HIV-1 Vpr inhibits the maturation and activation of macrophages and dendritic cells in vitro

Blood monocyte and dendritic cell profiles among people living with HIV with Mycobacterium tuberculosis co-infection

BACKGROUND

Understanding the complex interactions of the immune response mediated by Mycobacterium tuberculosis and HIV co-infection is fundamental to disease biomarker discovery, vaccine, and drug development. Using flow cytometry, we characterized the frequencies and phenotypic differences in monocytes and dendritic cell populations using peripheral blood mononuclear cells from individuals with recurrent, active pulmonary tuberculosis with and without coexisting HIV infection (CAPRISA 011, Clinicaltrials.gov, NCT02114684, 29/01/2014) and compared them to samples from HIV positive individuals and healthy controls. Additionally, we assessed the associations between the frequency of monocyte and dendritic cell subsets and time to culture conversion and cavitary disease in patients with active TB using a cox proportional hazards and logistic regression models.

RESULTS

Compared to healthy controls, the frequency of total monocytes (HLA-DR + CD14 +) was significantly higher in the TB/HIV and TB groups and the frequency of dendritic cells (HLA-DR + CD14-) was significantly higher in TB/HIV and HIV groups. We observed significant variation in the expression of CCR2, CD40, CD11b, CD86, CD163, CX3CR1 across different cell subsets in the four study groups. Increase in CCR2, CD11b and CD40 was associated with active TB infection, while decrease in CX3CR1 and increase in CD163 was associated with HIV infection. Expression of CX3CR1 (aHR 0.98, 95% CI 0.963 - 0.997, p = 0.019) on non-classical monocytes associated with longer time to TB culture conversion in the multivariable model correcting for randomization arm, age, sex, HIV status, lung cavitation, alcohol use, smoking and BMI. Higher surface expression of CD86 (aOR 1.017, 95% CI 1.001 - 1.032, p = 0.033) on intermediate monocytes associated with the presence of lung cavitation, while higher expression of transitional monocytes (aOR 0.944, 95% CI 0.892 - 0.999, p = 0.047) associated with the absence of lung cavitation in the multivariable model.

CONCLUSION

These data provide valuable insight into the heterogenous role of monocyte and dendritic cells in TB and HIV infections.

Molecular Pathogenesis of Human Immunodeficiency Virus-Associated Disease of Oropharyngeal Mucosal Epithelium

The oropharyngeal mucosal epithelia have a polarized organization, which is critical for maintaining a highly efficient barrier as well as innate immune functions. In human immunodeficiency virus (HIV)/acquired immune deficiency syndrome (AIDS) disease, the barrier and innate immune functions of the oral mucosa are impaired via a number of mechanisms. The goal of this review was to discuss the molecular mechanisms of HIV/AIDS-associated changes in the oropharyngeal mucosa and their role in promoting HIV transmission and disease pathogenesis, notably the development of opportunistic infections, including human cytomegalovirus, herpes simplex virus, and Epstein-Barr virus. In addition, the significance of adult and newborn/infant oral mucosa in HIV resistance and transmission was analyzed. HIV/AIDS-associated changes in the oropharyngeal mucosal epithelium and their role in promoting human papillomavirus-positive and negative neoplastic malignancy are also discussed.

Marginal Zone B-Cell Populations and Their Regulatory Potential in the Context of HIV and Other Chronic Inflammatory Conditions

Inflammation in the context of Human Immunodeficiency Virus (HIV) establishes early and persists beyond antiretroviral therapy (ART). As such, we have shown excess B-cell activating factor (BAFF) in the blood of HIV-infected progressors, as soon as in the acute phase, and despite successful ART. Excess BAFF was associated with deregulation of the B-cell compartment; notably, with increased frequencies of a population sharing features of both transitional immature (TI) and marginal zone (MZ) B-cells, we termed Marginal Zone precursor-like (MZp). We have reported similar observations with HIV-transgenic mice, Simian Immunodeficiency Virus (SIV)-infected macaques, and more recently, with HIV-infected Beninese commercial sex workers, which suggests that excess BAFF and increased frequencies of MZp B-cells are reliable markers of inflammation in the context of HIV. Importantly, we have recently shown that in healthy individuals, MZps present an important regulatory B-cell (Breg) profile and function. Herein, we wish to review our current knowledge on MZ B-cell populations, especially their Breg status, and that of other B-cell populations sharing similar features. BAFF and its analog A Proliferation-Inducing Ligand (APRIL) are important in shaping the MZ B-cell pool; moreover, the impact that excess BAFF—encountered in the context of HIV and several chronic inflammatory conditions—may exert on MZ B-cell populations, Breg and antibody producing capacities is a threat to the self-integrity of their antibody responses and immune surveillance functions. As such, deregulations of MZ B-cell populations contribute to autoimmune manifestations and the development of MZ lymphomas (MZLs) in the context of HIV and other inflammatory diseases. Therefore, further comprehending the mechanisms regulating MZ B-cell populations and their functions could be beneficial to innovative therapeutic avenues that could be deployed to restore MZ B-cell immune competence in the context of chronic inflammation involving excess BAFF.

In vivo Serial Passaging of Human-Simian Immunodeficiency Virus Clones Identifies Characteristics for Persistent Viral Replication

We previously reported that a human immunodeficiency virus type 1 with a simian immunodeficiency virus vif substitution (HSIV-vif_NL4-3) could replicate in pigtailed macaques (PTMs), demonstrating that Vif is a species-specific tropism factor of primate lentiviruses. However, infections did not result in high-peak viremia or setpoint plasma viral loads, as observed during simian immunodeficiency virus (SIV) infection of PTMs. Here, we characterized variants isolated from one of the original infected animals with CD4 depletion after nearly 4years of infection to identify determinants of increased replication fitness. In our studies, we found that the HSIV-vif clones did not express the HIV-1 Vpr protein due to interference from the vpx open reading frame (ORF) in singly spliced vpr mRNA. To examine whether these viral genes contribute to persistent viral replication, we generated infectious HSIV-vif clones expressing either the HIV-1 Vpr or SIV Vpx protein. And then to determine viral fitness determinants of HSIV-vif, we conducted three rounds of serial in vivo passaging in PTMs, starting with an initial inoculum containing a mixture of CXCR4-tropic [Vpr-HSIV-vif_NL4-3 isolated at 196 (C/196) and 200 (C/200) weeks post-infection from a PTM with depressed CD4 counts] and CCR5-tropic HSIV (Vpr⁺ HSIV-vif derivatives based NL-AD8 and Bru-Yu2 and a Vpx expressing HSIV-vif_Yu2). Interestingly, all infected PTMs showed peak plasma viremia close to or above 10⁵ copies/ml and persistent viral replication for more than 20weeks. Infectious molecular clones (IMCs) recovered from the passage 3 PTM (HSIV-P3 IMCs) included mutations required for HIV-1 Vpr expression and those mutations encoded by the CXCR4-tropic HSIV-vif_NL4-3 isolate C/196. The data indicate that the viruses selected during long-term infection acquired HIV-1 Vpr expression, suggesting the importance of Vpr for in vivo pathogenesis. Further passaging of HSIV-P3 IMCs in vivo may generate pathogenic variants with higher replication capacity, which will be a valuable resource as challenge virus in vaccine and cure studies.

The CD83 Molecule - An Important Immune Checkpoint

The CD83 molecule has been identified to be expressed on numerous activated immune cells, including B and T lymphocytes, monocytes, dendritic cells, microglia, and neutrophils. Both isoforms of CD83, the membrane-bound as well as its soluble form are topic of intensive research investigations. Several studies revealed that CD83 is not a typical co-stimulatory molecule, but rather plays a critical role in controlling and resolving immune responses. Moreover, CD83 is an essential factor during the differentiation of T and B lymphocytes, and the development and maintenance of tolerance. The identification of its interaction partners as well as signaling pathways have been an enigma for the last decades. Here, we report the latest data on the expression, structure, and the signaling partners of CD83. In addition, we review the regulatory functions of CD83, including its striking modulatory potential to maintain the balance between tolerance versus inflammation during homeostasis or pathologies. These immunomodulatory properties of CD83 emphasize its exceptional therapeutic potential, which has been documented in specific preclinical disease models.

Role Of Vitamin-D Supplementation In TB/HIV Co-Infected Patients

OBJECTIVE

This review aimed to assess the role of vitamin D supplementation on the decrement of mortality and morbidity rate among tuberculosis (TB)/human immune deficiency virus (HIV) co-infected clients.Method: Pub Med, google scholar and google search were accessed to find out all document to describe this review article.

RESULTS

Nowadays TB/HIV co-infection has become a major global concern, particularly in low and middle-income countries. Mycobacterium tuberculosis and HIV infections are co-endemic and more susceptible to the progression of TB. Immunosuppression associated with HIV is a strong risk factor for the reactivation of latent TB to the active form. Immune cells like macrophages recognized Mycobacterium tuberculosis through TLR2/1, and it increases the expression of the vitamin D receptor (VDR) and CYP27B1. The synthesis of 1,25-dihydroxy vitamin D promotes VDR-mediated transactivation of the antimicrobial peptide cathelicidin and the killing of intracellular Mycobacterium tuberculosis. Cathelicidins have a direct antimicrobial effect through membrane disruption. Besides, it has also antiviral effects via inhibition of retrovirus (HIV) replication. In fact, as some studies showed, there was a lower induction of cathelicidin in monocytes who have low vitamin D levels.Conclusion: Therefore, vitamin D supplementation can be directly involved in the reduction of TB/HIV co-infection and its progression.

Manipulation of Mononuclear Phagocytes by HIV: Implications for Early Transmission Events

Mononuclear phagocytes are antigen presenting cells that play a key role in linking the innate and adaptive immune systems. In tissue, these consist of Langerhans cells, dendritic cells and macrophages, all of which express the key HIV entry receptors CD4 and CCR5 making them directly infectible with HIV. Mononuclear phagocytes are the first cells of the immune system to interact with invading pathogens such as HIV. Each cell type expresses a specific repertoire of pathogen binding receptors which triggers pathogen uptake and the release of innate immune cytokines. Langerhans cells and dendritic cells migrate to lymph nodes and present antigens to CD4 T cells, whereas macrophages remain tissue resident. Here we review how HIV-1 manipulates these cells by blocking their ability to produce innate immune cytokines and taking advantage of their antigen presenting cell function in order to gain transport to its primary target cells, CD4 T cells.

Illuminating the Role of Vpr in HIV Infection of Myeloid Cells

Vpr is a 14 kDa accessory protein conserved amongst extant primate lentiviruses that is required for virus replication in vivo. Although many functions have been attributed to Vpr, its primary role, and the function under selective pressure in vivo, remains elusive. The minimal importance of Vpr in infection of activated CD4+ T cells in vitro suggests that its major importance lies in overcoming restriction to virus replication in non-cycling myeloid cell populations, such as macrophages and dendritic cells. HIV-1 replication is attenuated in the absence of Vpr in myeloid cells such as monocyte-derived dendritic cells (MDDCs) and macrophages, and is correlated with the ability of Vpr to overcome a post-integration transcriptional defect in these cells. Intriguingly, recent identification of the human hub silencing (HUSH) complex as a target for DCAF^CRL4-mediated degradation by numerous ancestral SIV Vpr alleles, and the Vpr paralog Vpx, signifies the potential function of HIV-1 Vpr to alter yet-to-be identified chromatin remodeling complexes and prevent host-mediated transcriptional repression of both invading viral genomes and pro-inflammatory responses. Myeloid cells constitute an important bridge between innate and adaptive immune responses to invading pathogens. Here, we seek to illustrate the numerous means by which Vpr manipulates the myeloid cellular environment and facilitates virus replication, myeloid cell-dependent HIV transmission, and systemic virus dissemination.

Mucosal dendritic cells in HIV-1 susceptibility: a critical role for C-type lectin receptors

Sexual transmission is the major route of HIV-1 infection worldwide. The interaction of HIV-1 with mucosal dendritic cells (DCs) might determine HIV-1 susceptibility as well as initial antiviral immunity controlling virus in the chronic phase. Different DC subsets reside in mucosal tissues and express specific C-type lectin receptors (CLRs) that interact with HIV-1 with different outcomes. HIV-1 has been shown to subvert CLRs for viral transmission and immune evasion, whereas CLRs can also protect against HIV-1 infection. Here, we will discuss the role of CLRs in HIV-1 transmission and adaptive immunity, and how the CLRs dictate the function of DCs in infection. Ultimately, understanding the interplay between CLRs and HIV-1 will lead to targeted approaches in the search for preventative measures.

Genome-wide transcriptional profiling reveals that HIV-1 Vpr differentially regulates interferon-stimulated genes in human monocyte-derived dendritic cells

Dendritic cells (DCs) are potent antigen-presenting cells (APCs) that directly link the innate and adaptive immune responses. HIV-1 infection of DCs leads to a diverse array of changes in gene expression and play a major role in dissemination of the virus into T-cells. Although HIV-1 Vpr is a pleiotropic protein involved in HIV-1 replication and pathogenesis, its exact role in APCs such as DCs remains elusive. In this study, utilizing a microarray-based systemic biology approach, we found that HIV-1 Vpr differentially regulates (fold change >2.0) more than 200 genes, primarily those involved in the immune response and innate immune response including type I interferon signaling pathway. The differential expression profiles of select genes involved in innate immune responses (interferon-stimulated genes [ISGs]), including MX1, MX2, ISG15, ISG20, IFIT1, IFIT2, IFIT3, IFI27, IFI44L, and TNFSF10, were validated by real-time quantitative PCR; the results were consistent with the microarray data. Taken together, our findings are the first to demonstrate that HIV-1 Vpr induces ISGs and activates the type I IFN signaling pathway in human DCs, and provide insights into the role of Vpr in HIV-1 pathogenesis.

HIV-1 Tat Protein Induces Production of Proinflammatory Cytokines by Human Dendritic Cells and Monocytes/Macrophages through Engagement of TLR4-MD2-CD14 Complex and Activation of NF-κB Pathway

We recently reported that the human immunodeficiency virus type-1 (HIV-1) Tat protein induced the expression of programmed death ligand-1 (PD-L1) on dendritic cells (DCs) through a TLR4 pathway. However, the underlying mechanisms by which HIV-1 Tat protein induces the abnormal hyper-activation of the immune system seen in HIV-1 infected patients remain to be fully elucidated. In the present study, we report that HIV-1 Tat protein induced the production of significant amounts of the pro-inflammatory IL-6 and IL-8 cytokines by DCs and monocytes from both healthy and HIV-1 infected patients. Such production was abrogated in the presence of anti-TLR4 blocking antibodies or soluble recombinant TLR4-MD2 as a decoy receptor, suggesting TLR4 was recruited by Tat protein. Tat-induced murine IL-6 and CXCL1/KC a functional homologue of human IL-8 was abolished in peritoneal macrophages derived from TLR4 KO but not from Wt mice, confirming the involvement of the TLR4 pathway. Furthermore, the recruitment of TLR4-MD2-CD14 complex by Tat protein was demonstrated by the activation of TLR4 downstream pathways including NF-κB and SOCS-1 and by down-modulation of cell surface TLR4 by endocytosis in dynamin and lipid-raft-dependent manners. Collectively, these findings demonstrate, for the first time, that HIV-1 Tat interacts with TLR4-MD2-CD14 complex and activates the NF-κB pathway, leading to overproduction of IL-6 and IL-8 pro-inflammatory cytokines by myeloid cells from both healthy and HIV-1 infected patients. This study reveals a novel mechanism by which HIV-1, via its early expressed Tat protein, hijacks the TLR4 pathway, hence establishing abnormal hyper-activation of the immune system.

SAMHD1 degradation enhances active suppression of dendritic cell maturation by HIV-1

A hallmark of HIV-1 infection is the lack of sterilizing immunity. Dendritic cells (DCs) are crucial in the induction of immunity, and lack of DC activation might underlie the absence of an effective anti-HIV-1 response. We have investigated how HIV-1 infection affects maturation of DCs. Our data show that even though DCs are productively infected by HIV-1, infection does not induce DC maturation. HIV-1 infection actively suppresses DC maturation, as HIV-1 infection inhibited TLR-induced maturation of DCs and thereby decreased the immune stimulatory capacity of DCs. Interfering with SAMHD1 restriction further increased infection of DCs, but did not lead to DC maturation. Notably, higher infection observed with SAMHD1 depletion correlated with a stronger suppression of maturation. Furthermore, blocking reverse transcription rescued TLR-induced maturation. These data strongly indicate that HIV-1 replication does not trigger immune activation in DCs, but that HIV-1 escapes immune surveillance by actively suppressing DC maturation independent of SAMHD1. Elucidation of the mechanism of suppression can lead to promising targets for therapy or vaccine design.

Accumulation of functionally immature myeloid dendritic cells in lymph nodes of rhesus macaques with acute pathogenic simian immunodeficiency virus infection

Myeloid dendritic cells (mDC) are key mediators of innate and adaptive immunity to virus infection, but the impact of HIV infection on the mDC response, particularly early in acute infection, is ill-defined. We studied acute pathogenic simian immunodeficiency virus (SIV) infection of rhesus macaques to address this question. The mDC in blood and bone marrow were depleted within 12 days of intravenous infection with SIVmac251, associated with a marked proliferative response. In lymph nodes, mDC were apoptotic, activated and proliferating, despite normal mDC numbers, reflecting a regenerative response that compensated for mDC loss. Blood mDC had increased expression of MHC class II, CCR7 and CD40, whereas in lymph nodes these markers were significantly decreased, indicating that acute infection induced maturation of mDC in blood but resulted in accumulation of immature mDC in lymph nodes. Following SIV infection, lymph node mDC had an increased capacity to secrete tumour necrosis factor-α upon engagement with a Toll-like receptor 7/8 ligand that mimics exposure to viral RNA, and this was inversely correlated with MHC class II and CCR7 expression. Lymph node mDC had an increased ability to capture and cleave soluble antigen, confirming their functionally immature state. These data indicate that acute SIV infection results in increased mDC turnover, leading to accumulation in lymph nodes of immature mDC with an increased responsiveness to virus stimulation.

Interactions with DCAF1 and DDB1 in the CRL4 E3 ubiquitin ligase are required for Vpr-mediated G2 arrest

Background

HIV-1 Vpr-mediated G₂ cell cycle arrest is dependent on the interaction of Vpr with an E3 ubiquitin ligase that contains damage-specific DNA binding protein 1 (DDB1), Cullin 4A (Cul4A), DDB1 and Cul4-associated factor 1 (DCAF1), and Rbx1. Vpr is thought to associate directly with DCAF1 in the E3 ubiquitin ligase complex although the exact interaction pattern of the proteins in the complex is not completely defined. The Vpr of SIV_agm induces G₂ arrest of cognate African Green Monkey (AGM) cells but not human cells. The molecular mechanism by which SIV_agm Vpr exhibits its species-specific function remained unknown.

Methods

Physical interaction of proteins in the E3 ubiquitin ligase complex was assessed by co-immunoprecipitation followed by western blotting. In addition, co-localization of the proteins in cells was investigated by confocal microscopy. The cell cycle was analyzed by propidium iodide staining and flow cytometry. DNA damage response elicited by Vpr was evaluated by detecting phosphorylation of H2AX, a marker for DNA damage response.

Results

We show that RNAi knock-down of DCAF1 prevented the co-immunoprecipitation of DDB1 with HIV-1 Vpr while DDB1 knock-down did not influence the binding of Vpr to DCAF1. HIV-1 Vpr mutants with a L64P or a R90K mutation maintained the ability to associate with DCAF1 but did not appear to be in a complex with DDB1. SIV_agm Vpr associated with AGM DCAF1 and DDB1 while, in human cells, it binds to human DCAF1 but hardly binds to human DDB1, resulting in the reduced activation of H2AX.

Conclusions

The identification of Vpr mutants which associate with DCAF1 but only poorly with DDB1 suggests that DCAF1 is necessary but the simple binding of Vpr to DCAF1 is not sufficient for the Vpr association with DDB1-containing E3 ligase complex. Vpr may interact both with DCAF1 and DDB1 in the E3 ligase complex. Alternatively, the interaction of Vpr and DCAF1 may induce a conformational change in DCAF1 or Vpr that promotes the interaction with DDB1. The ability of SIV_agm Vpr to associate with DDB1, but not DCAF1, can explain the species-specificity of SIV_agm Vpr-mediated G₂ arrest.

Immune activation and regulation in simian immunodeficiency virus-Plasmodium fragile-coinfected rhesus macaques

Human immunodeficiency virus (HIV) is characterized by immune activation, while chronic malaria is associated with elevated interleukin-10 (IL-10) levels. How these apparently antagonizing forces interact in the coinfected host is poorly understood. Using a rhesus macaque model of simian immunodeficiency virus (SIV)-Plasmodium fragile coinfection, we evaluated how innate immune effector cells affect the balance between immune activation and regulation. In vitro Toll-like receptor (TLR) responses of peripheral blood myeloid dendritic cells (mDC) and monocytes were temporarily associated with acute parasitemic episodes and elevated plasma IL-10 levels. Prolonged infection resulted in a decline of mDC function. Monocytes maintained TLR responsiveness but, in addition to IL-12 and tumor necrosis factor alpha, also produced IL-10. Consistent with the role of spleen in the clearance of parasite-infected red blood cells, coinfected animals also had increased splenic IL-10 mRNA levels. The main cellular source of IL-10 in the spleens of coinfected animals, however, was not splenic macrophages but T cells, suggesting an impairment of adaptive immunity. In contrast to those in spleen, IL-10-positive cells in axillary lymph nodes of coinfected animals were predominantly mDC, reminiscent of the immunosuppressive phenotype of peripheral blood mDC. Concurrent with IL-10 induction, however, SIV infection promoted elevated systemic IL-12 levels. The continuously increasing ratio of plasma IL-12 to IL-10 suggested that the overall host response in SIV-P. fragile-coinfected animals was shifted toward immune activation versus immune regulation. Therefore, SIV-P. fragile coinfection might be characterized by earlier manifestation of immune dysfunction and exhaustion than that of single-pathogen infections. This could translate into increased morbidity in HIV-malaria-coinfected individuals.

Immunobiology of dendritic cells and the influence of HIV infection

Recent progress in phenotyping of human dendritic cells (DCs) has allowed a closer alignment of the classification and functions of murine and human dendritic cell subsets. Marked differences in the functions of these human DC subsets and their response to HIV infection have become apparent, relevant to HIV pathogenesis and vaccine and microbicide development. Systems biology approaches to studying HIV uptake and infection of dendritic cells has revealed how markedly HIV subverts their functions, especially in relation to the trafficking pathways and viral transfer to T cells. Furthermore the interactions between DCs and other innate immune cells, NK cells, NKT cells and gamma delta T cells are now known to influence DC and T cell function and are also disturbed by HIV infection in vitro and in vivo. Such cellular interactions are potential targets for vaccine adjuvants and immunotherapy.

Lymphocyte-dendritic cell interactions and mucosal acquisition of SIV/HIV infection

PURPOSE OF REVIEW

Several previous models of HIV dissemination implicated dendritic cells as viral conduits to the lymphatics. However, recent macaque transmission and microbicide studies have highlighted a more complex situation.

RECENT FINDINGS

Resting CD4 lymphocytes are observed to be the major infected population in mucosal tissue after vaginal challenge with SIV. Resting lymphocytes appear to bridge infection over short distances, whereas activated lymphocytes provide long-distance virus dissemination as a result of greater virus amplification. In addition, dendritic cells might be early carriers of virus, transmitting virus to T cells locally and to the lymph nodes, and thus support parallel mechanisms in transmission. Microbicide studies using agents against CCR5 corroborate a model that infection at the mucosa must occur for transmission to be successful. The fast-rate dendritic cell trafficking of virus to the lymphatics may not result in immediate and efficient viral replication in lymphatic tissue. As dendritic cells might also be infected at the mucosa before lymphatic trafficking, this would enable them to transfer virus in this region at a later timepoint.

SUMMARY

There are now several models that can be attributed to the mucosal acquisition of SIV/HIV. One feature that unites these models is that infection in the mucosa must occur for dissemination to take place. Whether this is a feature of CD4 lymphocytes, dendritic cells or macrophage infection is still unclear. A model that intertwines one or more of the above cell types would be more prudent than addressing each in isolation.

Analysis of the scalp of women with AIDS subjected to autopsy: epithelial, follicular, and immunologic aspects

Hair keeps the scalp warmer and slightly moister than the rest of the skin, which contributes to a favorable environment for mycotic, bacterial, and parasitic infections. It is well established that AIDS makes the patient more susceptible to opportunistic infections and cutaneous manifestations. Because of this, the aim of this study was to analyze scalp fragments of autopsied women with AIDS. Twenty-eight scalp samples of women aged between 18 and 46 years were observed. These women were divided into 2 groups: with AIDS (n = 14) and without AIDS (n = 14). We conducted histochemical (hematoxylin-eosin, Picrosirius, and Verhoeff), morphometric (Image J; National Institutes of Health, Hamilton, ON, Canada and KS-300 Kontron-Zeiss; Kontron Elektronik, Carl-Zeiss, Germany), and immunohistochemical (S-100) analyses of the scalp. In patients with AIDS, epithelial thickness, number of epithelial cell layers, number of immature Langerhans cells in the epidermis, and percentages of elastic fibers in the dermis were significantly lower, whereas telogen hair follicles were significantly higher. The percentage of collagen fibers in the dermis and the diameter of the epithelial cells were smaller in patients with AIDS, without significant difference. AIDS possibly causes immunologic and morphologic alterations in the scalp. This study may establish parameters for better clinical and morphologic diagnostic in patients with AIDS.

A CD83-like molecule in sea bass (Dicentrarchus labrax): molecular characterization and modulation by viral and bacterial infection

The CD83 cell surface marker is an important and intriguing component of immune system. It is considered the best marker for mature human dendritic cells, but it is also important for thymic development of T cells, and it also plays a role as a regulator of peripheral B-cell function and homeostasis. A CD83-like molecule was identified in sea bass (Dicentrarchus labrax) by EST sequencing of a thymus cDNA library; the CD83 cDNA is composed of 816 bp and the mature CD83 peptide consists of 195 amino acids, with a putative signal peptide of 18 amino acids and two possible N-glycosylation sites. The comparison of sea bass CD83 sequence with its homologues in other fish species and mammals shows some differences, with two cysteine residues conserved from fish to mammals and a high variability both in the total number of cysteines and in mature CD83 sequence polypeptide length. Basal transcripts levels of CD83 mRNA are highest in liver, followed by thymus. The in vitro treatment of head kidney leukocytes with LPS resulted in a down-regulation on CD83 mRNA leves both after 4 and 24 h, whereas with poly I:C an up-regulation after 4h followed by a down-regulation at 24 h was observed. An in vivo infection of sea bass juveniles with nodavirus induced an increase of CD83 expression on head kidney leukocytes both after 6 and 24 h and a decrease after 72 h. On the other hand, an in vivo infection with Photobacterium damselae bacteria induced a decrease of CD83 transcript levels after 6 and 24 h and an increase after 72 h. These findings suggest in sea bass CD83 expression could be modulated by viral and bacterial immune response.

The HIV matrix protein p17 subverts nuclear receptors expression and induces a STAT1-dependent proinflammatory phenotype in monocytes

Background

Long-term remission of HIV-1 disease can be readily achieved by combinations of highly effective antiretroviral therapy (HAART). However, a residual persistent immune activation caused by circulating non infectious particles or viral proteins is observed under HAART and might contribute to an higher risk of non-AIDS pathologies and death in HIV infected persons. A sustained immune activation supports lipid dysmetabolism and increased risk for development of accelerated atehrosclerosis and ischemic complication in virologically suppressed HIV-infected persons receiving HAART.

Aim

While several HIV proteins have been identified and characterized for their ability to maintain immune activation, the role of HIV-p17, a matrix protein involved in the viral replication, is still undefined.

Results

Here, we report that exposure of macrophages to recombinant human p17 induces the expression of proinflammatory and proatherogenic genes (MCP-1, ICAM-1, CD40, CD86 and CD36) while downregulating the expression of nuclear receptors (FXR and PPARγ) that counter-regulate the proinflammatory response and modulate lipid metabolism in these cells. Exposure of macrophage cell lines to p17 activates a signaling pathway mediated by Rack-1/Jak-1/STAT-1 and causes a promoter-dependent regulation of STAT-1 target genes. These effects are abrogated by sera obtained from HIV-infected persons vaccinated with a p17 peptide. Ligands for FXR and PPARγ counteract the effects of p17.

Conclusions

The results of this study show that HIV p17 highjacks a Rack-1/Jak-1/STAT-1 pathway in macrophages, and that the activation of this pathway leads to a simultaneous dysregulation of immune and metabolic functions. The binding of STAT-1 to specific responsive elements in the promoter of PPARγ and FXR and MCP-1 shifts macrophages toward a pro-atherogenetic phenotype characterized by high levels of expression of the scavenger receptor CD36. The present work identifies p17 as a novel target in HIV therapy and grounds the development of anti-p17 small molecules or vaccines.

The tug-of-war between dendritic cells and human chronic viruses

The human immune system is under constant challenge from many viruses, some of which the body is successfully able to clear. Other viruses have evolved to escape the host immune responses and thus persist, leading to the development of chronic diseases. Dendritic cells are professional antigen-presenting cells that play a major role in both innate and adaptive immunity against different pathogens. This review focuses on the interaction of different chronic viruses with dendritic cells and the viruses' ability to exploit this critical cell type to their advantage so as to establish persistence within the host.

Human immunodeficiency virus viral protein R as an extracellular protein in neuropathogenesis

Numerous studies published in the past two decades have identified the viral protein R (Vpr) as one of the most versatile proteins in the life cycle of human immunodeficiency virus type 1 (HIV-1). In this regard, more than a thousand Vpr molecules are present in extracellular viral particles. Subsequent to viral entry, Vpr participates in early replicative events by assisting in viral genome nuclear import and, during the viral life cycle, by shuttling between the nucleus and the cytoplasm to accomplish its functions within the context of other replicative functions. Additionally, several studies have implicated Vpr as a proapoptotic protein because it promotes formation of permeability transition pores in mitochondria, which in turn affects transmembrane potential and adenosine triphosphate synthesis. Recent studies have identified Vpr as a virion-free protein in the serum and cerebrospinal fluid of patients infected with HIV-1 whose plasma viremia directly correlates with the extracellular concentration of Vpr. These observations pointed to a new role for Vpr as an additional weapon in the HIV-1 arsenal, involving the use of an extracellular protein to target and possibly inhibit HIV-1-uninfected bystander cells to enable them to escape immune surveillance. In addition, extracellular Vpr decreases adenosine triphosphate levels and affects the intracellular redox balance in neurons, ultimately causing their apoptosis. Herein, we review the role of Vpr as an extracellular protein and its downstream effects on cellular metabolism, functionality, and survival, with particular emphasis on how extracellular Vpr-induced oxidative stress might aggravate HIV-1-induced symptoms, thus affecting pathogenesis and disease progression.

Tuberculosis and HIV co-infection

Tuberculosis (TB) and HIV co-infections place an immense burden on health care systems and pose particular diagnostic and therapeutic challenges. Infection with HIV is the most powerful known risk factor predisposing for Mycobacterium tuberculosis infection and progression to active disease, which increases the risk of latent TB reactivation 20-fold. TB is also the most common cause of AIDS-related death. Thus, M. tuberculosis and HIV act in synergy, accelerating the decline of immunological functions and leading to subsequent death if untreated. The mechanisms behind the breakdown of the immune defense of the co-infected individual are not well known. The aim of this review is to highlight immunological events that may accelerate the development of one of the two diseases in the presence of the co-infecting organism. We also review possible animal models for studies of the interaction of the two pathogens, and describe gaps in knowledge and needs for future studies to develop preventive measures against the two diseases.

Interactions between human immunodeficiency virus (HIV)-1 Vpr expression and innate immunity influence neurovirulence

BACKGROUND

Viral diversity and abundance are defining properties of human immunodeficiency virus (HIV)-1's biology and pathogenicity. Despite the increasing availability of antiretroviral therapy, HIV-associated dementia (HAD) continues to be a devastating consequence of HIV-1 infection of the brain although the underlying disease mechanisms remain uncertain. Herein, molecular diversity within the HIV-1 non-structural gene, Vpr, was examined in RNA sequences derived from brain and blood of HIV/AIDS patients with or without HIV-associated dementia (HAD) together with the ensuing pathobiological effects.

RESULTS

Cloned brain- and blood-derived full length vpr alleles revealed that amino acid residue 77 within the brain-derived alleles distinguished HAD (77Q) from non-demented (ND) HIV/AIDS patients (77R) (p < 0.05) although vpr transcripts were more frequently detected in HAD brains (p < 0.05). Full length HIV-1 clones encoding the 77R-ND residue induced higher IFN-α, MX1 and BST-2 transcript levels in human glia relative to the 77Q-HAD encoding virus (p < 0.05) but both viruses exhibited similar levels of gene expression and replication. Myeloid cells transfected with 77Q-(pVpr77Q-HAD), 77R (pVpr77R-ND) or Vpr null (pVpr(-))-containing vectors showed that the pVpr77R-ND vector induced higher levels of immune gene expression (p < 0.05) and increased neurotoxicity (p < 0.05). Vpr peptides (amino acids 70-96) containing the 77Q-HAD or 77R-ND motifs induced similar levels of cytosolic calcium activation when exposed to human neurons. Human glia exposed to the 77R-ND peptide activated higher transcript levels of IFN-α, MX1, PRKRA and BST-2 relative to 77Q-HAD peptide (p < 0.05). The Vpr 77R-ND peptide was also more neurotoxic in a concentration-dependent manner when exposed to human neurons (p < 0.05). Stereotaxic implantation of full length Vpr, 77Q-HAD or 77R-ND peptides into the basal ganglia of mice revealed that full length Vpr and the 77R-ND peptide caused greater neurobehavioral deficits and neuronal injury compared with 77Q-HAD peptide-implanted animals (p < 0.05).

CONCLUSIONS

These observations underscored the potent neuropathogenic properties of Vpr but also indicated viral diversity modulates innate neuroimmunity and neurodegeneration.

HIV-1 accessory protein Vpr: relevance in the pathogenesis of HIV and potential for therapeutic intervention

The HIV protein, Vpr, is a multifunctional accessory protein critical for efficient viral infection of target CD4⁺ T cells and macrophages. Vpr is incorporated into virions and functions to transport the preintegration complex into the nucleus where the process of viral integration into the host genome is completed. This action is particularly important in macrophages, which as a result of their terminal differentiation and non-proliferative status, would be otherwise more refractory to HIV infection. Vpr has several other critical functions including activation of HIV-1 LTR transcription, cell-cycle arrest due to DCAF-1 binding, and both direct and indirect contributions to T-cell dysfunction. The interactions of Vpr with molecular pathways in the context of macrophages, on the other hand, support accumulation of a persistent reservoir of HIV infection in cells of the myeloid lineage. The role of Vpr in the virus life cycle, as well as its effects on immune cells, appears to play an important role in the immune pathogenesis of AIDS and the development of HIV induced end-organ disease. In view of the pivotal functions of Vpr in virus infection, replication, and persistence of infection, this protein represents an attractive target for therapeutic intervention.

Activation of human macrophages by bacterial components relieves the restriction on replication of an interferon-inducing parainfluenza virus 5 (PIV5) P/V mutant

Macrophages regulate immune responses during many viral infections, and can be a major determinant of pathogenesis, virus replication and immune response to infection. Here, we have addressed the question of the outcome of infection of primary human macrophages with parainfluenza virus 5 (PIV5) and a PIV5 mutant (P/V-CPI-) that is unable to counteract interferon (IFN) responses. In cultures of naïve monocyte-derived macrophages (MDMs), WT PIV5 established a highly productive infection, whereas the P/V-CPI- mutant was restricted for replication in MDMs by IFN-beta. Restricted replication in vitro was relieved in MDM that had been activated by prior exposure to heat killed Gram positive bacteria, including Listeria monocytogenes, Streptococcus pyogenes, and Bacillus anthracis. Enhanced replication of the P/V mutant in MDM previously activated by bacterial components correlated with a reduced ability to produce IFN-beta in response to virus infection, whereas IFN signaling was intact. Activated MDM were found to upregulate the synthesis of IRAK-M, which has been previously shown to negatively regulate factors involved in TLR signaling and IFN-beta production. We discuss these results in terms of the implications for mixed bacteria-virus infections and for the use of live RNA virus vectors that have been engineered to be attenuated for IFN sensitivity.

HIV-1 impairs in vitro priming of naïve T cells and gives rise to contact-dependent suppressor T cells

Priming of T cells in lymphoid tissues of HIV-infected individuals occurs in the presence of HIV-1. DC in this milieu activate T cells and disseminate HIV-1 to newly activated T cells, the outcome of which may have serious implications in the development of optimal antiviral responses. We investigated the effects of HIV-1 on DC–naïve T-cell interactions using an allogeneic in vitro system. Our data demonstrate a dramatic decrease in the primary expansion of naïve T cells when cultured with HIV-1-exposed DC. CD4⁺ and CD8⁺ T cells showed enhanced expression of PD-1 and TRAIL, whereas CTLA-4 expression was observed on CD4⁺ T cells. It is worth noting that T cells primed in the presence of HIV-1 suppressed priming of other naïve T cells in a contact-dependent manner. We identified PD-1, CTLA-4, and TRAIL pathways as responsible for this suppresion, as blocking these negative molecules restored T-cell proliferation to a higher degree. In conclusion, the presence of HIV-1 during DC priming produced cells with inhibitory effects on T-cell activation and proliferation, i.e. suppressor T cells, a mechanism that could contribute to the enhancement of HIV-1 pathogenesis.

Arcelis AGS-004 dendritic cell-based immunotherapy for HIV infection

Antiretroviral therapy represents a major breakthrough for the management of HIV-infected patients; however, it is not without side effects and is a life-long commitment. Thus, the development of novel strategies to enhance immune response and control viral replication are needed in order to limit exposure to antiretroviral therapy. To date, immunotherapies consisting of monocyte-derived dendritic cells expressing HIV antigens have elicited only limited immunogenicity and/or viral control. Thus, taking into consideration the variability of HIV, an investigational immunotherapeutic product (AGS-004, Argos Therapeutics Inc., NC, USA) that consists of autologous dendritic cells co-electroporated with in vitro transcribed RNA encoding four of the patient's own HIV antigens was developed. Based on the encouraging immunogenicity and tolerance observed in a Phase I study, a Phase II study has been initiated with good tolerance and partial viral control. A second Phase II placebo-controlled study is about to initiate.

Soluble HLA-G inhibits myeloid dendritic cell function in HIV-1 infection by interacting with leukocyte immunoglobulin-like receptor B2

Dendritic cells represent a specialized class of professional antigen-presenting cells that are responsible for priming and maintaining antigen-specific effector cell responses and regulating immune activation by cytokine secretion. In HIV-1 infection, myeloid dendritic cells are highly dysfunctional, but mechanisms contributing to their functional alterations are not well defined. Here, we show that soluble molecules of the nonclassical major histocompatibility complex class Ib (MHC-Ib) antigen HLA-G are highly upregulated in the plasma during progressive HIV-1 infection, while levels of membrane-bound HLA-G surface expression on dendritic cells, monocytes, and T cells only slightly differ among HIV-1 progressors, HIV-1 elite controllers, and HIV-1-negative persons. These elevated levels of soluble HLA-G in progressive HIV-1 infection likely result from increased secretion of intracellularly stored HLA-G molecules in monocytes and dendritic cells and contribute to a functional disarray of dendritic cells by inhibiting their antigen-presenting properties, while simultaneously enhancing their secretion of proinflammatory cytokines. Interestingly, we observed that these immunoregulatory effects of soluble HLA-G were mainly mediated by interactions with the myelomonocytic HLA class I receptor leukocyte immunoglobulin-like receptor B2 (LILRB2; ILT4), while binding of soluble HLA-G to its alternative high-affinity receptor, LILRB1 (ILT2), appeared to be less relevant for its immunomodulatory functions on dendritic cells. Overall, these results demonstrate a critical role for soluble HLA-G in modulating the functional characteristics of professional antigen-presenting cells in progressive HIV-1 infection and suggest that soluble HLA-G might represent a possible target for immunotherapeutic interventions in HIV-1-infected persons.

Inadequate clearance of translocated bacterial products in HIV-infected humanized mice

Bacterial translocation from the gut and subsequent immune activation are hallmarks of HIV infection and are thought to determine disease progression. Intestinal barrier integrity is impaired early in acute retroviral infection, but levels of plasma lipopolysaccharide (LPS), a marker of bacterial translocation, increase only later. We examined humanized mice infected with HIV to determine if disruption of the intestinal barrier alone is responsible for elevated levels of LPS and if bacterial translocation increases immune activation. Treating uninfected mice with dextran sodium sulfate (DSS) induced bacterial translocation, but did not result in elevated plasma LPS levels. DSS-induced translocation provoked LPS elevation only when phagocytic cells were depleted with clodronate liposomes (clodrolip). Macrophages of DSS-treated, HIV-negative mice phagocytosed more LPS ex vivo than those of control mice. In HIV-infected mice, however, LPS phagocytosis was insufficient to clear the translocated LPS. These conditions allowed higher levels of plasma LPS and CD8+ cell activation, which were associated with lower CD4+/CD8+ cell ratios and higher viral loads. LPS levels reflect both intestinal barrier and LPS clearance. Macrophages are essential in controlling systemic bacterial translocation, and this function might be hindered in chronic HIV infection.

HIV infection leads to continuous destruction of the body's immune defenses. Furthermore, disease progression is linked to heightened levels of immune activation. However, the underlying activating factors and their relationships to HIV pathogenesis are controversial. In patients with chronic HIV infection, bacteria and their products, such as lipopolysaccharide (LPS), translocate from the intestinal lumen into the systemic circulation. In the current study, we investigated the pathogenic potential of bacterial translocation in HIV-infected humanized mice. By modulating the amount of bacterial translocation in the mice, we determined that LPS elevation depends on intestinal barrier dysfunction and defective LPS clearance by macrophages. HIV-infected mice showed inadequate LPS clearance, leading to a cascade of uncontrolled bacterial translocation, T-cell activation, HIV replication, and T-cell loss. Our study highlights how important the interplay between different immune cells is for maintaining a healthy balance between immune activation with the goal to defend the body against microbes and detrimental activation that fuels HIV replication.

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.

Limelight on two HIV/SIV accessory proteins in macrophage infection: is Vpx overshadowing Vpr?

HIV viruses encode a set of accessory proteins, which are important determinants of virulence due to their ability to manipulate the host cell physiology for the benefit of the virus. Although these viral proteins are dispensable for viral growth in many in vitro cell culture systems, they influence the efficiency of viral replication in certain cell types. Macrophages are early targets of HIV infection which play a major role in viral dissemination and persistence in the organism. This review focuses on two HIV accessory proteins whose functions might be more specifically related to macrophage infection: Vpr, which is conserved across primate lentiviruses including HIV-1 and HIV-2, and Vpx, a protein genetically related to Vpr, which is unique to HIV-2 and a subset of simian lentiviruses. Recent studies suggest that both Vpr and Vpx exploit the host ubiquitination machinery in order to inactivate specific cellular proteins. We review here why it remains difficult to decipher the role of Vpr in macrophage infection by HIV-1 and how recent data underscore the ability of Vpx to antagonize a restriction factor which counteracts synthesis of viral DNA in monocytic cells.

The immunosuppressive properties of the HIV Vpr protein are linked to a single highly conserved residue, R90

BACKGROUND

A hallmark of AIDS progression is a switch of cytokines from Th1 to Th2 in the plasma of patients. IL-12, a critical Th1 cytokine secreted by antigen presenting cells (APCs) is suppressed by Vpr, implicating it as an important virulence factor. We hypothesize that Vpr protein packaged in the virion may be required for disabling APCs of the first infected mucosal tissues. Consistent with this idea are reports that defects in the C-terminus of Vpr are associated with long-term non-progression.

PRINCIPAL FINDINGS

Vpr RNA amplified from various sources was electroporated into monocyte-derived DC and IL-12 levels in supernatants were analyzed. The analysis of previously reported C-terminal Vpr mutations demonstrate that they do not alleviate the block of IL-12 secretion. However, a novel single conservative amino acid substitution, R90K, reverses the IL-12 suppression. Analysis of 1226 Vpr protein sequences demonstrated arginine (R) present at position 90 in 98.8%, with other substitutions at low frequency. Furthermore, none of sequences report lysine (K) in position 90. Vpr clones harboring the reported substitutions in position 90 were studied for their ability to suppress IL-12. Our data demonstrates that none of tested substitutions other than K relieve IL-12 suppression. This suggests a natural selection for sequences which suppress IL-12 secretion by DC and against mutations which relieve such suppression. Further analyses demonstrated that the R90K, as well as deletion of the C-terminus, directs the Vpr protein for rapid degradation.

CONCLUSION

This study supports Vpr as an HIV virulence factor during HIV infection and for the first time provides a link between evolutionary conservation of Vpr and its ability to suppress IL-12 secretion by DC. DC activated in the presence of Vpr would be defective in the production of IL-12, thus contributing to the prevailing Th2 cytokine profile associated with progressive HIV disease. These findings should be considered in the design of future immunotherapies that incorporate Vpr as an antigen.

Human immunodeficiency virus type 1 Vpr: functions and molecular interactions

Human immunodeficiency virus type 1 (HIV-1) viral protein R (Vpr) is an accessory protein that interacts with a number of cellular and viral proteins. The functions of many of these interactions in the pathogenesis of HIV-1 have been identified. Deletion of the vpr gene reduces the virulence of HIV-1 dramatically, indicating the importance of this protein for the virus. This review describes the current findings on several established functions of HIV-1 Vpr and some possible roles proposed for this protein. Because Vpr exploits cellular proteins and pathways to influence the biology of HIV-1, understanding the functions of Vpr usually involves the study of cellular pathways. Several functions of Vpr are attributed to the virion-incorporated protein, but some of them are attributed to the expression of Vpr in HIV-1-infected cells. The structure of Vpr may be key to understanding the variety of its interactions. Due to the critical role of Vpr in HIV-1 pathogenicity, study of the interactions between Vpr and cellular proteins may help us to understand the mechanism(s) of HIV-1 pathogenicity.

In vitro priming recapitulates in vivo HIV-1 specific T cell responses, revealing rapid loss of virus reactive CD4 T cells in acute HIV-1 infection

BACKGROUND

The requirements for priming of HIV-specific T cell responses initially seen in infected individuals remain to be defined. Activation of T cell responses in lymph nodes requires cell-cell contact between T cells and DCs, which can give concurrent activation of T cells and HIV transmission.

METHODOLOGY

The study aim was to establish whether DCs pulsed with HIV-1 could prime HIV-specific T cell responses and to characterize these responses. Both infectious and aldrithiol-2 inactivated noninfectious HIV-1 were compared to establish efficiencies in priming and the type of responses elicited.

FINDINGS

Our findings show that both infectious and inactivated HIV-1 pulsed DCs can prime HIV-specific responses from naïve T cells. Responses included several CD4(+) and CD8(+) T cell epitopes shown to be recognized in vivo by acutely and chronically infected individuals and some CD4(+) T cell epitopes not identified previously. Follow up studies of acute and recent HIV infected samples revealed that these latter epitopes are among the earliest recognized in vivo, but the responses are lost rapidly, presumably through activation-induced general CD4(+) T cell depletion which renders the newly activated HIV-specific CD4(+) T cells prime targets for elimination.

CONCLUSION

Our studies highlight the ability of DCs to efficiently prime naïve T cells and induce a broad repertoire of HIV-specific responses and also provide valuable insights to the pathogenesis of HIV-1 infection in vivo.

Co-immunization with an optimized plasmid-encoded immune stimulatory interleukin, high-mobility group box 1 protein, results in enhanced interferon-gamma secretion by antigen-specific CD8 T cells

DNA vaccination is a novel immunization strategy that has great potential for the development of vaccines and immune therapeutics. This strategy has been highly effective in mice, but is less immunogenic in non-human primates and in humans. Enhancing DNA vaccine potency remains a challenge. It is likely that antigen-presenting cells (APCs), and especially dendritic cells (DCs), play a significant role in the presentation of the vaccine antigen to the immune system. A new study reports the synergistic recruitment, expansion and activation of DCs in vivo by high-mobility group box 1 (HMGB1) protein. Such combinational strategies for delivering vaccine in a single, simple platform will hypothetically bolster the cellular immunity in vivo. Here, we combined plasmid encoding human immunodeficiency virus-1 (HIV-1) Gag and Env with an HMGB1 plasmid as a DNA adjuvant in BALB/c mice (by intramuscular immunization via electroporation), and humoral and cellular responses were measured. Co-administration of this potent immunostimulatory adjuvant strongly enhanced the cellular interferon-gamma (IFN-gamma) and humoral immune response compared with that obtained in mice immunized with vaccine only. Our results show that co-immunization with HMGB1 can have a strong adjuvant activity, driving strong cellular and humoral immunity that may be an effective immunological adjuvant in DNA vaccination against HIV-1.

Plasmacytoid and myeloid dendritic cells with a partial activation phenotype accumulate in lymphoid tissue during asymptomatic chronic HIV-1 infection

Dendritic cells (DCs) from HIV-1-infected individuals display numeric and functional defects, and recent evidence suggests that HIV-1 can directly and indirectly activate DCs in vitro. The in vivo activation state and compartmentalization of DC subsets during HIV-1 infection remain poorly understood, however. We evaluated phenotypic and functional characteristics of myeloid dendritic cells (mDCs) and plasmacytoid dendritic cells (pDCs) directly ex vivo in peripheral blood and lymphoid tissue from HIV-1-infected and HIV-seronegative individuals. Analysis of a wide range of chemokine receptors and activation/maturation markers on circulating DCs from viremic HIV-1-infected donors revealed a phenotype indicative of partial activation. Yet, blood DCs from viremic subjects still achieved full maturation when stimulated in vitro. In addition, blood pDCs from viremic individuals had a reduced capacity to migrate to CXCL12 in vitro. Total numbers of both DC subsets were increased in lymph nodes of asymptomatic untreated HIV-1-infected subjects, consistent with DC accumulation in the lymphoid compartment. Lymph node DCs also expressed high levels of CD40 in the absence of increases of other typical activation/maturation markers. Activation and depletion of DCs in blood with accumulation in lymphoid tissue may contribute to HIV-associated chronic immune activation and T-cell dysfunction.

Infection with Vpr-positive human immunodeficiency virus type 1 impairs NK cell function indirectly through cytokine dysregulation of infected target cells

Human immunodeficiency virus type 1 (HIV-1) infection has been implicated in impairing various aspects of NK cell function in viremic condition, and several viral factors contribute to these defects. Here, we evaluated the effect of HIV-1 Vpr on NK cell cytolytic function and cytokine (gamma interferon [IFN-gamma]) production in the context of infection and exposure. Our data indicate that NK cells derived from a peripheral blood mononuclear cell culture infected in vitro with HIV-1 vpr(+) virus or exposed to recombinant Vpr protein exhibited reduced target cell killing in conjunction with diminished expression of CD107a and reduced IFN-gamma production compared to their Vpr-negative counterparts. This Vpr-induced NK cell defect is in part through differential regulation of interleukin-12 and transforming growth factor beta production by the infected target cells and concomitant activation of Smad3 signaling pathway. Collectively, these results illustrate the ability of Vpr to impair NK cell-mediated innate immune functions indirectly by dysregulating multiple cytokines in the infected target cells, thus increasing disease severity and affecting the final outcome in HIV-1 infection.

Friend retrovirus infection of myeloid dendritic cells impairs maturation, prolongs contact to naïve T cells, and favors expansion of regulatory T cells

Retroviruses have developed immunmodulatory mechanisms to avoid being attacked by the immune system. The mechanisms of this retrovirus-associated immune suppression are far from clarified. Dendritic cells (DCs) have been attributed a decisive role in these pathogenic processes. We have used the Friend retrovirus (FV) mouse model in order to acquire further knowledge about the role of infection of DCs in virus-induced immunosuppression. About 20% of the myeloid DCs that were generated from the bone marrow of FV-infected mice carried FV proteins. The infection was productive, and infected DCs transmitted the virus in cell culture and in vivo. FV infection of DCs led to a defect in DC maturation, as infected cells expressed very little costimulatory molecules. Live imaging analysis of the cell contact between DCs and T cells revealed prolonged contacts of T cells with infected DCs compared with uninfected DCs. Although naive T cells were still activated by FV-infected DCs, this activation did not result in antigen-specific T-cell proliferation. Interestingly, infected DCs expanded a population of Foxp3+ regulatory T cells with immunosuppressive potential, suggesting that the contact between naive T cells and retrovirus-infected DCs results in tolerance rather than immunity. Thus, retroviral infection of DCs leads to an expansion of regulatory T cells, which might serve as an immune escape mechanism of the virus.

A viral CTL escape mutation leading to immunoglobulin-like transcript 4-mediated functional inhibition of myelomonocytic cells

Viral mutational escape can reduce or abrogate recognition by the T cell receptor (TCR) of virus-specific CD8⁺ T cells. However, very little is known about the impact of cytotoxic T lymphocyte (CTL) epitope mutations on interactions between peptide–major histocompatibility complex (MHC) class I complexes and MHC class I receptors expressed on other cell types. Here, we analyzed a variant of the immunodominant human leukocyte antigen (HLA)-B2705–restricted HIV-1 Gag KK10 epitope (KRWIILGLNK) with an L to M amino acid substitution at position 6 (L6M), which arises as a CTL escape variant after primary infection but is sufficiently immunogenic to elicit a secondary, de novo HIV-1–specific CD8⁺ T cell response with an alternative TCR repertoire in chronic infection. In addition to altering recognition by HIV-1–specific CD8⁺ T cells, the HLA-B2705–KK10 L6M complex also exhibits substantially increased binding to the immunoglobulin-like transcript (ILT) receptor 4, an inhibitory MHC class I–specific receptor expressed on myelomonocytic cells. Binding of the B2705–KK10 L6M complex to ILT4 leads to a tolerogenic phenotype of myelomonocytic cells with lower surface expression of dendritic cell (DC) maturation markers and co-stimulatory molecules. These data suggest a link between CTL-driven mutational escape, altered recognition by innate MHC class I receptors on myelomonocytic cells, and functional impairment of DCs, and thus provide important new insight into biological consequences of viral sequence diversification.

Distinct pathways for signaling maturation in macrophages and dendritic cells after infection with paramyxovirus simian virus 5

Professional antigen-presenting cells are critical components of both the innate and adaptive immune responses. Although dendritic cells (DCs) are generally thought to be the primary activators of naive T cells, macrophages have also been shown to fulfill this role. As with DCs, the capacity to induce optimal activation of T cells requires that macrophages undergo a process that results in the increased expression of costimulatory molecules, such as CD40, CD80, and CD86, and the production of cytokines. In this study we analyzed the effect of infection of macrophages generated from BALB/c mice with the paramyxovirus simian virus 5 (SV5). Here we have shown that bone marrow-derived macrophages (BMMs) are not productively infected at any multiplicity of infection tested. Analysis of activation markers revealed that SV5-infected BMMs robustly upregulated CD40 and modestly upregulated CD86, but did not upregulate the expression of CD80. Further, SV5-infected BMMs secreted low levels of interferon-beta and interleukin (IL)-12p40, but high levels of tumor necrosis factor-alpha and IL-6. Intriguingly, upregulation of these molecules on BMMs, unlike our previous results using bone marrow-derived dendritic cells, was not dependent on live virus. These findings provide evidence that different professional antigen-presenting cells can detect and respond to virus via distinct mechanisms.

Dendritic cells infected with vpr-positive human immunodeficiency virus type 1 induce CD8+ T-cell apoptosis via upregulation of tumor necrosis factor alpha

Human immunodeficiency virus type 1 (HIV-1) viral protein R (Vpr) plays a crucial role in viral replication and pathogenesis by inducing cell cycle arrest, apoptosis, translocation of preintegration complex, potentiation of glucocorticoid action, impairment of dendritic cell (DC) maturation, and T-cell activation. Recent studies involving the direct effects of Vpr on DCs and T cells indicated that HIV-1 containing Vpr selectively impairs phenotypic maturation, cytokine network, and antigen presentation in DCs and dysregulates costimulatory molecules and cytokine production in T cells. Here, we have further investigated the indirect effect of HIV-1 Vpr(+) virus-infected DCs on the bystander CD8(+) T-cell population. Our results indicate that HIV-1 Vpr(+) virus-infected DCs dysregulate CD8(+) T-cell proliferation and induce apoptosis. Vpr-containing virus-infected DC-mediated CD8(+) T-cell killing occurred in part through enhanced tumor necrosis factor alpha production by infected DCs and subsequent induction of death receptor signaling and activation of the caspase 8-dependent pathway in CD8(+) T cells. Collectively, these results provide evidence that Vpr could be one of the important contributors to the host immune escape by HIV-1 through its ability to dysregulate both directly and indirectly the DC biology and T-cell functions.

CD83: an update on functions and prospects of the maturation marker of dendritic cells

CD83 is one of the most characteristic cell surface markers for fully matured dendritic cells (DCs). In their function as antigen presenting cells they induce T-cell mediated immune responses. In this review we provide an overview on well described and proposed functions of this molecule as well as on very recent insights and new hypothesis. Already the CD83 messenger RNA processing differs remarkably from the processing of other cellular mRNAs: instead of the usual TAP mRNA export pathway, the CD83 mRNA is exported by the specific CRM1-mediated pathway, utilized only by a minority of cellular mRNAs. On the protein level, two different isoforms of CD83 exist: a membrane-bound and a soluble form. The isoforms are generated by different subsets of cells, including DCs, T-cells and B-cells, and also differ in their biological function. While the membrane-bound CD83 is of immune stimulatory capacity, activates T-cells and is important for the generation of thymocytes, the soluble CD83 has the opposite effect and has an immune inhibitory capacity. Due to its immune inhibitory function, CD83 has great potential for treatment of autoimmune diseases, for organ transplantations, and for immunotherapy, just to name a few examples. Moreover, some viruses prevent recognition by the host's immune system by specifically targeting CD83 surface expression.

Vpr in plasma of HIV type 1-positive patients is correlated with the HIV type 1 RNA titers

Vpr, an accessory gene product of HIV-1, has been reported in the plasma of HIV-1-positive patients, and exogenous Vpr induces the reactivation of viral production from latently infected cells and the apoptosis of T cells in vitro. These observations imply that Vpr is important in AIDS development, but the clinical relevance of the findings cannot be evaluated fully because the actual plasma Vpr concentration in HIV-1-positive patients is unknown. Here we generated two monoclonal antibodies against different portions of Vpr and successfully identified Vpr as a 14-kDa protein in HIV-1-positive patients. Semiquantitative analysis using a recombinant Vpr revealed that the concentration of Vpr in patient plasma was approximately 0.7 nM (10 ng/ml). Cross-sectional analysis of 52 HIV-1-positive patients revealed that the presence of Vpr detected in 20 patients was positively correlated with HIV-1 RNA copy number (p > 0.03), but not with the number of CD4(+) T cells. This is the first report demonstrating the actual amount of Vpr in HIV-1-positive patients, and the possible linkage of Vpr and viral titers indicates that it is important to continue to carry out the sequential analysis of Vpr, especially in clinical courses of HIV-1-positive patients. The threshold of viral titers, where Vpr appears in the patients' plasma, if present, contributes to better understanding the role of Vpr in AIDS pathogenesis.

Human immunodeficiency virus (HIV) type 1 Vpr induces differential regulation of T cell costimulatory molecules: Direct effect of Vpr on T cell activation and immune function

Human immunodeficiency virus type 1 (HIV-1) viral proteins disrupt the normal host cellular immune pathways thus exploiting the cellular machinery for replication, survival and to escape host immune attack. Here we evaluated the direct effects of HIV-1 Vpr-mediated immune modulation of infected T cells. Vpr specifically downregulated the expression of CD28 and increased the expression of CTLA-4, whereas no significant difference in the expression of CD25 and HLA-DR was observed. Interferon gamma (IFN-gamma) production in T cells was evaluated as a measure of the downstream effector functions. Results indicate that Vpr significantly inhibited IFN-gamma production and this may, in part, due to Vpr's ability to inhibit the nuclear translocation of NF-kappaB, and its transcriptional regulation. Together these results support that HIV-1 Vpr selectively dysregulates the immune functions at multiple levels and exerts its inhibitory effects in the presence of other viral proteins.

HIV induces maturation of monocyte-derived dendritic cells and Langerhans cells

In HIV infection, dendritic cells (DCs) may play multiple roles, probably including initial HIV uptake in the anogenital mucosa, transport to lymph nodes, and subsequent transfer to T cells. The effects of HIV-1 on DC maturation are controversial, with several recent conflicting reports in the literature. In this study, microarray studies, confirmed by real-time PCR, demonstrated that the genes encoding DC surface maturation markers were among the most differentially expressed in monocyte-derived dendritic cells (MDDCs), derived from human blood, treated with live or aldrithriol-2-inactivated HIV-1(BaL). These effects translated to enhanced cell surface expression of these proteins but differential expression of maturation markers was only partial compared with the effects of a conventional potent maturation stimulus. Such partially mature MDDCs can be converted to fully mature cells by this same potent stimulus. Furthermore, live HIV-1 stimulated greater changes in maturation marker surface expression than aldrithriol-2-inactivated HIV-1 and this enhanced stimulation by live HIV-1 was mediated via CCR5, thus suggesting both viral replication-dependent and -independent mechanisms. These partially mature MDDCs demonstrated enhanced CCR7-mediated migration and are also able to stimulate interacting T cells in a MLR, suggesting DCs harboring HIV-1 might prepare CD4 lymphocytes for transfer of HIV-1. Increased maturation marker surface expression was also demonstrated in native DCs, ex vivo Langerhans cells derived from human skin. Thus, HIV initiates maturation of DCs which could facilitate subsequent enhanced transfer to T cells.

HIV-1 infection of mononuclear phagocytic cells: the case for bacterial innate immune deficiency in AIDS

HIV-1 infection of mononuclear phagocytic cells, comprising monocytes, macrophages, and dendritic cells, has been the subject of extensive research over the past 20 years. The roles of mononuclear phagocytic cells in transmission of HIV-1 infection and as reservoirs of actively replicating virus have received particular attention. Experimental data have also accumulated about the effects of HIV-1 on the physiological function of mononuclear phagocytic cells, particularly their role in innate immunity to bacteria. The effects of HIV-1 on bacterial innate immune responses by mononuclear phagocytic cells are discussed here together with reports of direct interactions between HIV-encoded products and bacterial innate immune signalling pathways. These reports demonstrate mechanisms for HIV-mediated disruption of innate immune responses by mononuclear phagocytic cells that could provide novel therapeutic targets in HIV-infected patients. The clinical urgency is highlighted by greatly increased risk of invasive bacterial disease in this population, even in the era of highly active antiretroviral therapy. HIV-mediated injury to bacterial innate immunity provides an experimental paradigm that could broaden our overall understanding of innate immunity and be used to study responses to pathogens other than bacteria.

Microarray data on gene modulation by HIV-1 in immune cells: 2000-2006

Here, we review 34 HIV microarray studies in human immune cells over the period of 2000-March 2006 with emphasis on analytical approaches used and conceptual advances on HIV modulation of target cells (CD4 T cell, macrophage) and nontargets such as NK cell, B cell, and dendritic cell subsets. Results to date address advances on gene modulation associated with immune dysregulation, susceptibility to apoptosis, virus replication, and viral persistence following in vitro or in vivo infection/exposure to HIV-1 virus or HIV-1 accessory proteins. In addition to gene modulation associated with known functional correlates of HIV infection and replication (e.g., T cell apoptosis), microarray data have yielded novel, potential mechanisms of HIV-mediated pathogenesis such as modulation of cholesterol biosynthetic genes in CD4 T cells (relevant to virus replication and infectivity) and modulation of proteasomes and histone deacetylases in chronically infected cell lines (relevant to virus latency). Intrinsic challenges in summarizing gene modulation studies remain in development of sound approaches for comparing data obtained using different platforms and analytical tools, deriving unifying concepts to distil the large volumes of data collected, and the necessity to impose a focus for validation on a small fraction of genes. Notwithstanding these challenges, the field overall continues to demonstrate progress in expanding the pool of target genes validated to date in in vitro and in vivo datasets and understanding the functional correlates of gene modulation to HIV-1 pathogenesis in vivo.