Logan S. Dean

Although the interplay between the complement system, platelets, and neutrophils has been considered a major contributor to inflammation and thrombogenicity, little attention has been directed toward understanding their roles in people living with human immunodeficiency virus (PLWH). We quantified and compared expression levels of complement components (C2, C3a, C5a, C9), markers for coagulation (vWF-A2, ADAMTS13, tissue factor (TF), protein C, fibrinogen), and neutrophil activation (MPO, MMP-9) in plasma between virally suppressed PLWH (n = 40) and people living without HIV (PLWoH; n = 39). Platelet and activated platelet (CD62P+ cells) counts in the plasma samples were examined by flow cytometry analysis. To determine whether PLWH’s plasma promotes neutrophil extracellular traps (NETs) and whether C2 and C5a levels correlate with NET formation, an ex vivo NET assay was performed. PLWH showed significantly altered C2 and C5a levels in plasma that correlated strongly with protein C and MPO. C2 also showed a positive correlation with proinflammatory markers (SSA, SAP, IL-1β, and VEGF). Furthermore, HIV status was a significant predictor of C2 and C5a levels. CD62P expression on platelets was significantly increased in PLWH. In addition, treatment of healthy neutrophils with PLWH’s plasmapromoted NET formation, and this effect was inhibited by C5aR antibody treatment and platelet removal. These data suggest that activated platelets and soluble factors, such as higher C5a levels, contribute to NET formation in PLWH. Our findings provide evidence of complement dysregulation associated with inflammation and coagulation in PLWH. Altered soluble factors and platelet activation promote NET formation, potentially driving age-related non-AIDS comorbidities (NACMs).

Exposure of the lungs to particulate matter (i.e. dust, wildfire smoke, air pollution) places individuals at an increased risk for developing chronic respiratory disease. Recent work has demonstrated the efficacy of omega-3 fatty acids and their metabolites in promoting the resolution of prolonged inflammation, however a comprehensive understanding of how omega-3 fatty acid balance impacts immune cell populations and crosstalk remains undescribed. We developed a 17-marker, 14-color spectral flow cytometry method to characterize the immunophenotypic changes in the bronchoalveolar space and lung tissue following 14 days of repetitive organic dust exposure or PBS vehicle. The populations of immune cells were compared in C57BL/6 (WT) and a transgenic model of increased omega-3 fatty acid (Fat-1) mice. Histopathologic examination revealed no difference between WT and Fat-1 mice at baseline or following organic dust exposure. Immune cell makeup within the bronchoalveolar space and lung tissue differed between WT and Fat-1 mice, with and without organic dust exposure. Fat-1 mice demonstrated a monocyte-dominant response compared to WT in both the airway and the lung tissue. Intriguingly, this monocyte-dominance was more prominent in female Fat-1 mice in the lung tissue and male Fat-1 mice in the airway. This suggests that monocyte populations are preferentially loaded following organic dust exposure in the lung and airways as a result omega-3 fatty acid metabolite-linked resolution processes, and that sex-dependent factors in this immune response are pivotal to consider in therapeutic strategies aimed at mitigating disease.

Background: Although our understanding of the immunopathology and subsequent risk and severity of COVID-19 disease is evolving, a detailed account of immune responses that contribute to the long-term consequences of pulmonary complication in COVID-19 infection remain unclear. Few studies have detailed the immune and cytokine profiles associated with post-acute sequalae of SARS-CoV-2 infection with persistent pulmonary symptoms (PPASC). However, the dysregulation of the immune system that drives pulmonary sequelae in COVID-19 survivors and PASC sufferers remains largely unknown. Results: To characterize the immunological features of pulmonary PASC (PPASC), we performed droplet-based single-cell RNA sequencing to study the transcriptomic profiles of peripheral blood mononuclear cells (PBMCs) from participants naïve to SARS-CoV-2 (Control) and infected with SARS-CoV-2 with chronic pulmonary symptoms (PPASC). We analyzed more than 34,139 PBMCs by integrating our dataset with previously reported control datasets (GSM4509024) cell distribution. In total, 11 distinct cell populations were identified based on the expression of canonical markers. The proportion of myeloid-lineage cells ([MLCs]; CD14 ⁺ /CD16 ⁺ monocytes and dendritic cells) was increased in PPASC compared to controls. MLCs from PPASC displayed up-regulation of genes associated with pulmonary symptoms/fibrosis, while glycolysis metabolism-related genes were downregulated. Similarly, pathway analysis showed that fibrosis- related ( VEGF , WNT , and SMAD ) and cell death pathways were up-regulated, but immune pathways were down-regulated in PPASC. In PPASC, we observed interactive VEGF ligand- receptor pairs among MLCs, and network modules in CD14 ⁺ (cluster 4) and CD16 ⁺ (Cluster 5) monocytes displayed a significant enrichment for biological pathways linked to adverse COVID- 19 outcomes, fibrosis, and angiogenesis. Further analysis revealed a distinct metabolic alteration in MLCs with a down-regulation of glycolysis/gluconeogenesis in PPASC compared to SARS- CoV-2 naïve samples. Conclusion: This study offers valuable insights into the immune response and cellular landscape in PPASC. The presence of elevated MLC levels and their corresponding gene signatures associated with fibrosis, immune response suppression, and altered metabolic states suggests their potential role as a driver of PPASC.

Background: Monocytes and macrophages play a pivotal role in inflammation during acute SARS-CoV-2 infection. However, their contribution to the development of post-acute sequelae of SARS-CoV-2 infection (PASC) are not fully elucidated. Methods: A cross sectional study was conducted comparing plasma cytokine and monocyte levels among three groups: participants with pulmonary PASC (PPASC) with a reduced predicted diffusing capacity for carbon monoxide [DLCOc, + monocyte counts and higher CD169 expression was detected in intermediate and non-classical monocytes from RG and PG than that found in NG. Further correlation analysis with CD169 ⁺ monocyte subsets revealed that CD169 ⁺ intermediate monocytes negatively correlated with DLCOc%, and CD169 ⁺ non-classical monocytes positively correlated with IL-1α, IL-1β, MIP-1α, Eotaxin, and IFNγ. Conclusion: This study present evidence that COVID convalescents exhibit monocyte alteration beyond the acute COVID-19 infection period even in convalescents with no residual symptoms. These data provide further rational for determining the role of monocyte subsets in PPASC pathogenesis.

Highly effective combination antiretroviral therapy has reduced HIV infection to a manageable chronic disease, shifting the clinical landscape toward management of noninfectious comorbidities in people living with HIV (PLWH). These comorbidities are diverse, generally associated with accelerated aging, and present within multiple organ systems. Mechanistically, immune dysregulation and chronic inflammation, both of which persist in PLWH with well-controlled virally suppressive HIV infection, are suggested to create and exacerbate noninfectious comorbidity development. Persistent inflammation often leads to fibrosis, which is the common end point pathologic feature associated with most comorbidities. Fibrocytes are bone marrow–derived fibroblast-like cells, which emerged as key effector cells in tissue repair and pathologic fibrotic diseases. Despite their relevance to fibrosis, the circulating fibrocyte concentration in PLWH remains poorly characterized, and an understanding of their functional role in chronic HIV is limited. In this study, utilizing PBMCs from a cross-sectional adult HIV cohort study with matched uninfected controls (HIV−), we aimed to identify and compare circulating fibrocytes in blood. Both the percentage and number of fibrocytes and α-smooth muscle actin+ fibrocytes in circulation did not differ between the HIV+ and HIV− groups. However, circulating fibrocyte levels were significantly associated with increasing age in both the HIV+ and HIV− groups (the percentage and number; r = 0.575, p ≤ 0.0001 and r = 0.558, p ≤ 0.0001, respectively). Our study demonstrates that circulating fibrocyte levels and their fibroblast-like phenotype defined as collagen I and α-smooth muscle actin+ expression are comparable between, and strongly associated with, age irrespective of HIV status.

Low-density granulocytes (LDGs) are a distinct subset of neutrophils whose increased abundance is associated with the severity of COVID-19. However, the long-term effects of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection on LDG levels and phenotypic alteration remain unexplored. Using participants naïve to SARS-CoV-2 (NP), infected with SARS-CoV-2 with no residual symptoms (NRS), and infected with SARS-CoV-2 with chronic pulmonary symptoms (PPASC), we compared LDG levels and their phenotype by measuring the expression of markers for activation, maturation, and neutrophil extracellular trap (NET) formation using flow cytometry. The number of LDGs was significantly elevated in PPASC compared to NP. Individuals infected with SARS-CoV-2 (NRS and PPASC) demonstrated increased CD10 ⁺ and CD16HI subset counts of LDGs compared to NP group. Further characterization of LDGs demonstrated that LDGs from PPASC displayed higher NET forming ability and aggregation with platelets compared to LDGs from NP and NRS. Our data demonstrates that mature neutrophils with a heightened activation phenotype remain in circulation long after initial SARS-CoV-2 infection. Persistent elevation of markers for neutrophil activation and NET formation on LDGs, as well as an enhanced proclivity for platelet-neutrophil aggregation (PNA) formation in individuals with PPASC may be associated with the development of long-term pulmonary sequelae.