HIV-1 glycoprotein gp120 disrupts CD4-p56lck/CD3-T cell receptor interactions and inhibits CD3 signaling

Bioinformatic analysis of HIV-1 entry and pathogenesis

The evolution of human immunodeficiency virus type 1 (HIV-1) with respect to co-receptor utilization has been shown to be relevant to HIV-1 pathogenesis and disease. The CCR5-utilizing (R5) virus has been shown to be important in the very early stages of transmission and highly prevalent during asymptomatic infection and chronic disease. In addition, the R5 virus has been proposed to be involved in neuroinvasion and central nervous system (CNS) disease. In contrast, the CXCR4-utilizing (X4) virus is more prevalent during the course of disease progression and concurrent with the loss of CD4(+) T cells. The dual-tropic virus is able to utilize both co-receptors (CXCR4 and CCR5) and has been thought to represent an intermediate transitional virus that possesses properties of both X4 and R5 viruses that can be encountered at many stages of disease. The use of computational tools and bioinformatic approaches in the prediction of HIV-1 co-receptor usage has been growing in importance with respect to understanding HIV-1 pathogenesis and disease, developing diagnostic tools, and improving the efficacy of therapeutic strategies focused on blocking viral entry. Current strategies have enhanced the sensitivity, specificity, and reproducibility relative to the prediction of co-receptor use; however, these technologies need to be improved with respect to their efficient and accurate use across the HIV-1 subtypes. The most effective approach may center on the combined use of different algorithms involving sequences within and outside of the env-V3 loop. This review focuses on the HIV-1 entry process and on co-receptor utilization, including bioinformatic tools utilized in the prediction of co-receptor usage. It also provides novel preliminary analyses for enabling identification of linkages between amino acids in V3 with other components of the HIV-1 genome and demonstrates that these linkages are different between X4 and R5 viruses.

Patterns of HIV-1 protein interaction identify perturbed host-cellular subsystems

Human immunodeficiency virus type 1 (HIV-1) exploits a diverse array of host cell functions in order to replicate. This is mediated through a network of virus-host interactions. A variety of recent studies have catalogued this information. In particular the HIV-1, Human Protein Interaction Database (HHPID) has provided a unique depth of protein interaction detail. However, as a map of HIV-1 infection, the HHPID is problematic, as it contains curation error and redundancy; in addition, it is based on a heterogeneous set of experimental methods. Based on identifying shared patterns of HIV-host interaction, we have developed a novel methodology to delimit the core set of host-cellular functions and their associated perturbation from the HHPID. Initially, using biclustering, we identify 279 significant sets of host proteins that undergo the same types of interaction. The functional cohesiveness of these protein sets was validated using a human protein-protein interaction network, gene ontology annotation and sequence similarity. Next, using a distance measure, we group host protein sets and identify 37 distinct higher-level subsystems. We further demonstrate the biological significance of these subsystems by cross-referencing with global siRNA screens that have been used to detect host factors necessary for HIV-1 replication, and investigate the seemingly small intersect between these data sets. Our results highlight significant host-cell subsystems that are perturbed during the course of HIV-1 infection. Moreover, we characterise the patterns of interaction that contribute to these perturbations. Thus, our work disentangles the complex set of HIV-1-host protein interactions in the HHPID, reconciles these with siRNA screens and provides an accessible and interpretable map of infection.

HIV-1 gp120 induces anergy in naive T lymphocytes through CD4-independent protein kinase-A-mediated signaling

The ability of the envelope glycoprotein gp120 [human immunodeficiency virus (HIV) env] to induce intracellular signals is thought to contribute to HIV-1 pathogenesis. In the present study, we found that the exposure of CD4+ CD45RA+ naive T cells to HIVenv results in a long-lasting hyporesponsiveness to antigen stimulation. This phenomenon is not dependent on CD4-mediated signals and also can be generated by the exposure of naive T cell to soluble CD4-HIVenv complexes. The analysis of the proximal signaling reveals that HIVenv does not activate Lck as well as the mitogen-activated protein kinase intermediate cascade. Conversely, the envelope glycoprotein stimulates the cyclic adenosine monophosphate (cAMP)-dependent protein kinase A (PKA) activity and induces the progressive accumulation of the phosphorylated form of the cAMP-responsive element binding. Of note, the ligation of CXCR4 by stromal cell-derived factor-1alpha but not the engagement of CD4 by monoclonal antibody stimulates the PKA activity and induces a long-lasting hyporesponsivity state in naive CD4+ lymphocytes. The pretreatment of lymphocytes with H89, a cell-permeable PKA inhibitor, prevents the induction of anergy. These findings reveal a novel mechanism by which HIVenv may modulate the processes of clonal expansion, homeostatic proliferation, and terminal differentiation of the naive T lymphocyte subset.

RNA based vaccines

The recognition that CD8(+) T-cell mediated Th1 immune responses were necessary to produce immunity to intracellular and transformed self pathogens led to intense interest in the delivery of nucleic acids, DNA, or RNA encoding candidate antigens, as vaccines. Antigen presenting cells (APC) encounter most protein and vaccine immunogens as extracellular proteins and, thus, present them on major histocompatibility complex (MHC) class II molecules leading to the activation of CD4(+) T cells. Protein antigens encoded by nucleic acids delivered to dendritic cell (DC) are produced inside the cell and, thus, can stimulate MHC class I mediated activation of CD8(+) T-cell immune responses. Unfortunately, DCs are not readily transfected with DNA (Akbari et al., 1999) resulting in the requirement for high concentrations of DNA and repeated immunizations to achieved immune responses. RNA, on the other hand, is readily taken up and expressed by DC, making it an alternative vaccine candidate. In this article, we will discuss immune responses developed, interactions between APC and RNA that activate and dictate DC activation, and preliminary studies using RNA in vivo and in vitro to develop protective immunity.

Nef enhances human immunodeficiency virus type 1 infectivity and replication independently of viral coreceptor tropism

We investigated the infectivities and replicative capacities of a large panel of variants of the molecular human immunodeficiency virus type 1 (HIV-1) NL4-3 clone that differ exclusively in the V3 region of the viral envelope glycoprotein and the nef gene. Our results demonstrate that Nef enhances virion infectivity and HIV-1 replication independently of the viral coreceptor tropism.

Inhibition of the calcium release-activated calcium (CRAC) current in Jurkat T cells by the HIV-1 envelope protein gp160

The HIV-1 envelope glycoprotein gp120/160 has pleiotropic effects on T cell function. We investigated whether Ca(2+) signaling, a crucial step for T cell activation, was altered by prolonged exposure of Jurkat T cells to gp160. Microfluorometric measurements showed that Jurkat cells incubated with gp160 had smaller (approximately 40%) increases in [Ca(2+)](i) in response to phytohemagglutinin and had a reduced Ca(2+) influx (approximately 25%). gp160 had similar effects on Jurkat cells challenged with thapsigargin. We used the patch clamp technique to record the Ca(2+) current, which is responsible for Ca(2+) influx and has properties of the calcium release-activated Ca(2+) current (I(CRAC)). gp160 reduced I(CRAC) by approximately 40%. The inhibitory effects of gp160 were antagonized by staurosporine (0.1 microm), an inhibitor of protein-tyrosine kinases and protein kinase Cs (PKCs), and by Gö 6976 (5 microm), an inhibitor acting especially on PKC alpha and PKC beta I. 12-O-Tetradecanoyl phorbol 13-acetate (16 nm), a PKC activator, reproduced the effects of gp160 in untreated cells. A Western blotting analysis of PKC isoforms alpha, beta I, delta, and zeta showed that only the cellular distribution of PKC alpha and -beta I were significantly modified by gp160. In addition, gp160 was able to modify the subcellular distribution of PKC alpha and PKC beta I caused by phytohemagglutinin. Therefore the reduction in I(CRAC) caused by prolonged incubation with gp160 is probably mediated by PKC alpha or -beta I.

Identification of protein kinases dysregulated in CD4(+) T cells in pathogenic versus apathogenic simian immunodeficiency virus infection

Human immunodeficiency virus infection in humans and simian immunodeficiency virus (SIV) infection in rhesus macaques (RM) leads to a generalized loss of immune responses involving perturbations in T-cell receptor (TCR) signaling. In contrast, naturally SIV-infected sooty mangabeys (SM) remain asymptomatic and retain immune responses despite relatively high viral loads. However, SIV infection in both RM and SM led to similar decreases in TCR-induced Lck phosphorylation. In this study, a protein tyrosine kinase (PTK) differential display method was utilized to characterize the effects of in vivo SIV infection on key signaling molecules of the CD4(+) T-cell signaling pathways. The CD4(+) T cells from SIV-infected RM, but not SIV-infected SM, showed chronic downregulation of baseline expression of MLK3, PRK, and GSK3, and symptomatically SIV-infected RM showed similar downregulation of MKK3. In vitro TCR stimulation with or without CD28 costimulation of CD4(+) T cells did not lead to the enhancement of gene transcription of these PTKs. While the CD4(+) T cells from SIV-infected RM showed a significant increase of the baseline and anti-TCR-mediated ROR2 transcription, SIV infection in SM led to substantially decreased anti-TCR-stimulated ROR2 transcription. TCR stimulation of CD4(+) T cells from SIV-infected RM (but not SIV-infected SM) led to the repression of CaMKKbeta and the induction of gene transcription of MLK2. Studies of the function of these molecules in T-cell signaling may lead to the identification of potential targets for specific intervention, leading to the restoration of T-cell responses.

HIV-1 infection impairs cell cycle progression of CD4(+) T cells without affecting early activation responses

Failure of CD4(+) T cells to proliferate in response to antigenic stimulation is a characteristic of HIV infection. Analysis of the proliferation defect has been hampered by an inability to identify CD4(+) cells with T cell receptor specificity for antigen. To focus only on cells that had been stimulated through the T cell receptor, CD4(+) T cells were stimulated with an anti-Vbeta3 Ab that activates approximately 3-5% of peripheral blood T cells. This approach revealed proliferation defects in cells from HIV-infected patients that were not appreciated using anti-CD3 Ab stimulation and provided the capacity to examine responses on a single cell basis. After anti-Vbeta3 Ab stimulation, CD4(+)Vbeta3(+) cells from HIV-infected patients demonstrated defects in expression of cell cycle-associated proteins, D-type cyclins, and cyclin A. However, the expression of early activation markers, CD69 and CD25, was not significantly impaired in cells from most patients. Thus, CD4(+) T cell proliferation failure in HIV disease is characterized by dysregulated activation that precludes cell cycle progression. This proliferation defect was most apparent in patients with diminished CD4(+) T cell numbers and higher plasma HIV RNA levels. CD4(+) T cell proliferation failure may be a key determinant of immune impairment in HIV disease.

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.

Altered replication of human immunodeficiency virus type 1 (HIV-1) in T cell lines retrovirally transduced to express Herpesvirus saimiri proteins StpC and/or Tip

Human peripheral blood T lymphocytes are transformed in vitro to continuous proliferation by Herpesvirus saimiri subgroup C strains. It has been previously shown that H. saimiri-transformed human T cell lines are a permissive system for HIV-1 and 2 replication and are highly susceptible to infection by HIV-1 and 2. Two open reading frames of H. saimiri, StpC and Tip, are required for T cell transformation and are unique to this herpesvirus. The successful transduction of human T cells with retroviral vectors expressing H. saimiri proteins StpC and Tip has allowed us to extend the previously mentioned observations and investigate the role of StpC and Tip in replication of HIV-1 T-tropic strains (IIIB, MN, and RF) in human T cell lines. StpC expression in Molt4 dramatically enhanced HIV-1 replication as measured by Tat protein expression, syncytia formation, and accumulation of reverse transcriptase activity. In contrast, Tip expression in Molt4 cells inhibited HIV-1 replication and cytopathic effects relative to Molt4 cells transduced with the empty vector alone. The StpC-induced phenotype dominated in Molt4 cells transduced to express both StpC and Tip, suggesting that StpC is responsible for facilitating HIV-1 replication in H. saimiri-transformed T cells. Colony-forming ability of Tip-expressing Molt4 cells following HIV-1 infection was greatly enhanced over Molt4 cells expressing either StpC or no H. saimiri proteins at all. HIV-1 proviral DNA could be detected by PCR in surviving Molt4 cells expressing StpC or Tip, indicating that a persistent infection was established. A better understanding of the effects of Tip and StpC proteins on the biology of human hemopoietic stem cells may lead to novel therapeutic interventions for the treatment of AIDS.

Interactions of HIV-1 with antigen-presenting cells

There is currently much interest in the numerical and functional loss of antigen-presenting cells (APC) in HIV-1 disease and the contribution that this may make to HIV-1 pathology. The HIV-1 virus can interfere with the normal function of APC in a number of ways involving inappropriate signalling. These include changes in cytokine balance, cell-surface molecule expression and intracellular signalling pathways. This review examines how HIV-1 is able to disregulate APC function and discusses possible outcomes for the function of the immune system.

Human immunodeficiency virus-1 infection requires pertussis toxin sensitive G-protein-coupled signalling and mediates cAMP downregulation

The human immunodeficiency virus-1 (HIV-1) utilises CD4 and certain beta-chemokine receptors, mainly CCR-5 and CXCR4, for attachment and virus entry into T-lymphocytes and monocytes/macrophages. CD4 and beta-chemokine receptors participate in intracellular signalling via protein tyrosine kinases and G-protein-coupled signalling. The factors which influence HIV-1 replication and the intracellular signalling mechanisms elicited by the virus are not well understood. In this study, it was demonstrated that exposure of peripheral blood lymphocytes (PBLs) to a T-cell tropic strain of HIV-1 evokes signal(s) which results in downregulation of intracellular cAMP. In addition, pre-incubation of PBLs with the Gi-protein inhibitor Pertussis toxin mediated a significant inhibition of HIV-1 replication. These data strongly suggest that HIV-1 employs CD4 receptors and Gi-coupled proteins for entry into target cells and that productive HIV-1 infection is dependent on an active signalling event.

HIV-1 gp160 decreases the K+ voltage-gated current from Jurkat E6.1 T cells by up-phosphorylation

HIV-1 gp120/gp160 is known to disturb the activity of p56lck, protein kinase C (PKC) and Ca2+ homeostasis in T lymphocytes. We found that gp160 decreases the Kv1.3 current of Jurkat E6.1 cells probably by increasing the PKC-dependent phosphorylation of Kv channel protein after 5 days. This decrease is dose-dependent. In contrast, gp160 did not decrease the Kv1.3 current of the JCaM1.6 cell line, a p56(lck)-defective Jurkat cell line. This shows that p56lck was at the beginning of the events which induced the Kv1.3 current decrease. As a consequence of this decrease, Jurkat E6.1 cells were depolarized and exhibited a volume increase.

TCR Activation Inhibits Chemotaxis Toward Stromal Cell-Derived Factor-1: Evidence for Reciprocal Regulation Between CXCR4 and the TCR

Stromal cell-derived factor-1 (SDF-1), a C-X-C family chemokine, is a potent T lymphocyte chemoattractant. We investigated the effects of T cell activation on the chemotactic response to SDF-1. Anti-CD3 Ab stimulation of either Jurkat T cells or murine peripheral CD4+ T lymphocytes produced a dramatic inhibition of SDF-1-induced chemotaxis. In contrast, the SDF-1 responses of Jurkat clones with deficiencies in key TCR signaling components (Lck, CD45, and TCR-β), were only marginally reduced by anti-CD3 stimulation. Similar to PMA treatment, which abolished both CXCR4 receptor expression and the chemotactic response of Jurkat cells to SDF-1, anti-CD3 Ab treatment reduced cell surface expression of CXCR4 to 65% of the control value, an effect that was blocked by protein kinase C inhibitors. Our data suggest that initial T cell activation events inhibit the response of Jurkat T cells to CXCR4 stimulation. In contrast, SDF-1 treatment resulted in a reduction of tyrosine phosphorylation of the TCR downstream effectors, ZAP-70, SLP-76, and LAT (linker for activation of T cells), suggesting that this chemokine potentially regulates the threshold for T cell activation.

The Ick protein tyrosine kinase is not involved in antibody-mediated CD4 (CDR3-loop) signal transduction that inhibits HIV-1 transcription

Monoclonal antibodies (mAb) that bind to the immunoglobulin CDR3-like region in the D1 domain of the CD4 molecule can inhibit the HIV-1 life cycle in CD4-positive T cells and lymphoblastoid cell lines at the stage of transcription. This antiviral effect requires the integrity of the cytoplasmic tail of CD4 which is known to act as a signal transduction region through its association with the protein tyrosine kinase (PTK) p56lck. In this study, we investigated the putative role of this PTK in transducing inhibitory signals that act on HIV-1 replication after triggering by anti-CDR3-like region antibody treatment of infected T cell lines. CEM (CD4+/p56lck + inducible), MT2 (CD4+/p56lck - repressed), HSB-2 (CD4-/p56lck + constitutively), HSB-2 WTCD4 (CD4+/p56lck + constitutively), HSB-2 CD4.402 (CD4+ truncated form which lacks the cytoplasmic domain/p56lck + constitutively), and HSB-2 CD4mut (CD4+ unable to bind lck/p56lck + constitutively) were exposed to HIV-1 and cultured in medium supplemented with an anti-CDR3-like region-specific antibody or a control anti-CD4 mAb which does not inhibit HIV-1 transcription. We found that CDR3-loop-mediated inhibitory signals are efficiently transduced in CD4-positive cells which demonstrate a constitutive activation of p56lck or in CD4-positive cells lacking p56lck expression. Moreover, inhibitory signals were transduced in HSB-2 CD4mut cells expressing a cell surface CD4 with a double cysteine mutation in its cytoplasmic tail that renders the molecule unable to bind p56lck, but not HSB-2 CD4.402 cells expressing a truncated form of CD4 which lacks the cytoplasmic domain. These results indicate that the p56lck plays no direct role in this process and suggests the existence of another signaling partner for CD4.

Regulation of the serine-base exchange enzyme system by CD4: effects of monoclonal antibodies, jacalin, interleukin 16 and the HIV membrane protein gp120

Phosphatidylserine (PtdSer) is synthesized by an exchange of the polar head group of phospholipids for a serine residue. The enzyme responsible for this reaction, the serine-base exchange enzyme system (serine-BEES) is inhibited during lymphocyte activation. We show here that triggering the CD4 cell surface molecule in several CD4+ T-cell lines regulates the serine-BEES activity, thus resulting in marked changes in PtdSer synthesis. CD4 ligands able to generate an activating signal in T-cells such as the lectin jacalin, down-regulate the synthesis of PtdSer. In contrast, monoclonal antibodies (mAbs) directed against the CD4 molecule, such as IOT4 and IOT4a, which have previously been described as generating an inhibitory signal to T-cells, induced an up-regulation of the serine-BEES and impaired CD3-induced inhibition of PtdSer synthesis. Similarly, the HIV-gp120 envelope glycoprotein, in both soluble and cross-linked forms, induces an increase in PtdSer synthesis. The protein tyrosine kinase p56lck participates in the regulation of serine-BEES activity because the effect of CD4 mAbs was additive to that of amino-hydroxyflavone, an inhibitor of p56lck. Also, CD4 mAbs were inactive in J Cam 1.6 cells or when the CD3 signals were bypassed by using thapsigargin. These results demonstrate that the CD4 surface molecule can transmit both activating and inhibiting intracellular signals depending on the CD4 ligand used. We suggest that PtdSer synthesis would be one of the intracellular signals that could explain the opposite effects of different CD4 ligands on T-cells.

HIV-1 gp120 accelerates Fas-mediated activation-induced human lamina propria T cell apoptosis

Intestinal mucosa represents an important portal of entry of HIV and a site of virus reservoir and active replication. Recently, in HIV patients, an early depletion of intestinal lamina propria T lymphocytes (LPT) has been described. HIV-1 gp120 has been demonstrated to promote apoptosis in noninfected isolated peripheral blood T cells, therefore we investigated whether gpl20 modulates apoptosis of normal human intestinal lamina propria T cells. Purified T cells were obtained by immunomagnetic negative selection from human lamina propria mononuclear cells isolated from surgical specimens by enzymatic procedure. Cells were incubated with or without recombinant gpl20 (10 microg/ml) and cultured either in the absence of any stimulus or in the presence of plate-bound anti-CD3 Ab (OKT3) or soluble anti-CD2 Ab (T11(2) + T11[3]). Apoptosis was assessed by flow cytometric analysis after propidium iodide staining. We demonstrated that preincubation of normal LPT cells with HIV-1 gpl20 accelerates the apoptosis observed during CD2-pathway stimulation of LPT cells. This process is mediated by Fas/Fas ligand interaction and related to an increased induction of Fas ligand mRNA by gpl20. Therefore HIV-1 gp120 could contribute to the depletion of noninfected LPT cells inducing a premature cell death.

HIV-1 envelope protein, gp120, has no effects on inositol phosphate production and metabolism in the Jurkat T-cell line either in the presence or absence of receptor stimulation

We have used HPLC techniques to investigate the effects of gp120 upon inositol phosphate turnover in Jurkat E6-1 CD4+ T-cells, to pursue previous reports that this viral coat protein: (a) inhibits receptor-activated inositol phosphate release; (b) stimulates basal inositol phosphate release; (c) inhibits inositol polyphosphate 5-phosphatase. Treatment of cells with up to 10 microg/ml gp120 from between 10 min and 24 h was without effect upon inositol phosphate turnover in both basal cells, and in C305 and OKT3 stimulated cells. This is the first report that biologically competent gp120 does not affect any aspect of inositol phosphate turnover in either basal or receptor-activated lymphocytes.

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.

Priming of human CD4+ antigen-specific T cells to undergo apoptosis by HIV-infected monocytes. A two-step mechanism involving the gp120 molecule

The study of the pathology of HIV-1 infection in chimpanzees supports the idea of the crucial role of HIV-infected monocytes in the pathogenesis of AIDS, although viral mechanisms that lead to T cell dysfunction and deletion during HIV infection are still unclear. We show here that HIV-1-infected antigen-presenting monocytes (APCs) are able to prime in vitro non-HIV-infected antigen-specific CD4+ T cell lines or peripheral blood CD4+ T cells to undergo apoptosis after antigen-specific restimulation. The priming of T cells for apoptosis occurs in the absence of HIV replication in the T cells. Priming for apoptosis required two concomitant signals present on the same APC, an antigenic stimulus and a second signal provided by the HIV gp120 protein as demonstrated by the use as APCs of EBV-LCLs infected with different recombinant deleted proviruses or transfected with different HIV proteins. These results provide a mechanism for the priming for apoptosis of T cells in HIV-infected patients, implicating a role for HIV-infected APCs in the induction of T cell dysfunction and depletion in AIDS.

HIV type 1 glycoprotein 120 amplifies tumor necrosis factor-induced NF-kappa B activation in Jurkat cells

This article demonstrates that human immunodeficiency virus type 1 (HIV-1) gp120 amplifies the activity of tumor necrosis factor alpha (TNF-alpha), a cytokine that stimulates HIV-1 replication through activation of NF-kappa B. In CD4-positive Jurkat cells, gp120 potentiates TNF-induced NF-kappa B activation. TNF-mediated activation of NF-kappa B is known to involve the intracellular formation of reactive oxygen intermediates (ROIs). Accordingly, we examined the influence of gp120 on the cellular redox state. We found that gp 120-modulated TNF-induced NK-kappa B activation was inhibited by the antioxidant butylated hydroxyanisole, indicating the involvement of redox-dependent mechanisms. In addition, we showed that gp120 induces intracellular formation of hydrogen peroxide, which is accompanied by a decrease in the ratio of glutathione to glutathione disulfide. In contrast, in the p56lck-deficient J.CaM1.6 T cell line, a derivative of the Jurkat cell line, gp120 was unable to stimulate hydrogen peroxide, to decrease the ratio of GSH to GSSG, and has no effect on TNF-induced NF-kappa B activation. This demonstrated that p56lck protein tyrosine kinase plays an active role in transmitting a signal that increases the oxidative state of the cell and as a consequence amplifies TNF-mediated NF-kappa B DNA binding. We have demonstrated that Tat protein decreased both the Mn-dependent superoxide dismutase (MnSOD) and the cellular glutathione content (GSH). Here we show that, in contrast to Tat, gp120 is unable to inhibit activity and expression of MnSOD and to decrease GSH content. Taken together, our data suggest that gp120 potentiates TNF-induced NF-kappa B activation by stimulating a signal pathway that involves p56lck and the increased formation of reactive oxygen intermediates such as H2O2. These findings may be relevant for the regulation of HIV-1 replication in T cells.

Leukocyte chemotactic factor, a natural ligand to CD4, is expressed by lymphocytes and microglial cells of the MS plaque

The leukocyte chemotactic factor (LCF) is a proinflammatory cytokine and natural soluble ligand to the human CD4 molecule. LCF is produced by CD4+ and CD8+ T lymphocytes and is considered essential to the influx of CD4+ T lymphocytes and macrophages into an inflammatory lesion. In order to investigate the role of LCF in the multiple sclerosis (MS) lesion, we have used a synthetic gene to express LCF in E. coli and have produced monoclonal antibodies against LCF. Monoclonal antibodies are suited to demonstrate LCF in ELISAs. Western blots and paraffin-embedded tissue sections. In the MS lesion, immunopositive lymphocytes and microglial cells, notably, have been found. This is the first demonstration that LCF is present in MS lesions. Immunostaining of microglial cells is noteworthy, as these cells are strategically placed regulatory elements of CNS immunosurveillance and like other cells of the monocytic lineage express CD4 molecules. Thus, LCF might be a paracrine factor regulating T-lymphocyte chemoattraction and an autocrine molecule regulating microglial cell immune reactivity.

Detection of intracellular signal transduction molecules in PBMC from rhesus macaques and sooty mangabeys

One of the manifestations of human HIV-1 and nonhuman primate SIV infection that lead to disease is reasoned to be secondary to generalized T-cell dysfunction. The molecular mechanisms associated with the T-cell dysfunction remain to be elucidated. To address this issue, we sought to utilize the nonhuman primate model to study intracellular signaling events in cells from disease-susceptible rhesus macaques and disease-resistant sooty mangabeys. Because relatively little is known about these events in nonhuman primates, our laboratory defined optimal conditions, reagents, and assays for the study of signal transduction events in cells from nonhuman primates. The protein phosphorylation patterns in the two monkeys exhibited quantitative, qualitative, and kinetic differences. Antibodies to Stat6 detected a unique band in macaque cell lysates. This band is markedly decreased human cell lysates and never seen in mangabey cell lysates. Detection of various other intracellular signaling proteins is also described.

A herpesvirus saimiri membrane protein required for interleukin-2 independence forms a stable complex with p56lck

ORF-2, a 32-kDa viral protein expressed by herpesvirus saimiri-transformed lymphocytes, is essential for transformation and is expressed on the plasma membrane of transformed cells. The current work now shows that most (approximately 80%) of ORF-2 resides in the cytoplasm, while only a small portion protrudes from the cell surface. Expressed as a glutathione S-transferase fusion protein, ORF-2 was found to interact with a 56-kDa cellular protein in untransformed, herpesvirus saimiri-transformed, and Jurkat lymphocytes. Microsequencing proved that this protein is the lymphocyte-specific tyrosine protein kinase p56lck. Two regions of ORF-2 were found to be required for p56lck interaction. Current evidence suggests that the interaction of ORF-2 with p56lck plays a key role in the specific transformation of T lymphocytes to an interleukin-2-independent phenotype.

Differential susceptibility to monomeric HIV gp120-mediated apoptosis in antigen-activated CD4+ T cell populations

To support the hypothesis that indirect mechanisms mediated by viral products like the HIV envelope glycoprotein gp120 could be responsible for T lymphocyte depletion in HIV infection, we developed a system in which the impairment of T cell functions could be investigated in vitro. In particular, we characterized the conditions that allow T lymphocytes repeatedly stimulated with an antigen to be sensitive or resistant to gp120-mediated apoptotic signals. To achieve this goal, a panel of antigen-specific CD4+ T cell clones and primary CD4+ T lymphocytes were treated for 2 and 18 h with saturating amounts of monomeric gp120 (without cross-linking with specific antibodies) and antigen-driven T cell proliferation and apoptosis were analyzed. We show that monomeric gp120 induces apoptosis only in T lymphocytes repeatedly stimulated with the antigen, that primary T lymphocytes are resistant to programmed cell death mediated by monomeric gp120, but are sensitive to anti-CD4 antibodies, and that gp120-mediated apoptosis is dependent on the period of time between the binding of gp120 to CD4 and the encounter with antigen. To investigate the different susceptibility to gp120 induced apoptosis of primary CD4+ and T cell clones further, the number of membrane CD4 molecules and their affinity for gp120, together with Bcl-2 and Fas expression, were studied. Our data suggest that a down-modulation of membrane CD4 together with high expression of the Bcl-2 gene and protein characterizes the susceptibility to apoptosis of gp120-treated cells. In conclusion, our results define the phenotypic features of T cells susceptible to HIV gp120-induced apoptosis and demonstrate that the same clonotype, depending on the activation state, may present a differential sensitivity to apoptosis induction.