Macrophage-dependent apoptosis of CD4+ T lymphocytes from HIV-infected individuals is mediated by FasL and tumor necrosis factor

The Enigma of Lymphocyte Apoptosis in the Response to Influenza Virus Infection

In the pathogenesis of influenza virus infection, lymphocyte apoptosis as a part of the infection and/or the immune response to the virus can be somewhat puzzling. The percentage of human T lymphocytes within the peripheral blood mononuclear cell population that becomes apoptotic greatly exceeds the percentage that are infected after exposure to the virus, consistent with substantial apoptosis of bystander T lymphocytes. Studies reveal an important role of viral neuraminidase expression by co-cultured monocyte/macrophages in induction of apoptosis, including that of uninfected bystander lymphocytes. Despite these observations, it is a reasonable perspective to recognize that the development of lymphocyte apoptosis during the response to infection does not preclude a successful immune response and recovery of the infected host in the great majority of cases. Further investigation is clearly warranted to understand its role in the pathogenesis of influenza virus infection for human subjects.

The Interplay of HIV-1 and Macrophages in Viral Persistence

HIV-1 has evolved mechanisms to evade host cell immune responses and persist for lifelong infection. Latent cellular reservoirs are responsible for this persistence of HIV-1 despite the powerful effects of highly active antiretroviral therapies (HAART) to control circulating viral load. While cellular reservoirs have been extensively studied, much of these studies have focused on peripheral blood and resting memory CD4+ T cells containing latent HIV-1 provirus; however, efforts to eradicate cellular reservoirs have been stunted by reservoirs found in tissues compartments that are not easily accessible. These tissues contain resting memory CD4+ T cells and tissue resident macrophages, another latent cellular reservoir to HIV-1. Tissue resident macrophages have been associated with HIV-1 infection since the 1980s, and evidence has continued to grow regarding their role in HIV-1 persistence. Specific biological characteristics play a vital role as to why macrophages are latent cellular reservoirs for HIV-1, and in vitro and in vivo studies exhibit how macrophages contribute to viral persistence in individuals and animals on antiretroviral therapies. In this review, we characterize the role and evolutionary advantages of macrophage reservoirs to HIV-1 and their contribution to HIV-1 persistence. In acknowledging the interplay of HIV-1 and macrophages in the host, we identify reasons why current strategies are incapable of eliminating HIV-1 reservoirs and why efforts must focus on eradicating reservoirs to find a future functional cure.

Protein N-myristoylation: functions and mechanisms in control of innate immunity

Protein N-myristoylation is an important fatty acylation catalyzed by N-myristoyltransferases (NMTs), which are ubiquitous enzymes in eukaryotes. Specifically, attachment of a myristoyl group is vital for proteins participating in various biological functions, including signal transduction, cellular localization, and oncogenesis. Recent studies have revealed unexpected mechanisms indicating that protein N-myristoylation is involved in host defense against microbial and viral infections. In this review, we describe the current understanding of protein N-myristoylation (mainly focusing on myristoyl switches) and summarize its crucial roles in regulating innate immune responses, including TLR4-dependent inflammatory responses and demyristoylation-induced innate immunosuppression during Shigella flexneri infection. Furthermore, we examine the role of myristoylation in viral assembly, intracellular host interactions, and viral spread during human immunodeficiency virus-1 (HIV-1) infection. Deeper insight into the relationship between protein N-myristoylation and innate immunity might enable us to clarify the pathogenesis of certain infectious diseases and better harness protein N-myristoylation for new therapeutics.

Orchestrated efforts on host network hijacking: Processes governing virus replication

With the high pervasiveness of viral diseases, the battle against viruses has never ceased. Here we discuss five cellular processes, namely "autophagy", "programmed cell death", "immune response", "cell cycle alteration", and "lipid metabolic reprogramming", that considerably guide viral replication after host infection in an orchestrated manner. On viral infection, "autophagy" and "programmed cell death" are two dynamically synchronized cell survival programs; "immune response" is a cell defense program typically suppressed by viruses; "cell cycle alteration" and "lipid metabolic reprogramming" are two altered cell housekeeping programs tunable in both directions. We emphasize on their functionalities in modulating viral replication, strategies viruses have evolved to tune these processes for their benefit, and how these processes orchestrate and govern cell fate upon viral infection. Understanding how viruses hijack host networks has both academic and industrial values in providing insights toward therapeutic strategy design for viral disease control, offering useful information in applications that aim to use viral vectors to improve human health such as gene therapy, and providing guidelines to maximize viral particle yield for improved vaccine production at a reduced cost.

Immune Responses in Post Kala-azar Dermal Leishmaniasis

Kala-azar, commonly known as visceral leishmaniasis (VL), is a neglected tropical disease that has been targeted in South Asia for elimination by 2020. Presently, the Kala-azar Elimination Programme is aimed at identifying new low-endemic foci by active case detection, consolidating vector control measures, and decreasing potential reservoirs, of which Post Kala-azar Dermal Leishmaniasis (PKDL) is considered as the most important. PKDL is a skin condition that occurs after apparently successful treatment of VL and is characterized by hypopigmented patches (macular) or a mixture of papules, nodules, and/or macules (polymorphic). To achieve this goal of elimination, it is important to delineate the pathophysiology so that informed decisions can be made regarding the most appropriate and cost-effective approach. We reviewed the literature with regard to PKDL in Asia and Africa and interpreted the findings in establishing a potential correlation between the immune responses and pathophysiology. The overall histopathology indicated the presence of a dense, inflammatory cellular infiltrate, characterized by increased expression of alternatively activated CD68+ macrophages, CD8+ T cells showing features of exhaustion, CD20+ B cells, along with decreased CD1a+ dendritic cells. Accordingly, this review is an update on the overall immunopathology of PKDL, so as to provide a better understanding of host-parasite interactions and the immune responses generated which could translate into availability of markers that can be harnessed for assessment of disease progression and improvement of existing treatment modalities.

HIV-1 Nef-GCC185 interaction regulates assembly of cellular protein complexes at TGN targeting MHC-I downregulation

AIM

HIV-1 Nef downregulates surface MHC-I to protect the infected cells from CTLs-mediated killing. Although MHC-I downregulation has been extensively studied, the Nef-dependent assembly of the multi-protein complex and subsequent pathways activation has not yet been well explored. The present study is aimed for the identification of Nef-mediated sequential recruitment of cellular proteins that constitute the functional multi-protein complex, required for the downregulation of MHC-I.

MAIN METHODS

Different Cellular protein complexes were identified by co-immunoprecipitation in Nef or NefE4A mutant-expressing Jurkat T, and THP-1 cells followed by exposure to Nef-specific peptides 24 h post infection. The MHC-I downregulation was analyzed by confocal microscopy and flow cytometry.

KEY FINDINGS

We found the association of Nef with PACS-2, GCC185, PI3K, AP-1, SFK, and MHC-I proteins that probably constitute a functional multi-protein complex. Furthermore, the immunoprecipitations with PACS-2 and GCC185 in the presence or absence of Nef, Nef E4A mutant and Nef with CP-inhibitor divide the functional complex of Nef into Nef-dependent (AP-1 and PI3K) and GCC185-dependent complex (MHC-I and SFK). The molecular mechanisms for activation of cellular pathways have been deciphered on the basis of these interactions that are brought in close proximity through Nef-GCC185 interaction. Knockdown of GCC185 using siRNA in Jurkat T cells showed a direct relationship between the assembly of functional multi-protein complex and MHC-I accumulation at GCC185.

SIGNIFICANCE

Overall, our study elucidates that GCC185 is a focal point for the assembly of the Nef-mediated multi-protein complex at TGN.

RNAa Induced by TATA Box-Targeting MicroRNAs

Recent studies reveal that some nuclear microRNAs (miRNA) and synthesized siRNAs target gene promoters to activate gene transcription (RNAa). Interestingly, our group identified a novel HIV-1-encoded miRNA, miR-H3, which targets specifically the core promoter TATA box of HIV-1 and activates viral gene expression. Depletion of miR-H3 significantly impaired the replication of HIV-1. miR-H3 mimics could activate viruses from CD4⁺ T cells isolated from patients receiving suppressive highly active antiretroviral therapy, which is very intriguing for reducing HIV-1 latent reservoir. Further study revealed that many cellular miRNAs also function like miR-H3. For instance, let-7i targets the TATA box of the interleukin-2 (IL-2) promoter and upregulates IL-2 expression in T-lymphocytes. In RNAa induced by TATA box-targeting miRNAs, Argonaute (AGO) proteins are needed, but there is no evidence for the involvement of promoter-associated transcripts or epigenetic modifications. We propose that the binding of small RNA-AGO complex to TATA box could facilitate the assembly of RNA Polymerase II transcription preinitiation complex. In addition, synthesized small RNAs targeting TATA box can also efficiently activate transcription of interested genes, such as insulin, IL-2, and c-Myc. The discovery of RNAa induced by TATA box-targeting miRNA provides an easy-to-use tool for activating gene expression.

Cellular Determinants of HIV Persistence on Antiretroviral Therapy

The era of antiretroviral therapy has made HIV-1 infection a manageable chronic disease for those with access to treatment. Despite treatment, virus persists in tissue reservoirs seeded with long-lived infected cells that are resistant to cell death and immune recognition. Which cells contribute to this reservoir and which factors determine their persistence are central questions that need to be answered to achieve viral eradication. In this chapter, we describe how cell susceptibility to infection, resistance to cell death, and immune-mediated killing as well as natural cell life span and turnover potential are central components that allow persistence of different lymphoid and myeloid cell subsets that were recently identified as key players in harboring latent and actively replicating virus. The relative contribution of these subsets to persistence of viral reservoir is described, and the open questions are highlighted.

Impaired activation of lesional CD8+ T-cells is associated with enhanced expression of Programmed Death-1 in Indian Post Kala-azar Dermal Leishmaniasis

Post Kala-azar dermal leishmaniasis (PKDL), caused by Leishmania donovani is the dermal sequel of Visceral Leishmaniasis and importantly, is the proposed disease reservoir. The survival of Leishmania parasites within monocytes/macrophages hinges on its ability to effectively nullify immune activation mechanisms. Thus, delineating the disease-promoting immune mechanisms can facilitate development of immunotherapeutic strategies. Accordingly, in the absence of an animal model, this study aimed to delineate the status of CD8⁺ T-cells in patients with PKDL. At disease presentation, the absence of CD4⁺ T-cells at lesional sites was concomitant with an overwhelming infiltration of CD8⁺ T-cells that demonstrated an absence of Perforin, Granzyme and Zap-70, along with an enhanced expression of Programmed Death-1 (PD-1) and the skin-homing CCL17. Additionally, the lesional CCR4⁺CD8⁺ population was associated with an enhanced expression of IL-10 and IL-5. In circulation, the enhanced CD8⁺CCR4⁺ T-cell population and raised levels of CCL17/22 was associated with an increased frequency of PD-1, while CD127 was decreased. Taken together, in PKDL, the enhanced plasma and lesional CCL17 accounted for the dermal homing of CD8⁺CCR4⁺ T-cells, that along with a concomitant upregulation of PD-1 and IL-10 mediated immune inactivation, emphasizing the need for designing immunotherapies capable of reinvigorating T-cell potency.

Host and Viral Factors in HIV-Mediated Bystander Apoptosis

Human immunodeficiency virus (HIV) infections lead to a progressive loss of CD4 T cells primarily via the process of apoptosis. With a limited number of infected cells and vastly disproportionate apoptosis in HIV infected patients, it is believed that apoptosis of uninfected bystander cells plays a significant role in this process. Disease progression in HIV infected individuals is highly variable suggesting that both host and viral factors may influence HIV mediated apoptosis. Amongst the viral factors, the role of Envelope (Env) glycoprotein in bystander apoptosis is well documented. Recent evidence on the variability in apoptosis induction by primary patient derived Envs underscores the role of Env glycoprotein in HIV disease. Amongst the host factors, the role of C-C Chemokine Receptor type 5 (CCR5), a coreceptor for HIV Env, is also becoming increasingly evident. Polymorphisms in the CCR5 gene and promoter affect CCR5 cell surface expression and correlate with both apoptosis and CD4 loss. Finally, chronic immune activation in HIV infections induces multiple defects in the immune system and has recently been shown to accelerate HIV Env mediated CD4 apoptosis. Consequently, those factors that affect CCR5 expression and/or immune activation in turn indirectly regulate HIV mediated apoptosis making this phenomenon both complex and multifactorial. This review explores the complex role of various host and viral factors in determining HIV mediated bystander apoptosis.

Dual Role of Fas/FasL-Mediated Signal in Peripheral Immune Tolerance

Fas-mediated apoptosis contributes to physiological and pathological cellular processes, such as differentiation and survival. In particular, the roles of Fas in immune cells are complex and critical for the maintenance of immune tolerance. The precise pathways and unique functions associated with Fas/FasL-mediated signaling in the immune system are known. The dual character of Fas/FasL-mediated immune regulation that induces beneficial or harmful effects is associated with the onset or development of immune disorders. Studies on mutations in genes encoding Fas and FasL gene of humans and mice contributed to our understanding of the pathogenesis of autoimmune diseases. Here, we review the opposing functions of Fas/FasL-mediated signaling, bilateral effects of Fas/FasL on in immune cells, and complex pathogenesis of autoimmunity mediated by Fas/FasL.

Effect of Cocaine on HIV Infection and Inflammasome Gene Expression Profile in HIV Infected Macrophages

We have observed significantly increased HIV infection in HIV infected macrophages in the presence of cocaine that could be due to the downregulation of BST2 restriction factor in these cells. In human inflammasome PCR array, among different involved in inflammasome formation, in HIV infected macrophages in the presence of cocaine, we have observed significant upregulation of NLRP3, AIM2 genes and downstream genes IL-1β and PTGS2. Whereas negative regulatory gene MEFV was upregulated, CD40LG and PYDC1 were significantly downregulated. Among various NOD like receptors, NOD2 was significantly upregulated in both HIV alone and HIV plus cocaine treated cells. In the downstream genes, chemokine (C-C motif) ligand 2 (CCL2), CCL7 and IL-6 were significantly up regulated in HIV plus cocaine treated macrophages. We have also observed significant ROS production (in HIV and/or cocaine treated cells) which is one of the indirect-activators of inflammasomes formation. Further, we have observed early apoptosis in HIV alone and HIV plus cocaine treated macrophages which may be resultant of inflammasome formation and cspase-1 activation. These results indicate that in case of HIV infected macrophages exposed to cocaine, increased ROS production and IL-1β transcription serve as an activators for the formation of NLRP3 and AIM2 mediated inflammasomes that leads to caspase 1 mediated apoptosis.

HIV-1 Infection-Induced Suppression of the Let-7i/IL-2 Axis Contributes to CD4(+) T Cell Death

The mechanisms underlying HIV-1-mediated CD4⁺ T cell depletion are highly complicated. Interleukin-2 (IL-2) is a key cytokine that maintains the survival and proliferation of activated CD4⁺ T cells. IL-2 levels are disturbed during HIV-1 infection, but the underlying mechanism(s) requires further investigation. We have reported that cellular microRNA (miRNA) let-7i upregulates IL-2 expression by targeting the promoter TATA-box region, which functions as a positive regulator. In this study, we found that HIV-1 infection decreases the expression of let-7i in CD4⁺ T cells by attenuating its promoter activity. The reduced let-7i miRNA expression led to a decline in IL-2 levels. A let-7i mimic increased IL-2 expression and subsequently enhanced the resistance of CD4⁺ T cells to HIV-1-induced apoptosis. By contrast, the blockage of let-7i with a specific inhibitor resulted in elevated CD4⁺ T cell apoptosis during HIV-1 infection. Furthermore, by knocking down the expression of IL-2, we found that the let-7i-mediated CD4⁺ T cell resistance to apoptosis during HIV-1 infection was dependent on IL-2 signaling rather than an alternative CD95-mediated cell-death pathway. Taken together, our findings reveal a novel pathway for HIV-1-induced dysregulation of IL-2 cytokines and depletion of CD4⁺ T-lymphocytes.

Next-Generation mRNA Sequencing Reveals Pyroptosis-Induced CD4+ T Cell Death in Early Simian Immunodeficiency Virus-Infected Lymphoid Tissues

Lymphoid tissues (LTs) are the principal sites where human immunodeficiency virus type 1 (HIV-1) replicates and virus-host interactions take place, resulting in immunopathology in the form of inflammation, immune activation, and CD4(+) T cell death. The HIV-1 pathogenesis in LTs has been extensively studied; however, our understanding of the virus-host interactions in the very early stages of infection remains incomplete. We investigated virus-host interactions in the rectal draining lymph nodes (dLNs) of rhesus macaques at different times after intrarectal inoculation (days postinoculation [dpi]) with simian immunodeficiency virus (SIV). At 3 dpi, 103 differentially expressed genes (DEGs) were detected using next-generation mRNA sequencing (RNA-seq). At 6 and 10 dpi, concomitant with increased SIV replication, 366 and 1,350 DEGs were detected, respectively, including upregulation of genes encoding proteins that play a role in innate antiviral immune responses, inflammation, and immune activation. Notably, genes (IFI16, caspase-1, and interleukin 1β [IL-1β]) in the canonical pyroptosis pathway were significantly upregulated in expression. We further validated increased pyroptosis using flow cytometry and found that the number of CD4(+) T cells expressing activated caspase-1 protein, the hallmark of ongoing pyroptosis, were significantly increased, which is correlated with decreased CD4(+) T cells in dLNs. Our results demonstrated that pyroptosis contributes to the CD4(+) T cell death in vivo in early SIV infection, which suggests that pyroptosis may play a pivotal role in the pathogenesis of SIV, and by extension, that of HIV-1, since pyroptosis not only induces CD4(+) T cell death but also amplifies inflammation and immune activation. Thus, blocking CD4(+) T cell pyroptosis could be a complementary treatment to antiretroviral therapy.

IMPORTANCE

Although secondary lymphoid tissues (LTs) are principal sites of human immunodeficiency virus type 1 (HIV-1) replication, inflammation, immune activation, and CD4(+) T cell death, immunopathogenesis in LTs during early infection remains largely unknown. Using the simian immunodeficiency virus (SIV)/rhesus monkey model of HIV rectal infection, we investigated early virus-host interactions. Our results revealed elevated potent host responses in early infection in LTs, including upregulation of genes involved in antiviral immune response, inflammation, and immune activation. Importantly, genes involved in the canonical pyroptosis pathway were significantly upregulated, and there was a strong correlation between CD4(+) T cell decrease and increased number of CD4(+) T cells expressing activated caspase-1 protein, demonstrating that pyroptosis contributes to CD4(+) T cell death in vivo in very early SIV infection. Our finding suggests that blocking pyroptosis may be able to decrease CD4(+) T cell loss during early SIV infection.

Association between the tumor necrosis factor-α-308G/A gene polymorphism and HIV-1 susceptibility: a meta-analysis

The tumor necrosis factor-α (TNF-α)-308G/A gene polymorphism influences the pathogenesis and evolution of HIV-1 disease. Many studies have evaluated the association between this polymorphism and HIV-1 susceptibility, but the exact relationship between them remains ambiguous and contradictory. Accordingly, the present study evaluates the exact association between TNF-α-308G/A gene polymorphism and HIV-1 susceptibility. A systematic literature search was conducted and the case-control studies that were found assessing the association between TNF-α-308G/A gene polymorphism and HIV-1 susceptibility were analyzed. The pooled odds ratios (ORs) and 95% confidence interval (CI) were calculated by a fixed effect model. Heterogeneity was analyzed by Cochran's Q and the I(2) statistics. Publication bias was assessed using the Begg's funnel plot and Egger's test. A total of 679 cases and 873 controls from five studies were included. Overall, no significant relationship was found between TNF-α-308G/A gene polymorphism and HIV-1 susceptibility in this meta-analysis study (A versus G genotype model: OR=0.89, 95% CI=0.59-1.32, p=0.553; GG versus AA+AG model: OR=1.23, 95% CI=0.75-2.02, p=0.407; GG+AG versus AA model: OR=1.40, 95% CI=0.70-2.82, p=0.345; GG versus AA model: OR=1.39, 95% CI=0.69-2.80, p=0.362; AG versus AA model: OR=1.43, 95% CI=0.70-2.96, p=0.329; GG+AA versus AG model: OR=0.76, 95% CI=0.44-1.29, p=0.304). The meta-analysis found no marked association between TNF-α-308G/A gene polymorphism and HIV-1 susceptibility.

Eradication of HIV-1 from the macrophage reservoir: an uncertain goal?

Human immunodeficiency virus type 1 (HIV-1) establishes latency in resting memory CD4+ T cells and cells of myeloid lineage. In contrast to the T cells, cells of myeloid lineage are resistant to the HIV-1 induced cytopathic effect. Cells of myeloid lineage including macrophages are present in anatomical sanctuaries making them a difficult drug target. In addition, the long life span of macrophages as compared to the CD4+ T cells make them important viral reservoirs in infected individuals especially in the late stage of viral infection where CD4+ T cells are largely depleted. In the past decade, HIV-1 persistence in resting CD4+ T cells has gained considerable attention. It is currently believed that rebound viremia following cessation of combination anti-retroviral therapy (cART) originates from this source. However, the clinical relevance of this reservoir has been questioned. It is suggested that the resting CD4+ T cells are only one source of residual viremia and other viral reservoirs such as tissue macrophages should be seriously considered. In the present review we will discuss how macrophages contribute to the development of long-lived latent reservoirs and how macrophages can be used as a therapeutic target in eradicating latent reservoir.

Review article: the intersection of mucosal pathophysiology in HIV and inflammatory bowel disease, and its implications for therapy

BACKGROUND

The immunopathology of inflammatory bowel diseases (IBD) and HIV in the gastrointestinal (GI) tract can be viewed as ends of a spectrum with IBD being associated with 'immune excess' and HIV with 'immune paucity' within the GI tract.

AIM

To review the pathophysiology of IBD and HIV as they intersect in the gut immune system.

METHODS

A search was conducted in PubMed using defined keywords 'IBD, inflammatory bowel disease, Crohn's disease, ulcerative colitis, HIV, innate immunity, mucosal layer, macrophage, cytokine, dendritic cells, adaptive immunity, CD4, T cells, Th1, Th2, natural killer T cells (NKT)'.

RESULTS

Both the mucosal innate defence and adaptive immunity are profoundly affected by IBD and HIV. The pathophysiology of IBD and HIV with regard to mucosal barrier, macrophages, dendritic cells, NK cells, NKT cells and T-cell subsets is distinct yet closely interwoven. There is limited information on the clinical manifestations of patients who have both IBD and HIV. However, recent studies suggest that the clinical course of IBD may be attenuated by concurrent HIV infection - a premise that is reasonably supported by what is known of their pathophysiology.

CONCLUSIONS

It is apparent that through specific pathophysiological mechanisms, HIV is capable of attenuating inflammation in IBD. In the absence of experimental models, further clinical studies are necessary to better understand patients with concurrent disease and decipher the clinical and mechanistic relationship between HIV and IBD at mucosal surfaces. Such studies are critical to guide therapeutic decisions in the management of patients with IBD infected with HIV.

Alteration of sFAS and sFAS ligand expression during canine visceral leishmaniosis

Visceral leishmaniosis (VL) is caused by intracellular parasites of the genus Leishmania that affect humans and several animal species. Dogs are one of the main urban reservoirs of Leishmania infantum and play a central role in the transmission cycle to humans via sandflies. CD3+ cells apoptosis is involved in the immune response in VL. Dysregulation of apoptosis has been implicated in various disease states. An important regulator of apoptosis is the FAS-FAS-associated death domain protein (cluster of differentiation 95 - CD95) and FASL-FAS ligand protein (cluster of differentiation 178 - CD178) system involved in the down-regulation of immune reactions and in T cell-mediated cytotoxicity. FAS is a member of the tumor necrosis factor (TNF) receptor super family, which can be expressed in transmembrane or soluble forms. The soluble levels of FAS (sFAS), FASL (sFASL) and active Caspase-3, this last related to apoptotic cascade, were investigated in the spleen of 19 symptomatic dogs presenting moderate VL and 6 healthy dogs, determined by ELISA assay. The splenic parasite load was determined by real-time PCR monitoring of amplification of the intergenic internal transcribed spacer (ITS1) gene of parasite rRNA. sFAS levels were lower (p<0.05). sFASL and active Caspase-3 levels were higher (p<0.05) in dogs with VL compared with controls. Negative correlation was observed between parasite burden and sFASL levels. The increase in sFASL could be related to the mechanism involved in the elimination of the parasite.

HIV-1 latency in monocytes/macrophages

Human immunodeficiency virus type 1 (HIV-1) targets CD4⁺ T cells and cells of the monocyte/macrophage lineage. HIV pathogenesis is characterized by the depletion of T lymphocytes and by the presence of a population of cells in which latency has been established called the HIV-1 reservoir. Highly active antiretroviral therapy (HAART) has significantly improved the life of HIV-1 infected patients. However, complete eradication of HIV-1 from infected individuals is not possible without targeting latent sources of infection. HIV-1 establishes latent infection in resting CD4⁺ T cells and findings indicate that latency can also be established in the cells of monocyte/macrophage lineage. Monocyte/macrophage lineage includes among others, monocytes, macrophages and brain resident macrophages. These cells are relatively more resistant to apoptosis induced by HIV-1, thus are important stable hideouts of the virus. Much effort has been made in the direction of eliminating HIV-1 resting CD4⁺ T-cell reservoirs. However, it is impossible to achieve a cure for HIV-1 without considering these neglected latent reservoirs, the cells of monocyte/macrophage lineage. In this review we will describe our current understanding of the mechanism of latency in monocyte/macrophage lineage and how such cells can be specifically eliminated from the infected host.

The macrophage: a therapeutic target in HIV-1 infection

Human immunodeficiency virus (HIV) is still a serious global health concern responsible for more than 25 million deaths in last three decades. More than 34 million people are living with HIV infection. Macrophages and CD4+ T cells are the principal targets of HIV-1. The pathogenesis of HIV-1 takes different routes in macrophages and CD4+ T cells. Macrophages are resistant to the cytopathic effect of HIV-1 and produce virus for longer periods of time. In addition, macrophages being present in every organ system thus can disseminate virus to the different anatomical sites leading to the formation of viral sanctuaries. Complete cure of HIV-1 needs better understanding of viral pathogenesis in these reservoirs and implementation of knowledge into robust therapeutic products. In this review we will focus on the unique relationship between HIV-1 and macrophages. Furthermore, we will describe how successful antiretroviral therapy (ART) is in suppressing HIV and novel molecular and cellular strategies against HIV-1 in macrophages.

The macrophage: a therapeutic target in HIV-1 infection

Human immunodeficiency virus (HIV) is still a serious global health concern responsible for more than 25 million deaths in last three decades. More than 34 million people are living with HIV infection. Macrophages and CD4+ T cells are the principal targets of HIV-1. The pathogenesis of HIV-1 takes different routes in macrophages and CD4+ T cells. Macrophages are resistant to the cytopathic effect of HIV-1 and produce virus for longer periods of time. In addition, macrophages being present in every organ system thus can disseminate virus to the different anatomical sites leading to the formation of viral sanctuaries. Complete cure of HIV-1 needs better understanding of viral pathogenesis in these reservoirs and implementation of knowledge into robust therapeutic products. In this review we will focus on the unique relationship between HIV-1 and macrophages. Furthermore, we will describe how successful antiretroviral therapy (ART) is in suppressing HIV and novel molecular and cellular strategies against HIV-1 in macrophages.

Myeloid Cell COX-2 deletion reduces mammary tumor growth through enhanced cytotoxic T-lymphocyte function

Cyclooxygenase-2 (COX-2) expression is associated with poor prognosis across a range of human cancers, including breast cancer. The contribution of tumor cell-derived COX-2 to tumorigenesis has been examined in numerous studies; however, the role of stromal-derived COX-2 is ill-defined. Here, we examined how COX-2 in myeloid cells, an immune cell subset that includes macrophages, influences mammary tumor progression. In mice engineered to selectively lack myeloid cell COX-2 [myeloid-COX-2 knockout (KO) mice], spontaneous neu oncogene-induced tumor onset was delayed, tumor burden reduced, and tumor growth slowed compared with wild-type (WT). Similarly, growth of neu-transformed mammary tumor cells as orthotopic tumors in immune competent syngeneic myeloid-COX-2 KO host mice was reduced compared with WT. By flow cytometric analysis, orthotopic myeloid-COX-2 KO tumors had lower tumor-associated macrophage (TAM) infiltration consistent with impaired colony stimulating factor-1-dependent chemotaxis by COX-2 deficient macrophages in vitro. Further, in both spontaneous and orthotopic tumors, COX-2-deficient TAM displayed lower immunosuppressive M2 markers and this was coincident with less suppression of CD8(+) cytotoxic T lymphocytes (CTLs) in myeloid-COX-2 KO tumors. These studies suggest that reduced tumor growth in myeloid-COX-2 KO mice resulted from disruption of M2-like TAM function, thereby enhancing T-cell survival and immune surveillance. Antibody-mediated depletion of CD8(+), but not CD4(+) cells, restored tumor growth in myeloid-COX-2 KO to WT levels, indicating that CD8(+) CTLs are dominant antitumor effectors in myeloid-COX-2 KO mice. Our studies suggest that inhibition of myeloid cell COX-2 can potentiate CTL-mediated tumor cytotoxicity and may provide a novel therapeutic approach in breast cancer therapy.

Alveolar macrophages in pulmonary host defence the unrecognized role of apoptosis as a mechanism of intracellular bacterial killing

Alveolar macrophages play an essential role in clearing bacteria from the lower airway, as the resident phagocyte alveolar macrophages must both phagocytose and kill bacteria, and if unable to do this completely must co-ordinate an inflammatory response. The decision to escalate the inflammatory response represents the transition between subclinical infection and the development of pneumonia. Alveolar macrophages are well equipped to phagocytose bacteria and have a large phagolysosomal capacity in which ingested bacteria are killed. The rate-limiting step in control of extracellular bacteria, such as Streptococcus pneumoniae, is the capacity of alveolar macrophages to kill ingested bacteria. Therefore, alveolar macrophages complement canonical microbicidal strategies with an additional level of apoptosis-associated killing to help kill ingested bacteria.

Type I interferon upregulates Bak and contributes to T cell loss during human immunodeficiency virus (HIV) infection

The role of Type I interferon (IFN) during pathogenic HIV and SIV infections remains unclear, with conflicting observations suggesting protective versus immunopathological effects. We therefore examined the effect of IFNα/β on T cell death and viremia in HIV infection. Ex vivo analysis of eight pro- and anti-apoptotic molecules in chronic HIV-1 infection revealed that pro-apoptotic Bak was increased in CD4+ T cells and correlated directly with sensitivity to CD95/Fas-mediated apoptosis and inversely with CD4+ T cell counts. Apoptosis sensitivity and Bak expression were primarily increased in effector memory T cells. Knockdown of Bak by RNA interference inhibited CD95/Fas-induced death of T cells from HIV-1-infected individuals. In HIV-1-infected patients, IFNα-stimulated gene expression correlated positively with ex vivo T cell Bak levels, CD95/Fas-mediated apoptosis and viremia and negatively with CD4+ T cell counts. In vitro IFNα/β stimulation enhanced Bak expression, CD95/Fas expression and CD95/Fas-mediated apoptosis in healthy donor T cells and induced death of HIV-specific CD8+ T cells from HIV-1-infected patients. HIV-1 in vitro sensitized T cells to CD95/Fas-induced apoptosis and this was Toll-like receptor (TLR)7/9- and Type I IFN-dependent. This sensitization by HIV-1 was due to an indirect effect on T cells, as it occurred in peripheral blood mononuclear cell cultures but not purified CD4+ T cells. Finally, peak IFNα levels and viral loads correlated negatively during acute SIV infection suggesting a potential antiviral effect, but positively during chronic SIV infection indicating that either the virus drives IFNα production or IFNα may facilitate loss of viral control. The above findings indicate stage-specific opposing effects of Type I IFNs during HIV-1 infection and suggest a novel mechanism by which these cytokines contribute to T cell depletion, dysregulation of cellular immunity and disease progression.

CD95 (FAS) and CD178 (FASL) induce the apoptosis of CD4+ and CD8+ cells isolated from the peripheral blood and spleen of dogs naturally infected with Leishmania spp

Infected dogs are urban reservoirs of Leishmania chagasi, which is a causative agent of visceral leishmaniasis (VL). Dogs exhibit immune suppression during the course of this disease, and lymphocyte apoptosis is involved in this process. To investigate apoptosis and the expression levels of FAS-FAS-associated death domain protein (CD95 or APO-1), FASL-FAS ligand protein (CD178), and TRAIL-TNF-related apoptosis-inducing ligand (CD253) receptors in peripheral blood mononuclear cells and spleen leukocytes from 38 symptomatic dogs with moderate VL and 25 healthy dogs were evaluated by flow cytometry. The apoptosis rate of blood and splenic CD4+ and CD8+ cells was higher in infected dogs than in healthy dogs. The expression levels of FAS and FASL in blood and splenic CD4+ cells were lower in infected dogs than in healthy dogs. FAS expression in CD8+ cells was higher in infected dogs than in healthy dogs; in contrast, FASL expression was lower in infected dogs. The expression of the TRAIL receptor increased only in splenic CD8+ cells from infected dogs. The FAS and FAS-L blocking antibodies confirmed the importance of these receptors in apoptosis. Our results enhance the current understanding of the immune response in dogs infected with L. chagasi, facilitating the future development of therapeutic interventions to reduce lymphocyte depletion.

Macrophages and recently identified forms of cell death

Recent advances in cell death biology have uncovered an ever increasing range of cell death forms. Macrophages have a bidirectional relationship with cell death that modulates the immune response. Thus, macrophages engulf apoptotic cells and secrete cytokines that may promote cell death in parenchymal cells. Furthermore, the presence of apoptotic or necrotic dead cells in the microenvironment elicits differential macrophage responses. Apoptotic cells elicit anti-inflammatory responses in macrophages. By contrast macrophages may undergo a proinflammatory form of cell death (pyroptosis) in response to damage-associated molecular patterns (DAMPs) released from necrotic cells and also in response to pathogen-associated molecular patterns (PAMPs). Pyroptosis is a recently identified form of cell death that occurs predominantly in subsets of inflammatory macrophages and is associated to the release of interleukin-1β (IL-1β) and IL-18. Deregulation of these processes may result in disease. Thus, failure of macrophages to engulf apoptotic cells may be a source of autoantigens in autoimmune diseases, excessive macrophage release of proapoptotic factors or sterile pyroptosis may contribute to tissue injury and failure of pathogen-induced pyroptosis may contribute to pathogen survival. Ongoing research is exploring the therapeutic opportunities resulting this new knowledge.

The tumor necrosis factor superfamily in heart failure

Numerous clinical studies have established that tumor necrosis factor (TNF)-alpha may play a pathogenic role in the development and progression of heart failure (HF). Recent reports suggest that other ligands in the TNF superfamily could also play a pathogenic role in chronic HF. TNF superfamily ligands are expressed predominantly by cells in the immune system, while the TNF receptor superfamily are expressed by a wide variety of cells, including myocardial cells. Several pathways are activated by ligand-receptor interactions, but of particular importance is the nuclear factor (NF)-kappaB pathway which is activated in the failing human heart. All ligands in the TNF superfamily have the potential to activate NF-kappaB, leading to transcription of genes involved in apoptosis, cell survival, proliferation, inflammation and hypertrophic signaling in cardiomyocytes. Among several TNF superfamily members that are activated in HF, the authors' have recentlyshown that CD40L-CD40 and OPG-RANK-RANKL interactions may be implicated in the pathogenesis of HF through different mechanisms, possibly representing new targets for therapy in this disorder.

Monocytes regulate the mechanism of T-cell death by inducing Fas-mediated apoptosis during bacterial infection

Monocytes and T-cells are critical to the host response to acute bacterial infection but monocytes are primarily viewed as amplifying the inflammatory signal. The mechanisms of cell death regulating T-cell numbers at sites of infection are incompletely characterized. T-cell death in cultures of peripheral blood mononuclear cells (PBMC) showed 'classic' features of apoptosis following exposure to pneumococci. Conversely, purified CD3(+) T-cells cultured with pneumococci demonstrated necrosis with membrane permeabilization. The death of purified CD3(+) T-cells was not inhibited by necrostatin, but required the bacterial toxin pneumolysin. Apoptosis of CD3(+) T-cells in PBMC cultures required 'classical' CD14(+) monocytes, which enhanced T-cell activation. CD3(+) T-cell death was enhanced in HIV-seropositive individuals. Monocyte-mediated CD3(+) T-cell apoptotic death was Fas-dependent both in vitro and in vivo. In the early stages of the T-cell dependent host response to pneumococci reduced Fas ligand mediated T-cell apoptosis was associated with decreased bacterial clearance in the lung and increased bacteremia. In summary monocytes converted pathogen-associated necrosis into Fas-dependent apoptosis and regulated levels of activated T-cells at sites of acute bacterial infection. These changes were associated with enhanced bacterial clearance in the lung and reduced levels of invasive pneumococcal disease.

Signal transduction by tumor necrosis factor receptors

Tumor necrosis factor (TNF) is a key mediator in the inflammatory response which is implicated in the onset of a number of diseases. Research on TNF led to the characterization of the largest family of cytokines known until now, the TNF superfamily, which exert their biological effects through the interaction with transmembrane receptors of the TNFR superfamily. TNF itself exerts its biological effects interacting with two different receptors: TNFR1 and TNFR2. TNFR1 presents a death domain on its intracellular region. In contrast to TNFR1, TNFR2 does not have a death domain. Activation of TNFR1 implies the consecutive formation of two different TNF receptor signalling complexes. Complex I controls the expression of antiapoptotic proteins that prevent the triggering of cell death processes, whereas Complex II triggers cell death processes. TNFR2 only signals for antiapoptotic reactions. However, recent evidence indicates that TNFR2 also signals to induce TRAF2 degradation. TRAF2 is a key mediator in signal transduction of both TNFR1 and TNFR2. Thus, this novel signalling pathway has two important implications: on one hand, it represents an auto regulatory loop for TNFR2; on the other hand, when this signal is triggered TNFR1 activity is modified so that antiapoptotic pathways are inhibited and apoptotic reactions are enhanced.

TNF-related apoptosis-inducing ligand (TRAIL) regulates inflammatory neutrophil apoptosis and enhances resolution of inflammation

Novel therapeutics targeting neutrophilic inflammation are a major unmet clinical need in acute and chronic inflammation. The timely induction of neutrophil apoptosis is critical for inflammation resolution, and it is thought that acceleration of apoptosis may facilitate resolution at inflammatory sites. We previously demonstrated that a death receptor ligand, TRAIL, accelerates neutrophil apoptosis in vitro. We examined the role of TRAIL in neutrophil-dominant inflammation in WT and TRAIL-deficient mice. TRAIL deficiency did not alter constitutive neutrophil apoptosis, whereas exogenous TRAIL accelerated apoptosis of murine peripheral blood neutrophils. We compared TRAIL-deficient and WT mice in two independent models of neutrophilic inflammation: bacterial LPS-induced acute lung injury and zymosan-induced peritonitis. In both models, TRAIL-deficient mice had an enhanced inflammatory response with increased neutrophil numbers and reduced neutrophil apoptosis. Correction of TRAIL deficiency and supraphysiological TRAIL signaling using exogenous protein enhanced neutrophil apoptosis and reduced neutrophil numbers in both inflammatory models with no evidence of effects on other cell types. These data indicate the potential therapeutic benefit of TRAIL in neutrophilic inflammation.

Secretion modification region-derived peptide disrupts HIV-1 Nef's interaction with mortalin and blocks virus and Nef exosome release

Nef is secreted from infected cells in exosomes and is found in abundance in the sera of HIV-infected individuals. Secreted exosomal Nef (exNef) induces apoptosis in uninfected CD4⁺ T cells and may be a key component of HIV pathogenesis. The exosomal pathway has been implicated in HIV-1 virus release, suggesting a possible link between these two viral processes. However, the underlying mechanisms and cellular components of exNef secretion have not been elucidated. We have previously described a Nef motif, the secretion modification region (SMR; amino acids 66 to 70), that is required for exNef secretion. In silico modeling data suggest that this motif can form a putative binding pocket. We hypothesized that the Nef SMR binds a cellular protein involved in protein trafficking and that inhibition of this interaction would abrogate exNef secretion. By using tandem mass spectrometry and coimmunoprecipitation with a novel SMR-based peptide (SMRwt) that blocks exNef secretion and HIV-1 virus release, we identified mortalin as an SMR-specific cellular protein. A second set of coimmunoprecipitation experiments with full-length Nef confirmed that mortalin interacts with Nef via Nef's SMR motif and that this interaction is disrupted by the SMRwt peptide. Overexpression and microRNA knockdown of mortalin revealed a positive correlation between exNef secretion levels and mortalin protein expression. Using antibody inhibition we demonstrated that the Nef/mortalin interaction is necessary for exNef secretion. Taken together, this work constitutes a significant step in understanding the underlying mechanism of exNef secretion, identifies a novel host-pathogen interaction, and introduces an HIV-derived peptide with antiviral properties.

Structural variants of IFNα preferentially promote antiviral functions

IFNα, a cytokine with multiple functions in innate and adaptive immunity and a potent inhibitor of HIV, exerts antiviral activity, in part, by enhancing apolipoprotein B mRNA-editing enzyme-catalytic polypeptide-like 3 (APOBEC3) family members. Although IFNα therapy is associated with reduced viral burden, this cytokine also mediates immune dysfunction and toxicities. Through detailed mapping of IFNα receptor binding sites, we generated IFNα hybrids and mutants and determined that structural changes in the C-helix alter the ability of IFN to limit retroviral activity. Selective IFNα constructs differentially block HIV replication and their directional magnitude of inhibition correlates with APOBEC3 levels. Importantly, certain mutants exhibited reduced toxicity as reflected by induced indoleamine 2,3-dioxygenase (IDO), suggesting discreet and shared intracellular signaling pathways. Defining IFN structure and function relative to APOBEC and other antiviral genes may enable design of novel IFN-related molecules preserving beneficial antiviral roles while minimizing negative effects.

Comparative antiviral activity of integrase inhibitors in human monocyte-derived macrophages and lymphocytes

The activity of raltegravir and 4 other integrase inhibitors (MK-2048, L870,810, IN2, and IN5) was investigated in primary human macrophages, PBMC and C8166-lymphocytic T cells, in order to determine their relative potency and efficacy in different cellular systems of HIV infection. Raltegravir showed better protective efficacy in all cell types; MK-2048, L870,810 and IN5 showed a potent anti-HIV-1 activity in macrophages, while in lymphocytes only MK-2048 and L870,810 showed an inhibitory effect comparable to raltegravir. IN2 was a poorly effective anti-HIV-1 compound in all cellular systems. All effective integrase inhibitors exhibited a potent antiviral activity against both X4 and R5 HIV-1 strains. In general, raltegravir, MK-2048, L870,810 and IN5 showed anti HIV activity similar or slightly higher in macrophages compared to PBMC and C8166 T cells: for MK-2048, the EC(50) was 0.4, 0.9, 11.5 nM in macrophages, in PBMCs and T cells, respectively; for L870,810, the EC(50) was 1.5, 14.3, and 10.6 nM, respectively; for IN5 the EC(50) was 0.5, 13.7, and 5.7 nM, respectively.

Genome-wide association study identifies single nucleotide polymorphism in DYRK1A associated with replication of HIV-1 in monocyte-derived macrophages

BACKGROUND

HIV-1 infected macrophages play an important role in rendering resting T cells permissive for infection, in spreading HIV-1 to T cells, and in the pathogenesis of AIDS dementia. During highly active anti-retroviral treatment (HAART), macrophages keep producing virus because tissue penetration of antiretrovirals is suboptimal and the efficacy of some is reduced. Thus, to cure HIV-1 infection with antiretrovirals we will also need to efficiently inhibit viral replication in macrophages. The majority of the current drugs block the action of viral enzymes, whereas there is an abundance of yet unidentified host factors that could be targeted. We here present results from a genome-wide association study identifying novel genetic polymorphisms that affect in vitro HIV-1 replication in macrophages.

METHODOLOGY/PRINCIPAL FINDINGS

Monocyte-derived macrophages from 393 blood donors were infected with HIV-1 and viral replication was determined using Gag p24 antigen levels. Genomic DNA from individuals with macrophages that had relatively low (n = 96) or high (n = 96) p24 production was used for SNP genotyping with the Illumina 610 Quad beadchip. A total of 494,656 SNPs that passed quality control were tested for association with HIV-1 replication in macrophages, using linear regression. We found a strong association between in vitro HIV-1 replication in monocyte-derived macrophages and SNP rs12483205 in DYRK1A (p = 2.16 × 10(-5)). While the association was not genome-wide significant (p<1 × 10(-7)), we could replicate this association using monocyte-derived macrophages from an independent group of 31 individuals (p = 0.0034). Combined analysis of the initial and replication cohort increased the strength of the association (p = 4.84 × 10(-6)). In addition, we found this SNP to be associated with HIV-1 disease progression in vivo in two independent cohort studies (p = 0.035 and p = 0.0048).

CONCLUSIONS/SIGNIFICANCE

These findings suggest that the kinase DYRK1A is involved in the replication of HIV-1, in vitro in macrophages as well as in vivo.

Organ microenvironment plays significant roles through Fas ligand in vaccine-induced CD4(+) T cell dependent suppression of tumor growth at the orthotopic site

Growth of colon carcinoma cells transfected with mucin 1 (MUC1) was effectively suppressed by vaccination with MUC1 cDNA. The suppression was dependent on the presence of Fas ligand (FasL) in the cecum, whereas it was independent of FasL in the spleen and in the liver, as revealed by the use of gld/gld mice as the recipients of vaccination, and transplantation of tumor cells expressing MUC1. CD4(+) T cells were transferred from mice immunized with MUC1 cDNA to naive gld/gld or C57BL/6 mice, and the suppression of colon carcinoma growth in the cecum was tested. The results clearly showed that FasL in the recipient played a significant role. In the cecum, FasL was associated with intratumoral CD11b(+) cells, which are likely to be responsible for vaccine-induced tumor suppression. The T cell response to MUC1 was not influenced by the gld/gld status.

Transcriptome analysis of monocyte-HIV interactions

Background

During HIV infection and/or antiretroviral therapy (ART), monocytes and macrophages exhibit a wide range of dysfunctions which contribute significantly to HIV pathogenesis and therapy-associated complications. Nevertheless, the molecular components which contribute to these dysfunctions remain elusive. We therefore applied a parallel approach of genome-wide microarray analysis and focused gene expression profiling on monocytes from patients in different stages of HIV infection and/or ART to further characterise these dysfunctions.

Results

Processes involved in apoptosis, cell cycle, lipid metabolism, proteasome function, protein trafficking and transcriptional regulation were identified as areas of monocyte dysfunction during HIV infection. Individual genes potentially contributing to these monocyte dysfunctions included several novel factors. One of these is the adipocytokine NAMPT/visfatin, which we show to be capable of inhibiting HIV at an early step in its life cycle. Roughly half of all genes identified were restored to control levels under ART, while the others represented a persistent dysregulation. Additionally, several candidate biomarkers (in particular CCL1 and CYP2C19) for the development of the abacavir hypersensitivity reaction were suggested.

Conclusions

Previously described areas of monocyte dysfunction during HIV infection were confirmed, and novel themes were identified. Furthermore, individual genes associated with these dysfunctions and with ART-associated disorders were pinpointed. These genes form a useful basis for further functional studies concerning the contribution of monocytes/macrophages to HIV pathogenesis. One such gene, NAMPT/visfatin, represents a possible novel restriction factor for HIV.

Role of macrophages in HIV infection and persistence

Current antiretroviral therapy regimens can effectively suppress HIV in patients for prolonged periods of time, but do not constitute a cure, since they are incapable of eradicating viral reservoirs. It is, therefore, necessary for us to refocus on the partially understood pathogenesis of HIV, on the issue of viral persistence, and on the development of strategies for a temporally contained therapy capable of purging HIV from the body. Macrophages play a pivotal role in all three of these scenarios. This review summarizes important aspects of macrophage biology as they relate to HIV and discusses conceptual challenges for virus suppression and eradication in this cell type. We highlight a number of significant recent advances in understanding differences in HIV replication and pharmacotherapy between macrophages and CD4 T cells, as well as the role of macrophages in various aspects of the disease process and in different anatomical compartments. Finally, the importance of infected macrophages in the persistence of HIV, regarding both pathogenesis and advancement of eradication strategies, is discussed.

Caveolin-1 modulates HIV-1 envelope-induced bystander apoptosis through gp41

Human immunodeficiency virus (HIV) envelope (Env)-mediated bystander apoptosis is known to cause the progressive, severe, and irreversible loss of CD4(+) T cells in HIV-1-infected patients. Env-induced bystander apoptosis has been shown to be gp41 dependent and related to the membrane hemifusion between envelope-expressing cells and target cells. Caveolin-1 (Cav-1), the scaffold protein of specific membrane lipid rafts called caveolae, has been reported to interact with gp41. However, the underlying pathological or physiological meaning of this robust interaction remains unclear. In this report, we examine the interaction of cellular Cav-1 and HIV gp41 within the lipid rafts and show that Cav-1 modulates Env-induced bystander apoptosis through interactions with gp41 in SupT1 cells and CD4(+) T lymphocytes isolated from human peripheral blood. Cav-1 significantly suppressed Env-induced membrane hemifusion and caspase-3 activation and augmented Hsp70 upregulation. Moreover, a peptide containing the Cav-1 scaffold domain sequence markedly inhibited bystander apoptosis and apoptotic signal pathways. Our studies shed new light on the potential role of Cav-1 in limiting HIV pathogenesis and the development of a novel therapeutic strategy in treating HIV-1-infected patients.

Macrophage signaling in HIV-1 infection

The human immunodeficiency virus-1 (HIV-1) is a member of the lentivirus genus. The virus does not rely exclusively on the host cell machinery, but also on viral proteins that act as molecular switches during the viral life cycle which play significant functions in viral pathogenesis, notably by modulating cell signaling. The role of HIV-1 proteins (Nef, Tat, Vpr, and gp120) in modulating macrophage signaling has been recently unveiled. Accessory, regulatory, and structural HIV-1 proteins interact with signaling pathways in infected macrophages. In addition, exogenous Nef, Tat, Vpr, and gp120 proteins have been detected in the serum of HIV-1 infected patients. Possibly, these proteins are released by infected/apoptotic cells. Exogenous accessory regulatory HIV-1 proteins are able to enter macrophages and modulate cellular machineries including those that affect viral transcription. Furthermore HIV-1 proteins, e.g., gp120, may exert their effects by interacting with cell surface membrane receptors, especially chemokine co-receptors. By activating the signaling pathways such as NF-kappaB, MAP kinase (MAPK) and JAK/STAT, HIV-1 proteins promote viral replication by stimulating transcription from the long terminal repeat (LTR) in infected macrophages; they are also involved in macrophage-mediated bystander T cell apoptosis. The role of HIV-1 proteins in the modulation of macrophage signaling will be discussed in regard to the formation of viral reservoirs and macrophage-mediated T cell apoptosis during HIV-1 infection.

Surface modifications of nanocarriers for effective intracellular delivery of anti-HIV drugs

A variety of nanocarriers such as bioconjugates, dendrimers, liposomes, and nanoparticles have been widely evaluated as potential targeted drug delivery systems. Passive targeting of nanoscale carriers is based on a size-flow-filtration phenomenon that is usually limited to tumors, the reticular endothelial system, and possibly lymph nodes (LNs). In fact, targeting the delivery of drugs to pivotal physiological sites such as the lymph nodes has emerged as a promising strategy in treating HIV disease. Ligands for specific cell surface receptors can be displayed on nanocarriers in order to achieve active targeting. The approach has been extensively used preclinically in cancer where certain receptors are over-expressed at various stages of the disease. Unfortunately, markers of HIV infection are lacking and latently infected cells do not show any signs of infection on their surface. However, the disease naturally targets only a few cell types. The HIV receptor CD4, coreceptors (CCR5 and CXCR4), and some receptors relatively specific for macrophages provide potentially valuable surface targets for drug delivery to all susceptible cells in patients infected by HIV. This review focuses on nanoscale targeting with an emphasis on surface modifications of drug delivery nanocarriers for active targeting. A number of related issues, including HIV biology, targets, pharmacokinetics, and intracellular fate as well as literature-cited examples of emerging surface-modified targeted carrier systems are discussed.

Tumor necrosis factor blockade and the risk of viral infection

Tumor necrosis factor (TNF) blockers are widely used to treat rheumatoid arthritis and other chronic inflammatory diseases. Many studies have demonstrated an increased risk of opportunistic infections such as tuberculosis and fungal infection in patients treated with TNF blockers, which is thought to be related to the primary role of TNF both in host defense and in the immune response. Little is known, however, about the association between TNF blockade and the development of viral infection. Owing to the critical role of TNF in the control of viral infection, depletion of this cytokine with TNF blockers could facilitate the development or reactivation of viral infection. A number of large observational studies have found an increased risk of herpes zoster in patients receiving TNF blockers for the treatment of rheumatoid arthritis. This Review draws attention to the risk of several viral infections, including HIV, varicella zoster virus, Epstein-Barr virus, cytomegalovirus, and human papillomavirus, in patients receiving TNF-blocking therapy for chronic inflammatory conditions. In addition, implications for clinical practice and possible preventative approaches are discussed.

Genetic characterization of HIV type 1 Nef-induced vesicle secretion

The HIV-1 Nef protein is known to be secreted, and our group has shown that Nef is secreted from nef-transfected and HIV-1-infected cells in small exosome-like vesicles (d. 40-100 nm). The role of secreted Nef remains to be fully characterized. Thus, it is important to characterize the nature of and the mechanisms regulating Nef secretion. We hypothesized that specific structural domains on the Nef protein interact with components of the endosomal trafficking machinery, sorting Nef into multivesicular bodies (MVB) and packaging it in exosome-like vesicles. To identify those domains, a series of mutants spanning the entire nef sequence were made and cloned into the expression vector pQB1, which expresses the mutants as Nef-GFP fusion proteins. These constructs were used in transient transfection assays to identify sequences necessary for secretion of the Nef-GFP fusion protein. N-terminal domains were identified as critical for Nef-induced vesicle secretion: (1) a basic cluster of four arginine residues (aa 17, 19, 21, 22), (2) the phosphofurin acidic cluster sequence (PACS; Glu62-65), and (3) a previously uncharacterized domain spanning amino acid residues 66-70 (VGFPV), which we named the secretion modification region (SMR). Additional amino acids P25, 29GVG31, and T44 were identified in HIV-1 Nef as regulating its secretion. These residues have not been associated with other reported Nef functions. The myristoylation domain, ubiquitination lysine residues, and the C-terminal portion of Nef (aa 71-206) had no effect on secretion. A minimal HIV-1 Nef sequence, comprising the identified motifs, was sufficient for Nef-induced vesicle secretion.

Selective expression of human immunodeficiency virus Nef in specific immune cell populations of transgenic mice is associated with distinct AIDS-like phenotypes

We previously reported that CD4C/human immunodeficiency virus (HIV)(Nef) transgenic (Tg) mice, expressing Nef in CD4(+) T cells and cells of the macrophage/dendritic cell (DC) lineage, develop a severe AIDS-like disease, characterized by depletion of CD4(+) T cells, as well as lung, heart, and kidney diseases. In order to determine the contribution of distinct populations of hematopoietic cells to the development of this AIDS-like disease, five additional Tg strains expressing Nef through restricted cell-specific regulatory elements were generated. These Tg strains express Nef in CD4(+) T cells, DCs, and macrophages (CD4E/HIV(Nef)); in CD4(+) T cells and DCs (mCD4/HIV(Nef) and CD4F/HIV(Nef)); in macrophages and DCs (CD68/HIV(Nef)); or mainly in DCs (CD11c/HIV(Nef)). None of these Tg strains developed significant lung and kidney diseases, suggesting the existence of as-yet-unidentified Nef-expressing cell subset(s) that are responsible for inducing organ disease in CD4C/HIV(Nef) Tg mice. Mice from all five strains developed persistent oral carriage of Candida albicans, suggesting an impaired immune function. Only strains expressing Nef in CD4(+) T cells showed CD4(+) T-cell depletion, activation, and apoptosis. These results demonstrate that expression of Nef in CD4(+) T cells is the primary determinant of their depletion. Therefore, the pattern of Nef expression in specific cell population(s) largely determines the nature of the resulting pathological changes.

Mycobacterium tuberculosis 38-kDa lipoprotein is apoptogenic for human monocyte-derived macrophages

Mycobacterium tuberculosis is the main aetiologic agent of tuberculosis, a disease of great concern in less-developed regions. Apoptosis is a conspicuous event in macrophages infected in vitro with mycobacteria, a phenomenon also observed in vivo in granulomas of patients with tuberculosis. To determine its significance, it is important to define the mycobacterial moieties involved and how they cause apoptosis. Here we show that the 38-kDa lipoprotein induces macrophage caspase-dependent apoptosis involving TNF-alpha and FasL and, interestingly, with the upregulation of cell-death receptors TNFR1, TNFR2 and Fas. A role for the Toll-like receptor 2 was also demonstrated. In conclusion, the ability to induce apoptosis of host cells is another property of the 38-kDa lipoprotein, a molecule that has focused attention for being an immunodominant antigen that participates in phosphate transport.

Effects of antiretroviral therapy on cognitive impairment

Since the introduction of combination antiretroviral therapy, the manifestations of HIV-associated central nervous system (CNS) involvement have generally become less severe and more manageable. Patients initiating antiretroviral therapy have demonstrated improvement in cognitive functioning. Reduction of viral burden has been correlated with improved CNS functioning. Recent studies have focused on the importance of CNS-penetrating antiretroviral regimens to target active replication in this protected compartment. There were initial conflicting reports of whether CNS-penetrating antiretrovirals improved cognitive functioning, with more evidence supporting the importance of CNS penetration in reducing viral burden and improving cognitive outcomes. Cognitive loss remains a feature of HIV infection, and some patients still suffer from incident or progressing cognitive and motor dysfunction even on combination therapy. Because the virus enters the CNS within days of initial infection, latent infection may be chipping away at the brain during the long asymptomatic period in HIV. When to start antiretrovirals for the maximum cognitive benefit remains to be determined.

Transcriptional profiling in pathogenic and non-pathogenic SIV infections reveals significant distinctions in kinetics and tissue compartmentalization

Simian immunodeficiency virus (SIV) infection leads to AIDS in experimentally infected macaques, whereas natural reservoir hosts exhibit limited disease and pathology. It is, however, unclear how natural hosts can sustain high viral loads, comparable to those observed in the pathogenic model, without developing severe disease. We performed transcriptional profiling on lymph node, blood, and colon samples from African green monkeys (natural host model) and Asian pigtailed macaques (pathogenic model) to directly compare gene expression patterns during acute pathogenic versus non-pathogenic SIV infection. The majority of gene expression changes that were unique to either model were detected in the lymph nodes at the time of peak viral load. Results suggest a shift toward cellular stress pathways and Th1 profiles during pathogenic infection, with strong and sustained type I and II interferon responses. In contrast, a strong type I interferon response was initially induced during non-pathogenic infection but resolved after peak viral load. The natural host also exhibited controlled Th1 profiles and better preservation of overall cell homeostasis. This study identified gene expression patterns that are specific to disease susceptibility, tissue compartmentalization, and infection duration. These patterns provide a unique view of how host responses differ depending upon lentiviral infection outcome.

Differential effector mechanisms induced by vaccination with MUC1 DNA in the rejection of colon carcinoma growth at orthotopic sites and metastases

The effects of MUC1 DNA vaccination on the orthotopic growth and liver metastasis of colon carcinoma cells were investigated in mice. Vaccination with MUC1 DNA resulted in immune responses that were effective in suppressing mouse colon carcinoma cells transfected with MUC1 cDNA. CD4+ T cells but not CD8+ T cells mediated this antitumor response as shown by the in vivo depletion of lymphocyte subpopulations with the use of anti-CD4 or anti-CD8 antibody. The effects of neutralizing antibodies in vivo revealed that the predominant effector molecule in preventing orthotopic tumor growth was FasL, whereas the effector molecule effective in preventing liver metastasis was tumor necrosis factor-alpha. Colon carcinoma cells isolated from tumors growing in the ceca, spleens, and livers were shown to be equally sensitive to FasL and tumor necrosis factor-alpha. The results strongly suggest that elimination of tumor cells initiated by DNA vaccination in the present protocol is mediated by antigen-specific CD4+ T cells and the effector mechanisms in the cecum and in the liver are distinct due to a unique organ microenvironment.

Effect of macrophage depletion on viral DNA rebound following antiretroviral therapy in a murine model of AIDS (MAIDS)

In the attempt to eradicate HIV-1 infection, a strategy to eliminate macrophages, one of the most important cellular reservoirs in sustaining virus replication during HAART, could be of great benefit in the suppression of viral rebound. Aware of the ability of clodronate to cause macrophage depletion, the effect of the administration of clodronate encapsulated in erythrocytes on disease progression and on viral rebound was evaluated in a murine model of AIDS (MAIDS). One group of LP-BM5 retroviral complex-infected C57BL/6 mice received oral administrations of azidothymidine and dideoxyinosine daily for 12 weeks; two other groups received in addition, either clodronate-loaded erythrocytes or free clodronate at 7-10 day intervals. At the end of the treatment, the three groups maintained parameters characterizing disease progression similar to those of uninfected mice and showed a significantly lower level of BM5d DNA than infected mice in all organs and cells tested. To assess the viral rebound, some animals were left for an additional 4 month period without any treatment. After this time, the BM5d DNA content in blood leukocytes increased in all groups, but the group having received clodronate-loaded erythrocytes, in addition to transcriptase inhibitors, showed a significant delay in viral rebound.