gp120 is present on the plasma membrane of apoptotic CD4 cells prepared from lymph nodes of HIV-1-infected individuals: an immunoelectron microscopic study

Temsavir blocks the immunomodulatory activities of HIV-1 soluble gp120

While HIV-1-mediated CD4 downregulation protects infected cells from antibody-dependent cellular cytotoxicity (ADCC), shed gp120 binds to CD4 on uninfected bystander CD4+ T cells, sensitizing them to ADCC mediated by HIV+ plasma. Soluble gp120-CD4 interaction on multiple immune cells also triggers a cytokine burst. The small molecule temsavir acts as an HIV-1 attachment inhibitor by preventing envelope glycoprotein (Env)-CD4 interaction and alters the overall antigenicity of Env by affecting its processing and glycosylation. Here we show that temsavir also blocks the immunomodulatory activities of shed gp120. Temsavir prevents shed gp120 from interacting with uninfected bystander CD4+ cells, protecting them from ADCC responses and preventing a cytokine burst. Mechanistically, this depends on temsavir's capacity to prevent soluble gp120-CD4 interaction, to reduce gp120 shedding, and to alter gp120 antigenicity. This suggests that the clinical benefits provided by temsavir could extend beyond blocking viral entry.

Temporary Migration and the Spread of STDs/HIV in China: Is There a Link?

Using data from the literature and a specially designed community-level survey, this article examines the link between temporary migration and the spread of HIV/STDs in China. The results suggest that temporary migrants not only are overrepresented among people with STD/HIV risk-taking behaviors, but also account for disproportionately more STD patients and persons infected with HIV. It is imperative that STD and AIDS prevention intervention and education programs in China target temporary migrants. More research is needed that focuses on the underlying mechanisms by which the process of temporary migration renders migrants vulnerable to STD/HIV risk-taking behaviors.

Induction of apoptosis in MCF-7 cells by the hemagglutinin-neuraminidase glycoprotein of Newcastle disease virus Malaysian strain AF2240

Newcastle disease virus (NDV) exerts its naturally occurring oncolysis possibly through the induction of apoptosis. We hypothesized that the binding of the virus to the cell via the hemagglutinin-neuraminidase (HN) glycoprotein may be sufficient to not only induce apoptosis but to induce a higher apoptosis level than the parental NDV AF2240 virus. NDV AF2240 induction of apoptosis in MCF-7 human breast cancer cells was analyzed and quantified. In addition, the complete HN gene of NDV strain AF2240 was amplified, sequenced and cloned into the pDisplay eukaryotic expression vector. HN gene expression was first detected at the cell surface membrane of the transfected MCF-7 cells. HN induction of apoptosis in transfected MCF-7 cells was analyzed and quantified. The expression of the HN gene alone was able to induce apoptosis in MCF-7 cells but it was a less potent apoptosis inducer compared to the parental NDV AF2240 strain. In conclusion, the NDV AF2240 strain is a more suitable antitumor candidate agent than its recombinant HN gene unless the latter is further improved by additional modifications.

Critical roles for Akt kinase in controlling HIV envelope-mediated depletion of CD4 T cells

BACKGROUND

The cell surface receptors CD4 and CCR5 bind CCR5-tropic HIV Envelope (Env) glycoprotein during virus attachment. These same receptors have signaling activities related to normal immune cell functions. We also know that Env binds to CCR5 present at high levels on CD4-negative γδ T cells where it signals through p38 MAP kinase to activate caspases and Fas-independent cell death. Here, we asked whether Env signaling through cellular receptors is responsible for death among uninfected CD4+/CCR5+ T cells and what are the effects of Env on CD4+/CCR5-negative cells that might impact HIV infection. The outcomes of Env binding are analyzed in terms of signal transduction and the effects on cell activation or cell death pathways.

RESULTS

Env binding to CD4 signals through Erk and Akt kinases. Activation of Erk/Akt suppresses p38 due to CCR5 binding, and allows cell survival. When CD4 signaling was blocked by soluble CD4 or protein kinase inhibitors, p38 activation and Fas-independent cell death were increased among uninfected CD4+ CCR5+ T cells. We also noted specific effects of CD4 signaling on CCR5-negative CD4 T cells in tonsil lymphocyte cultures. Exposure to CCR5-tropic HIV Env (BaL strain) increased expression of CXCR5, PD-1, Fas and FasL. Among CD4+/CCR5- T cells expressing high levels of CXCR5 and PD-1, there were substantial amounts of Fas-dependent cell death. Increased CXCR5 and PD-1 expression was blocked by soluble CD4 or specific inhibitors of the Akt kinase, showing a direct relationship between CD4 signaling, T cell activation and Fas-dependent cell death.

CONCLUSIONS

Specific inhibition of Akt activation increased Env-dependent cell death of CCR5+ CD4 T cells. The same inhibitor, antibodies blocking the CD4 binding site on gp120, or soluble CD4 also prevented the increase in expression of CXCR5 or PD-1, and reduced the levels of Fas-dependent cell death. The Akt kinase and related signaling events, are key to cell survival that is needed for productive infection, and may be targets for the development of antivirals. Specific inhibitors of Akt would decrease productive infection, by favoring cell death during virus attachment to CD4+ CCR5+ target cells, and reduce immune activation to prevent Fas-dependent death of uninfected CXCR5+ PD-1+ CD4 T cells including T follicular helper cells that share this phenotype.

Mechanisms of HIV envelope-induced T lymphocyte apoptosis

Infection by the human immunodeficiency virus (HIV) is characterized by a progressive depletion of CD4 T lymphocytes, which leads to dysfunction of the immune system. Although a variety of mechanisms may contribute to the gradual T cell decline that occurs in HIV-infected patients, abnormal apoptosis of infected or bystander T lymphocytes is an important event leading to immunodeficiency. The HIV envelope glycoprotein plays a crucial role in HIV associated apoptosis through both death receptor-mediated and mitochondria-dependent pathways. This review summarizes current knowledge of Env-mediated T lymphocyte apoptosis.

Ethnicity and risk factors in needle sharing among intravenous drug users in Sichuan Province, China

Combining survey and ethnographic data, this research examined differences in the risk factors associated with needle sharing amongst intravenous drug users (IDUs) in the Sichuan Province of China. A comparison was made between the province's majority Han population and its Yi minority. We developed a theoretical framework consisting of risk factors at the individual level (including risk factors such as lack of AIDS knowledge, low self-efficacy, and economic pressure), interpersonal level (having an IDU primary partner and lack of family support), and community level (social discrimination). The findings suggested that the Yi minority group was more socially disadvantaged and had a higher risk of contracting HIV than the Han group. Furthermore, the factors that put them at risk were different to those which affected the Han group. OLS regression results showed that, for Han IDUs, needle sharing was positively associated with having an IDU primary partner and with economic pressure. On the other hand, for the minority group, needle sharing was significantly associated with being male, AIDS knowledge, the lack of family support, and social discrimination. These findings highlight the need for HIV prevention work to target marginalized populations in China, such as ethnic minorities, and to tailor appropriate prevention strategies to meet the specific needs of different groups.

A pilot study of the NGO-based relational intervention model for HIV prevention among drug users in China

The rapid growth of the HIV epidemic in China has raised a number of concerns among health care providers, governmental agencies, and nongovernmental organizations (NGOs). This article (a) briefly discusses the HIV epidemic in China, (b) explains why Chinese NGOs need to join the fight against the epidemic, (c) describes the development of an indigenous culture-based model for use by NGOs to prevent HIV among injection drug users, and (d) discusses a Chinese NGO's experience in piloting the model. Data from the pilot study indicate that the model was successful in increasing knowledge about HIV/AIDS, increasing condom use, and decreasing needle and syringe sharing among a sample of female injection drug users (n = 100). The results of this study could have potential for other NGOs that are interested in adopting and adapting this model for HIV prevention.

Knowledge, attitudes, behaviors, and perceptions of risk related to HIV/AIDS among Chinese university students in Hunan, China

The purpose of this paper is to describe HIV/AIDS knowledge, attitudes, and perceptions and identify personal risk behaviors among undergraduate students in China. A descriptive, cross-sectional survey of 1326 students between ages 17 through 28 was conducted in 2002. Results indicated that students held considerable misconceptions about HIV transmission by casual contact and needle sharing as well as stigmatizing attitudes about injection drug use, homosexuality and HIV-positive women who bear children. Results indicated that 14% of Chinese university students are sexually active and risk behaviors tended to increase with age. Additionally, 24% of the students considered themselves to be at moderate to very high risk of contracting HIV and 40% of sexually active students never used condoms. Therefore, it is important to design HIV prevention strategies that target university students in China.

Apoptosis of uninfected cells induced by HIV envelope glycoproteins

Apoptosis, or programmed cell death, is a key event in biologic homeostasis but is also involved in the pathogenesis of many human diseases including human immunodeficiency virus (HIV) infection. Although multiple mechanisms contribute to the gradual T cell decline that occurs in HIV-infected patients, programmed cell death of uninfected bystander T lymphocytes, including CD4+ and CD8+ T cells, is an important event leading to immunodeficiency. The HIV envelope glycoproteins (Env) play a crucial role in transducing this apoptotic signal after binding to its receptors, the CD4 molecule and a coreceptor, essentially CCR5 and CXCR4. Depending on Env presentation, the receptor involved and the complexity of target cell contact, apoptosis induction is related to death receptor and/or mitochondria-dependent pathways. This review summarizes current knowledge of Env-mediated cell death leading to T cell depletion and clinical complications and covers the sometimes conflicting studies that address the possible mechanisms of T cell death.

Afghanistan: HIV/AIDS Vulnerability and Prevention

Afghanistan is beginning to rebuild itselffollowing over 20years of war and civil strife. In post- conflict and humanitarian situations, HIV prevention is frequently overlooked because of other priorities. Yet it is exactly in such circumstances that HIV/AIDS thrives, as experienced by other war-affected countries such as Cambodia and Myanmar. Until reliable data on STI and HIV become available, immediate interventions are required to avert possible HIV transmission among vulnerable populations, induding refugees, drug users, uniformed personnel and their families. In responding to the global HIV epidemic, all countries have faced a decision between early and late intervention to reduce the impiact on society, communities and individuals. Delayed response is mostly associated with greater adverse impact at different levels, including higher HIV/AIDS- related costs, while early intervention has the potential to maintain HIV prevalence at low levels. Afghanistan still benefits from a window of opportunity for embarking on an early HIV prevention strategy for averting the rapid increase of HIV prevalence among vulnerable populations as experienced in neighbouring countries in Asia.

The role of the CD4 receptor versus HIV coreceptors in envelope-mediated apoptosis in peripheral blood mononuclear cells

We examined the role of CD4, CXCR4, and CCR5 in HIV envelope-mediated apoptosis by measuring the response of activated PBMCs to recombinant envelope proteins derived from CXCR4- and CCR5-utilizing viruses. Apoptosis of T cells was assessed by annexin-V staining and TdT-mediated dUTP-biotin nick-end labeling. Treatment of CCR5Delta32 homozygote PBMCs with a CCR5-specific envelope induced apoptosis in T cells, demonstrating that envelope--CD4 interactions are sufficient to induce apoptosis. However, a CXCR4-specific envelope induced higher levels of apoptosis than a CCR5-specific envelope, suggesting that envelope-mediated apoptosis can be enhanced by envelope--CXCR4 interactions. We conclude that envelope can induce apoptosis in T cells independently of the coreceptor specificity of a given envelope, or the expression profile of CXCR4 or CCR5 on a target cell. However, envelope--coreceptor interactions, and in particular, envelope--CXCR4 interactions, can contribute to this process.

Apoptotic effects in primary human umbilical vein endothelial cell cultures caused by exposure to virion-associated and cell membrane-associated HIV-1 gp120

During the course of HIV-1 infection, free virus, infected cells, and free HIV-1 proteins circulate within the host, exposing the host endothelium to these viral factors. We have previously presented evidence showing that soluble HIV-1 gp120 protein interacts with chemokine receptors on primary human endothelium and (through those interactions) induces apoptosis as well as other intracellular effects. The current study examines the effect of exposure of vascular endothelium to gp120 IIIb expressed on the surface of Jurkat cells and in the context of viral particles. Apoptosis was observed in human umbilical vein endothelial cell (HUVEC) cultures exposed to gp160-transfected Jurkat cells as well as to virion particles with gp120 on their surface. Additional experiments show that this apoptotic effect was caused by gp120 protein acting through chemokine receptors on the HUVEC surface, primarily the CXCR4 receptor. At higher concentrations of gp120, this lymphotrophic variant, which has been shown to interact predominantly with CXCR4, seems to interact with and induce apoptosis through the CCR5 receptor. Finally, this apoptotic effect in HUVEC cultures occurs at low levels of the inducing agent, gp120, on cell membranes or on virion particles. These results demonstrate that HIV-1 gp120 is capable of interacting with and killing vascular endothelial cells in multiple in vivo contexts.

HIV envelope proteins differentially utilize CXCR4 and CCR5 coreceptors for induction of apoptosis

The involvement of CXCR4 and CCR5 coreceptors in apoptosis induced by the HIV envelope (Env) proteins has not been well defined. We found that simian human immunodeficiency virus (SHIV) virus-like particles (VLPs) containing HIV Env proteins preferentially induce apoptosis of cells corresponding to their coreceptor usage in a CD4+ T cell line. We also demonstrated that induction of apoptosis by SHIV VLPs is correlated with coreceptor usage in a non-T cell line. We examined the effects of SHIV VLPs containing Env proteins derived from either a T-cell-tropic HIV (BH10) strain or a dual-tropic HIV (89.6) strain on induction of apoptosis in recombinant CD4+ human osteosarcoma (HOS) cells expressing either CXCR4 (HOS-CD4.CXCR4) or CCR5 coreceptors (HOS-CD4.CCR5). HOS-CD4.CXCR4 or HOS-CD4.CCR5 cells were activated with concanavalin A and cocultured with VLPs. By TUNEL (TdT-mediated dUTP-X nick end labeling) fluorescence staining and flow cytometry assays, SHIV BH10 VLPs were found to preferentially induce apoptosis in HOS-CD4.CXCR4 cells but not in HOS-CD4 or HOS-CD4.CCR5 cells. On the other hand, SHIV 89.6 VLPs induced an elevated level of apoptosis in both HOS-CD4.CXCR4 and HOS-CD4.CCR5 cells in a dose-dependent fashion. These data demonstrate that T-cell-tropic BH10 Env preferentially utilizes CXCR4, but not CCR5, for induction of apoptosis, whereas dual-tropic 89.6 Env induces apoptosis in both CXCR4- and CCR5-containing cell lines.

Chemokine-receptor activation by env determines the mechanism of death in HIV-infected and uninfected T lymphocytes

There is considerable confusion concerning the mechanism of lymphocyte death during HIV infection. During the course of HIV infection, M-tropic viruses (R5) that use CCR5 chemokine coreceptors frequently evolve to T-tropic viruses (X4) that use CXCR4 receptors. In this study we show that activation of the CD4 or CCR5 receptor by R5 HIVenv causes a caspase 8-dependent death of both uninfected and infected CD4 T cells. In contrast, CXCR4 activation by X4 HIVenv induces a caspase-independent death of both uninfected CD4 and CD8 T cells and infected CD4 cells. These results suggest that activation of the chemokine receptor by HIVenv determines the mechanism of death for both infected and uninfected T lymphocytes.

Reawakening the dragon: changing patterns of opiate use in Asia, with particular emphasis on China's Yunnan province

Asian countries adjacent to the Golden Triangle and their neighbors have witnessed an evolution in "drug abuse" from traditional opium smoking to heroin eating, smoking, and finally heroin injection. A recent study of 630 heroin users was conducted in China's Yunnan Province, located close to the Golden Triangle. Data collected between August 1997 and February 1998 indicate injecting heroin users, in comparison to noninjectors, were more likely to have used drugs for a longer period of time, and to use drugs more frequently everyday. Other major differences existed between urban and rural subjects, especially highlighting differences between men and women. Women comprised a much higher proportion of urban subjects than rural subjects. Rural injectors were much more likely to be male, but urban injectors were almost evenly split between men and women. The emerging epidemic of heroin use in China and the continuing substance abuse problem in the United States provide an opportunity for collaborative research of mutual benefit.

Involvement of protein kinase C in HIV-1 gp120-induced apoptosis in primary endothelium

We previously showed that HIV-1 gp120-induced apoptosis in primary human umbilical vein endothelial cell cultures (HUVEC), through CCR5 and CXCR4. Here, we have found that agonists of protein kinase C (PKC), basic fibroblast growth factor (bFGF), and short exposure to low concentrations of phorbol esters were found to block gp120-induced apoptosis in HUVEC cultures. PKC antagonists, sphingosine, H7, and extended exposure of cultures to high concentrations of phorbol esters were also found to block gp120-induced apoptosis in HUVEC cultures. A significant increase in the total amount of cellular PKC enzymatic activity was observed on exposure of HUVEC to gp120. No increase in total PKC activity was observed on exposure of HUVECs to the natural ligands SDF-1alpha, or regulated-on-activation normal T-expressed and secreted (RANTES) cells, and gp120-induced PKC induction was found to be totally blocked by CXCR4 antibodies and partially blocked by the caspase 3 inhibitor, DEVD-CHO. Alternatively, CXCR4 antibodies and DEVD-CHO totally blocked apoptosis. Finally, gp120-induced effects were found to be insensitive to pertussis toxin. Accumulated evidence suggests PKC involvement at multiple points in the gp120-induced apoptotic pathway; also suggests involvement of the CXCR4 receptor internalization pathway, and potentially suggests different downstream effects of gp120-receptor interactions and natural ligand-receptor interactions.

HIV-1 envelope induces activation of caspase-3 and cleavage of focal adhesion kinase in primary human CD4(+) T cells

Binding of HIV type 1 (HIV-1) envelope glycoproteins to the surface of a CD4(+) T cell transduces intracellular signals through the primary envelope receptor, CD4, and a coreceptor, either CCR5 or CXCR4. Furthermore, envelope-CD4(+) cell interactions increase rates of apoptosis in peripheral blood mononuclear cells (PBMCs). We demonstrate that in primary T lymphocytes, recombinant HIV-1 envelope proteins induce the activation of caspase-3 and caspase-6, which belong to a family of cysteine proteases that, upon activation, promote programmed cell death. Envelope-mediated activation of caspase-3 and caspase-6 depended on envelope-CD4 receptor interactions; CCR5-utilizing as well as CXCR4-utilizing envelopes elicited this response. Focal adhesion kinase (FAK) is a substrate of both caspase-3 and caspase-6, and inactivation of FAK by these caspases promotes apoptosis. En-velope treatment of lymphocytes led to the cleavage of FAK in a manner consistent with caspase-mediated cleavage.

Highly active anti-retroviral therapy (HAART) is associated with a lower level of CD4+ T cell apoptosis in HIV-infected patients

HAART may increase CD4+ T cell counts despite a persistently detectable HIV load. The impact of HAART on apoptosis, which may play a role in the disease process in HIV-infected patients, has not been extensively studied. We performed a study to compare the level of spontaneous T cell apoptosis and anti-retroviral treatments in a cohort of HIV-1-infected patients. Data were obtained from a computerized medical record. Quantification of apoptotic cells was by cytofluorometric technique. From November 1995 to December 1997 we studied T cell apoptosis in 112 HIV-infected patients. Forty patients were classified A, 36 B and 36 C. Thirty patients were naive and 82 received an anti-retroviral treatment, 49 including a protease inhibitor (PI). The median plasma viraemia determined in 63 patients was 3.6 (range 1.3-5.6) log10. The median apoptotic cell count was 22% (range 2-73%) and 12% (range 2-60%) for CD4+ and CD8+ T cells, respectively. We did not observe any correlation between the HIV viraemia and the level of apoptosis of T cell subsets. Patients with HAART showed a lower percentage of apoptotic CD4+ T cells only: 16% (range 2-61%) versus 25% (range 5-73%) for patients receiving two nucleoside analogues (P = 0.02). This effect was significant in stage A patients and remained observable during the whole course of HIV disease. In conclusion, HAART, without any relation to plasma viraemia, is able to reduce apoptosis of CD4+ T cells.

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.

Induction of Phosphorylation and Intracellular Association of CC Chemokine Receptor 5 and Focal Adhesion Kinase in Primary Human CD4+ T Cells by Macrophage-Tropic HIV Envelope

Binding of HIV-1 envelope glycoproteins to the surface of a CD4+ cell transduces intracellular signals through the primary envelope receptor, CD4, and/or the envelope coreceptor, a seven-transmembrane chemokine receptor. Macrophage-tropic strains of HIV-1 preferentially use CCR5 as an entry coreceptor, whereas T cell-tropic strains use CXC chemokine receptor-4 for entry. Intracellular signals transduced by HIV-1 envelope may have immunopathogenic consequences, including anergy, syncytium formation, apoptosis, and inappropriate cell trafficking. We demonstrate here that a recombinant envelope protein derived from an M-tropic isolate of HIV-1 can transduce CD4-dependent as well as CCR5-dependent intracellular signals in primary human CD4+ T cells. Novel HIV-induced intracellular signals that were identified include tyrosine phosphorylation of focal adhesion kinase (FAK) and CCR5, which are involved in cell adhesion and chemotaxis, respectively. HIV envelope-induced cellular association of FAK and CCR5 was also demonstrated, suggesting that ligation of CD4 and CCR5 leads to the formation of an activation complex composed of FAK and CCR5. Activation of this signaling pathway by HIV-1 envelope may be an important pathogenic mechanism of dysregulated cellular activation and trafficking during HIV infection.

Population biology of HIV-1 infection: viral and CD4+ T cell demographics and dynamics in lymphatic tissues

Human immunodeficiency virus-1 (HIV-1) is usually transmitted through sexual contact and in the very early stages of infection establishes a persistent infection in lymphatic tissues (LT). Virus is produced and stored at this site in a dynamic process that slowly depletes the immune system of CD4+ T cells, setting the stage for AIDS. In this review, I describe the changes in viral and CD4+ T cell populations in LT over the course of infection and after treatment. I present recent evidence that productively infected CD4+ T cells play an important role in establishing persistent infection from the onset, and that the LT are the major reservoir where virus is produced and stored on follicular dendritic cells (FDCs). I discuss the methods used to define the size of viral and CD4+ T cell populations in LT and the nature of virus-host cell interactions in vivo. These experimental approaches have identified populations of latently and chronically infected cells in which virus can elude host defenses, perpetuate infection, and escape eradication by highly active antiretroviral treatment (HAART). I discuss the dramatic impact of HAART on suppressing virus production, reducing the pool of stored virus, and restoring CD4+ T cell populations. I discuss the contributions of thymopoiesis and other renewal mechanisms, lymphatic homeostasis and trafficking to these changes in CD4+ T cell populations in LT, and conclude with a model of immune depletion and repopulation based on the limited regenerative capacity of the adult and the uncompensated losses of productively infected cells that treatment stems. The prediction of this model is that immune regeneration will be slow, variable, and partial. It is nonetheless encouraging to know that even in late stages of infection, control of active replication of HIV-1 provides an opportunity for the immune system to recover from the injuries inflicted by infection.

Increased expression of regeneration and tolerance factor in individuals with human immunodeficiency virus infection

Regeneration and tolerance factor (RTF) plays a pivotal role in successful pregnancy outcome and has potent immunomodulating properties. During pregnancy, it is abundantly expressed in the placenta and on peripheral B lymphocytes. Several lines of evidence suggest that both successful pregnancy outcome and progression from human immunodeficiency virus (HIV) infection to AIDS are associated with a Th2-type response. As a result, we hypothesized that the cellular expression of RTF may also be increased during infection with HIV. Using flow cytometric analysis, we showed a significantly (P < 0.01) increased expression of RTF on CD3(+) cells obtained from individuals with HIV over that for individuals without HIV. On average, 32.1% of the CD3(+) cells from individuals with HIV expressed high levels of RTF. In contrast, an average of only 6.7% of the CD3(+) cells from individuals without HIV expressed high levels of RTF. Similar results were obtained when CD19(+) cells from individuals with (mean, 44.1%) and without (mean, 25.8%) HIV were evaluated. Linear regression analysis suggested that high levels of RTF expression by CD3(+) cells correlated better with viral load (r value, 0.46) than with absolute CD4 count (r value, 0.09). While additional experiments are necessary to delineate the precise immunologic role of RTF, our current data suggest that RTF expression during HIV infection may be a useful marker of immune activation.

The role of complement and gp120-specific antibodies in virus lysis and CD4+ T cell depletion in HIV-1-infected patients

The substantial virus lysis was induced by HIV-1-infected patient serum and normal human complement serum in the presence of purified patient IgG. Non-infected CD4+ T cells coated with the whole virus or with a recombinant HIV-1 envelope gp120 and sensitised with patient IgG were also shown to be susceptible to complement-dependent lysis. The serum level of complement regulatory protein in a fluid phase, the C1-esterase inhibitor, was significantly correlated with serum concentration of C1q-circulating immune complexes (P=0.0062), but inversely with CD4+ T cell count (P < 0.0001). Accordingly, the disease progression in HIV-1-infected patients was significantly correlated with the level of complement activation as determined by serum level of C1-esterase inhibitor (P=0.0001), and inversely correlated with CD4+ cell count (P < 0. 0001) and gp120-specific antibody titre (P=0.0086). These results strongly suggest that the complement activation by gp120-specific antibodies play a very important role in virus clearance, but also in depletion of infected as well as gp120-coated non-infected CD4+ bystander T cells during the course of HIV-1 infection.

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.

Early T-cell apoptosis and Fas expression during antiretroviral therapy in individuals infected with human immunodeficiency virus-1

Several lines of evidence suggest that Fas-mediated apoptosis is involved in the CD4 T-cell depletion in human immunodeficiency virus-1 (HIV-1) infection. To investigate this, we studied changes in peripheral blood, early T-cell apoptosis and Fas expression after initiation of antiretroviral therapy (ART) in 18 HIV-1-infected individuals. Flow cytometric analysis was performed with Apostain and CD4, CD8 and Fas staining. Fas expression was quantified by standardized beads. The levels of CD4 and CD8 T cells with early apoptosis were increased comparably in HIV-1-infected individuals. Despite elevated CD4 T cell counts, no decline in early T-cell apoptosis could be detected during the first 8 weeks of ART. However, after 26 weeks of ART in five patients that showed a sustained reduction of viral replication there was a marked decrease in T cells with features of early apoptosis. No difference was found for Fas expression on early apoptotic T cells. Fas expression on CD4 and CD8 T cells was reduced after initiation of ART; this was independent of the CD4 T-cell trend and indicates that the immediate CD4 T-cell expansion during ART is probably not the result of a decreased rate of early apoptosis among peripheral blood CD4 T cells. However, preliminary data imply a long-term reduction of early T-cell apoptosis and Fas expression in patients who show a sustained reduction of viral replication.

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.

Interleukin-2 receptor beta and gamma chain dysregulation during the inhibition of CD4 T cell activation by human immunodeficiency virus-1 gp120

We have observed that CD4 T lymphocytes from human immunodeficiency virus (HIV)-infected patients marginally express interleukin-2 receptor (IL-2R) beta and IL-2R gamma chains which are essential for IL-2 signal transduction. To analyze this observation further, we studied the influence of gp120 on the cell surface expression of IL-2R beta and IL-2R gamma by purified CD4 lymphocytes in vitro. Cross-linking of the T cell receptors of these lymphocytes initiates entry into the cell cycle as measured by CD69 and CD71 cell surface expression and [3H]thymidine incorporation. It also induces the cell surface expression of IL-2R beta and IL-2R gamma. We have shown that treatment of the CD4 T lymphocytes with HIV-1 gp120 before anti-CD3 stimulation impedes cell cycle progression as measured by reduced CD71 expression and inhibition of [3H]thymidine incorporation. Furthermore, cell surface expression of IL-2R beta and IL-2R gamma subunits, which from the functional intermediate-affinity IL-2R, are significantly inhibited. More importantly, addition of exogenous IL-2 does not restore the proliferation of the CD4 T cells treated with gp120, suggesting that cells are anergic and/or that the remaining IL-2R are not functional. This is the first study of IL-2R beta and IL-2R gamma dysregulation in the context of HIV infection and shows that CD4 is also involved in IL-2R expression.