Human Mucosal Mast Cells Capture HIV-1 and Mediate Viral trans-Infection of CD4+ T Cells

Diagnostic and prognostic significance of mast cell markers in HIV/AIDS: Current insights and future directions

Human immunodeficiency virus (HIV) infection continues to pose significant global health challenges, necessitating advancements in diagnostic and prognostic approaches to optimize disease management. While primarily recognized for their roles in allergic responses, mast cells have emerged as potential markers with diagnostic and prognostic significance in the context of HIV/AIDS. This paper aims to synthesize current insights and delineate future directions regarding the utility of mast cell markers in diagnosing HIV infection, predicting disease progression, and guiding therapeutic strategies. Mast cells, equipped with distinct markers such as tryptase, chymase, carboxypeptidase A3, and c-kit/CD117 receptors, exhibit tissue-specific expression patterns that offer potential as diagnostic indicators for HIV infection. Understanding the dynamics of these markers in different tissues and body fluids holds promise for accurate HIV diagnosis, disease staging, and monitoring treatment responses. Moreover, the prognostic significance of mast cell markers in HIV/AIDS lies in their potential to predict disease progression, immune dysregulation, and clinical outcomes. The integration of mast cell markers into clinical applications offers promising avenues for refining diagnostic assays, patient monitoring protocols, and therapeutic strategies in HIV/AIDS. Future research directions involve the development of novel diagnostic tools and targeted therapies based on mast cell-specific markers, potentially revolutionizing clinical practice and enhancing patient care in the management of HIV/AIDS. Continued investigations into mast cell markers' diagnostic and prognostic implications hold immense potential to advance our understanding and improve outcomes in HIV/AIDS management.

Milk Transmission of Mammalian Retroviruses

The transmission of viruses from one host to another typically occurs through horizontal or vertical pathways. The horizontal pathways include transmission amongst individuals, usually through bodily fluids or excretions, while vertical transmission transpires from mother to their offspring, either during pregnancy, childbirth, or breastfeeding. While there are more than 200 human pathogenic viruses to date, only a small number of them are known to be transmitted via breast milk, including cytomegalovirus (CMV), human immunodeficiency virus type 1 (HIV-1), and human T cell lymphotropic virus type 1 (HTLV-1), the latter two belonging to the family Retroviridae. Breast milk transmission is a common characteristic among mammalian retroviruses, but there is a lack of reports summarizing our knowledge regarding this route of transmission of mammalian retroviruses. Here, we provide an overview of the transmission of mammalian exogenous retroviruses with a focus on Orthoretrovirinae, and we highlight whether they have been described or suspected to be transmitted through breast milk, covering various species. We also elaborate on the production and composition of breast milk and discuss potential entry sites of exogenous mammalian retroviruses during oral transmission.

High Heme and Low Heme Oxygenase-1 Are Associated with Mast Cell Activation/Degranulation in HIV-Induced Chronic Widespread Pain

An overwhelming number of people with HIV (PWH) experience chronic widespread pain (CWP) throughout their lifetimes. Previously, we demonstrated that PWH with CWP have increased hemolysis and attenuated heme oxygenase 1 (HO-1) levels. HO-1 degrades reactive, cell-free heme into antioxidants like biliverdin and carbon monoxide (CO). We found that high heme or low HO-1 caused hyperalgesia in animals, likely through multiple mechanisms. In this study, we hypothesized that high heme or low HO-1 caused mast cell activation/degranulation, resulting in the release of pain mediators like histamine and bradykinin. PWH who self-report CWP were recruited from the University of Alabama at Birmingham HIV clinic. Animal models included HO-1-/- mice and hemolytic mice, where C57BL/6 mice were injected intraperitoneally with phenylhydrazine hydrochloride (PHZ). Results demonstrated that plasma histamine and bradykinin were elevated in PWH with CWP. These pain mediators were also high in HO-1-/- mice and in hemolytic mice. Both in vivo and in vitro (RBL-2H3 mast cells), heme-induced mast cell degranulation was inhibited by treatment with CORM-A1, a CO donor. CORM-A1 also attenuated mechanical and thermal (cold) allodynia in hemolytic mice. Together, the data suggest that mast cell activation secondary to high heme or low HO-1 seen in cells and animals correlates with elevated plasma levels of heme, histamine, and bradykinin in PWH with CWP.

IFI27 is a potential therapeutic target for HIV infection

BACKGROUND

Therapeutic studies against human immunodeficiency virus type 1 (HIV-1) infection have become one of the important works in global public health.

METHODS

Differential expression analysis was performed between HIV-positive (HIV+) and HIV-negative (HIV-) patients for GPL6947 and GPL10558 of GSE29429. Coexpression analysis of common genes with the same direction of differential expression identified modules. Module genes were subjected to enrichment analysis, Short Time-series Expression Miner (STEM) analysis, and PPI network analysis. The top 100 most connected genes in the PPI network were screened to construct the LASSO model, and AUC values were calculated to identify the key genes. Methylation modification of key genes were identified by the chAMP package. Differences in immune cell infiltration between HIV + and HIV- patients, as well as between antiretroviral therapy (ART) and HIV + patients, were calculated using ssGSEA.

RESULTS

We obtained 3610 common genes, clustered into nine coexpression modules. Module genes were significantly enriched in interferon signalling, helper T-cell immunity, and HIF-1-signalling pathways. We screened out module genes with gradual changes in expression with increasing time from HIV enrolment using STEM software. We identified 12 significant genes through LASSO regression analysis, especially proteasome 20S subunit beta 8 (PSMB8) and interferon alpha inducible protein 27 (IFI27). The expression of PSMB8 and IFI27 were then detected by quantitative real-time PCR. Interestingly, IFI27 was also a persistently dysregulated gene identified by STEM. In addition, 10 of the key genes were identified to be modified by methylation. The significantly infiltrated immune cells in HIV + patients were restored after ART, and IFI27 was significantly associated with immune cells.

CONCLUSION

The above results provided potential target genes for early diagnosis and treatment of HIV + patients. IFI27 may be associated with the progression of HIV infection and may be a powerful target for immunotherapy.

Efficacy and toxicity of hydroxyurea in mast cell activation syndrome patients refractory to standard medical therapy: retrospective case series

Determine efficacy and adverse events (AEs) of hydroxyurea (HU) in mast cell activation syndrome (MCAS) patients who were refractory to standard medical therapy. An electronic chart review was performed to find MCAS patients who received HU in a MCAS medical practice. Diagnosis of MCAS was established on the basis of mast cell (MC) activation symptoms in ≥ 5 systems plus ≥ 1 abnormal MC mediators and/or ≥ 20 MC/high power field on duodenal biopsies. Medicines not providing significant clinical improvement prior to HU were tabulated. The following symptoms were evaluated by patients on a 0–10 scale prior to and at the study conclusion: bone pain, abdominal pain, diarrhea, bloating, and nausea. Safety labs were obtained on a regular basis. Twenty out of three hundred ten (8.4%) MCAS patients received HU. Patients included 22 females, average age 42.4 years. Dysautonomia was present in 60%. An average of 10.6 (SD 1.7, range 8–13) medications were used prior to adding HU to various concomitant medications. Average dose of HU was 634 mg. In 20 patients who continued therapy for ≥ 2 months, there was statistically significant reduction of bone pain, abdominal pain, diarrhea, bloating, and nausea. Fourteen patients noted prolonged success with therapy. Six patients stopped HU within 6 weeks owing to AEs. Four patients treated ≥ 2 months had AEs and 2 led to HU cessation. All AEs were reversible. Refractory MCAS patients showed clear significant improvement in bone pain and gastrointestinal symptoms on HU. Systematic monitoring was effective in preventing the occurrence of severe HU-induced adverse events.

Mast Cell Activation Triggered by Retrovirus Promotes Acute Viral Infection

Mast cells (MCs) are strategically located at the host-environment interface and their non-allergic roles in the immune-surveillance of pathogens have recently gained more attention. However, MC-caused detrimental regulation of immune inflammations can promote viral invasion. Currently, the role of MCs in retroviral infection remains elusive. We have recently proved that human gut MCs could capture and transfer HIV-1 to CD4⁺ T cells for promoting viral spread; MC-released histamine augments HIV-1-induced functional polarization of dendritic cells to cause immunosuppression via stimulating the differentiation of regulatory T cells. In this study, we used a murine model of MuLV/Friend virus infection to address MC role in acute retroviral infection in vivo. The acute infection of MuLV/Friend virus could be established in C57BL/6 wild type mice, but viral acquisition showed low efficiency in C57BL/6-Kit ^W - ^sh/W - ^sh (Sash) mice which lack MCs. In mechanism, we found that MuLV/Friend virus triggered MC activation for degranulation; MC degranulation subsequently activated the granulocyte-like myeloid derived suppressive cells (G-MDSCs) to inhibit CD8⁺ T cells- and NK cells-mediated antiviral immune responses. The reconstruction of MCs in Sash mice promoted acute retroviral infection by regulating G-MDSCs functions and antiviral immune responses. Importantly, the administration of MC stabilizers to block cell degranulation elevated antiviral immune response and consequently suppressed retrovirus infection. This study uncovers a specific role of MCs in acute retroviral infection and elucidates the underlying immune-mechanisms. Targeting MCs may provide a novel approach for controlling acute infection by retroviruses.

Mesenchymal Stromal Cells: a Possible Reservoir for HIV-1?

The introduction of antiretroviral therapy (ART) and highly active antiretroviral therapy (HAART) has transformed human immunodeficiency virus (HIV)-1 into a chronic, well-managed disease. However, these therapies do not eliminate all infected cells from the body despite suppressing viral load. Viral rebound is largely due to the presence of cellular reservoirs which support long-term persistence of HIV-1. A thorough understanding of the HIV-1 reservoir will facilitate the development of new strategies leading to its detection, reduction, and elimination, ultimately leading to curative therapies for HIV-1. Although immune cells derived from lymphoid and myeloid progenitors have been thoroughly studied as HIV-1 reservoirs, few studies have examined whether mesenchymal stromal/stem cells (MSCs) can assume this function. In this review, we evaluate published studies which have assessed whether MSCs contribute to the HIV-1 reservoir. MSCs have been found to express the receptors and co-receptors required for HIV-1 entry, albeit at levels of expression and receptor localisation that vary considerably between studies. Exposure to HIV-1 and HIV-1 proteins alters MSC properties in vitro, including their proliferation capacity and differentiation potential. However, in vitro and in vivo experiments investigating whether MSCs can become infected with and harbour latent integrated proviral DNA are lacking. In conclusion, MSCs appear to have the potential to contribute to the HIV-1 reservoir. However, further studies are needed using techniques such as those used to prove that cluster of differentiation (CD)4⁺ T cells constitute an HIV-1 reservoir before a reservoir function can definitively be ascribed to MSCs.

Why the HIV Reservoir Never Runs Dry: Clonal Expansion and the Characteristics of HIV-Infected Cells Challenge Strategies to Cure and Control HIV Infection

Antiretroviral therapy (ART) effectively reduces cycles of viral replication but does not target proviral populations in cells that persist for prolonged periods and that can undergo clonal expansion. Consequently, chronic human immunodeficiency virus (HIV) infection is sustained during ART by a reservoir of long-lived latently infected cells and their progeny. This proviral landscape undergoes change over time on ART. One of the forces driving change in the landscape is the clonal expansion of infected CD4 T cells, which presents a key obstacle to HIV eradication. Potential mechanisms of clonal expansion include general immune activation, antigenic stimulation, homeostatic proliferation, and provirus-driven clonal expansion, each of which likely contributes in varying, and largely unmeasured, amounts to maintaining the reservoir. The role of clinical events, such as infections or neoplasms, in driving these mechanisms remains uncertain, but characterizing these forces may shed light on approaches to effectively eradicate HIV. A limited number of individuals have been cured of HIV infection in the setting of bone marrow transplant; information from these and other studies may identify the means to eradicate or control the virus without ART. In this review, we describe the mechanisms of HIV-1 persistence and clonal expansion, along with the attempts to modify these factors as part of reservoir reduction and cure strategies.

Basophils and Mast Cells in COVID-19 Pathogenesis

Basophils and mast cells are among the principal inducers of Th2 responses and have a crucial role in allergic and anti-parasitic protective immunity. Basophils can function as antigen-presenting cells that bind antigens on their surface and boost humoral immune responses, inducing Th2 cell differentiation. Their depletion results in lower humoral memory activation and greater infection susceptibility. Basophils seem to have an active role upon immune response to SARS-CoV-2. In fact, a coordinate adaptive immune response to SARS-CoV-2 is magnified by basophils. It has been observed that basophil amount is lower during acute disease with respect to the recovery phase and that the grade of this depletion is an important determinant of the antibody response to the virus. Moreover, mast cells, present in a great quantity in the nasal epithelial and lung cells, participate in the first immune response to SARS-CoV-2. Their activation results in a hyperinflammatory syndrome through the release of inflammatory molecules, participating to the “cytokine storm” and, in a longer period, inducing pulmonary fibrosis. The literature data suggest that basophil counts may be a useful prognostic tool for COVID-19, since their reduction is associated with a worse prognosis. Mast cells, on the other hand, represent a possible therapeutic target for reducing the airway inflammation characteristic of the hyperacute phase of the disease.

Responses of Mast Cells to Pathogens: Beneficial and Detrimental Roles

Mast cells (MCs) are strategically located in tissues close to the external environment, being one of the first immune cells to interact with invading pathogens. They are long living effector cells equipped with different receptors that allow microbial recognition. Once activated, MCs release numerous biologically active mediators in the site of pathogen contact, which induce vascular endothelium modification, inflammation development and extracellular matrix remodeling. Efficient and direct antimicrobial mechanisms of MCs involve phagocytosis with oxidative and non-oxidative microbial destruction, extracellular trap formation, and the release of antimicrobial substances. MCs also contribute to host defense through the attraction and activation of phagocytic and inflammatory cells, shaping the innate and adaptive immune responses. However, as part of their response to pathogens and under an impaired, sustained, or systemic activation, MCs may contribute to tissue damage. This review will focus on the current knowledge about direct and indirect contribution of MCs to pathogen clearance. Antimicrobial mechanisms of MCs are addressed with special attention to signaling pathways involved and molecular weapons implicated. The role of MCs in a dysregulated host response that can increase morbidity and mortality is also reviewed and discussed, highlighting the complexity of MCs biology in the context of host-pathogen interactions.

Rapid Generation of a Recombinant Genotype VIII Newcastle Disease Virus (NDV) Using Full-Length Synthetic cDNA

Rescue of (-)ssRNA viruses involves the sequential assembly and cloning of the full-length cDNA, which is often a challenging and time-consuming process. The objective of this study was to develop a novel method to rapidly clone the full-length cDNA of a very virulent NDV by only one assembly step. A completely synthetic 15 kb cDNA of a Malaysian genotype VIII NDV known as strain AF2240-I with additional flanking BsmBI sites was synthesised. However, to completely follow the rule-of-six, the additional G residues that are traditionally added after the T7 promoter transcription initiation site were not synthesised. The synthetic fragment was then cloned into low-copy number transcription vector pOLTV5-phiX between the T7 promoter and HDV Rz sequences through digestion with BbsI. The construct was co-transfected with helper plasmids into BSRT7/5 cells. A recombinant NDV called rAF was successfully rescued using transfection supernatant harvested as early as 16 h post-transfection. Virus from each passage showed an intracerebral pathogenicity index (ICPI) and a mean death time (MDT) similar to the parent strain AF2240-I. Moreover, rAF possessed an introduced mutation which was maintained for several passages. The entire rescue using the one-step assembly procedure was completed within a few weeks, which is extremely fast compared to previously used methods.

Discovery of anti-cell migration activity of an anti-HIV heterocyclic compound by identification of its binding protein hnRNP M

One compound sometimes shows two biological functions, becoming important aspect of recent drug discovery. This study began with an attempt to confirm the previously reported molecular mechanism of the anti-human immunodeficiency virus (HIV) heterocyclic compound BMMP [2-(benzothiazol-2-ylmethylthio)-4-methylpyrimidine], i.e., induction of abnormal uncoating of the viral core at the post-entry step. Our mechanistic study gave results consistent with this mechanism. We further attempted to find out the molecular target of BMMP by a pulldown approach using previously synthesized biotinylated BMMP (Biotin-BMMP) and successfully identified heterogenous nuclear ribonucleoprotein M (hnRNP M) as a BMMP-binding protein. This protein was found not to be accountable for the anti-HIV activity of BMMP. As hnRNP M has been reported to promote cancer metastasis, we tested this mechanism and found that BMMP suppressed migration of the human lung carcinoma cell line A549 stimulated with transforming growth factor-β (TGF-β). Mechanistic study showed that BMMP suppressed the expression of CD44 mRNA via the regulation of hnRNP M. Furthermore, six new derivatives of BMMP were synthesized, and the patterns of their activities against HIV-1 and cell migration were not uniform, suggesting that the anti-HIV mechanism and the anti-cell migration mechanism of BMMP are independent. Taken together, the anti-cell migration activity of the anti-HIV heterocyclic compound BMMP was newly discovered by identification of its binding protein hnRNP M using a chemical biology approach.

Tetraspanins in the regulation of mast cell function

Mast cells (MCs) are long-living immune cells highly specialized in the storage and release of different biologically active compounds and are involved in the regulation of innate and adaptive immunity. MC degranulation and replacement of MC granules are accompanied by active membrane remodelling. Tetraspanins represent an evolutionary conserved family of transmembrane proteins. By interacting with lipids and other membrane and intracellular proteins, they are involved in organisation of membrane protein complexes and act as "molecular facilitators" connecting extracellular and cytoplasmic signaling elements. MCs express different tetraspanins and MC degranulation is accompanied by changes in membrane organisation. Therefore, tetraspanins are very likely involved in the regulation of MC exocytosis and membrane reorganisation after degranulation. Antiviral response and production of exosomes are further aspects of MC function characterized by dynamic changes of membrane organization. In this review, we pay a particular attention to tetraspanin gene expression in different human and murine MC populations, discuss tetraspanin involvement in regulation of key MC signaling complexes, and analyze the potential contribution of tetraspanins to MC antiviral response and exosome production. In-depth knowledge of tetraspanin-mediated molecular mechanisms involved in different aspects of the regulation of MC response will be beneficial for patients with allergies, characterized by overwhelming MC reactions.

HIV gp120 Induces the Release of Proinflammatory, Angiogenic, and Lymphangiogenic Factors from Human Lung Mast Cells

Human lung mast cells (HLMCs) express the high-affinity receptor FcεRI for IgE and are involved in chronic pulmonary diseases occurring at high frequency among HIV-infected individuals. Immunoglobulin superantigens bind to the variable regions of either the heavy or light chain of immunoglobulins (Igs). Glycoprotein 120 (gp120) of HIV-1 is a typical immunoglobulin superantigen interacting with the heavy chain, variable 3 (V_H3) region of human Igs. The present study investigated whether immunoglobulin superantigen gp120 caused the release of different classes of proinflammatory and immunoregulatory mediators from HLMCs. The results show that gp120 from different clades induced the rapid (30 min) release of preformed mediators (histamine and tryptase) from HLMCs. gp120 also caused the de novo synthesis of cysteinyl leukotriene C₄ (LTC₄) and prostaglandin D₂ (PGD₂) from HLMCs. Incubation (6 h) of HLMC with gp120 induced the release of angiogenic (VEGF-A) and lymphangiogenic (VEGF-C) factors from HLMCs. The activating property of gp120 was mediated through the interaction with IgE V_H3⁺ bound to FcεRI. Our data indicate that HIV gp120 is a viral superantigen, which induces the release of different proinflammatory, angiogenic, and lymphangiogenic factors from HLMCs. These observations could contribute to understanding, at least in part, the pathophysiology of chronic pulmonary diseases in HIV-infected individuals.

X-Linked RNA-Binding Motif Protein Modulates HIV-1 Infection of CD4+ T Cells by Maintaining the Trimethylation of Histone H3 Lysine 9 at the Downstream Region of the 5' Long Terminal Repeat of HIV Proviral DNA

HIV-1 latency featuring silence of transcription from HIV-1 proviral DNA represents a major obstacle for HIV-1 eradication. Reversible repression of HIV-1 5′-LTR-mediated transcription represents the main mechanism for HIV-1 to maintain latency. The 5′-LTR-driven HIV gene transcription can be modulated by multiple host factors and mechanisms. The hnRNPs are known to regulate gene expression. A member of the hnRNP family, RBMX, has been identified in this study as a novel HIV-1 restriction factor that modulates HIV-1 5′-LTR-driven transcription of viral genome in CD4⁺ T cells and maintains viral latency. These findings provide a new understanding of how host factors modulate HIV-1 infection and latency and suggest a potential new target for the development of HIV-1 therapies.

Reversible repression of HIV-1 5′ long terminal repeat (5′-LTR)-mediated transcription represents the main mechanism for HIV-1 to maintain latency. Identification of host factors that modulate LTR activity and viral latency may help develop new antiretroviral therapies. The heterogeneous nuclear ribonucleoproteins (hnRNPs) are known to regulate gene expression and possess multiple physiological functions. hnRNP family members have recently been identified as the sensors for viral nucleic acids to induce antiviral responses, highlighting the crucial roles of hnRNPs in regulating viral infection. A member of the hnRNP family, X-linked RNA-binding motif protein (RBMX), has been identified in this study as a novel HIV-1 restriction factor that modulates HIV-1 5′-LTR-driven transcription of viral genome in CD4⁺ T cells. Mechanistically, RBMX binds to HIV-1 proviral DNA at the LTR downstream region and maintains the repressive trimethylation of histone H3 lysine 9 (H3K9me3), leading to a blockage of the recruitment of the positive transcription factor phosphorylated RNA polymerase II (RNA pol II) and consequential impediment of transcription elongation. This RBMX-mediated modulation of HIV-1 transcription maintains viral latency by inhibiting viral reactivation from an integrated proviral DNA. Our findings provide a new understanding of how host factors modulate HIV-1 infection and latency and suggest a potential new target for the development of HIV-1 therapies.

Mast Cell Responses to Viruses and Pathogen Products

Mast cells are well accepted as important sentinel cells for host defence against selected pathogens. Their location at mucosal surfaces and ability to mobilize multiple aspects of early immune responses makes them critical contributors to effective immunity in several experimental settings. However, the interactions of mast cells with viruses and pathogen products are complex and can have both detrimental and positive impacts. There is substantial evidence for mast cell mobilization and activation of effector cells and mobilization of dendritic cells following viral challenge. These cells are a major and under-appreciated local source of type I and III interferons following viral challenge. However, mast cells have also been implicated in inappropriate inflammatory responses, long term fibrosis, and vascular leakage associated with viral infections. Progress in combating infection and boosting effective immunity requires a better understanding of mast cell responses to viral infection and the pathogen products and receptors we can employ to modify such responses. In this review, we outline some of the key known responses of mast cells to viral infection and their major responses to pathogen products. We have placed an emphasis on data obtained from human mast cells and aim to provide a framework for considering the complex interactions between mast cells and pathogens with a view to exploiting this knowledge therapeutically. Long-lived resident mast cells and their responses to viruses and pathogen products provide excellent opportunities to modify local immune responses that remain to be fully exploited in cancer immunotherapy, vaccination, and treatment of infectious diseases.

LDH hybrid thermosensitive hydrogel for intravaginal delivery of anti-HIV drugs

Microbicides based on hydrogel have become an effective way to prevent the HIV replication and transmission because of their convenience and prolonging drug release. In this study, a hybrid thermo-sensitive hydrogel constituted by nanosized layered double hydroxides and poloxamer 407 (P407) was constructed and co-loaded with both hydrophobic and hydrophilic drug. The LDH-P407 hydrogel could achieve sol-gel transition at body temperature. The in vivo experiment showed that LDH-P407 hydrogel can achieve controlled release of theaflavin and Nile red (hydrophobic drug model) into blood by vaginal drug delivery, meanwhile the hydrogel showed barely mucosal irritation. In addition, ex vivo experiment showed that the nifeviroc-loaded LDH-P407 hydrogel was able to specifically bind co-receptor CCR5 of DCs cells. Therefore, the LDH-P407 hydrogel would be a promising carrier for intravaginal delivery of anti-HIV drugs.

Intron-containing RNA from the HIV-1 provirus activates type I interferon and inflammatory cytokines

HIV-1-infected people who take drugs that suppress viremia to undetectable levels are protected from developing AIDS. Nonetheless, HIV-1 establishes proviruses in long-lived CD4⁺ memory T cells, and perhaps other cell types, that preclude elimination of the virus even after years of continuous antiviral therapy. Here we show that the HIV-1 provirus activates innate immune signaling in isolated dendritic cells, macrophages, and CD4⁺ T cells. Immune activation requires transcription from the HIV-1 provirus and expression of CRM1-dependent, Rev-dependent, RRE-containing, unspliced HIV-1 RNA. If rev is provided in trans, all HIV-1 coding sequences are dispensable for activation except those cis-acting sequences required for replication or splicing. Our results indicate that the complex, post-transcriptional regulation intrinsic to HIV-1 RNA is detected by the innate immune system as a danger signal, and that drugs which disrupt HIV-1 transcription or HIV-1 RNA metabolism would add qualitative benefit to current antiviral drug regimens.

During HIV infection, antiviral therapy can suppress viraemia to undetectable levels and hinder the progression towards AIDS; however the HIV-1 provirus can remain in long-lived CD4⁺ memory T cells. Here the authors show that intronic RNA from the HIV-1 provirus can induce type I interferon and inflammatory cytokine production.

Scaffold attachment factor B suppresses HIV-1 infection of CD4+ T cells by preventing binding of RNA polymerase II to HIV-1's long terminal repeat

The 5' end of the HIV, type 1 (HIV-1) long terminal repeat (LTR) promoter plays an essential role in driving viral transcription and productive infection. Multiple host and viral factors regulate LTR activity and modulate HIV-1 latency. Manipulation of the HIV-1 LTR provides a potential therapeutic strategy for combating HIV-1 persistence. In this study, we identified an RNA/DNA-binding protein, scaffold attachment factor B (SAFB1), as a host cell factor that represses HIV-1 transcription. We found that SAFB1 bound to the HIV-1 5' LTR and significantly repressed 5' LTR-driven viral transcription and HIV-1 infection of CD4⁺ T cells. Mechanistically, SAFB1-mediated repression of HIV-1 transcription and infection was independent of its RNA- and DNA-binding capacities. Instead, by binding to phosphorylated RNA polymerase II, SAFB1 blocked its recruitment to the HIV-1 LTR. Of note, SAFB1-mediated repression of HIV-1 transcription from proviral DNA maintained HIV-1 latency in CD4⁺ T cells. In summary, our findings reveal that SAFB1 binds to the HIV-1 LTR and physically interacts with phosphorylated RNA polymerase II, repressing HIV-1 transcription initiation and elongation. Our findings improve our understanding of host modulation of HIV-1 transcription and latency and provide a new host cell target for improved anti-HIV-1 therapies.

Simultaneous in vitro generation of human CD34+-derived dendritic cells and mast cells from non-mobilized peripheral blood mononuclear cells

Dendritic cells (DCs) and mast cells (MCs) are key players of the immune system, often coming in close proximity in peripheral tissues. The interplay of these cells is, however, still poorly understood, especially with regards to human cells. The reason for that is the absence of a well established in vitro human cell-based study system that would allow a simultaneous preparation of both cell types. In this study, we show a method for simultaneous generation of DCs and MCs from CD34⁺ stem cell progenitors that were isolated from the non-adherent fraction of non-mobilized peripheral blood mononuclear cells of healthy donors. We observed that combining stem cells factor (SCF), IL-3 and GM-CSF in serum-free StemPro-34 medium allowed CD34⁺ cells isolated from an equivalent of 450 ml of peripheral blood to expand to 10-92 × 10⁶ cells after 7 weeks of culturing. These cultures comprised of 6-53% of DCs and 1-21% of MCs as determined by the expression of, respectively, CD11c/HLA-DR or CD117/FcεRI. The DCs were CD1a^-CD14^-, did not express co-stimulatory molecules CD80 and CD83 and chemokine receptor CCR7. However, the DCs expressed co-stimulatory molecule CD86, and had a capacity to uptake dextran, phagocyte latex particles and induce alloreactivity. MCs, on the other hand, degranulated after crosslinking of FcεRI-bound IgE as determined by the externalization of CD107b. Collectively, our data show that CD34⁺-derived human DCs and MCs can be generated in a single culture using CD34⁺ cells isolated from non-mobilized human peripheral blood and that this method may allow ex vivo studies on DC-MC interplay in human system.

HIV Reprograms Human Airway Basal Stem/Progenitor Cells to Acquire a Tissue-Destructive Phenotype

While highly active anti-retroviral therapy has dramatically improved the survival of HIV-infected individuals, there is an increased risk for other co-morbidities, such as COPD, manifesting as emphysema. Given that emphysema originates around the airways and that human airway basal cells (BCs) are adult airway stem/progenitor cells, we hypothesized that HIV reprograms BCs to a distinct phenotype that contributes to the development of emphysema. Our data indicate that HIV binds to but does not replicate in BCs. HIV binding to BCs induces them to acquire an invasive phenotype, mediated by upregulation of MMP-9 expression through activation of MAPK signaling pathways. This HIV-induced "destructive" phenotype may contribute to degradation of extracellular matrix and tissue damage relevant to the development of emphysema commonly seen in HIV⁺ individuals.

Endoplasmic Reticulum Protein SCAP Inhibits Dengue Virus NS2B3 Protease by Suppressing Its K27-Linked Polyubiquitylation

Dengue viruses (DENVs) are an emerging threat to global public health. The NS2B3 protease complex of DENV has recently been shown to cleave the antiviral protein STING and thereby subvert the innate immune signaling to facilitate virus replication. Whether host cells have a mechanism to counteract this virus-mediated immunosuppression is unclear. We discovered that the K27-linked polyubiquitination of NS3 protein facilitates its recruitment of NS2B, the formation of NS2B3, and consequently the enhanced cleavage of STING. However, an endoplasmic reticulum (ER) protein, SCAP, through binding to NS2B protein, inhibits the ubiquitination of NS3, rendering NS2B3 protease incapable of binding and cleaving STING. Importantly, ectopic expression of SCAP impaired DENV infection, whereas silencing of SCAP potentiated DENV infection. Collectively, this study uncovered a novel function of SCAP of counteracting the inhibitory action of DENV NS2B3 protease on STING signaling, suggesting that modulation of SCAP levels may have therapeutic implications.IMPORTANCE This study reports the first ubiquitylation target protein in DENV, the NS3 protein, and the unique role of K27-linked polyubiquitylation in NS3's ability to recruit NS2B and formation of the NS2B3 protease complex. Additionally, this study identified novel functions of the ER protein SCAP: one is to compete with NS2B for binding to STING, and the other is to inhibit the ubiquitination of NS3. Both of these functions protect STING from being cleaved by the NS2B3 protease and thus contribute to host antiviral response.

A mature macrophage is a principal HIV-1 cellular reservoir in humanized mice after treatment with long acting antiretroviral therapy

BACKGROUND

Despite improved clinical outcomes seen following antiretroviral therapy (ART), resting CD4+ T cells continue to harbor latent human immunodeficiency virus type one (HIV-1). However, such cells are not likely the solitary viral reservoir and as such defining where and how others harbor virus is imperative for eradication measures. To such ends, we used HIV-1_ADA-infected NOD.Cg-Prkdc ^scid Il2rg ^tm1Wjl /SzJ mice reconstituted with a human immune system to explore two long-acting ART regimens investigating their abilities to affect viral cell infection and latency. At 6 weeks of infection animals were divided into four groups. One received long-acting (LA) cabotegravir (CAB) and rilpivirine (RVP) (2ART), a second received LA CAB, lamivudine, abacavir and RVP (4ART), a third were left untreated and a fourth served as an uninfected control. After 4 weeks of LA ART treatment, blood, spleen and bone marrow (BM) cells were collected then phenotypically characterized. CD4+ T cell subsets, macrophages and hematopoietic progenitor cells were analyzed for HIV-1 nucleic acids by droplet digital PCR.

RESULTS

Plasma viral loads were reduced by two log₁₀ or to undetectable levels in the 2 and 4ART regimens, respectively. Numbers and distributions of CD4+ memory and regulatory T cells, macrophages and hematopoietic progenitor cells were significantly altered by HIV-1 infection and by both ART regimens. ART reduced viral DNA and RNA in all cell and tissue compartments. While memory cells were the dominant T cell reservoir, integrated HIV-1 DNA was also detected in the BM and spleen macrophages in both regimen-treated mice.

CONCLUSION

Despite vigorous ART regimens, HIV-1 DNA and RNA were easily detected in mature macrophages supporting their potential role as an infectious viral reservoir.

Are Basophils and Mast Cells Masters in HIV Infection?

The World Health Organization AIDS epidemic update estimates that more than 37 million people are living with HIV infection. Despite the unprecedented success of antiretroviral treatments, significant challenges remain in the fight against HIV. In particular, how uninfected cells capture HIV and transmit virions to target cells remains an unanswered question. Tissue mast cells and peripheral blood basophils can be exposed to virions or HIV products during infection. Several HIV proteins (i.e., envelope glycoproteins gp120 and gp41, Tat, and Nef) can interact with distinct surface receptors expressed by human basophils and mast cells and modulate their functional responses at different levels. Additionally, several groups have provided evidence that human mast cells can be infected in vitro, as well as in vivo, by certain strains of HIV. Recently, it has been demonstrated that basophils purified from healthy donors and intestinal mast cells can efficiently capture HIV on their cell surface and, cocultured with CD4+ T cells, they can transfer the virus to the cocultured cells leading to infection. Direct contact between human basophils or intestinal mast cells and CD4+ T cells can mediate viral trans-infection of T cells through the formation of viral synapses. Thus, basophils and mast cells can provide a cellular basis for capturing and then spreading viruses throughout the body. Collectively, these findings suggest that human basophils and mast cells play a complex and possibly distinct role in HIV infection, warranting further investigations.

HIV-1 Nef promotes migration and chemokine synthesis of human basophils and mast cells through the interaction with CXCR4

Background

The Nef protein can be detected in plasma of HIV-1-infected patients and plays a role in the pathogenesis of HIV-1. Nef produced during the early stages of infection is fundamental in creating the ideal environment for viral replication, e.g. by reducing the ability of infected cells to induce an immune response.

Aim

Based on previous experience showing that both Tat and gp41 of HIV-1 are potent chemotactic factors for basophils and mast cells, and gp120 is a powerful stimulus for the release of histamine and cytokines (IL-4 and IL-13) from basophils, in this study we aimed to verify if the HIV Nef protein can exert some effects on basophils and mast cells purified from healthy volunteers through the interaction with the CXCL12 receptor, CXCR4.

Methods

Basophils purified from peripheral blood cells of 30 healthy volunteers and mast cells obtained from lung tissue of ten healthy volunteers were tested by flow cytometric analysis, chemotaxis and chemokine production by ELISA assays.

Results

Nef is a potent chemoattractant for basophils and lung mast cells obtained from healthy, HIV-1 and HIV-2 seronegative individuals. Incubation of basophils and mast cells with Nef induces the release of chemokines (CXCL8/IL-8 and CCL3/MIP-1α). The chemotactic activity of Nef on basophils and mast cells is mediated by the interaction with CXCR4 receptors, being blocked by preincubation of FcεRI⁺ cells with an anti-CXCR4 Ab. Stimulation with Nef or CXCL12/SDF-1α, a CXCR4 ligand, desensitizes basophils to a subsequent challenge with an autologous or heterologous stimulus.

Conclusions

These results indicate that Nef, a HIV-1-encoded α-chemokine homolog protein, plays a direct role in basophils and mast cell recruitment and activation at sites of HIV-1 replication, by promoting directional migration of human FcεRI⁺ cells and the release of chemokines from these cells. Together with our previous results, these data suggest that FcεRI⁺ cells contribute to the dysregulation of the immune system in HIV-1 infection.

HIV-1 gp120 Glycoprotein Interacting with Dendritic Cell-specific Intercellular Adhesion Molecule 3-grabbing Non-integrin (DC-SIGN) Down-Regulates Tight Junction Proteins to Disrupt the Blood Retinal Barrier and Increase Its Permeability

Approximately 70% of HIV-1 infected patients acquire ocular opportunistic infections and manifest eye disorders during the course of their illness. The mechanisms by which pathogens invade the ocular site, however, are unclear. Under normal circumstances, vascular endothelium and retinal pigment epithelium (RPE), which possess a well developed tight junction complex, form the blood-retinal barrier (BRB) to prevent pathogen invasion. We hypothesize that disruption of the BRB allows pathogen entry into ocular sites. The hypothesis was tested using in vitro models. We discovered that human RPE cells could bind to either HIV-1 gp120 glycoproteins or HIV-1 viral particles. Furthermore, the binding was mediated by dendritic cell-specific intercellular adhesion molecule 3-grabbing non-integrin (DC-SIGN) expressed on RPE cells. Upon gp120 binding to DC-SIGN, cellular NF-κB signaling was triggered, leading to the induction of matrix metalloproteinases, which subsequently degraded tight junction proteins and disrupted the BRB integrity. DC-SIGN knockdown or prior blocking with a specific antibody abolished gp120-induced matrix metalloproteinase expression and reduced the degradation of tight junction proteins. This study elucidates a novel mechanism by which HIV, type 1 invades ocular tissues and provides additional insights into the translocation or invasion process of ocular complication-associated pathogens.