Effect of extracellular human immunodeficiency virus type 1 glycoprotein 120 on primary human vascular endothelial cell cultures

During the course of an HIV-1 infection, free infectious and noninfectious virus particles, and free HIV-1 proteins, circulate within the host, exposing the host endothelium to these viral factors, even if the endothelium is not infected. This suggests that extracellular HIV-1 proteins could influence endothelial cell function, leading to pathogenesis. In light of this, we have used primary cultured human vascular endothelial cells (HUVECs) to screen for effects of the HIV-1 protein gp120 on endothelial cell function. The results of this study show that short exposure of HUVEC cultures to this protein causes significant levels of cytotoxicity. Further, using several different assays, we have shown that this cytotoxic effect on HUVECs appears to be due to induction of an apoptotic program. The biphasic nature of gp120 titration curves suggests that multiple cellular factors are mediating these gp120-induced effects. Competition studies appear to confirm this by showing that the apoptotic effect is mediated through two cell surface receptors on HUVECs, CCR5 and CXCR4. Alternatively, competition studies examining CD4 receptors suggests that CD4 played no role in gp12O-induced effects on HUVECs.

Impaired thymopoietic potential of immature CD3(-)CD4(+)CD8(-) T cell precursors from SIV-infected rhesus monkeys

Immature thymocyte subpopulations were examined for their capacity to differentiate in a newly developed xenogeneic monkey-mouse fetal thymus organ culture (FTOC) system. We provide evidence for impaired precursor function of CD3(-)CD4(+)CD8(-) thymocytes after in vivo infection with SIVmac251 as indicated by a reduced cell number per FTOC and a lower percentage of thymocytes with more mature phenotypes. Addition of recombinant SIV glycoprotein 120 (rgp120) also resulted in a dose-dependent impairment of T cell maturation in FTOC. The data suggest that in patients infected with HIV, T cell maturation and thus replenishment of peripheral pools may be compromised as a result of intrathymic infection or circulating viral gp120.

Chemokine receptor expression and signaling in macaque and human fetal neurons and astrocytes: implications for the neuropathogenesis of AIDS

Chemokines are believed to play a role in the neuropathogenesis of AIDS through their recruitment of neurotoxin-secreting, virally infected leukocytes into the CNS. Levels of chemokines are elevated in brains of patients and macaques with HIV/SIV-induced encephalitis. The chemokine receptors CCR3, CCR5, and CXCR4 are found on subpopulations of neurons in the cortex of human and macaque brain. We have developed an in vitro system using both macaque and human fetal neurons and astrocytes to further investigate the roles of these receptors in neuronal response to inflammation. Here we report the presence of functional HIV/SIV coreceptors CCR3, CCR5, and CXCR4 on fetal human and macaque neurons and CCR5 and CXCR4 on astrocytes immediately ex vivo and after several weeks in culture. Confocal imaging of immunostained neurons demonstrated different patterns of distribution for these receptors, which may have functional implications. Chemokine receptors were shown to respond to their appropriate chemokine ligands with increases in intracellular calcium that, in the case of neurons, required predepolarization with KCl. These responses were blocked by neutralizing chemokine receptor in mAbs. Pretreatment of neural cells with pertussis toxin abolished responses to stromal-derived factor-1alpha, macrophage inflammatory protein-1beta, and RANTES, indicating coupling of CCR5 and CXCR4 to a Gialpha protein, as in leukocytes. Cultured macaque neurons demonstrated calcium flux response to treatment with recombinant SIVmac239 envelope protein, suggesting a mechanism by which viral envelope could affect neuronal function in SIV infection. The presence of functional chemokine receptors on neurons and astrocytes suggests that chemokines could serve to link inflammatory and neuronal responses.

Selective activity of various antiviral compounds against HHV-7 infection

Human herpesvirus virus type 7 (HHV-7) is a T-lymphotropic herpesvirus which uses the CD4 receptor as main receptor to infect its target cells. Measuring the decrease of CD4 expression during HHV-7 infection is a convenient and accurate method to monitor the efficacy of antiviral agents against HHV-7 infection. Different classes of compounds, such as heparin, pentosan polysulfate (PS), dextran sulfate (DS), aurintricarboxylic acid (ATA), phosphonoformic acid (PFA), 9-(2-phosphonylmethoxyethyl)adenine (PMEA), 2-amino-7-[(1,3-dihydroxy-2-propoxy) methyl] purine (S2242), polyvinylalcohol sulfate (PVAS) and the co-polymer of vinylalcohol sulfate with acrylic acid (PAVAS), acyclovir (ACV), ganciclovir (GCV), penciclovir (PCV), brivudin (BVDU), cidofovir (HPMPC), lobucavir, (R)-9-[4-hydroxy-2-(hydroxymethyl)butyl]guanine] (H2G), (R)-9-(2-phosphonylmethoxypropyl)adenine (PMPA) and sorivudine (BVaraU), were evaluated for their anti-HHV-7 activity in the SupT1 T cell line and in purified CD4+ T lymphocytes. Antiviral activity was monitored by inhibition of: (i) CD4 expression down-regulation; (ii) giant cell formation and (iii) apoptosis induction. In general, PS, DS, PVAS, PAVAS, ATA, PFA, PMEA, S2242, lobucavir and HPMPC had comparable anti-HHV-7 activity in the two cell lines, irrespective of the parameters followed to monitor antiviral activity. One of the exceptions was heparin which had an IC50 of 9.6 microg/ml in SupT1 cells and >250 microg/ml in CD4+ T lymphocytes. The compounds PCV, GCV, H2G and PMPA showed some activity in CD4+ T lymphocytes, but not in SupT1 cells. ACV, BVDU and BVaraU did not show activity in either cell system. None of the chemokines tested, such as platelet factor-4 (PF-4), eotaxin, stromal cell-derived factor 1alpha(SDF-1alpha) and RANTES, had detectable activity against HHV-7. In contrast, the HIV-1 envelope glycoprotein, gp120, and the two anti-CD4 mAbs, 13B8-2 and OKT4, were clearly active against HHV-7 infection.

Chemokines and activated macrophages in HIV gp120-induced neuronal apoptosis

HIV-1 glycoprotein gp120 induces injury and apoptosis in rodent and human neurons in vitro and in vivo and is therefore thought to contribute to HIV-associated dementia. In addition to CD4, different gp120 isolates bind to the alpha- or beta-chemokine receptors CXCR4 and CCR5, respectively. These and other chemokine receptors are on brain macrophages/microglia, astrocytes, and neurons. Thus, apoptosis could occur via direct interaction of gp120 with neurons, indirectly via stimulation of glia to release neurotoxic factors, or via both pathways. Here we show in rat cerebrocortical cultures that recapitulate the type and proportion of cells normally found in brain, i.e., neurons, astrocytes, and macrophages/microglia, that the beta-chemokines RANTES (regulated on activation, normal T cell expressed and secreted) and macrophage inflammatory protein (MIP-1beta) protect neurons from gp120SF2-induced apoptosis. The gp120SF2 isolate prefers binding to CXCR4 receptors, similar to the physiological alpha-chemokine ligands, stromal cell-derived factor (SDF)-1alpha/beta. SDF-1alpha/beta failed to prevent gp120SF2 neurotoxicity, and in fact also induced neuronal apoptosis. We could completely abrogate gp120SF2-induced neuronal apoptosis with the tripeptide TKP, which inhibits activation of macrophages/microglia. In contrast, TKP or depletion of macrophages/microglia did not prevent SDF-1 neurotoxicity. Inhibition of p38 mitogen-activated protein kinase ameliorated both gp120SF2- and SDF-1-induced neuronal apoptosis. Taken together, these results suggest that gp120SF2 and SDF-1 differ in the cell type on which they stimulate CXCR4 to induce neuronal apoptosis, but both ligands use the p38 mitogen-activated protein kinase pathway for death signaling. Moreover, gp120SF2-induced neuronal apoptosis depends predominantly on an indirect pathway via activation of chemokine receptors on macrophages/microglia, whereas SDF-1 may act directly on neurons or astrocytes.

Role of Na+/H+ exchangers, excitatory amino acid receptors and voltage-operated Ca2+ channels in human immunodeficiency virus type 1 gp120-mediated increases in intracellular Ca2+ in human neurons and astrocytes

Human immunodeficiency virus type 1 (HIV-1) dementia is the commonest form of dementia in North American people less than 60 years of age. HIV-1 envelope glycoprotein gp120 has been implicated in the neurotoxicity observed in, and the pathogenesis of, HIV-1 dementia. Recombinant gp120 (gp120) was pressure-applied on to cultured human fetal neurons and astrocytes and, by using single-cell calcium imaging, we determined the mechanisms responsible for gp120-induced increases in the levels of intracellular calcium ([Ca2+]i). Significant dose-related increases in [Ca2+]i were observed in neurons and astrocytes. In neurons, 5 pM gp120 increased [Ca2+]i by 290+/-13 nM and increases of 2210+/-211 nM were found at 209 nM, the highest concentration of gp120 tested. The apparent EC50 value for gp120 of 223+/-40 pM in neurons was not significantly different from that in astrocytes. Immunoelution of gp120 with polyclonal anti-gp120 and Ca2+-free conditions blocked increases in [Ca2+]i by gp120. Increases in [Ca2+]i were significantly (P < 0.005) attenuated by the Na+/H+ exchange blocker 5-(N-methyl-N-isobutyl)-amiloride in neurons and astrocytes. The L-type calcium channel blockers nimodipine, diltiazem and CdCl2 + NiCl2 significantly (P < 0.005) reduced increases in [Ca2+]i in neurons, but not astrocytes. Increases in [Ca2+]i by gp120 were not significantly affected by blockers of N-, P- and Q-type calcium channels. The N-methyl-D-aspartate receptor antagonists (+/-)-2-amino-5-phosphonopentanoic acid (AP5), memantine and dizocilpine significantly (P < 0.01) lowered gp120-induced increases in [Ca2+]i in neurons. AP5 and memantine, but not dizocilpine, significantly (P < 0.01) reduced increases in [Ca2+]i by gp120 in astrocytes. Gp120 appears to activate astrocyte Na+/H+ exchangers to release glutamate and potassium and, subsequent to this, increases in [Ca2+]i in neurons and astrocytes result from activation of excitatory amino acid receptors on astrocytes and neurons, and voltage-operated calcium channels on neurons. Drugs that block gp120-induced changes in [Ca2+]i in neurons and astrocytes may help in the treatment of HIV-1 dementia.

Glucocorticoid modulation of gp120-induced effects on calcium-dependent degenerative events in primary hippocampal and cortical cultures

The HIV coat protein gp120 has been implicated in damaging the nervous system and may play a role in AIDS-related dementia complex. The glycoprotein triggers the release of a glutamatergic agent from infected microglia and macrophages, causing NMDA receptor- and calcium-dependent excitotoxic damage to neurons. We have previously shown that glucocorticoids, the adrenal steroids secreted during stress, worsen gp120 neurotoxicity and calcium mobilization in various brain regions. This study explores events down-stream of gp120-induced calcium mobilization, specifically, generation of reactive oxygen species (ROS) and subsequent lipid peroxidation, destruction of the cytoskeleton through spectrin proteolysis, and the glucocorticoid modulation of these events in primary hippocampal cultures. We observe that 200 pM gp120 causes a significant accumulation of ROS, including superoxide, and of lipid peroxidation. Counter to our predictions, pretreatment with the glucocorticoid corticosterone (CORT) did not worsen the effects of gp120 on ROS accumulation, but did increase lipid peroxidation. We also observed that neither gp120 alone nor gp120 plus CORT caused detectable proteolysis of the cytoskeletal protein spectrin, whose breakdown has been shown to be a damaging consequence of calcium excess in other models of necrotic neuronal injury.

Inhibition of tyrosine kinase activation blocks the down-regulation of CXC chemokine receptor 4 by HIV-1 gp120 in CD4+ T cells

Because the binding of HIV-1 envelope to CD4 initiates a configurational change in glycoprotein 120 (gp120), enabling it to interact with fusion coreceptors, we investigated how this process interferes with the expression and function of CXC chemokine receptor 4 (CXCR4) in CD4+ T lymphocytes. A recombinant gp120 (MN), after preincubation with CD4+ T lymphocytes, significantly inhibited the binding and chemotaxis of the cells in response to the CXCR4 ligand stromal cell-derived factor-1alpha (SDF-1alpha), accompanied by a markedly reduced surface expression of CXCR4. gp120, but not SDF-1alpha, induced rapid tyrosine phosphorylation of src-like kinase p56lck in CD4+ T cells, whereas both gp120 and SDF-1alpha caused phosphorylation of the CXCR4. The tyrosine kinase inhibitor herbimycin A abolished the phosphorylation of p56lck and CXCR4 induced by gp120 in association with maintenance of normal expression of cell surface CXCR4 and a migratory response to SDF-1alpha. Thus, a CD4-associated signaling molecule(s) including p56lck is activated by gp120 and is required for the down-regulation of CXCR4.

Involvement of interleukin-1beta in the mechanism of human immunodeficiency virus type 1 (HIV-1) recombinant protein gp120-induced apoptosis in the neocortex of rat

The effect of subchronic intracerebroventricular injection of the human immunodeficiency virus type 1 (HIV-1) recombinant protein gp120 (100 ng, given daily for up to seven consecutive days) on interleukin-1beta expression was studied by immunohistochemistry in the brain of adult rats. In comparison to control, bovine serum albumin (300 ng, given intracerebroventricularly for up to seven days) -treated animals (n=6), interleukin-1beta immunoreactivity increased in the brain cortex and hippocampus of rats (n=6) receiving a single injection of the viral protein 24 h before analysis with more substantial increases being observed in these regions of the brain (n=6) after seven days treatment. Double-labelling immunofluorescence experiments support a neuronal and, possibly, a microglial cell origin for gp120-enhanced interleukin-1beta expression. Transmission electron microscopy analysis of brain tissue sections revealed that combination treatments (given intracerebroventricularly daily for seven days) with gp120 (100 ng) and interleukin-1 receptor antagonist (80 ng) or with the interleukin converting enzyme inhibitor II (100 pmol), but not with leupeptin (100 pmol), prevented apoptotic death of rat (n=6/group) brain cortical cells typically elicited by the viral protein. These data demonstrate that gp120 enhances interleukin-1beta expression in the brain and this may be involved in the mechanism underlying apoptosis induced by gp120 in the brain cortex of rat. Further support to this hypothesis comes from the evidence that intracerebroventricular injection of murine recombinant interleukin-1beta (200 U, given daily for seven consecutive days) produces DNA fragmentation in the brain cortex of rat (n=6). Interestingly, the latter treatment enhanced nerve growth factor level in the hippocampus but not in the cerebral cortex and this coincides with a similar effect recently reported in identical brain areas of rats treated likewise with gp120. In conclusion, the present data demonstrate that treatment with gp120 enhances interleukin-1beta expression and this participates in the mechanism of apoptotic cell death in the brain cortex of rat. By contrast, in the hippocampus, gp120-enhanced interleukin-1beta expression elevates nerve growth factor that may prevent or delay apoptosis in this plastic region of the rat brain.

Chronic systemic administration of tumor necrosis factor alpha and HIV gp120: effects on adult rodent brain and blood-brain barrier

Since tumor necrosis factor alpha (TNF-alpha) and HIV gpl20 glycoprotein are both neurotoxic, the possibility that systemic sources of these two agents mediate AIDS-associated blood-brain barrier (BBB) breakdown and brain damage was tested in two murine models: (1) intramuscular implantation of a TNF-alpha-transfected tumor in nu/nu mice and (2) daily subcutaneous injections of HIV gpl20 in BALB/c mice. The BBB remained intact; brain damage was not found, and apoptotic cell numbers did not increase. These results show that normal adult brain and BBB is unaffected by exposure to TNF-alpha or HIV gpl20 and suggest that severity of brain disease is not directly affected by systemic levels of these compounds.

V3 loop-derived peptide SPC3 inhibits infection of CD4- and galactosylceramide- cells by LAV-2/B

SPC3, a synthetic multibranched peptide including the GPGRAF consensus motif of the human immunodeficiency virus type 1 (HIV-1) gp120 V3-loop is a potent inhibitor of HIV infection of human CD4+ lymphocytes, macrophages and CD4-/galactosylceramide+ human colon epithelial cells and is currently tested in phase II clinical trials (FDA protocol 257 A). The antiviral property of SPC3 was further investigated for its ability to inhibit LAV-2/B, an HIV-2 clone with a CD4-independent tropism. SPC3 inhibited the LAV-2/B-mediated infection of B-cell line which does not express the CD4 and the galactosylceramide molecules on their cell surface, suggesting an SPC3-sensitive CD4/galactosylceramide-independent pathway of viral infection in HIV susceptible cells. The molecular mechanism of the peptide inhibition was also investigated. The data suggested that the SPC3-mediated inhibition does not result from a direct competition between SPC3 and gp120 binding to the cell surface of the target cell.

Comparison of immunity generated by nucleic acid-, MF59-, and ISCOM-formulated human immunodeficiency virus type 1 vaccines in Rhesus macaques: evidence for viral clearance

The kinetics of T-helper immune responses generated in 16 mature outbred rhesus monkeys (Macaca mulatta) within a 10-month period by three different human immunodeficiency virus type 1 (HIV-1) vaccine strategies were compared. Immune responses to monomeric recombinant gp120SF2 (rgp120) when the protein was expressed in vivo by DNA immunization or when it was delivered as a subunit protein vaccine formulated either with the MF59 adjuvant or by incorporation into immune-stimulating complexes (ISCOMs) were compared. Virus-neutralizing antibodies (NA) against HIV-1SF2 reached similar titers in the two rgp120SF2 protein-immunized groups, but the responses showed different kinetics, while NA were delayed and their levels were low in the DNA-immunized animals. Antigen-specific gamma interferon (IFN-gamma) T-helper (type 1-like) responses were detected in the DNA-immunized group, but only after the fourth immunization, and the rgp120/MF59 group generated both IFN-gamma and interleukin-4 (IL-4) (type 2-like) responses that appeared after the third immunization. In contrast, rgp120/ISCOM-immunized animals rapidly developed marked IL-2, IFN-gamma (type 1-like), and IL-4 responses that peaked after the second immunization. To determine which type of immune responses correlated with protection from infection, all animals were challenged intravenously with 50 50% infective doses of a rhesus cell-propagated, in vivo-titrated stock of a chimeric simian immunodeficiency virus-HIVSF13 construct. Protection was observed in the two groups receiving the rgp120 subunit vaccines. Half of the animals in the ISCOM group were completely protected from infection. In other subunit vaccinees there was evidence by multiple assays that virus detected at 2 weeks postchallenge was effectively cleared. Early induction of potent type 1- as well as type 2-like T-helper responses induced the most-effective immunity.

The V3 loop-mimicking pseudopeptide 5[Kpsi(CH2N)PR]-TASP inhibits HIV infection in primary macrophage cultures

The V3 loop-mimicking pseudopeptide 5[Kpsi(CH2N)PR]-TASP [psi(CH2N) representing a reduced peptide bond], which presents pentavalently the tripeptide Kpsi(CH2N)PR, is a potent inhibitor of HIV entry. By its capacity to bind specifically protein components on the cell surface, 5[Kpsi(CH2N)PR]-TASP blocks the attachment of virus particles to permissive CD4+ cells. Here, the inhibitory effect of 5[Kpsi(CH2N)PR]-TASP was investigated in monocyte-derived macrophages (MDMs) infected by the monocytotropic HIV-1(Ba-L) isolate. We show that 5[Kpsi(CH2N)PR]-TASP inhibits HIV-1(Ba-L) infection in a dose-dependent manner, with more than 90% inhibition at 2 microM concentration. On the other hand, the control 5[QPQ]-TASP construct and the monovalent Kpsi(CH2N)PR tripeptide have no effect even at high concentrations. Under such experimental conditions, the biotin-labeled 5[Kpsi(CH2N)PR]-TASP, but not the Kpsi(CH2N)PR construct, binds specifically to the surface of MDMs and forms a stable complex with the cell surface-expressed nucleolin, as has been demonstrated to be the case in peripheral blood mononuclear cells. Infection of MDMs by HIV-1(Ba-L) could also be inhibited by beta-chemokines RANTES and MIP-1beta. Interestingly, association of low concentrations of 5[Kpsi(CH2N)PR]-TASP and beta-chemokines results in a synergistic inhibitory effect on HIV infection compared with the effect observed with each reagent alone. The inhibitory effect of 5[Kpsi(CH2N)PR]-TASP in primary macrophage cultures point out its potential as an anti-HIV drug in cells, which are the natural viral targets.

Inhibitory effect of interleukin-16 on interleukin-2 production by CD4+ T cells

Signalling through CD4 by human immunodeficiency virus (HIV)-1 envelope glycoprotein (gpl20) and/or anti-CD4 antibodies can promote T-cell activation and anergy. Interleukin (IL)-16 is a competence growth factor for CD4+ T cells that can induce a G0 to G1 cell cycle transition but cannot induce cell division. The receptor of this cytokine is thought to be the CD4 molecule, although the binding epitope of IL-16 differs from that of HIV. We have demonstrated that both HIV-1/gp120 and IL-16 induced CD4+ T-cell dysfunction, as indicated by suppression of mitogen-induced IL-2 production. Two anti-CD4 antibodies with different binding sites on CD4 also showed an inhibitory effect on IL-2 production. These results indicate that promotion of CD4+ T-cell anergy via the CD4 molecule does not depend on the binding sites of the CD4 ligands.

Evidence for a synergistic effect of the HIV-1 envelope protein gp120 and brain-derived neurotrophic factor (BDNF) leading to enhanced expression of somatostatin neurons in aggregate cultures derived from the human fetal cortex

Changes in the expression of somatostatin (SRIF) have been observed in the brains of HIV encephalitis. Since gp120 is thought to play a major role in AIDS-associated abnormalities in the brain, we addressed the question: Does gp120 alter the functional expression of human fetal SRIF neurons in culture and if so, is this effect fetal-age dependent? Aggregate cultures, obtained from cortices of nine fetuses (14.9-20.7 weeks), were exposed for 7 days to BDNF or BDNF+gp120; BDNF induced production of SRIF during the subsequent 24-48 h was assessed. Similar effects of BDNF and gp120 were observed in the 9 brain-cultures. A 7-day exposure to BDNF alone led to a significant increase in SRIF production (p=0.014), whereas exposure to gp120 alone did not. Co-exposure to BDNF and gp120 led to an increase in BDNF-induced SRIF production which was significantly greater than that after BDNF alone (p=0.006). These effects were BDNF- and gp120-dose dependent and they were not accompanied by changes in DNA content of the aggregates nor in lactate dehydrogenase activity in the medium; indicating that gp120 did not lead to a major loss of cell integrity. These results are consistent with a synergistic effect of BDNF and gp120 leading to enhanced functional expression of the signalling pathway(s) mediating BDNF induction of SRIF production; an effect expressed by fetal brains throughout the 2nd trimester of gestation. Thus, this culture system can serve as a model to study the mechanism(s) underlying the early interactions between gp120 BDNF in the developing human brain.

HIV-1 gp120 induces the activation of both c-fos and c-jun immediate-early genes in HEL megakaryocytic cells

We have previously demonstrated that the addition in culture of recombinant HIV-1 IIIB envelope gp120 affects the survival/growth of pluripotent haemopoietic progenitors, and, in particular, of those committed towards the megakaryocytic lineage. To characterize some of the molecular mechanisms involved in this phenomenon, we investigated the expression of members of the activating protein-1 (AP-1) complex in the HEL megakaryoblastic cell line. Following the treatment of HEL cells with recombinant IIIB envelope gp120, we noticed: (i) increased levels of endogenous c-fos and c-jun mRNA and proteins, (ii) activation of both c-fos and c-jun promoters, and (iii) a very rapid stimulation of a MAPK/ERK pathway.

HIV-1 gp120 increases the permeability of rat brain endothelium cultures by a mechanism involving substance P

OBJECTIVE

To analyse whether an HIV-1 envelope protein might play a role in damaging the blood-brain barrier as a fundamental step in the early invasion of the central nervous system by HIV-1.

DESIGN

Analysis of permeability of rat brain endothelium cultures to albumin, to assess the functional integrity of the vascular component of the blood-brain barrier.

METHODS

Rat brain endothelium cultures prepared by cerebral microvessels were exposed to recombinant gp120IIIB on microporous membranes and passage of biotin-labelled albumin was analysed. Scanning electron microscopy was used to analyse cell culture morphology. Some cultures were preincubated with N-nitro-L-arginine methyl ester (L-NAME), a selective inhibitor of nitric oxide synthase, or with spantide, a selective substance P antagonist.

RESULTS

HIV-1 gp120 increased the permeability of rat brain endothelial cells to albumin in a dose-dependent manner. Scanning electron microscopy revealed profound gp120-induced alterations in cell morphology accounting for the increased permeability to macromolecules. These alterations were neutralized by anti-gp120 monoclonal antibody but not by isotype control antibody or L-NAME. By contrast, spantide and anti-substance P polyclonal antibody completely blocked the gp120-induced increase in albumin permeability. Control cultures exposed to measles virus nucleoprotein showed an increase in permeability that was not blocked by spantide. Brain endothelial cells, exposed to gp120, displayed cell surface immunoreactivity for substance P, suggesting that substance P is secreted by brain endothelium in response to gp120 stimulation and binds to brain endothelial cells through a receptor-mediated mechanism.

CONCLUSIONS

These findings suggest a role for substance P in the gp120-induced increase in permeability of brain endothelium.

Human immunodeficiency virus induction of corticotropin in lymphoid cells

Disruption of the linkage among the immune, nervous, and endocrine systems may contribute to the pathology and symptoms of acquired immunodeficiency syndrome (AIDS). We investigated the role of human immunodeficiency virus (HIV) in altering these linkages via induction of corticotropin (ACTH) by lymphocytes. Cultured T lymphocytes (H9 cell line) were infected with HIV-1, after which ACTH production was measured and characterized at various time intervals by immunofluorescence and Western blotting. We report a coordinate expression of ACTH and p24 HIV core protein in H9 cells. Also, the kinetics of HIV-induced ACTH production by H9 T lymphoma cells are demonstrated using three different strains of HIV as well as UV-inactivated HIV. ACTH production corresponded with the appearance of p24 antigen and was maximal 35 days after infection. UV-inactivated HIV and the viral envelope protein, gp120, were also able to induce ACTH production in these cells, indicating that viral replication was not required for the ACTH induction. The HIV-induced ACTH was synthesized de novo and had the size and biological activity of pituitary ACTH. Inhibition of ACTH in HIV-infected lymphocyte cultures by anti-ACTH antiserum enhanced viral p24 expression. The significance of lymphocyte ACTH in AIDS is not clear, but these results suggest that it may restrict HIV replication and possibly infection.

T-tropic human immunodeficiency virus type 1 (HIV-1)-derived V3 loop peptides directly bind to CXCR-4 and inhibit T-tropic HIV-1 infection

Certain types of chemokine receptors have been identified as coreceptors for HIV-1 infection. The process of viral entry is initiated by the interaction between an envelope protein gp120 of HIV-1, CD4, and one of the relevant coreceptors. To understand the precise mechanism of the Env-mediated fusion and entry of HIV-1, we examined whether the V3 region of gp120 of T-cell line tropic (T-tropic) virus directly interacts with the coreceptor, CXCR-4, by using five synthetic V3 peptides: two cyclized V3 peptides (V3-BH10 and V3-ELI) which correspond to the V3 regions of the T-tropic HIV-1 IIIB and HIV-1 ELI strains, respectively, a linear V3 peptide (CTR36) corresponding to that of HIV-1 IIIB strain; and cyclized V3 peptides corresponding to that of the macrophage-tropic (M-tropic) HIV-1 ADA strain (V3-ADA) or the dualtropic HIV-1 89.6 strain (V3-89. 6). FACScan analysis with a CXCR-4(+) human B-cell line, JY, showed that V3-BH10, V3-ELI, and V3-89.6 but not CTR36 or V3-ADA blocked the binding of IVR7, an anti-CXCR-4 monoclonal antibody (MAb), to CXCR-4 with different magnitudes in a dose-dependent manner, while none of the V3 peptides influenced binding of an anti-CD19 MAb at all. Next, the effects of the V3 peptides on SDF-1beta-induced transient increases in intracellular Ca2+ were investigated. Three V3 peptides (V3-BH10, V3-ELI, and V3-89.6) prevented Ca2+ mobilization. Furthermore, the three peptides inhibited infection by T-tropic HIV-1 in a dose-dependent manner as revealed by an MTT assay and a reverse transcriptase assay, while the other peptides had no effects. These results present direct evidence that the V3 loop of gp120 of T-tropic HIV-1 can interact with its coreceptor CXCR-4 independently of the V1/V2 regions of gp120 or cellular CD4.

HIV-1 envelope gp120 inhibits the monocyte response to chemokines through CD4 signal-dependent chemokine receptor down-regulation

Since HIV-1 infection results in severe immunosuppression, and the envelope protein gp120 has been reported to interact with some of the chemokine receptors on human T lymphocytes, we postulated that gp120 may also affect monocyte activation by a variety of chemokines. This study shows that human peripheral blood monocytes when preincubated with gp120 either purified from laboratory-adapted strains or as recombinant proteins exhibited markedly reduced binding, calcium mobilization, and chemotactic response to chemokines. The gp-120-pretreated monocytes also showed a decreased response to FMLP. This broad inhibition of monocyte activation by chemoattractants required interaction of gp120 with CD4, since the effect of gp120 was only observed in CD4+ monocytes and in HEK 293 cells only if cotransfected with both chemokine receptors and an intact CD4, but not a CD4 lacking its cytoplasmic domain. Anti-CD4 mAbs mimicked the effect of gp120, and both anti-CD4 Ab and gp120 caused internalization of CXCR4 in HEK 293 cells provided they also expressed CD4. Staurosporine blocked the inhibitory effect of gp120 on monocytes, suggesting that cellular signaling was required for gp120 to inhibit the response of CD4+ cells to chemoattractants. Our study demonstrates a broad suppressive effect of gp120 on monocyte activation by chemoattractants through the down-regulation of cell surface receptors. Thus, gp120 may be used by HIV-1 to disarm the monocyte response to inflammatory stimulation.

HIV/gp120 and PMA/ionomycin induced apoptosis but not activation induced cell death require PKC for Fas-L upregulation

HIV protein gp120 in combination with T cell antigen receptor (TCR) triggering induces apoptosis (gp120-apoptosis) in Th1 cells. Gp120-apoptosis occurs by induction of Fas-L and subsequent triggering of the Fas apoptotic pathway. Here, through the use of several compounds inhibiting induction of Fas-L, we show that, in a Th1 clone, a protein kinase C (PKC) independent pathway activated by TCR stimulation is distinguishible from a PKC dependent pathway activated by either phorbol 12-myristate 13-acetate (PMA)/ionomycin or asynchronous stimulation of TCR and CD4 as occurs in gp120-apoptosis.

Ligands of CD4 inhibit the association of phospholipase Cgamma1 with phosphoinositide 3 kinase in T cells: regulation of this association by the phosphoinositide 3 kinase activity

We have previously shown that CD4 ligands inhibit interleukin-2 (IL-2) production and T cell proliferation in human peripheral CD4+ T lymphocytes, in an MHC-independent way. Two major pathways implicated in T cell activation are inhibited by binding of CD4 ligands to the CD4 molecule, i.e. Ca2+ signaling by phospholipase Cgamma1 (PLCgamma1), and ERK-2 activation, suggesting a p21ras inhibition. We have correlated these inhibitions with the disruption of multifunctional complexes containing PLCgamma1, p120GAP and Sam68, induced by T cell activation. We report here that T cell activation through the TCR/CD3 induces an association of the phosphoinositide 3 kinase (PI3 kinase) with PLCgamma1, both in peripheral CD4+ T lymphocytes and the HUT-78 CD4+ T cell line. PI3 kinase is present in the multifunctional complexes that we have described previously. Preincubation of human peripheral CD4+ T cells and HUT-78 CD4+ T cells with gp160 or a peptide analogue of the HLA class II DR molecule precludes the association of PLCgamma1 with PI3 kinase. We also demonstrate, using two specific inhibitors of PI3 kinase activity (LY294002 and wortmannin), that this activity plays a key role in the association of PLCgamma1 with PI3 kinase. Moreover, we demonstrate the implication of the PI3 kinase activity in the negative signal mediated by HIV gp160 binding to CD4 molecules. We propose that the products of the PI3 kinase are important mediators of the negative signaling induced by the binding of CD4 ligands to the CD4 molecule implicated in the regulation of the formation of multifunctional complexes.

Properties of HIV envelope expressed in the presence of SPC3, an Env-derived peptide drug under phase II clinical trials

A multibranched peptide construct (SPC3) derived from the conserved sequence of the third variable domain (V3) of the human immunodeficiency virus (HIV) envelope (Env) inhibits HIV infectivity. It is being tested in phase II clinical trials (FDA protocol 257A). Because some Env-derived peptides inhibit HIV infectivity through alteration of Env biosynthetic pathway, we studied whether SPC3 displays its activity through interference with Env biosynthesis or with its functions at the membrane. Syncytium formation was impaired when human CD4+ cells expressed recombinant HIV Env in the presence of SPC3. This inhibition was not due to an effect of SPC3 on the amount of Env expressed at the cell membrane. As assessed using antibodies, the conformation of the receptor binding site and of V3 presented on membrane Env was not affected by the presence of SPC3 during biosynthesis. Finally, despite the ability of SPC3 to bind to CD4+ cell membrane, SPC3 did not interfere with Env binding to CD4. These data suggest that SPC3 interferes with the infection process at a post-CD4 binding step, and not with the folding of Env.

lck-independent inhibition of T cell antigen response by the HIV gp120

Binding of the HIV envelope glycoprotein gp120 to CD4 inhibits T cell activation. We have used a murine T cell clone transfected with either wild-type human CD4 or mutated forms of CD4 to characterize the pathways involved in this inhibitory effect of gp120. Ag-induced proliferation of T cell clones transfected with human CD4 was completely inhibited in the presence of gp120, even though stimulation of this clone is independent of a CD4/MHC class II interaction. In addition, our results demonstrate that the inhibition by gp120 is not due to the sequestration of lck from TCR and does not require activation of lck by gp120. This suggests that CD4 can regulate the initiation of T cell activation independently of its interaction with lck. Moreover, we demonstrate that the nonresponsiveness induced by gp120 can be reversed by soluble CD4 when added early after onset of stimulation and that gp120 exerts its inhibitory effect when cells are in the G0 > or = 1 phase of the cell cycle.

Elevated levels of serum-soluble CD14 in human immunodeficiency virus type 1 (HIV-1) infection: correlation to disease progression and clinical events

Soluble (s) CD14, a marker for monocyte/macrophage activation and a mediator of bacterial lipopolysaccharide (LPS) action, was elevated in serum from human immunodeficiency virus type 1 (HIV- 1)-infected individuals (n = 92) compared with seronegative controls. The highest levels were found in patients with advanced clinical and immunological disease. Patients with ongoing clinical events had significantly higher sCD14 levels than symptomatic HIV-1-infected individuals without clinical events, with especially elevated levels in patients infected with Mycobacterium avium complex (MAC). On longitudinal testing of patients (n = 26) with less than 100 x 10(6) CD4 lymphocytes/L at baseline, we found that increasing sCD14 serum concentrations per time unit were associated with death, whereas no differences in CD4 cell number decrease were found between survivors and nonsurvivors. In vitro studies showed that HIV-1 glycoprotein 120 and purified protein derivative (PPD) from M avium (MAC-PPD) stimulated normal monocytes to release sCD14. Furthermore, MAC-PPD induced tumor necrosis factor (TNF) release from monocytes through interactions with CD14 and, importantly, the addition of sCD14 enhanced this MAC-PPD stimulatory effect. Our findings suggest that the CD14 molecule may be involved in the immunopathogenesis of HIV-1 infection, and it is conceivable that serial determination of sCD14 may give useful predictive information concerning disease progression and survival in HIV-1-infected patients.