Early divergence in neutrophil apoptosis between pathogenic and nonpathogenic simian immunodeficiency virus infections of nonhuman primates

ATF4 Signaling in HIV-1 Infection: Viral Subversion of a Stress Response Transcription Factor

Cellular integrated stress response (ISR), the mitochondrial unfolded protein response (UPRmt), and IFN signaling are associated with viral infections. Activating transcription factor 4 (ATF4) plays a pivotal role in these pathways and controls the expression of many genes involved in redox processes, amino acid metabolism, protein misfolding, autophagy, and apoptosis. The precise role of ATF4 during viral infection is unclear and depends on cell hosts, viral agents, and models. Furthermore, ATF4 signaling can be hijacked by pathogens to favor viral infection and replication. In this review, we summarize the ATF4-mediated signaling pathways in response to viral infections, focusing on human immunodeficiency virus 1 (HIV-1). We examine the consequences of ATF4 activation for HIV-1 replication and reactivation. The role of ATF4 in autophagy and apoptosis is explored as in the context of HIV-1 infection programmed cell deaths contribute to the depletion of CD4 T cells. Furthermore, ATF4 can also participate in the establishment of innate and adaptive immunity that is essential for the host to control viral infections. We finally discuss the putative role of the ATF4 paralogue, named ATF5, in HIV-1 infection. This review underlines the role of ATF4 at the crossroads of multiple processes reflecting host-pathogen interactions.

Intrinsic Apoptotic Pathway Genes of Circulating Blood Neutrophils Triggered during HIV Infection and Remained Stimulated in ART Patients

BACKGROUND

The intrinsic apoptotic pathway of neutrophils in Human Immunodeficiency Virus (HIV) infection results in spontaneous neutrophil death. There is a scarcity of data regarding the gene expression of an intrinsic apoptotic pathway of neutrophils in HIV patients.

OBJECTIVE

The objective of this study was to observe the differential expression of some important genes involved in the intrinsic apoptotic pathway of HIV patients, including those who were receiving antiretroviral therapy (ART).

METHODS

Blood samples were collected from asymptomatic, symptomatic, ART receiver HIV patients, and healthy individuals. Total RNA was extracted from neutrophils and subjected to quantitative real-time PCR assay. CD4+T cells and an automated complete blood count were performed.

RESULTS

Among the asymptomatic, symptomatic, and ART receiver HIV patients (n=20 in each group), median CD4+T counts were 633, 98, and 565 cells/ml, and the length of HIV infection in months (± SD) was 24.06 ± 21.36, 62.05 ± 25.51, and 69.2 ± 39.67, respectively. Compared with healthy controls, intrinsic apoptotic pathway genes, i.e., BAX, BIM, Caspase-3, Caspase-9, MCL-1, and Calpain-1, were upregulated to 1.21 ± 0.33, 1.8 ± 0.25, 1.24 ± 0.46, 1.54 ± 0.21, 1.88 ± 0.30, and 5.85 ± 1.34 fold in the asymptomatic group, and even more significantly, i.e., 1.51 ± 0.43, 2.09 ± 1.13, 1.85 ± 1.22, 1.72 ± 0.85, 2.26 ± 1.34, and 7.88 ± 3.31 fold in symptomatic patients, respectively. Despite CD4+ T-cell levels increased in the ART receiver group, these genes did not approach the level of healthy or asymptomatic and remained significantly upregulated.

CONCLUSION

The genes involved in the intrinsic apoptotic pathway in circulating neutrophils during HIV infection were stimulated in vivo, and ART reduced the expression of those upregulated genes but did not return to the level of asymptomatic or healthy individuals.

Systemic and mucosal mobilization of granulocyte subsets during lentiviral infection

Granulocytes mediate broad immunoprotection through phagocytosis, extracellular traps, release of cytotoxic granules, antibody effector functions and recruitment of other immune cells against pathogens. However, descriptions of granulocytes in HIV infection and mucosal tissues are limited. Our goal was to characterize granulocyte subsets in systemic, mucosal and lymphoid tissues during lentiviral infection using the rhesus macaque (RM) model. Mononuclear cells from jejunum, colon, cervix, vagina, lymph nodes, spleen, liver and whole blood from experimentally naïve and chronically SHIVsf162p3-infected RM were analysed by microscopy and polychromatic flow cytometry. Granulocytes were identified using phenotypes designed specifically for RM: eosinophils-CD45+  CD66+  CD49d+ ; neutrophils-CD45+  CD66+  CD14+ ; and basophils-CD45+  CD123+  FcRε+ . Nuclear visualization with DAPI staining and surface marker images by ImageStream (cytometry/microscopy) further confirmed granulocytic phenotypes. Flow cytometric data showed that all RM granulocytes expressed CD32 (FcRγII) but did not express CD16 (FcRγIII). Additionally, constitutive expression of CD64 (FcRγI) on neutrophils and FcRε on basophils indicates the differential expression of Fc receptors on granulocyte subsets. Granulocytic subsets in naïve whole blood ranged from 25·4% to 81·5% neutrophils, 0·59% to 13·3% eosinophils and 0·059% to 1·8% basophils. Interestingly, elevated frequencies of circulating neutrophils, colorectal neutrophils and colorectal eosinophils were all observed in chronic lentiviral disease. Conversely, circulating basophils, jejunal eosinophils, vaginal neutrophils and vaginal eosinophils of SHIVsf162p3-infected RM declined in frequency. Overall, our data suggest modulation of granulocytes in chronic lentiviral infection, most notably in the gastrointestinal mucosae where a significant inflammation and disruption occurs in lentivirus-induced disease. Furthermore, granulocytes may migrate to inflamed tissues during infection and could serve as targets of immunotherapeutic intervention.

Hepatosplenomegaly in liver cirrhosis is caused by reactive oxygen species formation, an increase in apoptosis and autophagy, and pronounced autoimmune reactions

Various factors of infectious and toxic genesis can lead to the liver cirrhosis, often accompanied by complications such as recurrent bleeding due to portal hypertension against the background of hepatosplenomegaly. Metabolic changes and disturbances in immunoreactivity occur in the liver and spleen. To substantiate the choice of personalized treatment tactics for patients with hepatosplenomegaly, we investigated individual metabolic predictors and immunopathological processes in patients with: liver cirrhosis and hepatitis B (HBV) and/or hepatitis C (HCV) viruses (I group, n = 52); with herpes viruses CMV (cytomegalovirus) and EBV (Epstein-Barr virus) (II group, n = 48), and with splenomegaly and frequent recurrent bleeding associated with hereditary enzymopathies (III group, n = 15). We used the methods of immunoturbidimetry; enzyme immunoassay; light, fluorescence and confocal microscopy. In group I (HBV/HCV), we revealed a decrease in the C4 component; a significant increase in the phagocytic index and phagocytic number, a reduced number of active phagocytes and the digestion index; a decrease in the IL-1β content and an increase in IL-18 and IL-6. In group II (CMV/EBV), we revealed a high activity of the C3 and a low activity of the C4 component against the background of a high level of ROS in neutrophils; the antineutrophil antibodies (ANCA) formation in 85.7% of patients (71.4% –perinuclear antibodies (pANCA) to myeloperoxidase; 14.3% – cytoplasmic antibodies (CANCA) to proteinase 3). Also, in group II, an increased level of pro-inflammatory cytokines IFN-γ, IL-1β, TNF-α, IL-18 and anti-inflammatory IL-6 was detected. Changes in links of immunity in II group led to the formation of autoimmune reactions in 64.7% of patients, which was expressed in the development of a broad range of antinuclear antibodies ANA (11 specificities, including ANA to chromatin and chromatin-associated proteins, to proteins cytoskeleton, enzymes and enzyme complexes). In group III, we revealed a low absorption capacity of neutrophils, a high frequency of antineutrophil antibodies pANCA occurrence and cANCA (in 67.2% of the examined), and low concentration of TNF-α. The developed model of the stepwise change of immunological markers makes it possible to substantiate the choice of a complex targeted treatment, including antiviral and immunotropic therapy.

Antibiotic-induced microbiome perturbations are associated with significant alterations to colonic mucosal immunity in rhesus macaques

The diverse bacterial communities that colonize the gastrointestinal tract play an essential role in maintaining immune homeostasis through the production of critical metabolites such as short-chain fatty acids (SCFAs) and this can be disrupted by antibiotic use. However, few studies have addressed the effects of specific antibiotics longitudinally on the microbiome and immunity. We evaluated the effects of four specific antibiotics: enrofloxacin, cephalexin, paromomycin, and clindamycin, in healthy female rhesus macaques. All antibiotics disrupted the microbiome, including reduced abundances of fermentative bacteria and increased abundances of potentially pathogenic bacteria, including Enterobacteriaceae in the stool, and decreased Helicobacteraceae in the colon. This was associated with decreased SCFAs, indicating altered bacterial metabolism. Importantly, antibiotic use also substantially altered local immune responses, including increased neutrophils and Th17 cells in the colon. Furthermore, we observed increased soluble CD14 in plasma, indicating microbial translocation. These data provide a longitudinal evaluation of antibiotic-induced changes to the composition and function of colonic bacterial communities associated with specific alterations in mucosal and systemic immunity.

The Dual Role of Neutrophils in HIV Infection

PURPOSE OF REVIEW

We summarize what is known about neutrophils in HIV infection, focusing on their potential roles in HIV protection, acquisition, and pathogenesis.

RECENT FINDINGS

Recent studies have demonstrated that neutrophil-associated proteins and cytokines in genital tissue pre-infection associate with HIV acquisition. However, recent in vivo assessment of highly exposed seronegative individuals and in vitro studies of anti-HIV functions of neutrophils add to older literature evidence that neutrophils may be important in a protective response to HIV infection. Neutrophils are important for containment of pathogens but can also contribute to tissue damage due to their release of reactive oxygen species, proteases, and other potentially harmful effector molecules. Overall, there is a clear evidence for both helpful and harmful roles of neutrophils in HIV acquisition and pathogenesis. Further study, particularly of tissue neutrophils, is needed to elucidate the kinetics, phenotype, and functionality of neutrophils in HIV infection to better understand this dichotomy.

Neutrophil progenitor populations of rhesus macaques

Captive-bred rhesus macaques of Indian origin represent one of the most important large animal models for infectious disease, solid organ transplantation, and stem cell research. There is a dearth of information defining hematopoietic development, including neutrophil leukocyte differentiation in this species using multicolor flow cytometry. In the current study, we sought to identify cell surface markers that delineate neutrophil progenitor populations with characteristic immunophenotypes. We defined four different postmitotic populations based on their CD11b and CD87 expression pattern, and further refined their immunophenotypes using CD32, CD64, lactoferrin, and myeloperoxidase as antigenic markers. The four subsets contained myelocyte, metamyelocyte, band, and segmented neutrophil populations. We compared our flow cytometry-based classification with the classical nuclear morphology-based classification. We found overlap of immunological phenotype between populations of different nuclear morphology and identified phenotypically different subsets within populations of similar nuclear morphology. We assessed the responsiveness of these populations to stimulatory signals, such as LPS, fMLP, or PMA, and demonstrated significant differences between human and rhesus macaque neutrophil progenitors. In this study, we provided evidence for species-specific features of granulopoiesis that ultimately manifested in the divergent immunophenotypes of the fully differentiated segmented neutrophils of humans and rhesus macaques. Additionally, we found functional markers that can be used to accurately quantify neutrophil progenitors by flow cytometry. Although these markers do not coincide with the classical nuclear-morphology-based grading, they enable us to perform functional studies monitoring immunophenotypic markers.

Neutrophil Vaccination Dynamics and Their Capacity To Mediate B Cell Help in Rhesus Macaques

Neutrophils are the most abundant leukocyte and play a critical role in the initial response to an Ag. Recently, their ability to contribute to adaptive immunity has been highlighted. We evaluated the ability of neutrophils from blood to contribute to the adaptive immune response in a preclinical rhesus macaque SIV vaccine trial. Replication-competent adenovirus-SIV recombinants induced neutrophil activation, B cell help markers, and enhanced ability to generate reactive oxygen species. Boosting with SIV vaccines (adjuvant together with ALVAC or DNA plus envelope protein) elicited significant neutrophil responses. Serum cytokine and chemokine levels induced correlated with the frequency of neutrophil subsets expressing IL-21, myeloperoxidase, and CD64. Post-SIV infection, neutrophils exhibited dysfunction, both phenotypically and functionally. B cells from protected and infected macaques cocultured with autologous polymorphonuclear cells, consisting primarily of neutrophils, were activated, underwent class switching, and produced Abs. This B cell help was not aided by addition of IL-10 and was largely contact dependent. Numerous genes associated with inflammation, Ab production, and chemotaxis were upregulated in the cocultured B cells. We conclude that immune stimulation by vaccination or antigenic exposure imparts a greater ability of neutrophils to contribute to the adaptive immune response. Harnessing this granulocytic response has the potential to improve vaccine efficacy.

The anti-caspase inhibitor Q-VD-OPH prevents AIDS disease progression in SIV-infected rhesus macaques

Apoptosis has been proposed as a key mechanism responsible for CD4+ T cell depletion and immune dysfunction during HIV infection. We demonstrated that Q-VD-OPH, a caspase inhibitor, inhibits spontaneous and activation-induced death of T cells from SIV-infected rhesus macaques (RMs). When administered during the acute phase of infection, Q-VD-OPH was associated with (a) reduced levels of T cell death, (b) preservation of CD4+/CD8+ T cell ratio in lymphoid organs and in the gut, (c) maintenance of memory CD4+ T cells, and (d) increased specific CD4+ T cell response associated with the expression of cytotoxic molecules. Although therapy was limited to the acute phase of infection, Q-VD-OPH-treated RMs showed lower levels of both viral load and cell-associated SIV DNA as compared with control SIV-infected RMs throughout the chronic phase of infection, and prevented the development of AIDS. Overall, our data demonstrate that Q-VD-OPH injection in SIV-infected RMs may represent an adjunctive therapeutic agent to control HIV infection and delaying disease progression to AIDS.

Aged Chinese-origin rhesus macaques infected with SIV develop marked viremia in absence of clinical disease, inflammation or cognitive impairment

Background

Damage to the central nervous system during HIV infection can lead to variable neurobehavioral dysfunction termed HIV-associated neurocognitive disorders (HAND). There is no clear consensus regarding the neuropathological or cellular basis of HAND. We sought to study the potential contribution of aging to the pathogenesis of HAND. Aged (range = 14.7–24.8 year) rhesus macaques of Chinese origin (RM-Ch) (n = 23) were trained to perform cognitive tasks. Macaques were then divided into four groups to assess the impact of SIVmac251 infection (n = 12) and combined antiretroviral therapy (CART) (5 infected; 5 mock-infected) on the execution of these tasks.

Results

Aged SIV-infected RM-Ch demonstrated significant plasma viremia and modest CSF viral loads but showed few clinical signs, no elevations of systemic temperature, and no changes in activity levels, platelet counts or weight. Concentrations of biomarkers of acute and chronic inflammation such as soluble CD14, CXCL10, IL-6 and TNF-α are known to be elevated following SIV infection of young adult macaques of several species, but concentrations of these biomarkers did not shift after SIV infection in aged RM-Ch and remained similar to mock-infected macaques. Neither acute nor chronic SIV infection or CART had a significant impact on accuracy, speed or percent completion in a sensorimotor test.

Conclusions

Viremia in the absence of a chronic elevated inflammatory response seen in some aged RM-Ch is reminiscent of SIV infection in natural disease resistant hosts. The absence of cognitive impairment during SIV infection in aged RM-Ch might be in part attributed to diminishment of some facets of the immunological response. Additional study encompassing species and age differences is necessary to substantiate this hypothesis.

Electronic supplementary material

The online version of this article (10.1186/s12977-018-0400-y) contains supplementary material, which is available to authorized users.

Innate Immune Basis for Rift Valley Fever Susceptibility in Mouse Models

Rift Valley fever virus (RVFV) leads to varied clinical manifestations in animals and in humans that range from moderate fever to fatal illness, suggesting that host immune responses are important determinants of the disease severity. We investigated the immune basis for the extreme susceptibility of MBT/Pas mice that die with mild to acute hepatitis by day 3 post-infection compared to more resistant BALB/cByJ mice that survive up to a week longer. Lower levels of neutrophils observed in the bone marrow and blood of infected MBT/Pas mice are unlikely to be causative of increased RVFV susceptibility as constitutive neutropenia in specific mutant mice did not change survival outcome. However, whereas MBT/Pas mice mounted an earlier inflammatory response accompanied by higher amounts of interferon (IFN)-α in the serum compared to BALB/cByJ mice, they failed to prevent high viral antigen load. Several immunological alterations were uncovered in infected MBT/Pas mice compared to BALB/cByJ mice, including low levels of leukocytes that expressed type I IFN receptor subunit 1 (IFNAR1) in the blood, spleen and liver, delayed leukocyte activation and decreased percentage of IFN-γ-producing leukocytes in the blood. These observations are consistent with the complex mode of inheritance of RVFV susceptibility in genetic studies.

Activation of GPR15 and its involvement in the biological effects of smoking

Smoking is one of the most significant modifiable environmental risk factors for many diseases. Smoking causes excessive mortality worldwide. Despite decades of long research, there has not been a clear understanding regarding the molecular mechanism that makes smoking harmful to health. Some recent studies have found that smoking influences most significantly the expression and methylation of GPR15. GPR15 is an orphan receptor that is involved in the regulation of the innate immunity and the T-cell trafficking in the intestinal epithelium. Further studies have confirmed that GPR15 is very strongly involved in smoking and smoking-induced molecular changes. Therefore, the altered expression and epigenetic regulation of GPR15 could have a significant role in the health impact of smoking. Impact statement The review describes an orphan receptor GPR15 that has recently been found to be influenced by smoking. This makes GPR15 very sensitive and adequate biomarker for smoking and smoking studies. Also, activation of GPR15 by smoking could help to explain its effects on health.

Influence of Plasma Cell Niche Factors on the Recruitment and Maintenance of IRF4hi Plasma Cells and Plasmablasts in Vaccinated, Simian Immunodeficiency Virus-Infected Rhesus Macaques with Low and High Viremia

In a recent study, we found that protection following simian immunodeficiency virus (SIV) exposure correlated with rectal plasma cell frequency in vaccinated female rhesus macaques. We sought to determine if the same macaques maintained high mucosal plasma cell frequencies postinfection and if this translated to reduced viremia. Although delayed SIV acquisition did not predict subsequent viral control, alterations existed in the distribution of plasma cells and plasmablasts between macaques that exhibited high or low viremia. Flow cytometric analysis of cells from rectal biopsy specimens, bone marrow, and mesenteric lymph nodes of vaccinated infected, unvaccinated infected, and uninfected macaques identified two main IRF4^hi subsets of interest: CD138⁺ plasma cells, and CD138^- plasmablasts. In rectal tissue, plasma cell frequency positively correlated with plasma viremia and unvaccinated macaques had increased plasma cells and plasmablasts compared to vaccinated animals. Likewise, plasmablast frequency in the mesenteric lymph node correlated with viremia. However, in bone marrow, plasmablast frequency negatively correlated with viremia. Accordingly, low-viremic macaques had a higher frequency of both bone marrow IRF4^hi subsets than did animals with high viremia. Significant reciprocal relationships between rectal and bone marrow plasmablasts suggested that efficient trafficking to the bone marrow as opposed to the rectal mucosa was linked to viral control. mRNA expression analysis of proteins involved in establishment of plasma cell niches in sorted bone marrow and rectal cell populations further supported this model and revealed differential mRNA expression patterns in these tissues.

IMPORTANCE

As key antibody producers, plasma cells and plasmablasts are critical components of vaccine-induced immunity to human immunodeficiency virus type 1 (HIV-1) in humans and SIV in the macaque model; however, few have attempted to examine the role of these cells in viral suppression postinfection. Our results suggest that plasmablast trafficking to and retention in the bone marrow play a previously unappreciated role in viral control and contrast the potential contribution of mucosal plasma cells to mediate protection at sites of infection with that of bone marrow plasmablasts and plasma cells to control viremia during chronic infection. Manipulation of niche factors influencing the distribution and maintenance of these critical antibody-secreting cells may serve as potential therapeutic targets to enhance antiviral responses postvaccination and postinfection.

Innate immune cell responses in non pathogenic versus pathogenic SIV infections

HIV-1/SIVmac infections deeply disturb innate host responses. Most studies have focused on the impact on dendritic cells and NK cells. A few but insufficient data are available on other innate immune cell types, such as neutrophils. It has been shown that innate lymphoid cells are depleted early and irreversibly during SIVmac/HIV-1 infections. Studies in natural hosts of SIV have contributed to pinpoint that early control of inflammation is crucial. In natural hosts, plasmacytoid dendritic cells, myeloid dendritic cells and NK cells are depleted during acute infection but return to normal levels by the end of acute infection. We summarize here the similarities and differences of various types of innate immune responses in natural hosts compared to pathogenic HIV/SIV mac infections.

Reversing Gut Damage in HIV Infection: Using Non-Human Primate Models to Instruct Clinical Research

Antiretroviral therapy (ART) has led to dramatic improvements in the lives of HIV-infected persons. However, residual immune activation, which persists despite ART, is associated with increased risk of non-AIDS morbidities. Accumulating evidence shows that disruption of the gut mucosal epithelium during SIV/HIV infections allows translocation of microbial products into the circulation, triggering immune activation. This disruption is due to immune, structural and microbial alterations. In this review, we highlighted the key findings of gut mucosa studies of SIV-infected macaques and HIV-infected humans that have revealed virus-induced changes of intestinal CD4, CD8 T cells, innate lymphoid cells, myeloid cells, and of the local cytokine/chemokine network in addition to epithelial injuries. We review the interplay between the host immune response and the intestinal microbiota, which also impacts disease progression. Collectively, these studies have instructed clinical research on early ART initiation, modifiers of microbiota composition, and recombinant cytokines for restoring gut barrier integrity.

A polysaccharide virulence factor of a human fungal pathogen induces neutrophil apoptosis via NK cells

Aspergillus fumigatus is an opportunistic human fungal pathogen that sheds galactosaminogalactan (GG) into the environment. Polymorphonuclear neutrophils (PMNs) and NK cells are both part of the first line of defense against pathogens. We recently reported that GG induces PMN apoptosis. In this study, we show that PMN apoptosis occurs via a new NK cell-dependent mechanism. Reactive oxygen species, induced by the presence of GG, play an indispensable role in this apoptotic effect by increasing MHC class I chain-related molecule A expression at the PMN surface. This increased expression enables interaction between MHC class I chain-related molecule A and NKG2D, leading to NK cell activation, which in turn generates a Fas-dependent apoptosis-promoting signal in PMNs. Taken together, our results demonstrate that the crosstalk between PMNs and NK cells is essential to GG-induced PMN apoptosis. NK cells might thus play a role in the induction of PMN apoptosis in situations such as unexplained neutropenia or autoimmune diseases.

Orphan receptor GPR15/BOB is up-regulated in rheumatoid arthritis

Chemokine receptors on leukocytes mediate the recruitment and accumulation of these cells within affected joints in chronic inflammatory diseases such as rheumatoid arthritis (RA). Identification of involved receptors offers potential for development of therapeutic interventions. The objective of this study was to investigate the expression of orphan receptor GPR15/BOB in the synovium of RA and non-RA patients and in peripheral blood of RA patients and healthy donors. GPR15/BOB protein and messenger RNA expression were examined in RA and non-RA synovium by immunofluorescence and reverse-transcription polymerase chain reaction (RT-PCR) respectively. GPR15/BOB expression on peripheral blood leukocytes was analysed by flow cytometry and GPR15/BOB messenger RNA was examined in peripheral blood monocytes by RT-PCR. GPR15/BOB protein was observed in CD68+ and CD14+ macrophages in synovia, with greater expression in RA synovia. GPR15/BOB protein was expressed in all patient synovia whereas in non-RA synovia expression was low or absent. Similarly GPR15/BOB messenger RNA was detected in all RA and a minority of non-RA synovia. GPR15/BOB protein was expressed on peripheral blood leukocytes from RA and healthy individuals with increased expression by monocytes and neutrophils in RA. GPR15/BOB messenger RNA expression was confirmed in peripheral blood monocytes. In conclusion GPR15/BOB is expressed by macrophages in synovial tissue and on monocytes and neutrophils in peripheral blood, and expression is up-regulated in RA patients compared to non-RA controls. This orphan receptor on monocytes/macrophages and neutrophils may play a role in RA pathophysiology.

SIV infection of rhesus macaques of Chinese origin: a suitable model for HIV infection in humans

Simian immunodeficiency virus (SIV) infection of Indian-origin rhesus macaques (RM) has been widely used as a well-established nonhuman primate (NHP) model for HIV/AIDS research. However, there have been a growing number of studies using Chinese RM to evaluate immunopathogenesis of SIV infection. In this paper, we have for the first time reviewed and discussed the major publications related to SIV or SHIV infection of Chinese RM in the past decades. We have compared the differences in the pathogenesis of SIV infection between Chinese RM and Indian RM with regard to viral infection, immunological response, and host genetic background. Given AIDS is a disease that affects humans of diverse origins, it is of importance to study animals with different geographical background. Therefore, to examine and compare results obtained from RM models of Indian and Chinese origins should lead to further validation and improvement of these animal models for HIV/AIDS research.

Interactions between human immunodeficiency virus type 1 and polymorphonuclear neutrophils

Polymorphonuclear neutrophils (PMN) are the most abundant circulating leukocytes. They represent a first line of innate immunity against a large panel of microbial pathogens, pending development of specific immune responses. The role of PMN in human immunodeficiency virus type 1 (HIV-1) disease has mainly been investigated from the point of view of the increased susceptibility of HIV-1-infected patients to bacterial and fungal infections. However, it is now clear that the relationship between PMN and HIV-1 is far more complex. This review examines both the beneficial and the detrimental effects of PMN during HIV infection.

Neutrophil apoptosis induction by tick-borne encephalitis virus

Tick-borne encephalitis virus infects neutrophils and induces their apoptosis, judging from moderate increase of succinate dehydrogenase activity and a trend to anaerobic energy production in neutrophils infected with the virus (shown by an increase of lactate dehydrogenase activity).

Cloning and analysis of sooty mangabey alternative coreceptors that support simian immunodeficiency virus SIVsmm entry independently of CCR5

Natural host sooty mangabeys (SM) infected with simian immunodeficiency virus SIVsmm do not develop AIDS despite high viremia. SM and other natural hosts express very low levels of CCR5 on CD4(+) T cells, and we recently showed that SIVsmm infection and robust replication occur in vivo in SM genetically lacking CCR5, indicating the use of additional entry pathways. SIVsmm uses several alternative coreceptors of human origin in vitro, but which molecules of SM origin support entry is unknown. We cloned a panel of putative coreceptors from SM and tested their ability to mediate infection, in conjunction with smCD4, by pseudotypes carrying Envs from multiple SIVsmm subtypes. smCXCR6 supported efficient infection by all SIVsmm isolates with entry levels comparable to those for smCCR5, and smGPR15 enabled entry by all isolates at modest levels. smGPR1 and smAPJ supported low and variable entry, whereas smCCR2b, smCCR3, smCCR4, smCCR8, and smCXCR4 were not used by most isolates. In contrast, SIVsmm from rare infected SM with profound CD4(+) T cell loss, previously reported to have expanded use of human coreceptors, including CXCR4, used smCXCR4, smCXCR6, and smCCR5 efficiently and also exhibited robust entry through smCCR3, smCCR8, smGPR1, smGPR15, and smAPJ. Entry was similar with both known alleles of smCD4. These alternative coreceptors, particularly smCXCR6 and smGPR15, may support virus replication in SM that have restricted CCR5 expression as well as SM genetically lacking CCR5. Defining expression of these molecules on SM CD4(+) subsets may delineate distinct natural host target cell populations capable of supporting SIVsmm replication without CD4(+) T cell loss.

A differential concentration-dependent effect of IVIg on neutrophil functions: relevance for anti-microbial and anti-inflammatory mechanisms

BACKGROUND

Polymorphonuclear neutrophils (PMN) play a key role in host defences against invading microorganisms but can also potentiate detrimental inflammatory reactions in case of excessive or misdirected responses. Intravenous immunoglobulins (IVIg) are used to treat patients with immune deficiencies and, at higher doses, in autoimmune, allergic and systemic inflammatory disorders.

METHODOLOGY/PRINCIPAL FINDINGS

We used flow cytometry to examine the effects of IVIg on PMN functions and survival, using whole-blood conditions in order to avoid artifacts due to isolation procedures. IVIg at low concentrations induced PMN activation, as reflected by decreased L-selectin and increased CD11b expression at the PMN surface, oxidative burst enhancement, and prolonged cell survival. In contrast, IVIg at higher concentrations inhibited LPS-induced CD11b degranulation and oxidative burst priming, and counteracted LPS-induced PMN lifespan prolongation.

CONCLUSIONS/SIGNIFICANCE

IVIg appears to have differential, concentration-dependent effects on PMN, possibly supporting the use of IVIg as either an anti-microbial or an anti-inflammatory agent.

Phosphorylation-dependent C-terminal binding of 14-3-3 proteins promotes cell surface expression of HIV co-receptor GPR15

Membrane trafficking is dictated by dynamic molecular interactions involving discrete determinants in the cargo proteins and the intracellular transport machineries. We have previously reported that cell surface expression of GPR15, a G protein-coupled receptor (GPCR) that serves as a co-receptor for HIV, is correlated with the mode III binding of 14-3-3 proteins to the receptor C terminus. Here we provide a mechanistic basis for the role of 14-3-3 in promoting the cell surface expression of GPR15. The Ala mutation of penultimate phospho-Ser (S359A) that abolishes 14-3-3 binding resulted in substantially reduced O-glycosylation and the cell surface expression of GPR15. The surface membrane protein CD8 fused with the C-terminal tail of GPR15(S359A) mutant was re-localized in the endoplasmic reticulum (ER). In the context of S359A mutation, the additional mutations in the upstream stretch of basic residues (RXR motif) restored O-glycosylation and the cell surface expression. The RXR motif was responsible for the interaction with coatomer protein I (COPI), which was inversely correlated with the 14-3-3 binding and cell surface expression. These results suggest that 14-3-3 binding promotes cell surface expression of GPR15 by releasing the receptor from ER retrieval/retention pathway that is mediated by the interaction of RXR motif and COPI. Moreover, 14-3-3 binding substantially increased the stability of GPR15 protein. Thus 14-3-3 proteins play multiple roles in biogenesis and trafficking of an HIV co-receptor GPR15 to control its cell surface density in response to the phosphorylation signal.

SIV infection in natural hosts: resolution of immune activation during the acute-to-chronic transition phase

SIV-infected natural hosts do not progress to clinical AIDS yet display high viral replication and an acute immunologic response similar to pathogenic SIV/HIV infections. During chronic SIV infection, natural hosts suppress their immune activation, whereas pathogenic hosts display a highly activated immune state. Here, we review natural host SIV infections with an emphasis on specific immune cells and their contribution to the transition from the acute-to-chronic phases of infection.

A novel CCR5 mutation common in sooty mangabeys reveals SIVsmm infection of CCR5-null natural hosts and efficient alternative coreceptor use in vivo

In contrast to HIV infection in humans and SIV in macaques, SIV infection of natural hosts including sooty mangabeys (SM) is non-pathogenic despite robust virus replication. We identified a novel SM CCR5 allele containing a two base pair deletion (Δ2) encoding a truncated molecule that is not expressed on the cell surface and does not support SIV entry in vitro. The allele was present at a 26% frequency in a large SM colony, along with 3% for a CCR5Δ24 deletion allele that also abrogates surface expression. Overall, 8% of animals were homozygous for defective CCR5 alleles and 41% were heterozygous. The mutant allele was also present in wild SM in West Africa. CD8+ and CD4+ T cells displayed a gradient of CCR5 expression across genotype groups, which was highly significant for CD8+ cells. Remarkably, the prevalence of natural SIVsmm infection was not significantly different in animals lacking functional CCR5 compared to heterozygous and homozygous wild-type animals. Furthermore, animals lacking functional CCR5 had robust plasma viral loads, which were only modestly lower than wild-type animals. SIVsmm primary isolates infected both homozygous mutant and wild-type PBMC in a CCR5-independent manner in vitro, and Envs from both CCR5-null and wild-type infected animals used CXCR6, GPR15 and GPR1 in addition to CCR5 in transfected cells. These data clearly indicate that SIVsmm relies on CCR5-independent entry pathways in SM that are homozygous for defective CCR5 alleles and, while the extent of alternative coreceptor use in SM with CCR5 wild type alleles is uncertain, strongly suggest that SIVsmm tropism and host cell targeting in vivo is defined by the distribution and use of alternative entry pathways in addition to CCR5. SIVsmm entry through alternative pathways in vivo raises the possibility of novel CCR5-negative target cells that may be more expendable than CCR5+ cells and enable the virus to replicate efficiently without causing disease in the face of extremely restricted CCR5 expression seen in SM and several other natural host species.

Temporal association of large granular lymphocytosis, neutropenia, proviral load, and FasL mRNA in cats with acute feline immunodeficiency virus infection

During acute feline immunodeficiency virus-C(PGammar) (FIV-C-PG) infection, we observed that cats develop large granular lymphocyte (LGL) lymphocytosis concurrent with a marked neutropenia that is temporally associated with the rise and fall of FIV-C-PG proviral loads. LGLs, generally considered to be analogous to natural killer (NK) cells, can also be highly cytolytic CD8/CD57 T cells. Neutropenia has been reported during acute human immunodeficiency virus (HIV-1) infection, but there is a paucity of information describing the pathogenesis of this condition. During HIV-1 infection, LGLs have been shown to be both CD16(+) NK cells and CD8(+)/CD57(+) T cells, but an association with neutropenia has not been described. However, neutropenia with concurrent LGL lymphocytosis has been demonstrated in both LGL leukemia and common variable immunodeficiency syndrome in people, and in both syndromes, an increase in soluble Fas ligand (FasL) has been associated with neutrophil apoptosis leading to neutropenia. Flow cytometric analysis demonstrated increases in CD56 and CD8 peripheral blood cell surface expression during acute FIV-C-PG infection. Expression of FasL mRNA was increased at the same time points as these peripheral hematologic abnormalities, and also decreased as FIV-C-PG proviral load reached set point. We describe an interesting temporal association between innate immune responses and viral load during acute FIV-C-PG infection, which has similarities to HIV-1 infection and other immune dyscrasias of people, and which may contribute to the neutropenia and LGL lymphocytosis during FIV-C-PG infection.

Flow cytometric investigation of neutrophil oxidative burst and apoptosis in physiological and pathological situations

Flow cytometric analysis provides a rapid screen for abnormalities of polymorphonuclear neutrophils (PMN) function and reflect their behavior in vivo more accurately. This review summarizes the major fluorescent probes used to study PMN oxidative burst and apoptosis using flow cytometry (FCM). We also provide examples of FCM studies in physiological and pathological situations, illustrating the advantages of FCM for assessment of PMN oxidative burst and PMN apoptosis. These data point to the role of FCM in detecting primary immunodeficiencies such as IRAK4 deficiency and support the use of the assessment of the PMN oxidative burst for routine testing in patients with bacterial infections. We also demonstrate the utility of whole-blood analysis using FCM for a better understanding of PMN functionality, i.e., tuning PMN responses to inflammatory stimuli. Finally, FCM permits a simultaneous analysis of phenotypic, functional and morphometric parameters assessing whole-blood PMN apoptosis, in particular in response to Toll-like receptor agonists and during simian immunodeficiency virus infection.

The Duffy-null state is associated with a survival advantage in leukopenic HIV-infected persons of African ancestry

Persons of African ancestry, on average, have lower white blood cell (WBC) counts than those of European descent (ethnic leukopenia), but whether this impacts negatively on HIV-1 disease course remains unknown. Here, in a large natural history cohort of HIV-infected subjects, we show that, although leukopenia (< 4000 WBC/mm(3) during infection) was associated with an accelerated HIV disease course, this effect was more prominent in leukopenic subjects of European than African ancestry. The African-specific -46C/C genotype of Duffy Antigen Receptor for Chemokines (DARC) confers the malaria-resisting, Duffy-null phenotype, and we found that the recently described association of this genotype with ethnic leukopenia extends to HIV-infected African Americans (AAs). The association of Duffy-null status with HIV disease course differed according to WBC but not CD4(+) T-cell counts, such that leukopenic but not nonleukopenic HIV(+) AAs with DARC -46C/C had a survival advantage compared with all Duffy-positive subjects. This survival advantage became increasingly pronounced in those with progressively lower WBC counts. These data highlight that the interaction between DARC genotype and the cellular milieu defined by WBC counts may influence HIV disease course, and this may provide a partial explanation of why ethnic leukopenia remains benign in HIV-infected AAs, despite immunodeficiency.

Neutrophil apoptosis during viral infections

Apoptosis, or programmed cell death, is a highly conserved cellular suicide mechanism. Apoptosis is critical to the effective resolution of inflammation, particularly in regulating the lifespan of neutrophils. Neutrophils are key components of the first line of defense against microorganisms. Thus, subversion of this critical host defense mechanism by pathogens can contribute to susceptibility to severe and recurrent infections. In this review, we describe the molecular mechanisms involved in PMN death in relationship with viral infections.

Increased neutrophil apoptosis in chronically SIV-infected macaques

Polymorphonuclear neutrophils (PMN) from chronically HIV-infected individuals have been reported to be more prone to die. However, although non-human primates models have been extensively used for improving our knowledge on T cell immunity, the impact of SIV-infection on PMN, in relationships with disease severity, has never been assessed. In our study, we demonstrate that PMN from Rhesus macaques (RMs) of Chinese origin chronically infected with the virulent strain SIVmac251 display increased susceptibility to undergo apoptosis as compared to PMN from RMs infected with the non-pathogenic SIVΔnef strain. PMN apoptosis was significantly increased in RMs progressing faster to AIDS as compared to non-progressors RMs. Furthermore, the percentage of apoptotic cells correlated with PMN activation state reflected by increased CD11b expression and reactive oxygen species production. Interestingly, whereas inflammatory cytokines IL-8 and IL-1β prevent in vitro PMN death, the levels of those cytokines were low in RMs progressing towards AIDS. Altogether, increased PMN death during SIV infection is a new pathogenic effect associated with AIDS progression, adding to the long list of markers associated with disruption of defense against infection.