Cytokines alter production of HIV-1 from primary mononuclear phagocytes

Predicting the impact of CD8+ T cell polyfunctionality on HIV disease progression

During the chronic phase of HIV-1 infection, polyfunctional CD8+ T cell responses, which are characterized by a high frequency of cells able to secrete multiple cytokines simultaneously, are associated with lower virus loads and slower disease progression. This relationship may arise for different reasons. Polyfunctional responses may simply be stronger. Alternatively, it could be that the increased functional diversity in polyfunctional responses leads to lower virus loads and slower disease progression. Lastly, polyfunctional responses could contain more CD8+ T cells that mediate a specific key function that is primarily responsible for viral control. Disentangling the influences of overall strength, functional diversity, and specific function on viral control and disease progression is very relevant for the rational design of vaccines and immunotherapy using cellular immune responses. We developed a mathematical model to study how polyfunctional CD8+ T cell responses mediating lytic and nonlytic effector functions affect the CD4+ T cell count and plasma viral load. We based our model on in vitro data on the efficacy of gamma interferon (IFN-γ) and macrophage inflammatory protein 1β (MIP-1β)/RANTES against HIV. We find that the strength of the response is a good predictor of disease progression, while functional diversity has only a minor influence. In addition, our model predicts for realistic levels of cytotoxicity that immune responses dominated by nonlytic effector functions most positively influence disease outcome.

IMPORTANCE

It is an open question in HIV research why polyfunctional CD8+ T cell responses are associated with better viral control, while individual functional correlates of protection have not been identified so far. Identifying the role of CD8+ T cells in HIV-1 infection has important implications for the potential development of effective T cell-based vaccines. Our analysis provides new ways to think about a causative role of CD8+ T cells by studying different hypotheses regarding why polyfunctional CD8+ T cells might be more advantageous. We identify measurements that have to be obtained in order to evaluate the role of CD8+ T cells in HIV-1 infection. In addition, our method shows how individual cell functionality data can be used in population-based virus dynamics models.

Can non-lytic CD8+ T cells drive HIV-1 escape?

The CD8+ T cell effector mechanisms that mediate control of HIV-1 and SIV infections remain poorly understood. Recent work suggests that the mechanism may be primarily non-lytic. This is in apparent conflict with the observation that SIV and HIV-1 variants that escape CD8+ T cell surveillance are frequently selected. Whilst it is clear that a variant that has escaped a lytic response can have a fitness advantage compared to the wild-type, it is less obvious that this holds in the face of non-lytic control where both wild-type and variant infected cells would be affected by soluble factors. In particular, the high motility of T cells in lymphoid tissue would be expected to rapidly destroy local effects making selection of escape variants by non-lytic responses unlikely. The observation of frequent HIV-1 and SIV escape poses a number of questions. Most importantly, is the consistent observation of viral escape proof that HIV-1- and SIV-specific CD8+ T cells lyse infected cells or can this also be the result of non-lytic control? Additionally, the rate at which a variant strain escapes a lytic CD8+ T cell response is related to the strength of the response. Is the same relationship true for a non-lytic response? Finally, the potential anti-viral control mediated by non-lytic mechanisms compared to lytic mechanisms is unknown. These questions cannot be addressed with current experimental techniques nor with the standard mathematical models. Instead we have developed a 3D cellular automaton model of HIV-1 which captures spatial and temporal dynamics. The model reproduces in vivo HIV-1 dynamics at the cellular and population level. Using this model we demonstrate that non-lytic effector mechanisms can select for escape variants but that outgrowth of the variant is slower and less frequent than from a lytic response so that non-lytic responses can potentially offer more durable control.

The interplay between viruses and the immune system cannot always be studied with current experimental techniques or commonly used mathematical models. Consequently, many important questions remain unanswered. The questions we wished to address fall into this category. Recent evidence strongly suggests that CD8+ T cells control SIV, and potentially HIV-1, primarily by secreting anti-viral factors rather than by killing infected cells. However, this does not seem compatible with the common observation that HIV and SIV evolve to escape the immune response. Soluble anti-viral factors, like RANTES which protects uninfected cells from infection, would be expected to inhibit both wild-type and variant virus. Furthermore, the high speed and motility of T cells in lymphoid tissue will increase homogeneity and again decrease the likelihood that an escape variant can have a selective advantage in the face of non-lytic control. We wanted to understand whether viral escape is proof that HIV-1- and SIV-specific CD8+ T cells kill infected cells, determine the factors that facilitate viral escape, and investigate the comparative efficiency of lytic and non-lytic responses in controlling viral infections. Here we develop an elaborate but robust computational framework that captures T cell kinetics and spatial interactions in lymphoid tissue to addresses these important questions.

Elevated cytokine and chemokine levels in the placenta are associated with in-utero HIV-1 mother-to-child transmission

OBJECTIVE

To determine whether there is an association between cytokine and chemokine levels in plasma isolated from the placenta and HIV-1 mother-to-child transmission (MTCT).

DESIGN

We designed a case-control study of HIV-infected, pregnant women enrolled in the Malaria and HIV in Pregnancy cohort. Participants were recruited in Blantyre, Malawi, from 2000 to 2004. Patients were women whose children were HIV-1 DNA-positive at birth (in-utero MTCT) or HIV-1 DNA-negative at birth and HIV-1 DNA-positive at 6 weeks postpartum (intrapartum MTCT); controls were women whose children were HIV-1 DNA-negative both at birth and 6 weeks postpartum.

METHODS

After delivery, blood was isolated from an incision on the basal plate of the placenta. We used a Bio-Plex human cytokine assay (Bio-Rad, Hercules, California USA) to simultaneously quantify 27 cytokines, chemokines and growth factors in placental plasma. HIV-1 RNA copies were quantified with the Roche Amplicor kit.

RESULTS

Levels of interleukin (IL) 4, IL-5, IL-6, IL-7, IL-9, eotaxin, IL-1Ra and interferon gamma-induced protein 10 (IP-10) were significantly elevated in placental plasma isolated from cases of in-utero HIV-1 MTCT. In contrast, only granulocyte colony-stimulating factor was elevated in placental plasma isolated from cases of intrapartum MTCT. After adjusting for maternal age, gestational age and peripheral CD4(+) T-cell count, every log(10) increase in placental IP-10 was associated with a three-fold increase in the prevalence of in-utero HIV-1 MTCT.

CONCLUSION

Elevated cytokine and chemokine levels in placental plasma were associated with in-utero and not intrapartum MTCT. IP-10, which is both a T-cell chemokine and potentiator of HIV-replication, was robustly and independently associated with prevalent, in-utero MTCT.

Proline-proline-glutamic acid (PPE) protein Rv1168c of Mycobacterium tuberculosis augments transcription from HIV-1 long terminal repeat promoter

Cells of the monocyte/macrophage lineage are shown to play a role in the pathogenesis of human immunodeficiency virus (HIV). The occurrence of HIV type 1 (HIV-1) infection is found to be accelerated in people infected with Mycobacterium tuberculosis, but the mechanism by which mycobacterial protein(s) induces HIV-1 LTR trans-activation is not clearly understood. We show here that the M. tuberculosis proline-proline-glutamic acid (PPE) protein Rv1168c (PPE17) can augment transcription from HIV-1 LTR in monocyte/macrophage cells. Rv1168c interacts specifically with Toll-like receptor-2 (TLR2) resulting in downstream activation of nuclear factor-κB (NF-κB) resulting in HIV-1 LTR trans-activation. Another PPE protein, Rv1196 (PPE18), was also found to interact with TLR2 but had no effect on HIV-1 LTR trans-activation because of its inability to activate the NF-κB signaling pathway. In silico docking analyses and mutation experiments have revealed that the N-terminal domain of Rv1168c specifically interacts with LRR motifs 15-20 of TLR2, and this site of interaction is different from that of Rv1196 protein (LRR motifs 11-15), indicating that the site of interaction on TLR2 dictates the downstream signaling events leading to activation of NF-κB. This information may help in understanding the mechanism of pathogenesis of HIV-1 during M. tuberculosis co-infection.

Down-regulation of CXCR-4 and CCR-5 expression by interferon-gamma is associated with inhibition of chemotaxis and human immunodeficiency virus (HIV) replication but not HIV entry into human monocytes

Alterations in the expression of CXCR4 and CCR5, the co-receptors for HIV entry, may be associated with susceptibility of monocytic cells to HIV infection. Interferon (IFN)-gamma has been shown to inhibit HIV replication in monocytic cells, but the molecular mechanism involved is not well understood. To determine if IFN-gamma regulates HIV replication by altering CXCR-4/CCR-5 expression and hence virus entry into monocytic cells, we investigated the effects of IFN-gamma on CXCR-4 and CCR-5 expression and its biological implications with respect to HIV entry, replication and chemotaxis towards the CXCR-4 and CCR-5 ligands SDF-1 and MIP-1alpha, respectively. IFN-gamma decreased CXCR-4 and CCR-5 expression on monocytes derived from HIV-negative adults, HIV-positive adults and HIV-negative cord blood. This down-regulation of chemokine receptor expression did not result in a corresponding change in mRNA expression but was associated with elevated levels of the endogenously produced chemokines SDF-1 and RANTES. Furthermore, IFN-gamma inhibited chemotaxis in response to SDF-1 and MIP-1alpha, inhibited HIV replication, but failed to inhibit virus entry in monocytic cells. These results suggest that although IFN-gamma-induced down-regulation of CXCR-4 and CCR-5 expression is associated with an inhibition of SDF-1-/MIP-1alpha-mediated chemotaxis, IFN-gamma-induced inhibition of HIV replication may be mediated at levels subsequent to the virus entry.

Comparative in vitro sensitivities of human immune cell lines, vaginal and cervical epithelial cell lines, and primary cells to candidate microbicides nonoxynol 9, C31G, and sodium dodecyl sulfate

In experiments to assess the in vitro impact of the candidate microbicides nonoxynol 9 (N-9), C31G, and sodium dodecyl sulfate (SDS) on human immune and epithelial cell viability, cell lines and primary cell populations of lymphocytic and monocytic origin were generally shown to be equally sensitive to exposures ranging from 10 min to 48 h. However, U-937 cells were more sensitive to N-9 and C31G after 48 h than were primary monocyte-derived macrophages. Cytokine activation of monocytes and lymphocytes had no effect on cell viability following exposure to these microbicidal compounds. Primary and passaged vaginal epithelial cultures and cell lines differed in sensitivity to N-9 and C31G but not SDS. These studies provide a foundation for in vitro experiments in which cell lines of human immune and epithelial origin can be used as suitable surrogates for primary cells to further investigate the effects of microbicides on cell metabolism, membrane composition, and integrity and the effects of cell type, proliferation, and differentiation on microbicide sensitivity.

Endothelial cells enhance human immunodeficiency virus type 1 replication in macrophages through a C/EBP-dependent mechanism

Macrophages are early targets of human immunodeficiency virus type 1 (HIV-1) infection and serve as potential reservoirs for long-term infection. Through inflammatory mediators and direct cell contact, infected macrophages interact with neighboring cell populations, such as the endothelium, which create a microenvironment favorable for HIV-1 replication. We hypothesize that the transcriptional activator C/EBPbeta is critical for macrophages to respond to endothelial cell-derived signals. We show that endothelial cells significantly enhance C/EBPbeta binding activity and HIV-1 replication in macrophages. This increase in HIV-1 transcription is due to cell-cell contact as well as the production of soluble factors, mediated in part by ICAM-1 and interleukin 6, respectively. Furthermore, C/EBP factors are necessary for endothelial cell-dependent activation of HIV-1 transcription in macrophages, and HIV-1 induction can be inhibited by a C/EBP dominant-negative protein. In addition, C/EBP binding sites are necessary for efficient LTR activity and HIV-1 replication in the presence of endothelial cells. Taken together, these results indicate that endothelial cells, through the activation of C/EBPbeta, provide a microenvironment that supports HIV-1 replication in monocytes/macrophages.

CD8+ T cell-mediated enhancement of tumour necrosis factor-alpha (TNF-alpha) production and HIV-1 LTR-driven gene expression in human monocytic cells is pertussis toxin-sensitive

HIV replication and LTR-mediated gene expression can be modulated by CD8+ T cells in a cell type-dependent manner. We have previously shown that supernatants of activated CD8+ T cells of HIV-infected individuals greatly enhanced p24 levels in human macrophages infected with NSI or SI primary isolates of HIV-1. Here we have examined the effect of culture with CD8+ T cell supernatants on HIV-1 LTR-mediated gene expression in monocytic cells. CD8+ T cell supernatants enhanced LTR-mediated gene expression in U38 cells activated with Tat in the absence or presence of phorbol myristate acetate (PMA) and ionomycin or TNF-alpha. Further, enhancement of LTR-mediated gene expression and virus replication in U38 cells and U1 cells, respectively, was pertussis toxin-sensitive. The enhancement of gene expression and virus replication was associated with increased levels of TNF-alpha and was significantly abrogated by antibody to TNF-alpha. In contrast, the suppression of LTR-mediated gene expression by CD8+ T cell supernatants in Jurkat T cells was not pertussis toxin-sensitive and TNF-alpha levels were not affected. These results demonstrate that factors produced by CD8+ T cells utilize different cellular pathways to mediate their effects on HIV transcription and replication in different cell types.

A Selective Defect of IFN-γ- But Not of IFN-α-Induced JAK/STAT Pathway in a Subset of U937 Clones Prevents the Antiretroviral Effect of IFN-γ Against HIV-1

IFN-γ induces transcription of several IFN-stimulated genes (ISGs). Recently, the IFN-γ-dependent Janus kinase (JAK)/STAT pathway has been shown to mediate the activation of some ISGs, by the sequential phosphorylation of two JAK kinases (JAK1 and JAK2) and of STAT1. Given that the JAK/STAT is the major, but not the only pathway linked to the IFN-γR, aim of our work was to investigate the signal-transduction pathway(s) by which IFN-γ exerts its effects on acute replication of HIV in monocytic cells. To this end, we utilized clones previously derived from the U937 promonocytic cell line, differing for their efficient (plus clones) or inefficient (minus clones) abilities of supporting HIV replication. Unlike IFN-α, IFN-γ did not inhibit HIV replication in plus clones, whereas virus production in minus cells was efficiently inhibited by both types of IFN. Plus clones generated a JAK/STAT signal-transduction pathway in response to IFN-α, but not IFN-γ. In contrast, minus clones responded to either cytokines. The functional defect of plus clones in response to IFN-γ was correlated to a selective defect of IFN-γR2, but not IFN-γR1, membrane expression. Surprisingly enough, IFN-γ stimulation of plus clones induced IFN-stimulated gene factor 3 (ISGF3γ). These results strongly support the hypothesis that the JAK/STAT pathway is responsible for the antiretroviral effect of IFN-γ, and further provide evidence for a potential second pathway triggered by IFN-γ in the absence of IFN-γR2 chain cell surface expression and involving ISGF3γ.

Norepinephrine Accelerates HIV Replication Via Protein Kinase A-Dependent Effects on Cytokine Production

To explore the role of sympathetic nervous system activation in HIV pathogenesis, we examined the effect of the neuroeffector molecule norepinephrine (NE) on HIV-1 replication in quiescently infected PBMCs that were subsequently activated with Abs to CD3 and CD28. NE accelerated HIV-1 replication at concentrations ranging from 10−8 to 10−5 M. This effect could be mimicked by protein kinase A (PKA) activators (forskolin or dibutyryl-cAMP) and abrogated by β-adrenoreceptor antagonists or the PKA inhibitor rp-cAMP, indicating transduction via the adrenoreceptor signaling pathway. NE reduced cellular activation and altered the production of several HIV-modulating cytokines: IL-10 and IFN-γ were markedly suppressed; TNF-α, IL-1β, IL-2, IL-4, and IL-6 were mildly suppressed; and levels of IL-12 were not significantly altered. The addition of either exogenous IFN-γ or IL-10 abrogated the effect of NE on virus production. Thus PKA-dependent suppression of cytokine production appears to mediate the enhancement of HIV-1 replication by NE.

Contact with thymic epithelial cells as a prerequisite for cytokine-enhanced human immunodeficiency virus type 1 replication in thymocytes

We report here that human immunodeficiency virus type 1 (HIV-1)-infected human thymocytes, in the absence of any exogenous stimulus but cocultivated with autologous thymic epithelial cells (TEC), obtained shortly (3 days) after thymus excision produce a high and sustained level of HIV-1 particles. The levels and kinetics of HIV-1 replication were similar for seven distinct viral strains irrespective of their phenotypes and genotypes. Contact of thymocytes with TEC is a critical requirement for optimal viral replication. Rather than an inductive signal resulting from the contact itself, soluble factors produced in the mixed culture are responsible for this effect. Specifically, the synergistic effects of tumor necrosis factor, interleukin-1 (IL-1), IL-6, and granulocyte-macrophage colony-stimulating factor may account by themselves for the high level of HIV-1 replication in thymocytes observed in mixed cultures. In conclusion, the microenvironment generated by TEC-thymocyte interaction might greatly favor optimal HIV-1 replication in the thymus.

HIV-1 does not alter in vitro and in vivo IL-10 production by human monocytes and macrophages

The present study analyses the ability of HIV-1 to modulate IL-10 production in cells of monocyte-macrophage lineage cultured in the presence of macrophage colony-stimulating factor (M-CSF). Both monocytes and macrophages spontaneously produced low amount of IL-10. Lipopolysaccharide (LPS) induced a strong IL-10 response in fresh monocytes and in M-CSF-treated macrophages. In contrast, macrophages cultured in the absence of M-CSF exhibited a marked decrease in their susceptibility to LPS stimulation. M-CSF increased the IL-10 response of macrophages to LPS by enhancing both the expression of membrane-bound CD14, the protein that serves as LPS receptor, and the sensibility of CD14-expressing cells to LPS stimulation. Neither spontaneous nor LPS-induced expression of IL-10 was modulated in monocytes and macrophages by infection with eight monocytotropic strains, as demonstrated by ELISA and cytofluorimetric analysis. In contrast, all the HIV-1 strains primed macrophages for an increased IL-6 response to LPS stimulation. To determine whether IL-10 production was associated with in vivo infection, monocytes from AIDS individuals were analysed for IL-10 production. We found that neither spontaneous nor LPS-induced IL-10 production were different between healthy controls and HIV-infected patients. Taken together, these data strongly suggest that HIV-1 infection of monocytes-macrophages does not play a significant role in the regulation of IL-10 in infected patients. This study also emphasizes the role of M-CSF activation in the regulation of the cytokine response in macrophages.

Effect of hematopoietic growth factors on human blood monocytes/macrophages in in vitro culture

The production of mature monocytes/macrophages is regulated by a group of hematopoietic growth factors, or colony-stimulating factors (CSF). We investigated the in vitro effect of human hematopoietic growth factors on human blood monocyte/macrophage differentiation and proliferation in short- and long-term in vitro cultures. The addition of macrophage CSF, granulocyte-macrophage CSF, and granulocyte CSF and interleukin-6 and interleukin-3 growth factors to monocyte/macrophage cultures induced morphological changes in cultured cells, including enhancement of cell growth and the formation of multinucleated giant cells, spindle-like cells, and fibroblast-like cells. In addition, CD4 and HLA-DR antigen expression was down regulated by the addition of growth factors without a change in the expression of other surface antigens, including CD3, CD11B, CD14, CD15, NK H1, and B1. The proliferating cell nuclear antigen was not detected in growth factor-treated nonadherent monocytes/macrophages in long-term cultures. Bromodeoxyuridine was incorporated in the adherent monocytes/macrophages, and intense staining in the small rounded cells which occur above the adherent cells in these cultures was observed after a 72-h pulse, indicating that monocytes/macrophages are slowly dividing cells.

Quantification of HIV by PCR in monocytes and lymphocytes in patients receiving antiviral treatment and low dose recombinant human granulocyte macrophage colony stimulating factor

Neutropenia induced by antiviral treatment, in particular AZT, can be improved with recombinant human granulocyte macrophage colony stimulating factor (RHGMCSF) in HIV positive patients. However, there has been concern that this may increase the HIV load in the mononuclear cells of such patients. Five patients receiving AZT plus low dose RHGMCSF are reported. There was no consistent change in the levels of HIV DNA in the monocytes and lymphocytes. Additionally, all patients had stable disease with no opportunistic infection during the study period. It is concluded, therefore, that low dose RHGMCSF does not significantly change the viral DNA load in patients receiving AZT.

Cytokine-mediated induction of human immunodeficiency virus (HIV) expression and cell death in chronically infected U1 cells: do tumor necrosis factor alpha and gamma interferon selectively kill HIV-infected cells?

Infection with several DNA or RNA viruses induces a state of increased sensitivity to cell lysis mediated by tumor necrosis factor (TNF), particularly in the presence of gamma interferon (IFN-gamma). Infection of human cells with the human immunodeficiency virus (HIV) may induce a similar phenomenon. However, TNF and IFN-gamma are known upregulators of HIV replication, raising the question of the potential role of these cytokines in the selective elimination of cells infected with this virus. The present study demonstrates that chronically infected U1 cells were killed with much greater efficiency by costimulation with TNF-alpha and IFN-gamma than their uninfected parental cell line U937. However, synergistic induction of viral expression also occurred in U1 cells as a consequence of treatment with the two cytokines. Cell death in U1 cells was not caused by the massive production of virions, in that costimulation with glucocorticoid hormones and TNF-alpha or IFN-gamma resulted in high levels of virion production without cytopathicity. To investigate the nature of the selective cytotoxic effect observed in U1 cells costimulated with TNF-alpha plus IFN-gamma, a panel of uninfected cell clones was generated by limiting dilution of U937 cells and tested for response to TNF-alpha and/or IFN-gamma. In contrast to the uncloned bulk parental U937 cell line, most uninfected cell clones showed a very high susceptibility to being killed by TNF-alpha and IFN-gamma. Similar findings were obtained when both infected U1 cells and several uninfected U937 cell clones were costimulated with an anti-Fas monoclonal antibody in the presence of IFN-gamma, although, unlike cells stimulated with TNF-alpha, cells treated with anti-Fas antibody did not express virus. Therefore, the increased susceptibility to cytokine-mediated lysis observed in cell lines infected with HIV is likely due to the selection of preexisting cell clones rather than viral infection.

Equine infectious anemia virus derived from a molecular clone persistently infects horses

A full-length molecular clone of equine infectious anemia virus (EIAV) was isolated from a persistently infected canine fetal thymus cell line (Cf2Th). Upon transfection of equine dermis cells, the clone, designated CL22, yielded infectious EIAV particles (CL22-V) that replicated in vitro in both Cf2Th cells and an equine dermis cell strain. Horses infected with CL22-V developed an antibody response to viral proteins and possessed viral DNA in peripheral blood mononuclear cells, as determined by polymerase chain reaction assays. In addition, horses infected with CL22-V became persistently infected and were capable of transmitting the infection by transfer of whole blood to uninfected horses. However, CL22-V, like the parental canine cell-adapted virus, did not cause clinical signs in infected horses. Reverse transcriptase assays of CL22-V- and virulent EIAV-infected equine mononuclear cell cultures indicated that the lack of virulence of CL22-V was not due to an inability to infect and replicate in equine mononuclear cells in vitro.