it is useful for the survival of the species in a given environment. Within this framework, the finality of the biological cycle of HIV consists in a search for harmony (biological coherence) with man, which is to say a stable condition. Cellular activation appears to be the strategy developed by HIV in order to achieve this coherence. The price of this strategy is the AIDS. The first contact between HIV and immune system appears to determine the subsequent clinical outcome and the future of HIV. Lymphocytic activation varies during the course of the vital cycle of HIV. For each individual, this lymphocytic activation depends on both the HLA repertoire acquired during thymic ontogenesis and the antigenic experience before and after HIV infection. Thus intercurrent infections alter the immune condition of the organism and influence the outcome of HIV. We described a synthetic analysis of the effects of HIV on the surface protein expression and the cellular activation pathways which should provide insights in the evolutionary relationship between HIV and man and should permit to do a more physiological therapeutic approach.

Attenuated signaling associated with immune activation in HIV-1-infected individuals

Chronic immune activation is associated with impaired signal transduction. Since such activation is commonly found during HIV-1 infection, we studied cellular responses to non-specific T-cell receptor stimulation of PBMC obtained from 20 HIV-1 non-infected individuals and 23 highly or partially immune activated HIV-1 infected individuals. PBMC proliferation and ERK-1/2 phosphorylation following anti-CD3 stimulation, and constitutive levels of Cbl-b, were determined. Increased levels of Cbl-b, decreased proliferation, and lower ERK-1/2 phosphorylation were found in PBMC of highly immune activated HIV-1 infected individuals. The elevated expression of Cbl-b and impaired phosphorylation of ERK-1/2 associated with immune activation probably contribute to the attenuated proliferative and cellular responses characteristic of HIV-1 infection. Therefore, targeting immune negative modulators, such as Cbl-b, may serve as a novel approach for controlling HIV-1 disease progression.

Modulation of CD8 and CD3 by HIV or HIV antigens

To investigate whether human immunodeficiency virus (HIV)-1 and HIV-1 antigens modulate surface and cytoplasmic CD8 or CD3, as well as CD4, we used cell permeabilization reagents, surface/cytoplasmic fluorescent staining, multiparameter flow cytometric techniques and an in vitro culture system in which relatively few lymphocytes are actively infected with HIV. Human peripheral blood lymphocytes were: not stimulated, not stimulated but HIV-inoculated, phytohaemagglutinin (PHA)-stimulated, PHA/HIV-inoculated (PHA/HIV), or placed into media with soluble gp120, Rev or Nef. HIV inoculation and Nef had striking modulatory effects on CD8. The cytoplasmic CD8 median fluorescent intensity (MFI) of positive lymphocytes was lower for cells in unstimulated/HIV-infected cultures than unstimulated cultures (44 versus 62% of ex vivo value, P = 0.032) and lower for cells in PHA/HIV cultures than in PHA cultures (56 versus 100% of ex vivo, P = 0.041). The surface CD8 MFI values for Nef were significantly lower than the ex vivo value (75% of ex vivo, P = 0.006). At days 2-7 of culture, Rev was associated with slight reductions in surface CD4 MFI (58% of ex vivo versus 78% of ex vivo for unstimulated cultures, P = 0.047) and greater effects on cytoplasmic CD3 MFI (131 versus 179% of ex vivo for unstimulated cultures, P = 0.035), and surface CD8 MFI (70% of ex vivo, P = 0.006 versus ex vivo value). The globality of Rev's effects suggests these are related to a shared processing pathway, i.e. not due to direct interaction with CD3, CD4 and CD8; the effects of HIV inoculation and Nef on CD8 expression appear to be more CD8 specific. Because CD8 is essential for cytotoxic T-cell function, its down-modulation could inhibit this activity, including anti-HIV cytotoxicity. Given the critical roles of CD3 and CD8 in T-lymphocyte signal transduction and antigen responsiveness, the effects of HIV, Rev and Nef on these molecules have clinically significant implications concerning the pathogenesis and treatment of HIV.

Evidence that anoreceptive intercourse with ejaculate exposure is associated with rapid CD4 cell loss

OBJECTIVE

To determine whether ejaculate exposure through anoreceptive intercourse is associated with rapid CD4 cell loss.

DESIGN

Self-reported behavioral, demographic data and blood samples were gathered longitudinally at ten semiannual visits from individuals participating in the Multicenter AIDS Cohort Study (MACS).

PATIENTS/PARTICIPANTS

A group of 937 HIV-seropositive men who were continuously followed for four to ten semiannual visits.

OUTCOME MEASURES

A loss of 10% or more in CD4 cells between the first two of any three consecutive semiannual visits that was followed by a 10% or greater loss between the second and third visits.

RESULTS

A period of rapid CD4 cell loss over three semiannual visits occurred in 389 of the 937 (42%) HIV-seropositive men studied. Men who reported one or more anoreceptive intercourse partners with whom they were exposed to ejaculate (RAI-E) during the 12 months immediately preceding their visits were more than twice as likely to show this rapid CD4 cell loss compared with men with no such partners.

CONCLUSIONS

The association between RAI-E partnerships and rapid CD4 cell loss suggests factors associated with ejaculate exposure (e.g., sexually transmitted diseases) may hasten the clinical progression of HIV disease. It is suggested that infectious diseases, which are known to be associated with ejaculate exposure, may be the causal factor underlying the association between RAI-E partnerships and rapid CD4 cell loss in these men, although the presence of these diseases was not ascertained in these data. HIV-infected individuals should be cautioned against unprotected anoreceptive intercourse.

Infection of mice by a Toxoplasma gondii isolate from an AIDS patient: virulence and activation of hosts' immune responses are independent of parasite genotype

Virulence of a Toxoplasma gondii isolate from an AIDS patient (designated as PTN) was compared with that of PLK, a variant of P-strain. Virulence was assessed in term of host survival upon inoculation in different strains of mice. All C57BL/6 mice died of acute toxoplasmosis by 7-10 days following intraperitoneal infection with 1 x 105 tachyzoites of PTN and 40% of BALB/c died on day 23 of infection, whereas 100% CBA/J infected with the same dose of PTN survived, as did outbred Swiss Webster mice. All C57BL/6, BALB/c, CBA/J, or Swiss Webster died of acute toxoplasmosis by 3-9 days postinfection upon inoculation with same dose of tachyzoites of the PLK strain. Further studies in CBA/J mice demonstrated that mice infected with PTN elicited a significantly higher lymphoproliferative response to crosslinked anti-CD3 mAb or Con A than PLK infected mice, and augmented production of TNFalpha, lower levels of nitrite and a higher number of NK cells. Genetical analysis indicated that both PLK and PTN strains of T. gondii are from type ll. Interestingly, being of the same genotype, the later showed less virulence upon inoculation in mice and had greater capacity to activate host immune system than the PLK strain.

Alteration of Intracellular Calcium Flux and Impairment of Nuclear Factor-AT Translocation in T Cells During Acute Toxoplasma gondii Infection in Mice

Down-regulation of host immune response to Toxoplasma gondii is associated with the expression of specific cytokines, in particular IL-10, and the induction of CD4+ T cell anergy. In the present study we report that the expression of both CD4 and CD2 antigen is down-regulated during the acute phase of infection. A decrease in the expression of CD2 was apparent during the acute phase of T. gondii infection in three genetically distinct strains of mice, CBA/J, C57BL/6, and BALB/c. The lymphoproliferative response induced by cross-linked anti-CD3 mAb or by Con A was markedly depressed. This suppressed response was associated with a reduction in the influx of Ca2+. We have examined whether lymphocytes from T. gondii mice maintain NF-AT transcription factors in the nucleus where they participate in the Ca2+-dependent induction of genes required for lymphocyte activation and proliferation. Immunofluorescence with confocal microscopy using an Ab to NF-ATc demonstrates a decrease in translocation of NF-ATc in T lymphocytes from acutely infected mice. Together, these results suggest that the defect in T cell expansion that occurs during acute murine toxoplasmosis is related to reduced activity of NF-AT, a calcium-dependent transcription factor required for T cell proliferation.

Differential production of IL-10 by T cells and monocytes of HIV-infected individuals: association of IL-10 production with CD28-mediated immune responsiveness

Immune unresponsiveness in HIV-1 infection can result from impaired signals delivered by the costimulatory CD28-B7 pathway and the altered production of immunoregulatory cytokines, in particular IL-10, whose production is altered in HIV-1 infection. In this study we investigate IL-10 regulation in T cells and monocytes from HIV+ individuals, and its association with CD28-mediated T cell proliferation. IL-10 production as analysed in T cell- and monocyte-depleted peripheral blood mononuclear cells (PBMC), and by intracellular staining at the single-cell level, reveals a defect in IL-10 production by CD4+ and CD8+ T cells, whereas monocytes constitute the major IL-10-producing cell type. To investigate the impact of IL-10 on immune responsiveness, CD28-mediated proliferative responses in HIV+ individuals were correlated with PHA-induced IL-10 production. CD4+ T cells expressed CD28, yet exhibited markedly reduced CD28-mediated cell proliferation. This CD28-mediated CD4+ T cell proliferation was found to be inversely associated with the levels of PHA-induced IL-10 production and could be restored, at least in part, by anti-IL-10 antibodies. These results suggest that IL-10 production is differentially regulated in T cells and monocytes of HIV+ individuals, and that IL-10 may have a role in inducing immune unresponsiveness by modulating the CD28-B7 pathway.

Inhibition of HIV type 1 production by hygromycin B

HIV infection alters the cellular uptake of ions and other small molecules. This study was designed to determine whether hygromycin B, a low molecular weight (MW 527) aminoglycoside protein synthesis inhibitor that is normally impermeable to mammalian cells at micromolar concentrations, can selectively inhibit HIV expression and cytopathology. CD4+ T lymphoblastoid cells (H9) and peripheral blood mononuclear cells (PBMCs) were infected with HIV-1, then incubated in medium containing various concentrations of hygromycin B. HIV-1-induced formation of multinucleated giant cells and single cell killing were dramatically reduced in the presence of micromolar concentrations of hygromycin B. Hygromycin B also inhibited HIV-1 production in a dose-dependent manner during acute infection. G418, a larger and more hydrophobic aminoglycoside (MW 692), did not display the same selective inhibition of HIV-1 production as hygromycin B. Relative to mock-infected cells, protein synthesis in acutely infected H9 cells was selectively inhibited by hygromycin B. Hygromycin B also reduced HIV production in PBMCs and in H9 cells persistently infected with HIV. PCR analysis demonstrated that hygromycin B did not inhibit HIV-1 reverse transcription. These results demonstrate that HIV-1 infection renders cells more sensitive to hygromycin B than uninfected cells, and provides support for the hypothesis that HIV-1 induces an alteration of plasma membrane permeability. The HIV-modified cell membrane may be a potential target for antiviral intervention and chemotherapy.

Tandem peptide epitopes facilitate CD4-dependent activation of T cell clones

Peptides that consist of two tandemly repeated epitopes joined by a flexible linker have an increased affinity for class II molecules and are more potent at inducing proliferation of T cell clones than monomeric epitopes. The increase in potency of peptides with two epitopes for individual T cell clones is proportional to the relative CD4 dependence of the clones. We show that epitope dimers activate T cell clones that respond sub-optimally to monomeric epitopes presented by APC from HIV-infected donors. We hypothesize that HIV+ APC normally fail to stimulate the clones because virally encoded gp 120 sequesters CD4 from the activation complex, but epitope dimers overcome this effect because they are better able to recruit CD4. The alpha beta heterodimer of human class II (HLA-DR1) is further ordered as a dimer of heterodimers (superdimer) at least in its crystal form. Since class II molecules have an open-ended antigen binding groove, the superdimer is theoretically permissive of stable binding of two peptide epitopes linked in tandem. Our data support a role for the MHC class II dimer of heterodimers in amplifying the proliferative response of T cells to antigen by dint of the superdimers having a higher affinity for CD4 than the nominal class II alpha beta heterodimers.

Chronic immune stimulation, oxidative stress, and apoptosis in HIV infection

Infection with the human immunodeficiency virus (HIV) is accompanied by a decrease in CD4+ T cell numbers and the ultimate disruption of immunological functions. In sera of infected patients, elevated levels of interferon-gamma are detected, which is indicative of an activated TH1-type immune response. T-cell-derived interferon-gamma leads to the expression of various proinflammatory cytokines and enhanced macrophage capacity to secrete reactive oxygen intermediates. In addition, interferon-gamma is the major stimulator for the biosynthesis of neopterin and its reduced form, 7,8-dihydroneopterin. Neopterin is known as a sensitive immune activation marker in clinical laboratory diagnosis. Recent data implied a potential role of neopterin derivatives in oxygen free-radical-mediated processes, e.g. high concentrations of 7,8-dihydroneopterin were found to interfere with the oxidant-antioxidant balance, and may lead to apoptosis of human cells. In addition, 7,8-dihydroneopterin was found to be effective in the activation of redox-sensitive transcription factors and in the induction of HIV-1 gene expression. In this commentary, we describe our current view as to how neopterin derivatives, in concert with cytokines and reactive oxygen intermediates, may lead the way to the final destruction of the cellular immune system.

Calmodulin-binding function of LLP segments from the HIV type 1 transmembrane protein is conserved among natural sequence variants

LLP1 is a peptide, derived from the cytoplasmic tail of HIV-1 TM glycoprotein, that binds and inhibits calmodulin; this region is generally conserved among isolates, but amino acid variation does exist both within clade B and among different clades, as well as SIV. In light of previous studies showing that selected single amino acid changes can have a qualitatively significant effect on the calmodulin-binding properties of this peptide, we sought to examine the properties of naturally occurring variant LLP1 sequences. Using a quantitative fluorescence-based method to measure dissociation constants of calmodulin-LLP1 complexes, a remarkable conservation of calmodulin-binding function among natural variants was revealed. In contrast, engineered nonconservative single amino acid changes altered the affinity of the peptide for calmodulin. The results show that the calmodulin-binding function is well preserved despite the sequence variation observed in nature, suggesting that this region of the TM protein is important to viral replication.

gp160 of HIV or anti-CD4 monoclonal antibody ligation of CD4 induces inhibition of JNK and ERK-2 activities in human peripheral CD4+ T lymphocytes

Under physiological conditions, activation of CD4+ T cells by major histocompatibility complex (MHC)antigen complexes requires engagement of both the T cell receptor and the CD4 molecule. However, CD4 ligands binding to the CD4 molecule has also been shown to inhibit T cell proliferation and interleukin (IL)-2 production in human CD4+ T cells, in an MHC-independent way. We have previously shown that this inhibition was associated with a diminished binding activity of the IL-2 transcription factors NF-AT, NF-kappaB, and AP-1. AP-1 plays a key role in the regulation of IL-2 transcription, and ERK and JNK activities are necessary for regulating AP-1 at both the transcriptional and the post-transcriptional levels. We therefore studied, in human peripheral CD4+ T cells, the regulation of the activities of extracellular signal-regulated protein kinases (ERK) and c-Jun N-terminal kinases (JNK) by two CD4 ligands, gp160 the envelope glycoprotein of human immunodeficiency virus (HIV) and an anti-CD4 monoclonal antibody (mAb). Pre-incubation of CD4+ T lymphocytes in the presence of anti-CD4 mAb or gp160 inhibits the activation of JNK in response to phorbol 12-myristate 13-acetate and ionomycin. In the same conditions, phosphorylation and activation of ERK-2 were also inhibited. Inhibition of both JNK and ERK-2 activities are specific for binding of CD4 ligands to the CD4 molecule. They were not observed in CD8+ T lymphocytes. These results suggest that a specific inhibition of JNK and ERK-2 activities contributes to defective IL-2 production in T lymphocytes pre-incubated with CD4 ligands.

Repression of human immunodeficiency virus type 1 long terminal repeat-driven gene expression by binding of the virus to its primary cellular receptor, the CD4 molecule

We have previously postulated that the binding of the human immunodeficiency virus type 1 (HIV-1) to cell surface CD4 induces signal transduction pathways that down-modulate production of progeny virions in acutely infected T cells (M. Tremblay, S. Meloche, S. Gratton, M. A. Wainberg, and R.-P. Sékaly, EMBO J. 13:774-783, 1994). To evaluate the possibility that CD4 cross-linking might indeed affect viral gene expression, we have introduced a molecular construct made of the luciferase reporter gene placed under the control of the regulatory elements of HIV-1 in several CD4-positive T-cell lines. We found that cross-linking of CD4 with defective HIV-1 particles and heat-inactivated viruses inhibits long terminal repeat-dependent luciferase expression. Experiments revealed that the gp120-CD4 interaction was necessary to repress HIV-1 long terminal repeat-dependent luciferase activity. The cytoplasmic domain of CD4 was also found to be required for this effect to occur. The virus-mediated signal transduction was shown to be mediated via p56lck-dependent and -independent pathways. These results indicate that the earliest event in the HIV-1 replicative cycle, namely, the binding of the virus to its cellular receptor, can lead to signal transduction culminating in down-modulation of viral gene expression. Thus we propose that defective viruses could regulate the pathogenesis of HIV disease as they constitute the vast majority of circulating HIV-1 particles.

Modulation of CD3-gamma gene expression after HIV type 1 infection of the WE17/10 T cell line is progressive and occurs in concert with decreased production of viral p24 antigen

HIV-1 infection of WE17/10, an IL-2-dependent CD4+ human T cell line, abrogates T cell receptor (TCR)/CD3 expression due to a transcription level defect in the CD3-gamma chain gene. Kinetic examination of surface receptor density reveals that these complexes are progressively reduced early after HIV-1 infection as the cells transition from TCR/CD3hi-->TCR/CD3lo-->TCR/CD3-. The passage from TCR/CD3hi reversible TCR/CD3lo is characterized by a steady decrease in receptor density from 100 to 50% of control values with similar kinetic for all of the viral variants tested. This first phase in TCR/CD3 downmodulation was found to occur in concert with a decrease in viral p24 antigen production. The switch from TCR/CD3- is distinguished by the conversion of individual cells to the receptor negative phenotype. Although broad kinetic differences in this second phase were observed between viral variants, its onset was consistently accompanied by a further reduction in virus production. In some of the HIV-1-infected WE17/10 cell lines, surface receptor expression was spontaneously upregulated during the second phase of infection, reversing the progression from TCR/CD3(-)-->TCR/CD3lo-->TCR/CD3hi. Thus, in HIV-1-infected WE17/10 cells, changes in CD3-gamma gene transcription are accompanied by altered viral p24 antigen production and the resulting modulation of surface receptor expression can be summarized by the formula: TCR/CD3hi reversible TCR/CD3lo reversible TCR/CD3-.

Biologic activities of HIV-1 envelope glycoprotein: the effects of crosslinking

We have examined the biologic activities of native and recombinant preparations of human immunodeficiency virus envelope glycoprotein (gp120), both derived from the HIV-1B strain. Antibody to gp120 was used to evaluate the effects of crosslinking gp120 on signalling by the CD4 receptor. Our results indicate that native and recombinant gp120 produce identical effects in our assay systems. Crosslinking gp120 amplified its chemoattractant activity for lymphocytes and monocytes and increased the peak intracellular calcium level, compared with binding of gp120 alone. The induction of inositol trisphosphate (IP3) production, induction of interleukin 2 receptors (IL2R), and inhibition of lymphocyte proliferation following treatment with gp120 were not enhanced by the addition of crosslinking antibody.

Effect of amino acid substitutions on calmodulin binding and cytolytic properties of the LLP-1 peptide segment of human immunodeficiency virus type 1 transmembrane protein

Previous studies have identified two highly basic amphipathic helical regions in the human immunodeficiency virus type 1 transmembrane protein that, in vitro, display both cytolytic and calmodulin-binding and -inhibitory properties that could contribute to cellular dysfunctions and cytopathogenesis during a persistent viral infection. In the current study, the structural specificity of the cytolytic and calmodulin-binding activities of the human immunodeficiency virus type 1 lentivirus lytic peptide (LLP-1) are examined with synthetic peptide homologs and analogs. The results of these studies demonstrate that even minor changes in LLP-1 amino acid content can markedly affect these properties, suggesting that sequence variation in these highly conserved LLP sequences may correlate with alterations in viral cytopathic properties.

Detection of CD4+ T cells harboring human immunodeficiency virus type 1 DNA by flow cytometry using simultaneous immunophenotyping and PCR-driven in situ hybridization: evidence of epitope masking of the CD4 cell surface molecule in vivo

Human immunodeficiency virus type 1 (HIV-1) infection of T cells and cells of the monocyte/macrophage lineage requires a specific interaction between the CD4 antigen expressed on the cell surface and the HIV-1 external envelope glycoprotein (gp120). To study the association between HIV-1 infection and modulation of cell surface expression of the CD4 molecule in vivo, we examined the CD4+ T cells harboring proviral DNA obtained from HIV-1-infected individuals who had received no antiretroviral therapy for at least 90 days. Simultaneous immunophenotyping of CD4 cell surface expression and PCR-driven in situ hybridization for HIV-1 DNA were used to resolve the CD4+ T cells into distinct populations predicted upon the presence or absence of proviral DNA. Among the HIV-1-infected study subjects, the percentage of CD4+ T cells harboring proviral DNA ranged from 17.3 to 55.5%, with a mean of 40.5%. Cell surface fluorescent staining with anti-CD4 antibody directed against a non-gp120 binding site-related epitope (L120) or a conformation-dependent epitope of the gp120 binding site (Leu 3A) demonstrated either an equivalent or a 1.5- to 3-fold-lower cell surface staining intensity for the HIV-1 DNA-positive subpopulation relative to the HIV-1 DNA-negative subpopulation, respectively. These data suggest that masking or alteration of specific epitopes on the CD4 molecule occurs after viral infection.

Insulin-like growth factor 1 and insulin inhibit HIV type 1 replication in cultured cells

Insulin-like growth factor 1 and insulin, considered primarily as metabolic and growth modulatory hormones, were found to inhibit the replication of HIV-1 in cultured cord blood mononuclear cells and chronically HIV-infected U937 cells. The effect of IGF-1 was seen at physiological concentrations or lower (1.7 x 10(-10) M) while that of insulin was observed at supraphysiological concentrations (8 x 10(-7) M). The EC50 for IGF-1 was found to be in the physiological range (2.5-4.5 x 10(-9) M) while that for insulin was considerably higher (1.1-3.3 x 10(-6) M). Insulin-like growth factor 1 and insulin at the concentrations employed exhibited no toxicity on the cells used in these studies. Furthermore, neither IGF-1 nor insulin exhibited any inhibitory activity on purified reverse transcriptase in vitro. Epidermal growth factor from 1.6 x 10(-10) to 1.6 x 10(-8) M demonstrated no inhibition of HIV-1 replication, while IGF-1 inhibited p24 antigen production 49 and 42% at 1.3 x 10(-9) and 1.3 x 10(-8) M IGF-1, respectively. These results suggest that IGF-1 under certain conditions has significant inhibitory effects on HIV-1 replication at physiological concentrations. This may prove to be of therapeutic value in patients infected with HIV-1.

The role of p56lck in CD4-mediated suppression of CD3-induced early signaling events in T lymphocytes

Crosslinking of the CD4 coreceptor can inhibit subsequent T-cell activation via the T-cell antigen receptor (TCR)/CD3 complex. The ability of the human immunodeficiency virus (HIV) envelope protein, gp 120, to cause similar inhibition has implicated this inhibitory signal in the induction of T-cell anergy and apoptosis observed in the acquired immunodeficiency syndrome (AIDS). In order to clarify the biochemical basis of this inhibition, we analyzed the effect of CD4 ligation on early signaling events induced by subsequent CD3xCD4 co-crosslinking. By comparison with CD3 crosslinking alone, CD3xCD4 co-crosslinking of a CD3+CD4+ human T-cell leukemia line (SupT1) resulted in an enhanced increase in free intracellular calcium concentration and tyrosine phosphorylation of several cellular substrates, including the prominent phosphorylation of an unidentified 120-kDa protein (p120). Prior CD4 ligation inhibited these responses. Similar results were obtained with A3.01, another CD3+CD4+ T leukemic line. However, P120 was only minor phosphorylated on tyrosine upon receptor crosslinking in A2.01/CD4(-cyt401), a derivative line expressing a truncated CD4 coreceptor lacking its cytoplasmic domain which binds the p56lck protein tyrosine kinase (PTK). Furthermore, prior CD4 ligation failed to inhibit in this line the increased tyrosine phosphorylation induced by subsequent CD3xCD4 co-crosslinking. Thus, prior CD4 crosslinking, or expression of truncated CD4, are both associated with reduced p120 phosphorylation. These results suggest that p120 is a p56lck substrate playing an important role during T-cell activation.

HIV population dynamics in vivo: implications for genetic variation, pathogenesis, and therapy

Several recent reports indicate that the long, clinically latent phase that characterizes human immunodeficiency virus (HIV) infection of humans is not a period of viral inactivity, but an active process in which cells are being infected and dying at a high rate and in large numbers. These results lead to a simple steady-state model in which infection, cell death, and cell replacement are in balance, and imply that the unique feature of HIV is the extraordinarily large number of replication cycles that occur during infection of a single individual. This turnover drives both the pathogenic process and (even more than mutation rate) the development of genetic variation. This variation includes the inevitable and, in principle, predictable accumulation of mutations such as those conferring resistance to antiviral drugs whose presence before therapy must be considered in the design of therapeutic strategies.

Modulation of T cell proliferative response by accessory cell interactions

Antigen-specific activation of the T cell is accomplished by engagement of the T cell receptor (TCR) by an antigen (Ag)/MHC complex presented on the surface of an antigen- presenting cell (APC). However, it has been demonstrated that engagement of the TCR by Ag/HC complexes alone is normally insufficient to lead to a proliferative response and the development of effector function. Thus it has been proposed that the APC also provides additional signals which serve to modulate the T cell's response. These second or costimulatory signals are thought to be critical in the generation of a T cell-driven immune response. Several receptors have been proposed to be capable of serving as costimulatory receptors. Candidate molecules include CD28 and LFA-1 as well as other receptors. In this review the studies that we have performed to clarify the role of both LFA-1 and CD28 in providing costimulatory activity for T cell activation are discussed. In addition, we present evidence that under certain conditions, TCR signalling alone can be sufficient to lead to T cell proliferation.

Indirect mechanisms of HIV pathogenesis: how does HIV kill T cells?

Although twelve years have passed since the identification of HIV as the cause of AIDS, we do not yet know how HIV kills its target, the CD4+ T cell, nor how this killing cripples the immune system. Prominent theories include direct killing of infected CD4+ T cells by the action or accumulation of cytopathic viral DNA, transcripts or proteins, or by virus-specific cytotoxic T lymphocytes, and indirect killing of uninfected CD4+ T cells (and other immune cells) by autoimmune mechanisms, cytokines, superantigens, or apoptosis. In the past year, studies have provided tantalizing clues as to why infected cells may not die and how these infected cells kill innocent bystander cells.

Tracking HIV during disease progression

Several recent advances have been made in the delineation of the multiple pathogenic mechanisms involved in the progression of HIV disease. Included among these are the virological and immunological events associated with primary infection and the delineation of the role of lymphoid organs.

Human immunodeficiency virus type 1 (HIV-1) and human hematopoietic progenitor cells

Besides a progressive depletion of CD4+ T-lymphocytes, other peripheral blood cytopenias, (granulocytopenia, anemia and thrombocytopenia) are frequently observed in HIV-1 seropositive individuals, especially in patients with overt AIDS. Various experimental evidences suggest that HIV-1 could play a direct role in the pathogenesis of HIV-1 related peripheral blood cytopenias, affecting the survival/proliferation capacity of hematopoietic progenitors. CD34+ human hematopoietic progenitors, however, are substantially not susceptible to HIV-1 infection either in vitro and in vivo and their defects seem rather related to an alteration of bone marrow and peripheral blood microenvironments due to the presence of soluble HIV-1 specific products.

Induction of apoptosis in a T lymphoblastoid cell line infected with feline immunodeficiency virus

The mechanism of cell death induced by feline immunodeficiency virus (FIV) infection was investigated in an interleukin 2(IL-2)-dependent T-lymphoblastoid cell line (MYA-1). DNA extracted from FIV-infected MYA-1 cells showed a ladder of nucleosomal DNA, indicating that the cytopathic effect (CPE) observed in these cells was due to apoptosis. Infection of MYA-1 cells with FIV was associated with suppression of the proliferative response of the cells to exogenous IL-2 prior to DNA fragmentation. These findings suggest that FIV-induced CPE in these T-lymphoblastoid cells is associated with apoptosis possibly due to a defect in the IL-2 signal transduction pathway.

Cross-reactivity between autoimmune anti-U1 snRNP antibodies and neutralizing epitopes of HIV-1 gp120/41

We report extensive amino acid sequence homology between HIV-1 gp120/41, and > 33% of a U1 RNA-associated splicing protein, 70K. The latter is a target of autoimmune anti-RNP antibodies in mixed connective tissue disease (MCTD). The homologies, involving dominant epitopes of 70K and neutralizing epitopes of gp120/41, are the basis for mutual antibody cross-reactivity. A key finding is that the epitope GRAFVTIG in the V3 loop of gp120 (strain IIIB) is homologous to the functionally essential U1 RNA-binding site of 70K. ELISA data reveal a mean reactivity of anti-RNP antibodies to V3 IIIB that is as high as that of HIV sera. V3 MN, containing the framework sequence G-AF-T, also cross-reacts with anti-RNP antibodies, as do hydrophilic epitopes in gp41 homologous to the COOH end of 70K. Further, there is strong cross-reactivity between HIV sera and 70K in Western blots. In contrast, antibodies from a related autoimmune disorder, Sjögren's syndrome (SS), are neither V3 nor gp41 selective. We conclude that the substantial cross-reactivities reported here are due to conserved, antigenically dominant B cell epitopes having homologous counterparts in 70K and gp120/41. Because antibody production in both MCTD and HIV-1 infection is T cell dependent, the results imply that common T cell clones are also activated in these two disease paradigms. Further exploration of the mechanisms that activate these clones, and that control their divergent fates in MCTD and AIDS, may provide new insights into immune dysregulation in HIV infection.(ABSTRACT TRUNCATED AT 250 WORDS)

Human immunodeficiency virus type 1-associated CD4 downmodulation

This chapter discusses human immunodeficiency virus type 1 (HIV-1) associated with CD4 downmodulation. It also discusses the structure and function of CD4 and p56^lck and factors involved in hiv-1-associated cd4 downmodulation. There are, at present, at least three HIV-1 gene products known to be involved in cell surface CD4 downmodulation. These are Nef, Vpu, and gp160. Whereas Nef is expressed during the early phase of HIV-1 gene expression, both Vpu and gp160, which appear to act coordinately, are expressed during the late phase. This functional convergence of HIV-1 proteins on cell surface CD4 downmodulation, whether specific or nonspecific in activity, suggests that this event is of critical importance in the life cycle of HIV-1. Further elucidation of the mechanisms that underlie CD4 cell surface downmodulation may lead to the development of novel strategies aimed at preventing such events, and potentially to the development of new therapeutic approaches.

Different proliferative response of human and chimpanzee lymphocytes after contact with human immunodeficiency virus type 1 gp120

T cell functional defects are a common aspect of human immunodeficiency virus (HIV) infection. Moreover, it has been suggested that indirect mechanisms are involved in CD4+ cell depletion. Unresponsiveness to proliferative stimuli of lymphocytes incubated with HIV particles or with viral proteins is well documented. Nevertheless, drawing a clear picture of the anergy phenomenon is difficult because of several unresolved and controversial questions. Here we report that recombinant gp120 induces anergy in T helper lymphocytes cultured with different stimuli. The proliferative responses to interleukin (IL)-2, IL-4, IL-6, anti-CD2, anti-CD3 and phorbol 12-myristate 13-acetate are inhibited. Moreover, anergic cells show a different distribution in cell cycle phases as compared to control cells, leading us to suggest that the progression in the cell cycle is hampered and that a pre-mitotic block takes place. Furthermore, since chimpanzees are susceptible to HIV-1 infection without showing immunodeficiency signs, we analyzed the proliferation of chimpanzee lymphocytes without observing anergy in cells preincubated with gp120. Taken together, these results support the hypothesis that anergy plays an important role in HIV infection in vivo.

Bryodin, a single-chain ribosome-inactivating protein, selectively inhibits the growth of HIV-1-infected cells and reduces HIV-1 production

Bryodin, a single-chain ribosome-inactivating protein (RIP) isolated from Bryonia cretica ssp dioica (cucurbitaceae), was found to selectively inhibit the growth of persistently HIV-1-infected T lymphoma cells (KE37/1) and human lung fibroblast when used in concentrations from 2-20 micrograms/ml. Uninfected KE37/1 cells remained unaffected at the same doses of bryodin. In addition, bryodin reduced HIV production in the surviving infected cells. Two isoforms of bryodin were purified by dye ligand chromatography. Both isoforms exerted the growth-inhibiting influence and reduced HIV production. Trichosanthin, another member of the RIP family, had similar inhibitory effects on the growth of HIV-1 infected cells and on HIV-1 production. Bryodin and trichosanthin were effective in about the same dose range. No selective effects for HIV-infected cells were observed with the RIPs gelonin and ricin.

Costimulation of T-cell activation and virus production by B7 antigen on activated CD4+ T cells from human immunodeficiency virus type 1-infected donors

Infection with the human immunodeficiency virus type 1 (HIV-1) requires T-cell activation. Recent studies have shown that interactions of the T-lymphocyte receptors CD28 and CTLA-4 with their counter receptor, B7, on antigen-presenting cells are required for optimal T-cell activation. Here we show that HIV-1 infection is associated with decreased expression of CD28 and increased expression of B7 on CD4+ T-cell lines generated from seropositive donors by alloantigen stimulation. Loss of CD28 expression was not seen on CD4+ T-cell lines from seronegative donors, but up-regulation of B7 expression was observed upon more prolonged culture. Both T-cell proliferation and interleukin 2 mRNA accumulation in HIV-1-infected cultures required costimulation with exogenous B7 because these events were blocked by CTLA4Ig, a soluble form of CTLA-4 that binds B7 with high avidity. In contrast, levels of HIV-1 RNA were not affected by CTLA4Ig, indicating that regulation of virus transcription in these cultures did not depend upon CD28-B7 engagement. Infected T cells could present alloantigen to fresh, uninfected CD4+ T cells, leading to increased proliferation and virus spread to the activated cells. Both of these events were blocked by CTLA4Ig. Thus, chronic activation of HIV-1-infected CD4+ T cells reduces expression of CD28 and increases expression of B7, thereby enabling these T cells to become antigen-presenting cells for uninfected CD4+ T cells; this might be another mechanism for HIV-1 transmission via T-cell-T-cell contact.

Selective impairment of T lymphocyte activation through the T cell receptor/CD3 complex after cytomegalovirus infection

Cytomegalovirus (CMV) infection is reported to cause transient immunosuppression in man. In this study we have analysed the effect of CMV on T lymphocyte function in 29 children diagnosed for acute CMV infection. Peripheral blood mononuclear cells (PBMC) obtained from the patients showed a significant specific impairment in their proliferative response to enterotoxins A and C1, to concanavalin A and to the anti-CD3 MoAb OKT3. The impaired responses were corrected with exogenous IL-2. In contrast, stimulation using phytohaemagglutinin, as well as activation signals delivered through the surface molecules CD26 or CD28, elicited normal proliferative responses in CMV PBMC. The results indicate that the T cell anergy associated with CMV infection is restricted to the T cell receptor/CD3 activation pathway.

Present status and future prospects for HIV therapies

Since the discovery of human immunodeficiency virus (HIV) in 1983, significant progress has been made toward the discovery, development, and licensing of anti-HIV drugs. In vitro screens against whole virus are now being complemented by screens against specific viral targets, resulting in the development of clinical candidates acting at several critical stages of the viral life cycle. Despite these advances, clinical therapy remains largely palliative. In addition, it has recently been recognized that HIV resistance to most drugs may pose even greater obstacles. Moreover, emerging data on immunopathogenesis raise the possibility that even if virus was eliminated from an infected individual, the patient's immune system might not be capable of restoration to normal function. In the face of such obstacles, deeper insights into the pathogenic mechanisms of disease, aggressive exploitation of those mechanisms for therapeutic gain, and continued commitment of both public and private sectors to support and collaborate in this research are needed.

Blunted rise in intracellular calcium in CD4+ T cells in response to mitogen following autologous bone marrow transplantation

Following autologous bone marrow transplantation (ABMT), both impaired T cell activation and defective production of the principal T cell growth factor, interleukin-2 (IL-2), has been observed. These processes are dependent on a rise of intracellular calcium ([Ca2+]i), a step which follows binding of T cell receptor (TCR) and transduction of signal via the generation of cytoplasmic second messengers. In order to better understand the nature of defective cellular immunity in ABMT, in the present study we investigated the rise of [Ca2+]i in T cells of recipients of ABMT. By concomitant labelling lymphocytes with anti-CD4 antibody and addition of fluo-3 as fluorescent calcium indicator, we have selected for the T cell subset which is the principal source of IL-2. Short-term (less than 1 year post-transplantation) recipients of ABMT show a statistically significant blunted rise in [Ca2+]i in response to concanavalin A as compared to normal controls not accounted for solely by a decreased percentage of CD4+ cells in these patients. The [Ca2+]i response of CD4+ cells from long-term (greater than 1 year post-transplant) recipients was lower than that of the normal group although not to a statistically significant level. These findings suggest that following ABMT is a defect in the early stages of T cell activation involving either T cell receptor binding or early signal transduction ultimately resulting in depressed transcription of IL-2 mRNA. These defects are analogous to findings in both allogeneic transplantation where factors of histoincompatibility and graft-versus-host disease (GVHD) come into play, as well as in the defective T cell activation of the normal ageing process.

High levels of HIV-1 in plasma during all stages of infection determined by competitive PCR

Quantitative competitive polymerase chain reaction (QC-PCR) methods were used to quantify virion-associated human immunodeficiency virus type-1 (HIV-1) RNA in plasma from 66 patients with Centers for Disease Control stage I to IVC1 infection. HIV-1 RNA, ranging from 100 to nearly 22,000,000 copies per milliliter of plasma (corresponding to 50 to 11,000,000 virions per milliliter), was readily quantified in all subjects, was significantly associated with disease stage and CD4+ T cell counts, and decreased by as much as 235-fold with resolution of primary infection or institution of antiretroviral therapy. Plasma virus levels determined by QC-PCR correlated with, but exceeded by an average of 60,000-fold, virus titers measured by endpoint dilution culture. Quantitation of HIV-1 in plasma by QC-PCR may be useful in assessing the efficacy of antiretroviral agents, especially in early stage disease when conventional viral markers are often negative.

Antiretroviral treatment reverses HIV-induced reduction in the expression of surface antigens on alveolar macrophages in AIDS patients

MoAbs and immunoperoxidase methods were used to identify antigen-presenting and phagocytic cells and to assess expression of HLA-DR molecules on cells obtained by bronchoalveolar lavage (BAL) from 33 AIDS patients and nine normal volunteers. In 17 patients, not receiving antiretroviral therapy, the expression of HLA-DR molecules (MoAb RFDR1) as well as the percentages of cells expressing RFD1 marker for antigen-presenting cells and RFD7 marker for mature phagocytes were significantly reduced. However, in BAL obtained after commencing treatment with zidovudine (AZT) in 21 patients or with 2',3'-dideoxyinosine (DDI) in five patients, the expression of the markers studied was found to have returned to levels of expression seen in normal lavages. The changes observed were clearly associated with antiretroviral treatment and did not correlate with applications of other drugs, blood CD4 counts or presence of infectious organisms in BAL fluid. As the alterations in the expression of HLA-DR molecules and RFD1 marker on macrophages have been shown to be associated with functional capacities of these cells, the reversal of impaired expression of phenotypic markers on alveolar macrophages in AIDS patients by AZT and DDI signifies an important ability of these drugs to modify immune reactivity and emphasizes the need to monitor such functions in HIV disease.

Membrane alterations linked to early interactions of HIV with the cell surface

Ultrastructural studies suggest that cell surface alterations occur early during the course of HIV-1 infection of CD4+T-lymphoblastoid cells. Attachment and penetration of HIV resulted in formation of membrane discontinuities and pores and "ballooning." Distention of the endoplasmic reticulum occurred in some cells within the first hour after HIV infection, and this correlated with the numbers of virions bound at the cell surface. These results suggest that HIV virion components may directly damage the cell membrane.

Influence of amphipathic peptides on the HIV-1 production in persistently infected T lymphoma cells

The effects of several amphipathic peptides on HIV-1 production in persistently infected cells are described. Melittin, a 26 amino acid alpha-helical amphipathic peptide, reduces HIV-1 production dose-dependently, whereas other amphipathic peptides do not. Six melittin derivatives which retain the alpha-helical portion have similar effects as melittin. The reduction of viral infectivity is not due to an effect of melittin on the virus particles but to an intracellular action of the peptide, which is readily taken up into cells, as shown by quantitative ELISA. Western blots of cells from melittin-treated cultures suggest that the processing of the gag/pol precursor is impaired.

Signal transduction in Sjögren's syndrome T cells. Abnormalities associated with a newly described human A-type retrovirus

OBJECTIVE

To study the effects of a novel A-type retrovirus, detected in cocultures of lip biopsy specimens from Sjögren's syndrome (SS) patients and a human T cell line, on the infected T cells.

METHODS

Interleukin-2 (IL-2) and IL-6 secretion were measured by bioassay and enzyme-linked immunosorbent assay, respectively, in the infected and noninfected cell lines. Surface antigen expression was determined by flow cytometry, using monoclonal antibodies. Protein kinase C (PKC) activity was measured using an enzyme assay kit, and calcium mobilization was assessed with a fluorescent probe.

RESULTS

Infected cells expressed less CD4 and IL-6 receptor, but more HLA-DR, compared with noninfected cells. Infected cells also produced less IL-2 and displayed reduced PKC activation and calcium mobilization. A similar defect in calcium mobilization was detected in T cells from SS patients.

CONCLUSION

These data suggest a possible involvement of the newly described retrovirus in T cell abnormalities.