Expression of CD206 and CD163 on intermediate CD14++CD16+ monocytes are increased in hemorrhagic fever with renal syndrome and are correlated with disease severity

Single cells and TRUST4 reveal immunological features of the HFRS transcriptome

The etiology of hemorrhagic fever with renal syndrome (HFRS) is significantly impacted by a variety of immune cells. Nevertheless, the existing techniques for sequencing peripheral blood T cell receptor (TCR) or B cell receptor (BCR) libraries in HFRS are constrained by both limitations and high costs. In this investigation, we utilized the computational tool TRUST4 to generate TCR and BCR libraries utilizing comprehensive RNA-seq data from peripheral blood specimens of HFRS patients. This facilitated the examination of clonality and diversity within immune libraries linked to the condition. Despite previous research on immune cell function, the underlying mechanisms remain intricate, and differential gene expression across immune cell types and cell-to-cell interactions within immune cell clusters have not been thoroughly explored. To address this gap, we performed clustering analysis on 11 cell subsets derived from raw single-cell RNA-seq data, elucidating characteristic changes in cell subset proportions under disease conditions. Additionally, we utilized CellChat, a tool for cell-cell communication analysis, to investigate the impact of MIF family, CD70 family, and GALECTIN family cytokines-known to be involved in cell communication-on immune cell subsets. Furthermore, hdWGCNA analysis identified core genes implicated in HFRS pathogenesis within T cells and B cells. Trajectory analysis revealed that most cell subsets were in a developmental stage, with high expression of transcription factors such as NFKB and JUN in Effector CD8+ T cells, as well as in Naive CD4+ T cells and Naive B cells. Our findings provide a comprehensive understanding of the dynamic changes in immune cells during HFRS pathogenesis, identifying specific V genes and J genes in TCR and BCR that contribute to advancing our knowledge of HFRS. These insights offer potential implications for the diagnosis and treatment of this autoimmune disease.

Disparate macrophage responses are linked to infection outcome of Hantan virus in humans or rodents

Hantaan virus (HTNV) is asymptomatically carried by rodents, yet causes lethal hemorrhagic fever with renal syndrome in humans, the underlying mechanisms of which remain to be elucidated. Here, we show that differential macrophage responses may determine disparate infection outcomes. In mice, late-phase inactivation of inflammatory macrophage prevents cytokine storm syndrome that usually occurs in HTNV-infected patients. This is attained by elaborate crosstalk between Notch and NF-κB pathways. Mechanistically, Notch receptors activated by HTNV enhance NF-κB signaling by recruiting IKKβ and p65, promoting inflammatory macrophage polarization in both species. However, in mice rather than humans, Notch-mediated inflammation is timely restrained by a series of murine-specific long noncoding RNAs transcribed by the Notch pathway in a negative feedback manner. Among them, the lnc-ip65 detaches p65 from the Notch receptor and inhibits p65 phosphorylation, rewiring macrophages from the pro-inflammation to the pro-resolution phenotype. Genetic ablation of lnc-ip65 leads to destructive HTNV infection in mice. Thus, our findings reveal an immune-braking function of murine noncoding RNAs, offering a special therapeutic strategy for HTNV infection.

The clinical utility of CD163 in viral diseases

Macrophage activation and hypercytokinemia are notable presentations in certain viral infections leading to severe disease and poor prognosis. Viral infections can cause macrophage polarization into the pro-inflammatory M1 or anti-inflammatory M2 phenotype. Activated M1 macrophages usually restrict viral replication whereas activated M2 macrophages suppress inflammation and promote tissue repair. In response to inflammatory stimuli, macrophages polarize to the M2 phenotype expressing hemoglobin scavenger CD163 surface receptor. The CD163 receptor is shed as the soluble form, sCD163, into plasma or tissue fluids. sCD163 causes detoxification of pro-oxidative hemoglobin which produces anti-inflammatory metabolites that promote the resolution of inflammation. Hence, increased CD163 expression in tissues and elevated circulatory levels of sCD163 have been associated with acute and chronic inflammatory diseases. CD163 and other macrophage activation markers have been commonly included in the investigation of disease pathogenesis and progression. This review provides an overview of the involvement of CD163 in viral diseases. The clinical utility of CD163 in viral disease diagnosis, progression, prognosis and treatment evaluation is discussed.

Elevated Plasma Fractalkine Level Is Associated with the Severity of Hemorrhagic Fever with Renal Syndrome in Humans

Hantaan virus infection may cause severe lethal hemorrhagic fever with renal syndrome (HFRS) in humans. The chemokine fractalkine (CX3CL1) acts as a proinflammatory cytokine, and it is elevated in several infectious diseases. However, little is known about the contributions of CX3CL1 to HFRS pathogenesis. Present study detected plasma CX3CL1 levels and expression of the receptor CX3CR1 in HFRS patients and discussed the possible effects of CX3CL1 on pathogenesis of HFRS. Plasma CX3CL1 in acute phase and Critical/Severe groups of HFRS patients were significantly increased compared to that in normal controls (p < 0.001 and p < 0.01, respectively). High plasma CX3CL1 was negatively correlated with platelet count (r = -0.5844, p < 0.0001) and positively correlated with blood urea nitrogen (r = 0.3668, p = 0.0039), creatinine (r = 0.42, p = 0.0008), and white blood cells (r = 0.2646, p = 0.0411). Expression of CX3CR1 on nonclassical and intermediate monocytes was also increased in the acute phase (p < 0.01 for both the cells) and Critical/Severe groups (p < 0.05 and p < 0.01, respectively) of HFRS patients compared to that in normal controls. Taken together, elevation of plasma CX3CL1 in HFRS patients and expression of CX3CR1 on nonclassical and intermediate monocyte subsets might provide new insights into the potential role of CX3CL1/CX3CR1 in pathogenesis of HFRS.

Severe Clinical Worsening in COVID-19 and Potential Mechanisms of Immune-Enhanced Disease

Infection by the novel SARS-CoV-2 coronavirus produces a range of outcomes, with the majority of cases producing mild or asymptomatic effects, and a smaller subset progressing to critical or fatal COVID-19 disease featuring severe acute respiratory distress. Although the mechanisms driving severe disease progression remain unknown, it is possible that the abrupt clinical deterioration observed in patients with critical disease corresponds to a discrete underlying expansion of viral tropism, from infection of cells comprising respiratory linings and alveolar epithelia to direct infection and activation of inflammatory monocytes and macrophages. Dysregulated immune responses could then contribute to disease severity. This article discusses the potential role of monocyte/macrophage (Mo/Mϕ) infection by SARS-CoV-2 in mediating the immune response in severe COVID-19. Additional mechanisms of immune-enhanced disease, comprising maladaptive immune responses that may aggravate rather than alleviate severity, are also discussed. Severe acute clinical worsening in COVID-19 patients may be influenced by the emergence of antibodies that participate in hyperinflammatory monocyte response, release of neutrophil extracellular traps (NETs), thrombosis, platelet apoptosis, viral entry into Fc gamma receptor (FcγR)-expressing immune cells, and induction of autoantibodies with cross-reactivity against host proteins. While the potential roles of Mo/Mϕ infection and immune-enhanced pathology in COVID-19 are consistent with a broad range of clinical and laboratory findings, their prominence remains tentative pending further validation. In the interim, these proposed mechanisms present immediate avenues of inquiry that may help to evaluate the safety of candidate vaccines and antibody-based therapeutics, and to support consideration of pathway-informed, well-tolerated therapeutic candidates targeting the dysregulated immune response.

Decreased classical monocytes and CD163 expression in TB patients: an indicator of drug resistance

Tuberculosis (TB) is a disease instigated by Mycobacterium tuberculosis. Peripheral blood monocytes represent highly efficient effector cells of innate immunity against TB. Little is known about monocyte subsets and their potential involvement in the development of M. tuberculosis drug resistance in patients with TB. This study was conducted to investigate alterations in monocyte subsets, CD163 expression on monocytes, and its serum level in patients without and with rifampicin resistance TB (RR-TB) and healthy controls. A total of 164 patients with TB (84 without RR-TB and 80 patients with RR-TB) and 85 healthy controls were enrolled in this study. The percentages of various monocyte subsets and surface expression of CD163 on monocytes were quantitatively determined using flow cytometry. The serum level of CD163 was determined by commercially available ELISA kits. Decreased frequency of classical monocytes was detected in patients with RR-TB. Non-classical monocytes were decreased in patients without RR-TB; however, intermediate monocytes were raised in patients with RR-TB. The serum level of CD163 was decreased in patients of RR-TB that showsed a positive correlation with the frequency of CD14++CD16-CD163+ and CD14++CD16+CD163+ monocytes. It is concluded that decreased classical monocytes and sCD163 in patients with RR-TB could be an indicator of drug resistance.

Monocyte subset redistribution from blood to kidneys in patients with Puumala virus caused hemorrhagic fever with renal syndrome

Innate immune cells like monocytes patrol the vasculature and mucosal surfaces, recognize pathogens, rapidly redistribute to affected tissues and cause inflammation by secretion of cytokines. We previously showed that monocytes are reduced in blood but accumulate in the airways of patients with Puumala virus (PUUV) caused hemorrhagic fever with renal syndrome (HFRS). However, the dynamics of monocyte infiltration to the kidneys during HFRS, and its impact on disease severity are currently unknown. Here, we examined longitudinal peripheral blood samples and renal biopsies from HFRS patients and performed in vitro experiments to investigate the fate of monocytes during HFRS. During the early stages of HFRS, circulating CD14-CD16+ nonclassical monocytes (NCMs) that patrol the vasculature were reduced in most patients. Instead, CD14+CD16- classical (CMs) and CD14+CD16+ intermediate monocytes (IMs) were increased in blood, in particular in HFRS patients with more severe disease. Blood monocytes from patients with acute HFRS expressed higher levels of HLA-DR, the endothelial adhesion marker CD62L and the chemokine receptors CCR7 and CCR2, as compared to convalescence, suggesting monocyte activation and migration to peripheral tissues during acute HFRS. Supporting this hypothesis, increased numbers of HLA-DR+, CD14+, CD16+ and CD68+ cells were observed in the renal tissues of acute HFRS patients compared to controls. In vitro, blood CD16+ monocytes upregulated CD62L after direct exposure to PUUV whereas CD16- monocytes upregulated CCR7 after contact with PUUV-infected endothelial cells, suggesting differential mechanisms of activation and response between monocyte subsets. Together, our findings suggest that NCMs are reduced in blood, potentially via CD62L-mediated attachment to endothelial cells and monocytes are recruited to the kidneys during HFRS. Monocyte mobilization, activation and functional impairment together may influence the severity of disease in acute PUUV-HFRS.

Replication in the Mononuclear Phagocyte System (MPS) as a Determinant of Hantavirus Pathogenicity

Members of different virus families including Hantaviridae cause viral hemorrhagic fevers (VHFs). The decisive determinants of hantavirus-associated pathogenicity are still enigmatic. Pathogenic hantavirus species, such as Puumala virus (PUUV), Hantaan virus (HTNV), Dobrava-Belgrade virus (DOBV), and Sin Nombre virus (SNV), are associated with significant case fatality rates. In contrast, Tula virus (TULV) only sporadically causes mild disease in immunocompetent humans and Prospect Hill virus (PHV) so far has not been associated with any symptoms. They are thus defined here as low pathogenic/apathogenic hantavirus species. We found that productive infection of cells of the mononuclear phagocyte system (MPS), such as monocytes and dendritic cells (DCs), correlated well with the pathogenicity of hantavirus species tested. HTNV (intermediate case fatality rates) replicated more efficiently than PUUV (low case fatality rates) in myeloid cells, whereas low pathogenic/apathogenic hantavirus species did not produce any detectable virus titers. Analysis of PHPUV, a reassortant hantavirus derived from a pathogenic (PUUV) and an apathogenic (PHV) hantavirus species, indicated that the viral glycoproteins are not decisive for replication in MPS cells. Moreover, blocking acidification of endosomes with chloroquine decreased the number of TULV genomes in myeloid cells suggesting a post-entry block for low pathogenic/apathogenic hantavirus species in myeloid cells. Intriguingly, pathogenic but not low pathogenic/apathogenic hantavirus species induced conversion of monocytes into inflammatory DCs. The proinflammatory programming of MPS cells by pathogenic hantavirus species required integrin signaling and viral replication. Our findings indicate that the capacity to replicate in MPS cells is a prominent feature of hantaviral pathogenicity.

Monocyte Based Correlates of Immune Activation and Viremia in HIV-Infected Long-Term Non-Progressors

Background: Disease progression monitoring through CD4 counts alone can be inadequate in HIV infection as ongoing immune activation may result in Serious non-AIDS events (SNAEs). SNAEs involve monocyte activation driven chronic inflammation with significant sequelae observed even during HAART. Here, we attempted to delineate functional monocyte based signatures across stages of HIV disease progression. Methods: Participants spanning four cohorts were recruited-pre-ART (PA; <7 years of infection; n = 20), long-term non-progressors (LTNP; >7 years of infection, CD4 > 350 cells/μL, n = 20), individuals on therapy (ART; n = 18) and seronegative controls (SN; n = 15). Immunophenotyping of monocyte subsets and evaluation of expression of HIV-binding receptors-CD4 and CCR5, marker of immune activation- HLA-DR and M2 phenotype-mannose receptor (CD206) was followed by association of monocyte-specific parameters with conventional markers of disease progression such as absolute CD4 count, CD4/CD8 ratio, viral load, and T cell activation. Results: A significant expansion of intermediate monocytes (CD14++CD16+) with a concomitant decline in classical subset (CD14++CD16-) was observed in all infected cohorts compared to seronegative controls. In addition, an expansion of the non-classical subset (CD14+CD16++) was observed in long-term non-progressors. Dysregulation in monocyte subsets associated with CD4 count and CD4/CD8 ratio in PAs but not in LTNPs. We report for the first time that expression of CD206 is most prominent on intermediate monocytes which also have the highest expression of CD4, CCR5, and HLA-DR. Despite preserved CD4 counts, LTNPs had similar immune activation profiles to PAs, as evidenced by elevated HLA-DR expression across monocyte subsets. HLA-DR expression, similar to that in SNs, observed in the ART group indicated partial immune restoration within the monocyte compartment. Increased CD206 expression on monocytes together with frequency of activated CD4+ T lymphocytes (HLA-DR+CD38+) showed significant and positive association with viral load in LTNPs, but not PAs. Conclusion: Our results describe for the first time the presence of monocyte dysregulation involving increased activation in LTNPs, who, in spite of preserved CD4 counts, may remain susceptible to prolonged effects of systemic inflammation and highlight CD206, as a unique non-T correlate of viremia, in viremic non-progression.