SARS-CoV-2 mRNA Vaccines Induce Greater Complement Activation and Decreased Viremia and Nef Antibodies in Men With HIV-1.

BACKGROUND: Immune dysregulation in people with human immunodeficiency virus-1 (PWH) persists despite potent antiretroviral therapy and, consequently, PWH tend to have lower immune responses to licensed vaccines. However, limited information is available about the impact of mRNA vaccines in PWH. This study details the immunologic responses to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) mRNA vaccines in PWH and their impact on HIV-1. METHODS: We quantified anti-S immunoglobulin G (IgG) binding and neutralization of 3 SARS-CoV-2 variants of concern and complement activation in blood from virally suppressed men with HIV-1 (MWH) and men without HIV-1 (MWOH), and the characteristics that may impact the vaccine immune responses. We also studied antibody levels against HIV-1 proteins and HIV-1 plasma RNA. RESULTS: MWH had lower anti-S IgG binding and neutralizing antibodies against the 3 variants compared to MWOH. MWH also produced anti-S1 antibodies with a 10-fold greater ability to activate complement and exhibited higher C3a blood levels than MWOH. MWH had decreased residual HIV-1 plasma viremia and anti-Nef IgG approximately 100 days after immunization. CONCLUSIONS: MWH respond to SARS-CoV-2 mRNA vaccines with lower antibody titers and with greater activation of complement, while exhibiting a decrease in HIV-1 viremia and anti-Nef antibodies. These results suggest an important role of complement activation mediating protection in MWH.

Infiltration of inflammatory macrophages and neutrophils and widespread pyroptosis in lung drive influenza lethality in nonhuman primates.

Severe influenza kills tens of thousands of individuals each year, yet the mechanisms driving lethality in humans are poorly understood. Here we used a unique translational model of lethal H5N1 influenza in cynomolgus macaques that utilizes inhalation of small-particle virus aerosols to define mechanisms driving lethal disease. RNA sequencing of lung tissue revealed an intense interferon response within two days of infection that resulted in widespread expression of interferon-stimulated genes, including inflammatory cytokines and chemokines. Macaques with lethal disease had rapid and profound loss of alveolar macrophages (AMs) and infiltration of activated CCR2+ CX3CR1+ interstitial macrophages (IMs) and neutrophils into lungs. Parallel changes of AMs and neutrophils in bronchoalveolar lavage (BAL) correlated with virus load when compared to macaques with mild influenza. Both AMs and IMs in lethal influenza were M1-type inflammatory macrophages which expressed neutrophil chemotactic factors, while neutrophils expressed genes associated with activation and generation of neutrophil extracellular traps (NETs). NETs were prominent in lung and were found in alveolar spaces as well as lung parenchyma. Genes associated with pyroptosis but not apoptosis were increased in lung, and activated inflammatory caspases, IL-1ß and cleaved gasdermin D (GSDMD) were present in bronchoalveolar lavage fluid and lung homogenates. Cleaved GSDMD was expressed by lung macrophages and alveolar epithelial cells which were present in large numbers in alveolar spaces, consistent with loss of epithelial integrity. Cleaved GSDMD colocalized with viral NP-expressing cells in alveoli, reflecting pyroptosis of infected cells. These novel findings reveal that a potent interferon and inflammatory cascade in lung associated with infiltration of inflammatory macrophages and neutrophils, elaboration of NETs and cell death by pyroptosis mediates lethal H5N1 influenza in nonhuman primates, and by extension humans. These innate pathways represent promising therapeutic targets to prevent severe influenza and potentially other primary viral pneumonias in humans.

Tissue-specific transcriptional profiling of plasmacytoid dendritic cells reveals a hyperactivated state in chronic SIV infection.

HIV associated immune activation (IA) is associated with increased morbidity in people living with HIV (PLWH) on antiretroviral therapy, and remains a barrier for strategies aimed at reducing the HIV reservoir. The underlying mechanisms of IA have not been definitively elucidated, however, persistent production of Type I IFNs and expression of ISGs is considered to be one of the primary factors. Plasmacytoid DCs (pDCs) are a major producer of Type I IFN during viral infections, and are highly immunomodulatory in acute HIV and SIV infection, however their role in chronic HIV/SIV infection has not been firmly established. Here, we performed a detailed transcriptomic characterization of pDCs in chronic SIV infection in rhesus macaques, and in sooty mangabeys, a natural host non-human primate (NHP) species that undergoes non-pathogenic SIV infection. We also investigated the immunostimulatory capacity of lymph node homing pDCs in chronic SIV infection by contrasting gene expression of pDCs isolated from lymph nodes with those from blood. We observed that pDCs in LNs, but not blood, produced high levels of IFNα transcripts, and upregulated gene expression programs consistent with T cell activation and exhaustion. We apply a novel strategy to catalogue uncharacterized surface molecules on pDCs, and identified the lymphoid exhaustion markers TIGIT and LAIR1 as highly expressed in SIV infection. pDCs from SIV-infected sooty mangabeys lacked the activation profile of ISG signatures observed in infected macaques. These data demonstrate that pDCs are a primary producer of Type I IFN in chronic SIV infection. Further, this study demonstrated that pDCs trafficking to LNs persist in a highly activated state well into chronic infection. Collectively, these data identify pDCs as a highly immunomodulatory cell population in chronic SIV infection, and a putative therapeutic target to reduce immune activation.

Contribution of Coronavirus-Specific Immunoglobulin G Responses to Complement Overactivation in Patients with Severe Coronavirus Disease 2019.

BACKGROUND: Excessive complement activation has been implicated in the pathogenesis of coronavirus disease 2019 (COVID-19), but the mechanisms leading to this response remain unclear. METHODS: We measured plasma levels of key complement markers, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA and antibodies against SARS-CoV-2 and seasonal human common cold coronaviruses (CCCs) in hospitalized patients with COVID-19 of moderate (n = 18) and critical severity (n = 37) and in healthy controls (n = 10). RESULTS: We confirmed that complement activation is systemically increased in patients with COVID-19 and is associated with a worse disease outcome. We showed that plasma levels of C1q and circulating immune complexes were markedly increased in patients with severe COVID-19 and correlated with higher immunoglobulin (Ig) G titers, greater complement activation, and higher disease severity score. Additional analyses showed that the classical pathway was the main arm responsible for augmented complement activation in severe patients. In addition, we demonstrated that a rapid IgG response to SARS-CoV-2 and an anamnestic IgG response to the nucleoprotein of the CCCs were strongly correlated with circulating immune complex levels, complement activation, and disease severity. CONCLUSIONS: These findings indicate that early, nonneutralizing IgG responses may play a key role in complement overactivation in severe COVID-19. Our work underscores the urgent need to develop therapeutic strategies to modify complement overactivation in patients with COVID-19.

Severe Acute Respiratory Syndrome Coronavirus 2 Viremia Is Associated With Coronavirus Disease 2019 Severity and Predicts Clinical Outcomes.

BACKGROUND: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) viral RNA (vRNA) is detected in the bloodstream of some patients with coronavirus disease 2019 (COVID-19), but it is not clear whether this RNAemia reflects viremia (ie, virus particles) and how it relates to host immune responses and outcomes. METHODS: SARS-CoV-2 vRNA was quantified in plasma samples from observational cohorts of 51 COVID-19 patients including 9 outpatients, 19 hospitalized (non-intensive care unit [ICU]), and 23 ICU patients. vRNA levels were compared with cross-sectional indices of COVID-19 severity and prospective clinical outcomes. We used multiple imaging methods to visualize virions in plasma. RESULTS: SARS-CoV-2 vRNA was detected in plasma of 100%, 52.6%, and 11.1% of ICU, non-ICU, and outpatients, respectively. Virions were detected in plasma pellets using electron tomography and immunostaining. Plasma vRNA levels were significantly higher in ICU > non-ICU > outpatients (P < .0001); for inpatients, plasma vRNA levels were strongly associated with higher World Health Organization (WHO) score at admission (P = .01), maximum WHO score (P = .002), and discharge disposition (P = .004). A plasma vRNA level >6000 copies/mL was strongly associated with mortality (hazard ratio, 10.7). Levels of vRNA were significantly associated with several inflammatory biomarkers (P < .01) but not with plasma neutralizing antibody titers (P = .8). CONCLUSIONS: Visualization of virus particles in plasma indicates that SARS-CoV-2 RNAemia is due, at least in part, to viremia. The levels of SARS-CoV-2 RNAemia correlate strongly with disease severity, patient outcome, and specific inflammatory biomarkers but not with neutralizing antibody titers.

Peripheral Blood Biomarkers of Disease Outcome in a Monkey Model of Rift Valley Fever Encephalitis.

Rift Valley Fever (RVF) is an emerging arboviral disease of livestock and humans. Although the disease is caused by a mosquito-borne virus, humans are infected through contact with, or inhalation of, virus-laden particles from contaminated animal carcasses. Some individuals infected with RVF virus (RVFV) develop meningoencephalitis, resulting in morbidity and mortality. Little is known about the pathogenic mechanisms that lead to neurologic sequelae, and thus, animal models that represent human disease are needed. African green monkeys (AGM) exposed to aerosols containing RVFV develop a reproducibly lethal neurological disease that resembles human illness. To understand the disease process and identify biomarkers of lethality, two groups of 5 AGM were infected by inhalation with either a lethal or a sublethal dose of RVFV. Divergence between lethal and sublethal infections occurred as early as 2 days postinfection (dpi), at which point CD8+ T cells from lethally infected AGM expressed activated caspase-3 and simultaneously failed to increase levels of major histocompatibility complex (MHC) class II molecules, in contrast to surviving animals. At 4 dpi, lethally infected animals failed to demonstrate proliferation of total CD4+ and CD8+ T cells, in contrast to survivors. These marked changes in peripheral blood cells occur much earlier than more-established indicators of severe RVF disease, such as granulocytosis and fever. In addition, an early proinflammatory (gamma interferon [IFN-γ], interleukin 6 [IL-6], IL-8, monocyte chemoattractant protein 1 [MCP-1]) and antiviral (IFN-α) response was seen in survivors, while very late cytokine expression was found in animals with lethal infections. By characterizing immunological markers of lethal disease, this study furthers our understanding of RVF pathogenesis and will allow the testing of therapeutics and vaccines in the AGM model.IMPORTANCE Rift Valley Fever (RVF) is an important emerging viral disease for which we lack both an effective human vaccine and treatment. Encephalitis and neurological disease resulting from RVF lead to death or significant long-term disability for infected people. African green monkeys (AGM) develop lethal neurological disease when infected with RVF virus by inhalation. Here we report the similarities in disease course between infected AGM and humans. For the first time, we examine the peripheral immune response during the course of infection in AGM and show that there are very early differences in the immune response between animals that survive infection and those that succumb. We conclude that AGM are a novel and suitable monkey model for studying the neuropathogenesis of RVF and for testing vaccines and therapeutics against this emerging viral pathogen.

Widespread Virus Replication in Alveoli Drives Acute Respiratory Distress Syndrome in Aerosolized H5N1 Influenza Infection of Macaques.

Human infections with highly pathogenic avian influenza A (H5N1) virus are frequently fatal but the mechanisms of disease remain ill-defined. H5N1 infection is associated with intense production of proinflammatory cytokines, but whether this cytokine storm is the main cause of fatality or is a consequence of extensive virus replication that itself drives disease remains controversial. Conventional intratracheal inoculation of a liquid suspension of H5N1 influenza virus in nonhuman primates likely results in efficient clearance of virus within the upper respiratory tract and rarely produces severe disease. We reasoned that small particle aerosols of virus would penetrate the lower respiratory tract and blanket alveoli where target cells reside. We show that inhalation of aerosolized H5N1 influenza virus in cynomolgus macaques results in fulminant pneumonia that rapidly progresses to acute respiratory distress syndrome with a fatal outcome reminiscent of human disease. Molecular imaging revealed intense lung inflammation coincident with massive increases in proinflammatory proteins and IFN-α in distal airways. Aerosolized H5N1 exposure decimated alveolar macrophages, which were widely infected and caused marked influx of interstitial macrophages and neutrophils. Extensive infection of alveolar epithelial cells caused apoptosis and leakage of albumin into airways, reflecting loss of epithelial barrier function. These data establish inhalation of aerosolized virus as a critical source of exposure for fatal human infection and reveal that direct viral effects in alveoli mediate H5N1 disease. This new nonhuman primate model will advance vaccine and therapeutic approaches to prevent and treat human disease caused by highly pathogenic avian influenza viruses.

Persistent accumulation of gut macrophages with impaired phagocytic function correlates with SIV disease progression in macaques.

The contribution of macrophages in the gastrointestinal tract to disease control or progression in HIV infection remains unclear. To address this question, we analyzed CD163+ macrophages in ileum and mesenteric lymph nodes (LN) from SIV-infected rhesus macaques with dichotomous expression of controlling MHC class I alleles predicted to be SIV controllers or progressors. Infection induced accumulation of macrophages into gut mucosa in the acute phase that persisted in progressors but was resolved in controllers. In contrast, macrophage recruitment to mesenteric LNs occurred only transiently in acute infection irrespective of disease outcome. Persistent gut macrophage accumulation was associated with CD163 expression on α4ß7+ CD16+ blood monocytes and correlated with epithelial damage. Macrophages isolated from intestine of progressors had reduced phagocytic function relative to controllers and uninfected macaques, and the proportion of phagocytic macrophages negatively correlated with mucosal epithelial breach, lamina propria Escherichia coli density, and plasma virus burden. Macrophages in intestine produced low levels of cytokines regardless of disease course, while mesenteric LN macrophages from progressors became increasingly responsive as infection advanced. These data indicate that noninflammatory CD163+ macrophages accumulate in gut mucosa in progressive SIV infection in response to intestinal damage but fail to adequately phagocytose debris, potentially perpetuating their recruitment.

Macrophage accumulation in gut mucosa differentiates AIDS from chronic SIV infection in rhesus macaques.

The relationship between recruitment of mononuclear phagocytes to lymphoid and gut tissues and disease in HIV and SIV infection remains unclear. To address this question, we conducted cross-sectional analyses of dendritic cell (DC) subsets and CD163(+) macrophages in lymph nodes (LNs) and ileum of rhesus macaques with acute and chronic SIV infection and AIDS. In LNs significant differences were only evident when comparing uninfected and AIDS groups, with loss of myeloid DCs and CD103(+) DCs from peripheral and mesenteric LNs, respectively, and accumulation of plasmacytoid DCs and macrophages in mesenteric LNs. In contrast, there were fourfold more macrophages in ileum lamina propria in macaques with AIDS compared with chronic infection, and this increased to 40-fold in Peyer's patches. Gut macrophages exceeded plasmacytoid DCs and CD103(+) DCs by ten- to 17-fold in monkeys with AIDS but were at similar low frequencies as DCs in chronic infection. Gut macrophages in macaques with AIDS expressed IFN-α and TNF-α consistent with cell activation. CD163(+) macrophages also accumulated in gut mucosa in acute infection but lacked expression of IFN-α and TNF-α. These data reveal a relationship between inflammatory macrophage accumulation in gut mucosa and disease and suggest a role for macrophages in AIDS pathogenesis.

Macrophages and Myeloid Dendritic Cells Lose T Cell-Stimulating Function in Simian Immunodeficiency Virus Infection Associated with Diminished IL-12 and IFN-α Production.

Impaired T cell responses are a defining characteristic of HIV infection, but the extent to which altered mononuclear phagocyte function contributes to this defect is unclear. We show that mononuclear phagocytes enriched from rhesus macaque lymph nodes have suppressed ability to stimulate CD4 T cell proliferation and IFN-γ release after acute SIV infection. When individual populations were isolated, myeloid dendritic cells (mDC) and macrophages but not plasmacytoid DC (pDC) had suppressed capacity to stimulate CD4 T cell proliferation, with macrophage function declining as infection progressed. Macrophages, but not pDC or mDC, had suppressed capacity to induce IFN-γ release from CD4 T cells in acute infection, even after stimulation with virus-encoded TLR7/8 ligand. Changes in expression of costimulatory molecules did not explain loss of function postinfection. Conversely, pDC and mDC had marked loss of IFN-α and IL-12 production, respectively, and macrophages lost production of both cytokines. In T cell cocultures without TLR7/8 ligand, macrophages were the primary source of IL-12, which was profoundly suppressed postinfection and correlated with loss of IFN-γ release by T cells. TLR7/8-stimulated pDC, mDC and macrophages all produced IL-12 in T cell cocultures, which was suppressed in chronic infection. Supplementing IL-12 enhanced mDC-driven IFN-γ release from T cells, and IL-12 and IFN-α together restored function in TLR7/8-activated macrophages. These findings reveal loss of macrophage and mDC T cell-stimulating function in lymph nodes of SIV-infected rhesus macaques associated with diminished IL-12 and IFN-α production that may be a factor in AIDS immunopathogenesis.

Blocking TLR7- and TLR9-mediated IFN-α production by plasmacytoid dendritic cells does not diminish immune activation in early SIV infection.

Persistent production of type I interferon (IFN) by activated plasmacytoid dendritic cells (pDC) is a leading model to explain chronic immune activation in human immunodeficiency virus (HIV) infection but direct evidence for this is lacking. We used a dual antagonist of Toll-like receptor (TLR) 7 and TLR9 to selectively inhibit responses of pDC but not other mononuclear phagocytes to viral RNA prior to and for 8 weeks following pathogenic simian immunodeficiency virus (SIV) infection of rhesus macaques. We show that pDC are major but not exclusive producers of IFN-α that rapidly become unresponsive to virus stimulation following SIV infection, whereas myeloid DC gain the capacity to produce IFN-α, albeit at low levels. pDC mediate a marked but transient IFN-α response in lymph nodes during the acute phase that is blocked by administration of TLR7 and TLR9 antagonist without impacting pDC recruitment. TLR7 and TLR9 blockade did not impact virus load or the acute IFN-α response in plasma and had minimal effect on expression of IFN-stimulated genes in both blood and lymph node. TLR7 and TLR9 blockade did not prevent activation of memory CD4+ and CD8+ T cells in blood or lymph node but led to significant increases in proliferation of both subsets in blood following SIV infection. Our findings reveal that virus-mediated activation of pDC through TLR7 and TLR9 contributes to substantial but transient IFN-α production following pathogenic SIV infection. However, the data indicate that pDC activation and IFN-α production are unlikely to be major factors in driving immune activation in early infection. Based on these findings therapeutic strategies aimed at blocking pDC function and IFN-α production may not reduce HIV-associated immunopathology.

Emerging concepts in dengue pathogenesis: interplay between plasmablasts, platelets, and complement in triggering vasculopathy.

Dengue is a mosquito-borne disease caused by infection with dengue virus (DENV) that represents a serious and expanding global health threat. Most DENV infections are inapparent or produce mild and self-limiting illness; however a significant proportion results in severe disease characterized by vasculopathy and plasma leakage that may culminate in shock and death. The cause of dengue-associated vasculopathy is likely to be multifactorial but remains essentially unknown. Severe disease is manifest during a critical phase from 4 to 7 days after onset of symptoms, once the virus has disappeared from the circulation but before the peak of T-cell activation, suggesting that other factors mediate vasculopathy. Here, we present evidence for a combined role of plasmablasts, complement, and platelets in driving severe disease in DENV infection. Massive expansion of virus-specific plasmablasts peaks during the critical phase of infection, coincident with activation of complement and activation and depletion of platelets. We propose a step-wise model in which virus-specific antibodies produced by plasmablasts form immune complexes, leading to activation of complement and release of vasoactive anaphylatoxins. Platelets become activated through binding of complement- and antibody-coated virus, as well as direct binding of virus to DC-SIGN, leading to the release of inflammatory microparticles and cytokines and sequestration of platelets in the microvasculature. We suggest that the combined effects of anaphylatoxins, inflammatory microparticles, and platelet sequestration serve as triggers of vasculopathy in severe dengue.

Virus-encoded TLR ligands reveal divergent functional responses of mononuclear phagocytes in pathogenic simian immunodeficiency virus infection.

The role of mononuclear phagocytes in the pathogenesis or control of HIV infection is unclear. In this study, we monitored the dynamics and function of dendritic cells (DC) and monocytes/macrophages in rhesus macaques acutely infected with pathogenic SIVmac251 with and without antiretroviral therapy (ART). SIV infection was associated with monocyte mobilization and recruitment of plasmacytoid DC (pDC) and macrophages to lymph nodes, which did not occur with ART treatment. SIVmac251 single-stranded RNA encoded several uridine-rich sequences that were potent TLR7/8 ligands in mononuclear phagocytes of naive animals, stimulating myeloid DC (mDC) and monocytes to produce TNF-α and pDC and macrophages to produce both TNF-α and IFN-α. Following SIV infection, pDC and monocytes/macrophages rapidly became hyporesponsive to stimulation with SIV-encoded TLR ligands and influenza virus, a condition that was reversed by ART. The loss of pDC and macrophage function was associated with a profound but transient block in the capacity of lymph node cells to secrete IFN-α upon stimulation. In contrast to pDC and monocytes/macrophages, mDC increased TNF-α production in response to stimulation following acute infection. Moreover, SIV-infected rhesus macaques with stable infection had increased mDC responsiveness to SIV-encoded TLR ligands and influenza virus at set point, whereas animals that progressed rapidly to AIDS had reduced mDC responsiveness. These findings indicate that SIV encodes immunostimulatory TLR ligands and that pDC, mDC, and monocytes/macrophages respond to these ligands differently as a function of SIV infection. The data also suggest that increased responsiveness of mDC to stimulation following SIV infection may be beneficial to the host.

Association between magnitude of the virus-specific plasmablast response and disease severity in dengue patients.

Dengue is a globally expanding disease caused by infection with dengue virus (DENV) that ranges from febrile illness to acute disease with serious complications. Secondary infection predisposes individuals to more severe disease, and B lymphocytes may play a role in this phenomenon through production of Ab that enhance infection. To better define the acute B cell response during dengue, we analyzed peripheral B cells from an adult Brazilian hospital cohort with primary and secondary DENV infections of varying clinical severity. Circulating B cells in dengue patients were proliferating, activated, and apoptotic relative to individuals with other febrile illnesses. Severe secondary DENV infection was associated with extraordinary peak plasmablast frequencies between 4 and 7 d of illness, averaging 46% and reaching 87% of B cells, significantly greater than those seen in mild illness or primary infections. On average >70% of IgG-secreting cells in individuals with severe secondary DENV infection were DENV specific. Plasmablasts produced Ab that cross-reacted with heterotypic DENV serotypes, but with a 3-fold greater reactivity to DENV-3, the infecting serotype. Plasmablast frequency did not correlate with acute serum-neutralizing Ab titers to any DENV serotype regardless of severity of disease. These findings indicate that massive expansion of DENV-specific and serotype cross-reactive plasmablasts occurs in acute secondary DENV infection of adults in Brazil, which is associated with increasing disease severity.

Massive mobilization of dendritic cells during influenza A virus subtype H5N1 infection of nonhuman primates.

Highly pathogenic avian influenza virus infection is characterized by a marked inflammatory response, but the impact of infection on dendritic cells (DCs) is unknown. We show that influenza A virus subtype H5N1 infection rapidly and profoundly impacts DCs in cynomolgus macaques, increasing the number of blood myeloid and plasmacytoid DCs by 16- and 60-fold, respectively. Infection was associated with recruitment, activation, and apoptosis of DCs in lung-draining lymph nodes; granulocyte and macrophage infiltration in lungs was also detected, together with expression of CXCL10. This degree of DC mobilization is unprecedented in viral infection and suggests a potential role for DCs in the pathogenesis of highly pathogenic avian influenza virus.

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.

The Dynamic Relationship between Dengue Virus and the Human Cutaneous Innate Immune Response.

Dengue virus (DENV) is a continuing global threat that puts half of the world's population at risk for infection. This mosquito-transmitted virus is endemic in over 100 countries. When a mosquito takes a bloodmeal, virus is deposited into the epidermal and dermal layers of human skin, infecting a variety of permissive cells, including keratinocytes, Langerhans cells, macrophages, dermal dendritic cells, fibroblasts, and mast cells. In response to infection, the skin deploys an array of defense mechanisms to inhibit viral replication and prevent dissemination. Antimicrobial peptides, pattern recognition receptors, and cytokines induce a signaling cascade to increase transcription and translation of pro-inflammatory and antiviral genes. Paradoxically, this inflammatory environment recruits skin-resident mononuclear cells that become infected and migrate out of the skin, spreading virus throughout the host. The details of the viral-host interactions in the cutaneous microenvironment remain unclear, partly due to the limited body of research focusing on DENV in human skin. This review will summarize the functional role of human skin, the cutaneous innate immune response to DENV, the contribution of the arthropod vector, and the models used to study DENV interactions in the cutaneous environment.

SIV infection of rhesus macaques differentially impacts mononuclear phagocyte responses to virus-derived TLR agonists.

BACKGROUND: During progressive simian immunodeficiency virus (SIV) infection, the ability of innate mononuclear phagocytes to function when responding to the invading pathogen has yet to be determined. METHODS: We generated single-stranded RNA (ssRNA) oligonucleotides from the infecting strain of virus and utilized them to stimulate mononuclear phagocytes from blood and lymph nodes of naïve and SIVmac251-infected rhesus macaques. RESULTS: Soon after infection and continuing through to chronic disease, plasmacytoid dendritic cells (pDC), monocytes, and macrophages from SIV-infected macaques were less able to produce pro-inflammatory cytokines after exposure to virus-derived toll-like receptor (TLR) agonists. In contrast, myeloid dendritic cells (mDC) became hyper-responsive during acute and stable chronic infection. CONCLUSIONS: Plasmacytoid dendritic cells, monocytes, and macrophages may not instigate continued immune activation by recognizing the single-stranded RNA from SIV as they are left dysfunctional after infection. Conversely, mDC functionality may be beneficial as their hyper-responsiveness is related to slowed disease progression.

Rapid Emergence of Potentially Transmissible Severe Acute Respiratory Syndrome Coronavirus 2 With Resistance to Combination Monoclonal Antibody Therapy.

Prolonged coronavirus disease 2019 may generate new viral variants. We report an immunocompromised patient treated with monoclonal antibodies who experienced rebound of viral RNA and emergence of an antibody-resistant (>1000-fold) variant containing 5 mutations in the spike gene. The mutant virus was isolated from respiratory secretions, suggesting the potential for secondary transmission.

Refined semi-lethal aerosol H5N1 influenza model in cynomolgus macaques for evaluation of medical countermeasures.

Highly pathogenic avian influenza A H5N1 viruses cause high mortality in humans and have pandemic potential. Effective vaccines and treatments against this threat are urgently needed. Here, we have refined our previously established model of lethal H5N1 infection in cynomolgus macaques. An inhaled aerosol virus dose of 5.1 log10 plaque-forming unit (pfu) induced a strong febrile response and acute respiratory disease, with four out of six macaques succumbing after challenge. Vaccination with three doses of adjuvanted seasonal quadrivalent influenza vaccine elicited low but detectable neutralizing antibody to H5N1. All six vaccinated macaques survived four times the 50% lethal dose of aerosolized H5N1, while four of six unvaccinated controls succumbed to disease. Although vaccination did not protect against severe influenza, vaccinees had reduced respiratory dysfunction and lower viral load in airways compared to controls. We anticipate that our macaque model will play a vital role in evaluating vaccines and antivirals against influenza pandemics.