ImmunoHorizons

Cannabis use is increasing globally, yet the immunological effects of {Delta}9-tetrahydrocannabinol (THC), the main intoxicating component of cannabis, remain incompletely understood. Given prior evidence that endocannabinoid signaling influences helminth immunity and type 2 inflammation, we investigated how sustained THC exposure alters immune responses to the helminth Nippostrongylus brasiliensis (Nb), which infects the lung and small intestine of mice. C57BL/6J mice were treated with THC (5 mg/kg/day) or vehicle for 14 days prior to helminth infection and assessed for parasite burden, innate immune cell and T cell responses, and transcriptional changes in lung eosinophils and macrophages. THC exposure did not significantly alter infection-associated weight loss or helminth burden; however, THC selectively restrained infection-induced circulating eosinophils and monocytes while increasing regulatory T cells. T cell activation assays showed reduced TNF and IFN{gamma} secretion in splenocytes from THC-treated infected mice. Bulk RNA sequencing showed that THC shifted lung eosinophils and CD11c lung macrophage-enriched cells from inflammatory, fibrotic, and costimulatory pathways toward stress and metabolic-adaptive transcriptional programs. Within the infected macrophage-enriched population, THC reduced CD80 expression while increasing MHC class II and antigen presentation-associated genes, suggesting a potential shift in macrophage-mediated T cell activation. Consistent with altered inflammatory and tissue remodeling-associated programs, immunofluorescent staining showed that THC mitigated infection-associated loss of lung collagen. Collectively, these findings indicate that THC reshapes the immune response to helminth infection by restraining innate and T cell effector responses while altering lung eosinophil and macrophage activation programs. Summary SentenceTHC reshapes helminth-induced type 2 inflammation by restraining inflammatory leukocyte responses and reprogramming lung eosinophils and macrophages.

Severe infections can trigger systemic inflammatory response syndrome (SIRS), wherein excessive cytokine release generates a "cytokine storm" causing tissue damage, multiorgan failure, and death. Natural killer T (NKT) cells are innate-like lymphocytes that respond rapidly to infection and can either amplify or suppress inflammation. Distinct NKT subsets may have opposing roles in acute infection, but their specific contributions to hyperinflammation remain unclear. Using a murine model of the cytokine storm, we demonstrate that type I NKT cells act as dominant suppressors of infection-induced hyperinflammation, whereas type II NKT cells confer minimal protection. This immunoregulation occurs via secreted mediators rather than direct cytotoxicity or cell-cell contact. Notably, we identify IL-22 as a key type I NKT cell effector that suppresses pro-inflammatory cytokine levels. These findings define a novel IL-22-dependent immunoregulatory axis wherein type I NKT cells limit pathological inflammation, providing insight for therapies targeting cytokine storms.

Autoimmune diseases, such as systemic lupus erythematosus (SLE), are underscored by dysregulated B cell function including the production of autoantibodies, skewed population ratios, and aberrant signaling. Given that the family of nuclear factor kappa B (NF-{kappa}B) transcription factors govern responses to stimuli, survival, differentiation, and so forth understanding the intricate regulatory network of NF-{kappa}B in B cell biology is paramount for unraveling treatments for B cell-linked autoimmune diseases. Here, we focus on a negative regulator of NF-{kappa}B signaling, A20 (TNFAIP3), that deactivates NF-{kappa}B transcription factor translocation through the ubiquitination and deubiquitination of target proteins. Haploinsufficiency in A20 results in an autoimmune phenotype and mutations to A20 have been associated with SLE, suggesting implications to B cell function. To investigate the role of A20 in NF-{kappa}B in human B cells, we generated a TNFAIP3 knockout (KO) Raji cell line. Cells were stimulated with either anti-IgM or Resiquimod (R848) to activate distinct NF-{kappa}B signaling pathways. Using qRT-PCR, western blotting, and flow cytometry, we assessed differences in gene expression, protein production, and NF-{kappa}B activation. We observed key limitations in using Epstein-Barr virus transformed B cell lines to model inducible NF-{kappa}B signaling.

Glycosylphosphatidylinositol (GPI) anchors are involved in the organization of membrane microdomains that support T cell receptor (TCR) signaling. However, their role in regulating expression of TCR-related proteins and downstream functional output remains unclear. This study aimed to characterize the effects of GPI-deficiency on TCR, cluster of differentiation 3 (CD3), and CD28 expression as well as interleukin-2 (IL-2) production using a GPI-deficient Jurkat T cell line (S12). Flow cytometry confirmed the complete loss of GPI anchors and GPI-anchored proteins (GPI-APs) in the S12 cell line. Compared to GPI-producing parental Jurkat, S12 had significantly higher expression of CD3 and TCR{beta} while CD28 had similar expression. IL-2 production by S12 was assessed following stimulation with anti-CD3/anti-CD28 beads and following stimulation with phorbol 12-myristate 13-acetate (PMA) and ionomycin. Neither S12 nor parental Jurkat produced detectable IL-2 in response to anti-CD3/anti-CD28 bead-mediated stimulation. Both parental Jurkat and S12 produced IL-2 following PMA/ionomycin-mediated stimulation. No significant difference in IL-2 production was observed between S12 and parental Jurkat following PMA/ionomycin-mediated stimulation. These findings demonstrate that GPI-deficiency influences surface receptor expression but does not significantly impair downstream IL-2 production under PMA/ionomycin stimulation. This finding suggests that GPI anchors and GPI-APs contribute to proximal signaling organization but are not required for cytokine production when downstream pathways are directly activated.

Cutaneous leishmaniasis is a parasitic skin disease for which current treatments often fail, highlighting the need for new therapeutic approaches. While high parasite burdens are associated with delayed healing, excessive protective immune responses, including elevated IFN-{gamma} production, have also been linked to worse clinical outcomes, indicating that immunopathology contributes significantly to disease progression. Acriflavine is an antimicrobial compound with reported anti-leishmanial activity and the ability to inhibit hypoxia-driven responses. Because Leishmania-infected skin is hypoxic in both mice and humans, and hypoxia has been implicated in disease pathogenesis, we investigated whether acriflavine alters the course of cutaneous leishmaniasis by affecting parasite control and/or host immune responses. We found that acriflavine treatment significantly reduced lesion size in Leishmania major-infected mice. Unexpectedly, this improvement occurred without changes in parasite burden. Instead, acriflavine treatment reduced the frequency of dendritic cells within lesions and decreased their expression of MHC class II, which correlated with fewer IFN-{gamma}-producing CD4 T cells at the site of infection. These findings indicate that acriflavine ameliorates disease by limiting dendritic cell activation and subsequent IFN-{gamma}-driven immunopathology rather than enhancing parasite clearance. Together, our results identify acriflavine as a potential host-directed therapeutic strategy for cutaneous leishmaniasis and support targeting hypoxia-associated pathways to reduce tissue damage driven by excessive inflammatory responses.

Macrophages in the tumor microenvironment are known to upregulate PD-L1 expression, thereby suppressing T cells through PD-1 ligation. However, the manner in which PD-L1 expression intrinsically impacts macrophages and their immunomodulatory phenotype is less clear. Clarifying this knowledge gap would yield insight into the mechanisms of immunosuppression within the tumor microenvironment. To characterize the macrophage intrinsic role of PD-L1, we used complementary genetic and pharmacological approaches by analyzing primary murine bone marrow-derived macrophages (BMDMs) with complete genetic PD-L1 deletion and wildtype BMDMs treated with anti-PD-L1 blocking antibodies. Macrophages were evaluated across naive, pro-inflammatory (M1), and tumor conditioned (TCM) polarization states in vitro. Unlike prior reports, neither genetic deletion nor antibody blockade dramatically altered the expression of macrophage polarization markers or in vitro phagocytic capacity. Both conditions consistently reduced surface levels of the M1-associated costimulatory molecule CD80, prompting further analysis of T cell interacting and antigen presenting proteins, in which we revealed disparate effects of genetic deletion and antibody blockade on the surface levels of MHCI, MHCII, PD-1, and PD-L2. These findings suggest that PD-L1 deletion and antibody-mediated blockade contribute to macrophage immune regulatory profiles in distinct manners. This difference supports a model in which PD-L1 functions in macrophages beyond its canonical role as a ligand for PD-1, influencing antigen presentation and checkpoint molecule levels and playing a broader role in immune regulation in the tumor microenvironment.

BackgroundIdiopathic pulmonary fibrosis (IPF) is a progressive, chronic lung disease with limited therapeutic options. Tryptophan metabolism is significantly dysregulated during lung fibrogenesis, with the metabolite kynurenine (kyn) accumulating in lung tissue and driving pathology via the aryl hydrocarbon receptor (AHR). This study evaluates the cell-specific contributions of kyn-mediated AHR signaling across different pulmonary cell types to clarify its role in disease progression. MethodsUsing a murine model of bleomycin-induced pulmonary fibrosis, lung tryptophan metabolites were profiled via liquid chromatography-mass spectrometry. The functional and transcriptomic impacts of kyn administration and AHR modulation were subsequently characterized across three distinct cellular compartments: CD103+ dendritic cells (DCs), fibroblasts, and alveolar epithelial cells (AECs). ResultsKyn levels were elevated in fibrotic lungs, and exogenous kyn selectively exacerbated collagen deposition during the fibrogenic phase rather than altering acute injury. In vitro monocultures of primary lung fibroblasts and AECs revealed negligible functional responses to kyn or AHR inhibition regarding myofibroblast differentiation, migration, or epithelial barrier disruption. Intriguingly, primary tissue-resident CD103+ DCs exhibited a hyperinflammatory, non-canonical AHR signaling profile in vivo. While ex vivo monoculture rapidly reverted these DCs to an anti-inflammatory, canonical AHR state, directly co-culturing DCs with fibrotic primary lung fibroblasts successfully restored the pathogenic, non-canonical signaling phenotype characterized by augmented IL-6 production and suppressed canonical targets. ConclusionsPathogenic AHR signaling in pulmonary fibrosis is highly cell-context dependent and driven by complex cell-cell interactions. Reductionist monocultures fail to replicate tissue- level dendritic cell phenotypes, highlighting the necessity of co-culture models and providing a cautionary note for the systemic clinical use of AHR-targeted therapeutics.

Group 2 innate lymphoid cells (ILC2s) regulate type 2 immune responses partly by recruiting eosinophils, but the mechanisms underlying this process remain incompletely understood. Although both ILC2s and type 2 T helper (Th2) cells are capable of expressing IL-5, a cytokine critical for recruiting eosinophils, ILC2s are more potent than Th2 cells in this process. Here, we show that the transcription factor Bhlhe40 promotes GM-CSF production in ILC2s, and Bhlhe40 expression in ILC2s is required for efficient eosinophil recruitment during both papain- and helminth-induced type 2 immune responses. However, Bhlhe40 deficiency in ILC2s had no effect on the production of classical type 2 cytokines, including IL-4, IL-5 and IL-13, despite Bhlhe40 being required for type 2 cytokine production by Th2 cells. Furthermore, in contrast to ILC2s, Th2 cells produced little GM-CSF and administration of GM-CSF rescued eosinophil recruitment in ILC2-specific Bhlhe40-deficient mice. In addition to promoting GM-CSF expression, Bhlhe40 repressed IL-10 production in ILC2s as it did in Th2 cells, particularly during chronic inflammation. Single-cell transcriptomic analyses further supported this regulatory network, and the ChIP-Seq data revealed direct binding of Bhlhe40 to the enhancer and promoter regions within the Il10 and Csf2 loci. Collectively, our findings show that Bhlhe40 exerts distinct gene regulatory functions in ILC2s and Th2 cells, and Bhlhe40 modulates the inflammatory and anti-inflammatory functions of ILC2s by promoting GM-CSF while suppressing IL-10 production.

Chronic obstructive pulmonary disease (COPD) is a progressive inflammatory airway disease in which impaired mucosal barrier function may increase susceptibility to aspirated oral microbial products. Periodontal disease has been associated with COPD development and exacerbation, but the epithelial mechanisms linking periodontal pathogens to pulmonary immune remodeling remain unclear. Here, we investigated whether gingipain-containing Porphyromonas gingivalis culture supernatant (PCS) promotes {gamma}{delta} T-cell-associated inflammation in COPD-like airways. Repeated intratracheal administration of PCS to {beta}ENaC-transgenic mice induced airway-centered immune cell accumulation and increased {gamma}{delta} TCR-positive cell accumulation, together with elevated expression of the {gamma}{delta} T-cell-associated cytokines Ifng and Il17a. PCS also increased pulmonary Ccl20 and Ccr6 expression, whereas epithelial alarmin-related genes and M2 macrophage-associated responses were not induced in parallel. In ENaC-overexpressing human airway epithelial cells, PCS induced CCL20 and F2RL1, the gene encoding protease-activated receptor 2 (PAR-2), and reduced the N-terminal PAR-2 signal, consistent with proteolytic receptor cleavage. Direct PAR-2 activation reproduced CCL20 induction, whereas pharmacological PAR-2 inhibition suppressed PCS-induced CCL20 expression. In contrast, PAR-1 inhibition or LPS neutralization with polymyxin B did not suppress this response. These findings support a mucosal epithelial protease-sensing model in which gingipain-containing P. gingivalis products activate PAR-2-dependent CCL20 production in airway epithelial cells and are associated with CCR6-linked {gamma}{delta} T-cell accumulation in COPD-like airways.

Immune biomarkers of tuberculosis (TB) disease severity present a challenging area of research that remains poorly understood. New technologies are able to perform larger, unbiased studies that can unravel the complex host-pathogen dynamics occurring during a Mycobacterium tuberculosis infection, the causative agent of TB. In this study, we designed a high dimensional approach combining viable bacterial burden (CFU, colony forming units) with time-of-flight mass cytometry (CyTOF) analysis to profile differences in cell-type abundance and cell-type specific protein expression during states of low, intermediate and high TB disease burden. Broadly, we segregated cell-type specific immune responses into those driven by bacterial burden and/or the mycobacterial infection strain. Interrogating these immune signatures allowed us to identify ATP-catabolizing protein CD39 as a correlate of disease severity. Treatment of mice with a small molecule inhibitor of CD39 promoted effector T cell functions and CD4 T cell expansion during Mtb infection. Collectively, our data defines the differential lung immune environment between various mycobacterial disease severity states and uncovers a potential immune biomarker of infection and therapeutic immunomodulating target to aid in the treatment of TB.

RationaleEosinophilic airway inflammation is common in severe asthma and strongly associated with symptoms, exacerbations, and impaired lung function. Although type 2 (T2)-targeted biologics improve outcomes and reduce eosinophils, many patients experience residual symptoms and exacerbations. Emerging evidence suggests that these biologics may differentially affect specific airway eosinophil subpopulations, representing a potential mechanism of suboptimal treatment response. ObjectiveDetermine the effect of biologic treatment on eosinophil subpopulations in adults with severe asthma using in-depth immune profiling with mass cytometry (CyTOF). MethodsFifty adults with severe asthma (28 biologic-naive, 22 on stable-dose biologic therapy for [&ge;]6 months) underwent clinical phenotyping, spirometry, blood sampling, and sputum induction. Twenty-nine sputum samples passed quality control thresholds and were profiled by CyTOF. Manually gated sputum eosinophils were clustered using FlowSOM to identify eosinophil subpopulations, and cluster abundances and marker expression were compared across treatment groups. Measurements and Main ResultsCyTOF revealed treatment-associated shifts in circulating immune cells (lower CD4+ T cells and B cells, higher monocytes) and lower sputum CD8+ T cells. Unsupervised clustering of sputum eosinophils identified eight distinct subpopulations, and selective depletion of Cluster 6 was noted in biologic-treated participants (biologic-naive vs anti-TSLP logFC -4.98, p=0.003; biologic-naive vs anti-IL5 logFC -6.89, p=0.01). Higher Cluster 6 proportion correlated with worse ACT scores (rho = -0.44, p = 0.02) and lung function (FEV1 % predicted: rho = -0.47, p < 0.01; FEV1/FVC: rho = -0.40, p = 0.03). Functionally, Cluster 6 displayed enriched trafficking/activation markers (CCR3/Eotaxin-1, CD69, CD80, CRTH2) and non-T2 inflammatory mediators (TNF, IL-8, TLR7). ConclusionBiologic therapy in severe asthma was associated with selective depletion of a highly activated sputum eosinophil subpopulation with capability to drive both T2 and non-T2 inflammatory pathways. This cluster correlated with worse asthma control and lung function, indicating it may be a biologically important driver of persistent disease and potential biomarker to more accurately predict treatment response.

Tissue-resident memory (TRM) T-cells are increasingly recognized as key mediators of chronic autoimmune inflammation, yet their organization and functional adaptation within the eye remain poorly understood. We investigated paired vitreous body biopsies and peripheral blood T cells from patients with chronic posterior segment uveitis using multiparameter flow cytometry, antigen-specific stimulation assays, single-cell RNA sequencing, and T-cell receptor sequencing to define the intraocular tissue-adaptive immune states. Vitreous T cells were phenotypically, transcriptionally, and clonally distinct from their circulating counterparts and enriched for canonical TRM markers. However, tissue adaptation differed substantially between CD4+ and CD8+ lineages. Vitreous CD4+ T cells segregated into clonally expanded tissue-adaptive states characterized by greater CXCR6 expression, enhanced antigen-specific cytokine responses, and well-defined transcriptional profiles. In contrast, vitreous CD8+ T cells expressed higher levels of the retention-associated markers CD103 and CD49a yet maintained greater clonal and phenotypic continuity with peripheral blood T cells. Both vitreous CD4+ and CD8+ subsets exhibited a restrained effector profile associated with tissue-adaptive transcriptional programs. Our data reveal that CD4+ and CD8+ T cells in chronic uveitis assume distinct states in the vitreous microenvironment, such that the intraocular immune response relies on both localized tissue retention and active adaptation to the inflammatory niche.

BackgroundSevere eosinophilic asthma (SEA), eosinophilic granulomatosis with polyangiitis (EGPA) and nasal polyposis (NP) are immune-mediated diseases characterised by eosinophilic inflammation. However, there is also increasing interest in the potential pathological roles of autoantibodies in these diseases. Understanding their B cell receptor (BCR) repertoires may provide valuable insights into disease mechanisms, and potential role of B cells in their pathology. MethodsWe conducted BCR repertoire sequencing using peripheral blood from 43 patients, comprising SEA with nasal polyps (SEA+NP), SEA without nasal polyps (SEA-NP), and EGPA, along with 16 healthy controls (HCs). ResultsCompared to HCs, patients with EGPA exhibited increased relative proportions of IgA1, IgG1, IgG2, and IgG4 subclasses. Similarly, SEA-NP patients demonstrated significantly high proportion of IgG2 sequences. Notably, the IgG4 subclass was significantly elevated across all patient groups compared to HCs. Patients receiving anti-IL-5/5R biologic treatments showed increased relative proportions of IgA2 and IgG2 subclasses compared to untreated patients. Some variation across participant groups in mean somatic hypermutation and mutation frequency was evident. 1,508 clones shared across patients, but not healthy controls, were evident though the majority showed low clonal expansion. Nevertheless, a few shared clones did show either high prevalence across patients and/or higher clonal expansion. ConclusionChanges in BCR repertoires in SEA/EGPA are consistent with a pattern of a more mature B cell component in the periphery and with the T2 inflammatory response observed in SEA and EGPA. BCR clonotypes shared across patients were evident, however, whether such clonotypes are pathological in SEA/EGPA requires further investigation.

Recognition of infected macrophages by CD4+ T cells is essential to immune protection against Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB). However, not all infected macrophage subsets successfully elicit T cell activation. We recently discovered that M2-like macrophages fail to efficiently activate memory CD4+ T cells when infected with Mtb, yet successfully elicit T cell activation when loaded with peptides, {gamma}-irradiated bacteria, or Mtb whole cell lysate. Since the mechanisms underlying CD4+ T cell evasion by infected M2 but not M1-like macrophages remain underexplored, we sought to determine the genes and pathways unique to Mtb infection of M2-like cells, including alveolar macrophages. RNA sequencing of human macrophages infected with virulent Mtb identified enrichment of IL-10 and type I interferon (IFN) signaling genes, including IL10RA and HERC5, respectively, in infected M2-like monocyte-derived and alveolar macrophages. However, genes involved in MHC-II trafficking, such as AP1M2, were higher in infected M1-like macrophages. In complementary experiments using fluorescence microscopy and flow cytometry, we observed impaired trafficking of newly synthesized MHC-II to the plasma membrane of Mtb-infected M2-like macrophages despite high total surface MHC-II levels. Neutralization of IL-10 or knockdown of HERC5 restored MHC-II trafficking to the cell surface among infected M2-like macrophages and significantly enhanced activation of memory CD4+ T cells in an MHC-II-dependent manner. These findings identify coordinated IL-10 and type I IFN signaling as key mechanisms that restrict MHC-II trafficking to the plasma membrane in Mtb-infected M2-like macrophages, thereby limiting antigen presentation and CD4+ T cell activation. We propose that host-directed therapies targeting these pathways in infected alveolar macrophages will facilitate T cell recognition for the prevention or treatment of active TB. Author SummaryRecognition of infected macrophages by CD4+ T cells is essential to immune protection against Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB). However, not all infected macrophage subsets successfully elicit T cell activation. We recently discovered that M2-like macrophages fail to efficiently activate memory CD4+ T cells when infected with Mtb, yet they successfully elicit T cell activation when treated with peptides, {gamma}-irradiated bacteria, or Mtb whole cell lysate. In this study, we identified genes and pathways uniquely upregulated in Mtb-infected M2-like macrophages that are linked to inefficient CD4+ T cell activation, including IL-10 signaling and type I interferon (IFN) pathways. These pathways were linked to reduced MHC-II trafficking to the plasma membrane in Mtb-infected M2-like macrophages. Neutralization of IL-10 or knockdown of HERC5 restored MHC-II trafficking and augmented memory CD4+ T cell activation. Our study demonstrates that IL-10 signaling and type I IFN pathways play detrimental roles in macrophages during Mtb infection, impairing MHC-II trafficking and CD4+ T cell activation. Since lung-resident alveolar macrophages express a dominant M2-like phenotype, these findings suggest that targeting IL-10 and type I IFN signaling may offer a strategy to enhance CD4+ T cell-mediated immunity and improve TB outcomes.

Influenza-associated pulmonary aspergillosis (IAPA) is a severe complication of influenza infection associated with substantial mortality. Influenza disrupts pulmonary host defenses and alters innate immune responses, predisposing patients to invasive fungal infection. Interleukin-27 (IL-27) is an immunoregulatory cytokine with context-dependent antiviral and antifungal effects; however, its role during IAPA remains undefined. A mouse model of IAPA was established by infecting wild-type and IL-27 receptor -deficient (Il27ra-/-) mice with influenza A, followed by Aspergillus fumigatus challenge. IL-27 and IL-27R expression were increased during IAPA. Single-cell RNA sequencing identified monocytes as the primary source of IL-27 and T cells as major IL-27r-expressing cells. Il27ra-/- mice exhibited significantly increased pulmonary fungal and influenza viral burden, enhanced type 2 immune responses characterized by elevated IL-4, IL-5, IL-9, IL-13, eosinophils, Th2 cells, pathogenic Th2 cells, and ILC2s. Despite increased eosinophil abundance, eosinophil-mediated conidial killing was impaired in Il27ra-/- mice. IL-27R deficiency also reduced macrophage abundance and impaired macrophage conidial uptake. Conversely, timed administration of rIL-27 enhanced fungal clearance, improved survival, and increased macrophage conidial uptake and augmented eosinophil killing capacity during IAPA. IL-27 signaling is a protective immunoregulatory cytokine during IAPA that limits pathological type 2 inflammation and enhances antifungal effector function of both eosinophils and macrophages. These findings identify IL-27 as a potential therapeutic in IAPA.

Cutaneous leishmaniasis is characterized by chronic inflammatory skin lesions in which CD8{square} T cells exhibit paradoxical functions. While IFN-{gamma}-producing CD8{square} T cells contribute to the development of protective immunity in the draining lymph node, CD8{square} T cells recruited to the infected skin lose their ability to produce IFN-{gamma} and instead acquire cytotoxic functions that exacerbate tissue damage. We previously demonstrated that the hypoxic microenvironment of leishmanial lesions promotes CD8{square} T cell cytotoxicity through induction of Blimp-1. Whether hypoxia also suppresses protective CD8{square} T cell functions, however, is unknown. Here, we show that hypoxia simultaneously suppresses production of the protective cytokines IFN-{gamma} and TNF- while enhancing expression of granzyme B and perforin in activated CD8{square} T cells. In vitro, HIF-1, but not HIF-2, was required for hypoxia-induced expression of granzyme B, perforin, and Blimp-1, whereas suppression of IFN-{gamma} and TNF- occurred independently of HIF signaling, indicating that distinct oxygen-related pathways regulate pathogenic and protective CD8{square} T cell functions. Hypoxia also increased expression of multiple inhibitory receptors on CD8{square} T cells, although lesional CD8{square} T cells lacked expression of the terminal exhaustion-associated transcription factor TOX, suggesting that hypoxia promotes an inhibitory phenotype distinct from terminal exhaustion. Finally, adoptive transfer studies demonstrated that in vivo both HIF-1 and HIF-2 expression in CD8{square} T cells contributed to immunopathology during cutaneous leishmaniasis. Together, these findings identify hypoxia as a key regulator that functionally reprograms CD8{square} T cells by promoting pathogenic cytotoxicity while suppressing protective cytokine production within lesions.

Numbers of ARID3a (AT-Rich Interaction Domain 3a) -expressing B lymphocytes from patients with systemic lupus erythematosus (SLE) are associated with increased disease activity. Normally, ARID3a-expressing circulating naive B cells are rare, but in SLE naive B cells dramatically increase ARID3a expression. We found that in vitro stimulation of B lymphocytes from healthy individuals with a cocktail of cytokines and agonists induced ARID3a in a subset of activated naive B cells and in IgD-CD27- double negative B cells previously associated with autoimmunity. Single cell RNA-seq of isolated naive B cells from ten SLE patients, with varying frequencies of ARID3a-expressing cells, revealed that ARID3a-associated genes included activation markers. Moreover, our data revealed the unexpected co-expression of the scavenger receptor CD68 with ARID3a, at both the transcript and protein level, in activated subsets of naive B cells. Inhibition of ARID3a in stimulated B cell cultures blocked naive B cell activation and CD68 expression. Together, these data identify ARID3a and CD68 as markers of naive B cell precursors associated with autoimmunity in SLE.

In polymicrobial infections, how the host recognizes and responds to pathogens influences which species will persist to cause chronic infections. The human respiratory tract is a common anatomical site for viral-bacterial co-infections, where primary viral infections predispose to secondary bacterial infections, leading to increased morbidity and mortality. Additionally, co-infections are disproportionately prevalent in people with chronic lung diseases, such as chronic obstructive pulmonary disease and cystic fibrosis. We previously reported that primary viral infections and antiviral interferon (IFN) signaling stimulate Pseudomonas aeruginosa (PA) biofilm formation on airway epithelial cells (AECs). IFN signaling induces aerobic glycolysis in AECs and generates lactate as a cellular byproduct. Given that innate immune systems play an integral role in co-infection dynamics, we investigated the role of host-secreted metabolites (i.e. lactate) on innate immune cell activity during respiratory co-infections. We found that exposure to the apical secretions from IFN{beta}-treated AECs significantly compromised macrophage antibacterial activity, with the soluble metabolite lactate playing an important role. Macrophages used monocarboxylate transporters and G-protein receptors to transport and/or sense lactate, respectively, and this exposure to lactate diminished their bacterial-killing activity in a time-exposure dependent manner. Lactate exposure particularly reprogrammed macrophage cellular metabolism towards an anti-inflammatory state by increasing oxidative phosphorylation and fatty acid oxidation. Collectively, these findings provide insight into metabolites as complex regulators of trans-kingdom interactions and epithelial-macrophage crosstalk during respiratory co-infections.

IntroductionT cell activation is central to the adaptive immune response. In vitro studies on T cell activation often utilize two distinct approaches: first, engaging T cell receptors (TCR) using plate-bound CD3 together with soluble CD28 (TCR-dependent). Second, triggering intracellular signalling cascades using phorbol 12-myristate 13-acetate (PMA) and Ionomycin or P+I (TCR-independent). Both methods are widely used; however, a systematic comparison of the activation methods across a range of stimulation strengths to evaluate their effects on T cell function and metabolism has not been investigated in great detail. In this study, we compared the consequences of engaging T cells using TCR-dependent and TCR-independent activation pathways across varying signal strengths. MethodsT cells from BALB/c mice were isolated and activated under four conditions: CD3, CD3+CD28, PMA with low Ionomycin (P+IL) and PMA with high Ionomycin (P+IH). We studied differences with respect to several parameters: morphology, flow analysis, metabolic activities, cytokines. The roles of Protein kinase C (PKC) and Ca{superscript 2} pathways were addressed by supplementing CD3+CD28 cultures with different doses of exogenous PMA or Ionomycin. ResultsP+I activation outperformed the CD3+CD28 activation system across most readouts by displaying enhanced blasts, higher cycling, greater glucose uptake, increased lactate and ROS production, together with higher upregulation of CD25 and CD44 activation markers. P+IH activation dampened several responses including CD69 expression. CD4 co-receptor was downregulated greatly with P+I activation but not CD3+CD28. Most cytokines followed signal strength comparably between both systems; however, differences were observed with others: P+I stimulation favoured IL-6 and IL-12 induction whereas CD3+CD28 activation preferentially induced CCL2 and IL-1{beta}. Importantly, PKC activity was substantially lower upon CD3+CD28 stimulation and the addition of PMA, but not Ionomycin, to CD3+CD28 cultures enhanced proliferation, metabolism and expression of activation markers. DiscussionTCR-dependent and TCR-independent T cell activation models have clear functional and metabolic differences. The observation that PKC signalling can boost T cell activation with CD3+CD28 is likely to be significant and may have translational implications such as CAR-T cell anti-tumor therapy where CD3+CD28 stimulation is widely used. The implications of our findings with regard to augmenting T cell mediated immunotherapies are discussed.

Monocytes are critical regulators of allergic inflammation, whose functions are modified by IgE-driven processes. Monocytes are heterogeneous; comprised of multiple subsets which implies differential functions. In allergic inflammation, this heterogeneity is likely influenced by IgE-mediated effects. We sought to identify phenotypically distinct monocyte subsets related to allergic disease and then further delineate functional differences in cytokine release and antiviral responses. Using high dimensional spectral flow cytometry, we identified monocyte surface phenotypes directly related to surface levels of the high affinity IgE receptor (Fc{epsilon}RI) and surface-bound IgE. Fc{epsilon}RI+IgE+ monocytes, or FIMs, correlated with allergic disease and the level of atopy (i.e. serum IgE levels) of individual subjects. The FIM population also had differential surface expression of other molecules of monocyte maturation, which closely resembled a type 2 conventional dendritic cell (cDC2) phenotype. Functionally, FIMs had enhanced antiviral responses and IgE-driven IL-10 cytokine release. Finally, we showed that FIMs could be identified at higher levels in lung tissue from individuals with asthma. This study supports that atopic disease drives differential monocyte phenotypes, with the FIM population, specifically, as a more mature cell population closely related to dendritic cells with enhanced antiviral responses. The presence of monocytes in lung tissue during lethal asthma exacerbation further supports a role in regulating tissue inflammatory responses in allergic airway disease.