CD4 ligands inhibit the formation of multifunctional transduction complexes involved in T cell activation

Ligands binding to the CD4 molecule can inhibit TCR-mediated T cell activation. We have previously reported that transcription factors regulating the expression of the IL-2 gene, NF-AT, NF-kappaB, and AP-1, are targets of this inhibitory effect in an in vitro model using peripheral human CD4+ T cells activated by a CD3 mAb. Two T cell activation pathways involved in the regulation of these transcription factors, calcium flux and the p21ras pathway, were investigated as potential targets. Binding of HIV envelope glycoprotein gp160/gp120 or a CD4 mAb to the CD4+ T cells, prior to TCR/CD3 activation, inhibited the intracellular calcium elevation. This event strongly suggested an inhibition of PLCgamma1 activity. Tyrosine phosphorylation of PLCgamma1, induced by CD3 activation, was not affected, but its association with tyrosine-phosphorylated proteins, including a 62-kDa protein, was disrupted. This PLCgamma1-associated p62 was found to be immunoreactive to p62-Sam68 Abs. The activation-induced phosphorylation of two p21ras effectors, Raf-1 and Erk2, was inhibited by the CD4 ligands, indirectly pointing to inhibition of the p21ras activation pathway. In addition, we demonstrate that TCR activation of normal CD4+ T cells induced the formation of p120GAP and PLCgamma1-containing complexes. These complexes also contain other unidentified proteins. CD4 ligand binding induced a defective formation of these transduction complexes. This may result in inefficient signaling, partially accounting for the inhibitory effects of the CD4 ligands on both p21ras and calcium-activation pathways.

HIV glycoprotein gp120 inhibits TCR-CD3-mediated activation of fyn and lck

HIV major glycoprotein gp120 interacts with CD4 molecules and perturbs signaling through the TCR-CD3 complex. We examined the effects of gp120 on TCR-CD3-induced phosphorylation and activation of the src-type protein tyrosine kinases (PTK), fyn and lck. gp120 caused minimal changes in lck phosphorylation or lck enzymatic activity, but preincubation of Jurkat cells with gp120 for 20 min strongly inhibited TCR-CD3-mediated phosphorylation and activation of lck and fyn, as well as phosphorylation of CD3 zeta. Inhibition of TCR-CD3 signaling in T cells preincubated with gp120 was paralleled by inhibition of T cell proliferation to the antigen tetanus toxoid. Neither surface CD4 expression nor CD4-lck association was affected by gp120. Furthermore, gp120 inhibited lck phosphorylation induced by cross-linking of TCR-CD3 and CD4 suggesting that the inhibition of lck phosphorylation could not be simply accounted for by sequestration of CD4 molecules. gp120 selectively enhanced the phosphorylation of the lck peptide containing the autoinhibitory tyrosine residue Tyr505 relative to the lck peptide containing the positive regulatory residue Tyr394, suggesting that a qualitative alteration in lck may underlie the inhibition of TCR-CD3 signaling by gp120.

Immunologic NO synthase: elevation in severe AIDS dementia and induction by HIV-1 gp41

Indirect mechanisms are implicated in the pathogenesis of the dementia associated with human immunodeficiency virus-type 1 (HIV-1) infection. Proinflammatory molecules such as tumor necrosis factor alpha and eicosanoids are elevated in the central nervous system of patients with HIV-1-related dementia. Nitric oxide (NO) is a potential mediator of neuronal injury, because cytokines may activate the immunologic (type II) isoform of NO synthase (iNOS). The levels of iNOS in severe HIV-1-associated dementia coincided with increased expression of the HIV-1 coat protein gp41. Furthermore, gp41 induced iNOS in primary cultures of mixed rat neuronal and glial cells and killed neurons through a NO-dependent mechanism. Thus, gp41-induced NO formation may contribute to the severe cognitive dysfunction associated with HIV-1 infection.

SPC3, a V3 loop-derived synthetic peptide inhibitor of HIV-1 infection, binds to cell surface glycosphingolipids

Synthetic multibranched peptides derived from the V3 domain of human immunodeficiency virus type 1 (HIV-1) gp120 inhibit HIV-1 entry into CD4+ and CD4- cells by two distinct mechanisms: competitive inhibition of HIV-1 binding to CD4-/GalCer+ colon cells and postbinding inhibition of HIV-1 fusion with CD4+ lymphocytes. In the present study, we have characterized the cellular binding sites for the V3 peptide SPC3, which possesses eight V3 consensus motifs GPGRAF radially branched on a neutral polyLys core matrix. These binding sites are glycosphingolipids that share a common structural determinant, i.e., a terminal galactose residue with a free hydroxyl group in position 4: GalCer/sulfatide on CD4-/GalCer+ colon cells; LacCer and its sialosyl derivatives GM3 and GD3 on CD4+ human lymphocytes. These data suggest that the V3 peptide binds to the GalCer/sulfatide receptor for HIV-1 gp120 on HT-29 cells and thus acts as a competitive inhibitor of virus binding to these CD4- cells, in full agreement with previously published virological data. In contrast, SPC3 does not bind to the CD4 receptor, in agreement with the data showing that the peptide inhibits HIV-1 infection of CD4+ cells by acting at a postattachment step. The binding of SPC3 to LacCer, GM3, and GD3, expressed by CD4+ lymphocytes, suggests a role for these glycosphingolipids in the fusion process between the viral envelope and the plasma membrane of CD4+ cells. Since the multivalent peptide can theoretically bind to several of these glycosphingolipids, we hypothesize that the resulting cross-linking of membrane components may affect the fluidity of the plasma membrane and/or membrane curvature, altering the virus-cell fusion mechanism.

Immunodominance of cytotoxic T lymphocyte epitopes co-injected in vivo and modulation by interleukin-12

Immunodominance (ID) of T cell epitopes is a well-documented phenomenon that might have profound significance in the evolution of T cell responses to pathogens, tumors, autoantigens and vaccines. With the intention of developing vaccines composed of several cytotoxic T cell (CTL) epitopes, we injected mice with peptide mixtures containing two to five CTL epitopes and observed clear patterns of ID. In a first case, ID strictly correlated with the competitor activity of the individual peptides for H-2Kd, whereas in a second case, the absence of correlation between ID and competitor activity, binding affinity, half-life of the peptides in serum, induction of proliferation in vitro and the individual immunogenicity of the peptides, suggested to us that ID of co-injected CTL epitopes can be determined both at the peptide level (binding affinity to H-2Kd) and at the T cell level. This hypothesis is supported by our finding that interleukin-12 strongly modulates ID when it is not correlated with MHC binding.

Evidence for cell-surface association between fusin and the CD4-gp120 complex in human cell lines

Accessory cell-surface molecules involved in the entry of human immunodeficiency virus-type 1 into cells have recently been identified and shown to belong to the family of chemokine receptors. Treatment of human cell lines with soluble monomeric gp120 at 37 degrees C induced an association between the surface CD4-gp120 complex and a 45-kilodalton protein, which can be down-modulated by the phorbol ester phorbol 12-myristate 13-acetate. The three proteins were coprecipitated from the cell membranes with antibodies to CD4 or to gp120. The 45-kilodalton protein comigrated with fusin on sodium dodecyl sulfate gels and reacted with rabbit antisera to fusin in protein immunoblots. No 45-kilodalton protein could be coprecipitated from similarly treated nonhuman cells. However, infection of 3T3.CD4.401 cells with vaccinia-fusin recombinant virus (vCBYF1), followed by gp120 treatment, resulted in coprecipitation of fusin and CD4.401 molecules from their membranes. Together these data provide evidence for physical association between fusin and the CD4-gp120 complex on cell membranes.

Antibody-producing effects in mice by synthetic immunoactive lipopeptides with the conjugated amino acid sequence of gp120 in human immunodeficiency virus

To induce peptide-specific antibodies in mice, as a model for vaccination against human immunodeficiency virus (HIV), lipopeptide analogs conjugated with three repeating units (KAB-112; designated as gp120-peptide) of a part (Gly-Pro-Gly-Arg-Ala-Phe) of the amino acid sequences of the V3 loop region in gp120 of HIV were synthesized. The mitogenicity, production of nitric oxide (NO) and induction of peptide-specific antibodies in mice by synthetic lipopeptides were examined. Compounds, KAB-8 (diacylglycerol-tetrapeptide having a part of the amino acid sequence in Escherichia coli), KAB-116 (diacylglycerol-cysteine), KAB-117 (diacylglycerol with gp120-peptide) and KAB-121 (KAB-8 with gp120-peptide) were capable of increasing significantly the incorporation of [3H]thymidine into splenocytes of C3H/He mice at concentrations ranging from 12.5 to 100 microM, but KAB-112 (gp120-peptide) and KAB-115 (monoacylglycerol with gp120-peptide) did not show such activity. The compounds, KAB-8, KAB-117 and 121, exhibited NO production in murine macrophages. When 50 nmol of these compounds was administered intraperitoneally into BALB/c mice on days 0, 16 and 46, the peptide-specific antibody titers in their sera produced by each compound were determined with ELISA. The sera of KAB-117 and KAB-121, which were obtained on days 14, 30, 42, 57 and 70, had a higher titer than that of KAB-112 and KAB-115, suggesting that the diacylglycerol derivative enhance the production of the peptide-specific antibodies.

Anti-HIV activity of multibranched peptide constructs derived either from the cleavage sequence or from the transmembrane domain (gp41) of the human immunodeficiency virus type 1 envelope

Multibranched peptides (SPCs) derived either from the fusion protein (gp41) sequence or from the cleavage sequence of the human immunodeficiency virus type 1 envelope were chemically synthesized and tested for their ability to inhibit both syncytium formation and HIV production in CD4+ cells. The gp41-derived SPCs had no effect. In contrast, an SPC encompassing the envelope cleavage sites strongly inhibited both HIV Env-induced syncytium formation and viral production.

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.

HIV-1 gp 120 blocks jacalin-induced proliferative response in CD4+ T cells: jacalin as a useful surrogate marker for qualitative and quantitative deficiency of CD4+ T cells in HIV-1 infection

Jacalin is a plant lectin that induces mitogenic responses selectively in CD4+ T lymphocytes and has been shown to block infection by the human immunodeficiency virus type 1 (HIV-1) in a T lymphoid cell line, but the relationship of jacalin to the HIV envelope glycoprotein gp 120 in its interaction with the CD4 molecule is unclear. Here we demonstrate that pretreatment of normal T cells with native HIV-1 gp 120 impairs their ability to proliferate and secrete IL-2 in response to jacalin. This effect was not observed with deglycosylated gp 120, which fails to bind to CD4 molecule, or with gp 120 that has been premixed with soluble CD4. Flow cytometric studies and Western blotting analysis indicated that gp 120 and jacalin compete with each other in binding to CD4 molecules. In HIV-infected patients, proliferative responses of PBMC in response to jacalin were found to correlate quantitatively with percentages of CD4+ T cells but also showed a qualitative defect in comparison to healthy volunteers based on responses that were correlated for CD4+ T cell numbers. These findings suggest that (i) gp 120 and jacalin compete with each other for CD4 binding and (ii) jacalin might be a useful surrogate marker for quantitative as well as qualitative deficiency of CD4+ T cells in HIV-1 infection.

The effects of the HIV-1 envelope protein gp120 on the production of nitric oxide and proinflammatory cytokines in mixed glial cell cultures

Although the neurotoxicity induced by the HIV envelope protein, gp120, has been demonstrated to require the presence of glial cells (microglia/astrocytes), the mechanisms for the gp120-induced neurotoxicity are not well understood. Moreover, the neurotoxic potencies of gp120s obtained from various HIV isolates are different. Since nitric oxide (NO) and proinflammatory cytokines (TNF-alpha, IL-1, IL-6) produced by glial cells have been involved in the neuropathogenesis of various diseases, this study examined the effects of gp120 obtained from two strains, HIV-1IIIB and HIV-1SF2, of the HIV-1 virus on the production of NO, TNF-alpha, IL-1 alpha, IL-1 beta, and IL-6 in murine primary mixed glial cell cultures. The glial cells exposed to HIV-1IIIB gp120 released NO, TNF-alpha, and IL-6 in a dose-dependent manner, whereas IL-1 alpha and IL-1 beta were undetectable. The cells exposed to HIV-1SF2 gp120 increased the release of IL-6 only. The gp120-induced effects were significantly enhanced by priming glial cells with IFN-gamma. To investigate the cellular sources and mechanisms of the gp120-induced IL-6 production, in situ hybridization with mRNA for IL-6 was performed in HIV-1IIIB gp120- or HIV-1SF2 gp120-stimulated microgliaenriched or astrocyte-enriched cultures. HIV-1IIIB gp120 or HIV-1SF2 gp120 induced the expression of IL-6 mRNA in both microglia-enriched and astrocyte-enriched cultures, indicating that both microglia and astrocytes produce IL-6, and that the transcriptional regulation is involved in the gp120-induced IL-6 production. Taken together, these results demonstrate that the production of NO, TNF-alpha, IL-1, or IL-6 from glial cells is differentially regulated by HIV-1IIIB gp120 and HIV-1SF2 gp120. These results may provide insights into the roles of NO and proinflammatory cytokines in the neurotoxicity of gp120s and the neuropathology of different strains of HIV-1 viruses.

Human immunodeficiency virus type 1 gp120 induces anergy in human peripheral blood lymphocytes by inducing interleukin-10 production

The effects of recombinant gp120 on the proliferative responses and cytokine production by normal peripheral blood mononuclear cells (PBMC) were investigated. gp120 inhibited in a dose-dependent fashion the anti-CD3 monoclonal antibody (MAb)- and concanavalin A-induced proliferative responses. The production of interleukin-2 (IL-2) and IL-4 was diminished by gp120 in the anti-CD3- and concanavalin A-stimulated cultures. In unstimulated PBMC, gp120 induced the production of considerable amounts of IL-10, gamma interferon, and tumor necrosis factor alpha. The gp120-induced reduction in the proliferative responses of PBMC was at least partially reversed by the addition of IL-2, anti-CD28 MAb, or transfectants expressing CD80, CD86, or CD40 but not with exogenous IL-4. Also, a neutralizing anti-IL-10 MAb reversed the inhibitory effect of gp120 on the proliferative responses whereas exogenous IL-10 further enhanced this inhibitory effect. These findings indicate that IL-10 plays an important role in the inhibitory effect of gp120 on PBMC proliferation. The ratio of CD3+CD4+ to CD3+CD8+ T cells was the same in gp120-treated and untreated cell cultures. No apoptosis in these two T-cell populations was observed. However, the number of activated CD3+CD4+ T cells and CD3+CD8+ T cells, as judged by CD25, CD69, and HLA-DR expression, was consistently reduced. gp120 induced the expression of IL-10 in the monocyte/macrophage population, and therefore gp120 also reduced the proliferative responses of CD4+ T-cell-depleted PBMC. Taken together, our observations point to the importance of the cytokine pattern changes and, in particular, the role of IL-10 (produced by the monocytes) in the inhibitory effect of gp120. This mechanism of gp120-induced immunosuppression, if operative in vivo, could contribute to the depressed immune responses associated with human immunodeficiency virus infection and thus have important implications for immunotherapeutic strategies to slow down disease progression in AIDS.

Antibody to native human immunodeficiency virus type 1 envelope glycoproteins induced by IIIB and MN recombinant gp120 vaccines. The NIAID AIDS Vaccine Evaluation Group

The ability of antibody induced by MN and IIIB recombinant gp120 (rgp120) human immunodeficiency virus type 1 (HIV-1) vaccines the bind to oligomeric native and monomeric recombinant HIV-1 envelope glycoproteins (rgp 120) was measured in 25 uninfected, healthy adult volunteers. A major focus was to evaluate the effect of simultaneous and sequential immunization with vaccines representing different strains of HIV-1 on the ability to broaden cross-reactivity of antibodies against these and other HIV-1 strains. A flow cytometric indirect immunofluorescence assay (FIFA) to detect vaccine-induced antibody to envelope glycoprotein expressed by infected and rgp120-coated target cells was used, MN rgp120 HIV-1 vaccine given alone and coadministered with IIIB rgp120 HIV-1 vaccine elicited antibody which bound to cells infected with HIV-1MN, HIV-IIIB, HIV-1RF, and HIV-1-SF2. The presence of envelope glycoprotein-binding antibody detected by FIFA correlated to a moderate degree with functional antibody against HIV-1MN and HIV-IIIB. Priming immunization with IIIB rgp120 HIV-1 vaccine followed by booster injections of MN rgp120 HIV-1 vaccine resulted in increased cross-reactive antibody binding to these and heterologous clade B HIV-1 strains infecting cells. MN rgp120 HIV-1 vaccine given alone was better able to induce cross-reactive antibody to cells infected with heterologous HIV-1 laboratory strains than was IIIB rgp120 HIV-1 vaccine given alone. The vaccines induced binding antibody to rgp120 possessing the amino acid sequence of a clade E HIV-1 strain as measured by enzyme-linked immunosorbent assay. Levels of antibody binding to cells infected with clade B HIV-1 and cells coated with monomeric rgp120 were greater than that induced by HIV-1IIIB-based gp160 vaccines in previous studies.

gp120-induced neurotoxicity in hippocampal pyramidal neuron cultures: protective action of TGF-beta1

We found that TGF-beta1, a cytokine that previously has been reported to have neuroprotective effects, was able to prevent the toxicity induced by the HIV-1 coat protein gp120 in hippocampal pyramidal neuron cultures. In the presence of glia, gp120 induced time- and dose-dependent cell death, which was more pronounced in mature (7-19 d in culture) than in young neurons (2-7 d in culture). Staining with nuclear dyes (propidium iodide and Hoechst 33342), in situ detection of DNA fragments, and DNA analysis on agarose gels indicated that apoptosis was mainly responsible for the death caused by the viral protein. However, after several days of treatment, death-displaying necrotic features also occurred. Neurotoxicity induced by gp120 was dependent on the activation of NMDA receptors and required the presence of glia as well as new protein synthesis. Thus, the effect of gp120 was abolished by the NMDA receptor antagonist APV and partially reduced by cycloheximide. Only modest neurotoxicity was observed in pure neuronal cultures deprived of the glia feeder layer. Fura-2-based videoimaging showed that treatment with gp120 enhanced the ability of NMDA to increase neuronal [Ca2+]i. The impairment of neuronal Ca2+ homeostasis was prevented completely by TGF-beta1. Therefore, it is likely that the neuroprotective action of the cytokine is attributable to its ability to stabilize neuronal [Ca2+]i.

Implication of sperm head agglutination induced by a V3 peptide (fragment 307-330, HIV-1 envelope protein gp120) solution

Human semen is the main vehicle for the transmission of human immunodeficiency virus (HIV); therefore, the interaction of HIV with the sperm is worthy of study. The motile sperm head fixation method was used as an in vitro model system to demonstrate the interaction of sperm with the peptide of HIV envelope protein. A micropipette loaded with semen was put into phosphate-buffered saline (PBS) containing V3 peptide (HIV-1IIIB envelope protein, fragment 307-330) or C2 peptide (HIV-1IIIB envelope protein, fragment 254-274). The V3 peptide caused a significant number of head-to-head binding sperm while the C2 peptide did not. This V3 peptide carries a high positive charge, which may overcome the electrostatic resistance on the cell to bring the sperm together. An HIV-CD4+ cell attachment inhibitor, dextran sulfate (DS, molecular weight about 5000), enhanced the sperm head agglutination induced by the V3 peptide. DS is presumed able to bind with specific sites near the V3 domain of gp120 to induce conformational change so as to prevent the binding of anti-V3 monoclonal antibodies or CD4+ cells to the V3 domain. This study suggests that DS interacts directly with the V3 peptide to enhance the sperm head agglutination.

Induction of interleukin-12 (IL-12) by recombinant glycoprotein gp120 of human immunodeficiency virus type 1 in human monocytes/macrophages: requirement of gamma interferon for IL-12 secretion

We studied the effects of the gp120 glycoprotein of human immunodeficiency virus type 1 on the expression of interleukin-12 (IL-12) in human monocytes and in monocyte-derived macrophages. Induction of the mRNA for both the p35 and p40 subunits of IL-12 was observed in both cell types after gp120 treatment. We then evaluated cytokine secretion by using an enzyme-linked immunosorbent assay which recognizes only the IL-12 heterodimer. No IL-12 was detected in monocytes/macrophages treated with gp120 alone. A consistent IL-12 secretion was found in macrophages primed with gamma interferon (IFN-gamma) and subsequently treated with gp120. Low levels of IL-12 were occasionally observed in IFN-gamma-primed monocytes stimulated with gp120. The greater response of macrophages than of monocytes to the priming effect of IFN-gamma was consistent with the finding that IFN-gamma induced a much stronger antiviral state to vesicular stomatitis virus in macrophages than in monocytes. These data indicate that gp120 is an inducer of IL-12 expression in monocytes/macrophages and that IFN-gamma is an essential cofactor for IL-12 secretion, especially in differentiated macrophages.

Human brain N-methyl-D-aspartate receptors regulating noradrenaline release are positively modulated by HIV-1 coat protein gp120

OBJECTIVE

To investigate the effect of HIV-1 gp120 on the function of glutamate receptors of the N-methyl-D-aspartate (NMDA) type in the human brain.

DESIGN

The monitoring of neurotransmitter release from superfused isolated nerve endings is widely recognized as a technique appropriate for the study of neurotransmitter release and to attribute a precise localization to the site(s) of action of drugs able to modulate release.

METHODS

Synaptosomes (pinched-off nerve endings) were prepared from fresh human brain tissue samples removed during neurosurgery, labelled with [3H]-noradrenaline and superfused at a rate of 0.5 ml/min with NMDA in the presence of gp41, gp160, gp120 or the V3 loop, with or without NMDA receptor antagonists. Fractions of superfusate were collected and measured for radioactivity.

RESULTS

NMDA elicited a glycine-sensitive release of [3H]-noradrenaline from human brain synaptosomes. HIV-1 gp120 potentiated the NMDA (1 mM)-evoked [3H]-noradrenaline release (maximal effect approximately 110% at 1 nM). The release elicited by NMDA plus gp120 was prevented by the classical NMDA receptor antagonists dizocilpine or 7-chlorokynurenic acid, as well as by memantine. The potentiation by gp120 of the NMDA-evoked [3H]-noradrenaline release was mimicked by gp160 but not by gp41. The effect of gp120 was retained by the V3 loop. Finally, gp120 reversed (1 nM) and surmounted (10nM) the antagonism by 10 microM 7-chlorokynurenate of the NMDA-evoked [3H]-noradrenaline release.

CONCLUSION

gp 120 binds directly through the V3 loop at noradrenergic axon terminals in human brain neocortex and may alter the function of presynaptic NMDA receptors mediating regulation of noradrenaline release.

HIV-1 envelope glycoprotein gp120 down-regulates CD4 expression in primary human macrophages through induction of endogenous tumour necrosis factor-alpha

Among immunological abnormalities present in human immunodeficiency virus type 1 (HIV-1)-infected individuals are dysregulation of cytokine production and CD4 down-regulation in both T-helper cells and monocytes/macrophages. The HIV-1 envelope glycoprotein 120 (gp120) has the ability to induce different cytokines in peripheral blood mononuclear cells and in monocytes/macrophages in vitro which in some instances have been reported to down-regulate macrophage CD4 expression. This study provides evidence that HIV-1 recombinant gp120 (rgp120) down-regulates both surface and total CD4 expression in primary tissue culture-differentiated macrophages (TCDM) at the level of transcription. The CD4 down-regulation observed in TCDM occurred between 6 and 12 hr after rgp120 treatment preceded by a peak of endogenous tumour necrosis factor-alpha (TNF-alpha) observed at 3-6 hr post-treatment. We demonstrate that the TCDM CD4 down-regulation observed after rgp120 treatment was inhibited by the use of an anti-huTNF-alpha monoclonal antibody (mAb), but not by mAb directed against other cytokines induced by rgp120, such as interleukin-1 beta (IL-1 beta) and interferon-alpha (IFN-alpha). The present findings roughly parallel those observed both in the sera of patients and in the monocytes/macrophages isolated from HIV-positive individuals, suggesting that gp120 by stimulating endogenous TNF-alpha production could be a good candidate for the CD4 down-regulation observed in the monocytes/macrophages of HIV-1-infected individuals. In contrast to CD4 down-regulation in HIV-infected lymphocytes, which results from a direct effect of viral genes on CD4 expression, soluble factors such as cytokines induced during HIV infection might explain the monocyte/macrophage CD4 dysregulation observed in acquired immune deficiency syndrome.

A combinatorial peptide library around variation of the human immunodeficiency virus (HIV-1) V3 domain leads to distinct T helper cell responses

The hypervariable domain of the HIV gp120, the V3 loop domain, represents a target for neutralizing antibodies and for HIV vaccine strategies. In this study, we have investigated in murine species the potential cross-reactivity of immune responses elicited by immunization either with individual V3 peptides, derived from distinct HIV sequences (BRU, RF, SF2, MN and ELI sequences), or with a V3 combinatorial peptide library. We observed that individual V3 peptides are immunogenic but elicit a specific B- and T-cell immune response that is mainly restricted to the sequence of the immunizing peptide. In particular, T-cell responses that depend on T-cell receptor recognition of peptides bound to the molecules encoded by the major histocompatibility complex were significantly influenced by small differences in the peptide amino acid sequence. The combinatorial V3 peptide library, previously described as B- and T-cell immunogens, induced a more broadly reactive immune response, specially when T-cell cytokine secretion was used as a readout for restimulation of T-cells with individual V3 peptides. These data suggest that amino acid variations in the sequence of an antigenic peptide could lead to the induction of different transducing signals in the primed T-cell population and to the activation of T-cells with distinct cytokine secretion properties. These observations may have implications in the understanding of antigenic variability and in the design of vaccine strategies.

Human immunodeficiency virus envelope glycoprotein 120 alters sleep and induces cytokine mRNA expression in rats [published errata appear in Am J Physiol 1996 Aug;271(2 Pt 2):section R following table of contents and 1996 Dec;271(6 Pt 3):section R following table of contents]

Sleep is altered during the course of viral infection, including that in which the human immunodeficiency virus (HIV) is the etiologic agent. Alterations in the sleep of HIV-infected individuals occur early in the course of infection, prior to the onset of AIDS. The mechanisms for such alterations in sleep are not known. The HIV envelope glycoprotein 120 (gp120) induces the synthesis and secretion of cytokines that enhance [e.g., interleukin (IL)-1 and tumor necrosis factor] and suppress (e.g., IL-10 and IL-1 receptor antagonist) sleep. We used a well-defined rat model to test the hypothesis that the HIV gp120 alters sleep. Recombinant HIV-1IIIB gp120 was injected intracerebroventricularly (20- 500 ng) into rats prior to dark onset. Sleep-wake behavior was not altered after the 20-ng dose, whereas both non-rapid eye movement sleep (NREMS) and rapid eye movement sleep (REMS) were initially enhanced and subsequently suppressed after the 100-ng dose. NREMS was enhanced for 8 h after the 500-ng dose; REMS was not affected by this dose. Brain temperature was not altered by any of the gp120 doses used in this study. In addition, mRNA expression for IL-1 beta and IL-10 was induced in the hypothalamus by gp120; this brain region is crucial for the regulation of sleep. These new data support the hypothesis that altered cytokine concentrations within the central nervous system play a pivotal role in the complex alterations in sleep observed during HIV infection.

In vivo trapping of nitric oxide in the brain of neonatal rats treated with the HIV-1 envelope protein gp 120: protective effects of alpha-phenyl-tert-butylnitrone

AIDS dementia complex is a neurological syndrome characterized by cognitive deficits and motor and behavioral dysfunction. The HIV-1 envelope glycoprotein gp 120 has been implicated in the development of AIDS dementia. This protein has been shown to be neurotoxic and to cause learning impairment and retardation of the development of complex motor behavior in rat neonates. Nitric oxide has been implicated in gp 120-induced neurotoxicity. In the present study, we report for the first time in vivo evidence for the formation of nitric oxide in the CNS as a result of multiple subcutaneous injections of gp 120 to neonatal rats. Nitric oxide was trapped in the brain of neonatal rats by N-methyl-D-glucamine dithiocarbamate-Fe and the nitric oxide content measured by electron paramagnetic resonance spectroscopy. The nitrone-based spin trap alpha-phenyl-tert-butylnitrone at 50 mg/kg was found to prevent gp 120-mediated nitric oxide formation and to also protect against gp 120-induced behavioral impairment.

Transduction signals induced in rat brain cortex astrocytes by the HIV-1 gp120 glycoprotein

Cultures of rat brain cortex astrocytes were exposed to 10(-10)-10(-9)M of the HIV-1 envelope glycoprotein, gp120. No specific binding was revealed by the iodinated protein, suggesting expression of only a few sites onto the cells. In contrast, two transduction signals were rapidly induced by gp120: increased tyrosine phosphorylation of a approximately 56 kDa protein and increased [Ca2+]i. This latter effect, present in 1/3 of the investigated astrocytes, consisted in: discrete or biphasic peaks; slowly rising plateaus; and various types of oscillations. Moreover, in apparently unresponsive cells [Ca2+]i rose slowly (45 min) to double the resting levels. Rat brain cortex astrocytes thus appear highly sensitive to gp120. The induced array of signals might contribute to neurotoxicity during HIV infection.

Toxicity of TNF alpha and platelet activating factor for human NT2N neurons: a tissue culture model for human immunodeficiency virus dementia

A significant proportion of HIV-1 infected individuals develop a symptom complex consisting of dementia and motor deficits termed HIV Dementia (HIVD) or the AIDS Dementia complex (ADC). The pathophysiology of this neurologic complication is unclear, but neuronal injury and death may occur as a direct result of the release of cytokines from HIV-1 infected microglial cells (Everall et al, 1991). To evaluate the utility of a human neuronal cell line, NT2N, for studies of HIV-related neuronal cytotoxicity, we studied cellular viability after exposure to HIV-1 gp120, tumor necrosis factor alpha (TFN alpha), platelet activating factor (PAF), interleukin 1 beta (IL-1 beta), and interferon gamma (IFN gamma), all of which have been implicated in previous publications as having a role in HIVD (Brenneman et al, 1988; Dreyer et al, 1990; Merrill et al, 1992; Gelbard et al, 1993). Neither gp 120 nor the cytokines IL-1 beta and IFN gamma resulted in significant NT2N cell death. However, TNF alpha and PAF were highly neurotoxic in this assay. Pentoxifylline, which inhibits the effects of TNF alpha, had a significant protective effect. This system provides an excellent substrate for the evaluation of neurotoxicity and for the development of pharmacologic agents that may be useful in HIV dementia.

Identification of complement activation sites in human immunodeficiency virus type-1 glycoprotein gp120

Recombinant glycoprotein 120 (rgp120) of human immunodeficiency virus type-1 (HIV-1) activates the human complement system in the absence of anti-gp120 antibodies. HIV-1 glycoprotein gp120 can dissociate from the viral envelope either spontaneously or after binding of HIV-1 to the CD4 molecule. As a consequence, gp120 can circulate in the patient's serum and attach to the surface of uninfected CD4+ T cells. Complement activation by cell-bound HIV-1 glycoprotein gp120 with subsequent opsonization may represent a mechanism for the elimination of uninfected CD4+ cells by the reticuloendothelial system, thereby enhancing the progression of HIV disease. In the current study, the complement proteins C4,C3,C5,C9, and properdin were found to bind to a synthetic peptide covering positions 233-251 of the gp120BRU sequence on incubation with normal human serum. Complement activation by the peptide was comparable with that induced by aggregated IgG, complete rgp120, and the previously described complement-activating gp41-peptide 609-623. Activation occurred via the classical pathway and was abrogated in the presence of EDTA, Mg2+/EGTA, or C4-deficient human serum. Peptides partly overlapping the sequence 233-251 activated complement to a lesser extent. The complement-activating capacity of the gp120 sequence 233-251 was not restricted to the HIV-1BRU isolate, because a peptide from the corresponding sequence of the HIV-1MN strain was also capable of activating complement. An additional strong complement-activating site was identified in the gp120 sequence 321-360 of the HIV-1MN strain. These data indicate that distinct sites in gp120 are able to activate human serum complement via the classical pathway in the absence of anti-gp120 and independent of glycosylation.