ImmunoHorizons

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.

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.

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.

Infection by Mycobacterium tuberculosis (Mtb) is characterized by pathogen persistence in lung cells derived from blood monocytes. Since monocyte-derived lung subsets differ in their ability to restrict the growth of intracellular Mtb in mice, understanding the ontogeny of these subsets can inform development of host-directed therapies. Circulating monocytes are proposed to be heterogeneous, arising from distinct bone marrow or spleen progenitors that direct local differentiation. However, the role of the Mtb-infected lung environment in this process has not been addressed. We found that infected and uninfected mice had similar bone marrow monopoiesis, resulting in equivalent monocyte differentiation within the infected lung. While pulmonary Mtb infection also induced splenic monopoiesis, we found no impact on lung monocyte differentiation in splenectomized mice. However, when wildtype monocytes were transferred into Mtb-infected Sp140-/- recipients, in which excess Type I interferons and neutrophils alter the lung environment, we observed that donor-derived lung subsets resembled recipient-derived cells. In the lungs of Mtb-infected mice, we identified monocyte-derived lung subsets with unique gene expression, associated with specific spatial distributions and cell neighborhoods. These findings suggest that the local lung environment has a larger influence on the phenotypic diversity of monocyte-derived lung cells than does the peripheral environment.

Background: This study aimed to elucidate B cell subset pathology in COPD, a poorly characterized area, with a focus on its similarities to and differences from classical autoimmune disorders. Methods: Single-cell RNA-sequencing (scRNA-seq) data from COPD and autoimmune diseases were obtained from the Gene Expression Omnibus (GEO) for comparative analyses of B cell subsets and functions via differentially expressed genes (DEGs), KEGG, protein-protein interaction (PPI), and cell-cell communication analyses. Serum IgG4 was measured by ELISA and correlated with clinical parameters. Peripheral blood B cells were sorted by flow cytometry for single-cell B cell receptor (BCR) sequencing. A v-Abl-Bcl2 pro-B cell line was stimulated with cigarette smoke extract (CSE) to assess abnormal development in vitro. Results: In lung tissue, IgG4 plasma cells were enriched and expressed BCR activation and inflammatory genes and TNF-NF-kB-MAPK pathways. Serum IgG4 concentrations correlated negatively with pre- and post-bronchodilator FEV1-FVC. B cells interacted with monocytes, macrophages, fibroblasts, and endothelial cells via IL-1B-IL-6, integrin, and chemokine signaling, contributing to chronic inflammation and remodeling. In peripheral blood, transitional T1 B cells were increased, accompanied by lambda-chain enrichment and increased IGLV1-47 usage, as well as enrichment of autoimmune pathways. In the bone marrow, the numbers of pre-B I cells were increased while those of small pre-B III cells were reduced, with altered expression of BCR development genes. CSE stimulation of the pro-B cell line reduced lambda expression in a concentration-dependent manner. Conclusions: The autoimmune abnormalities in COPD appear more restricted, although IgG4 antibody generation may contribute to immune-mediated lung damage.

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.

Multiple sclerosis (MS) is a chronic T cell-mediated autoimmune disease characterized by blood-brain barrier (BBB) disruption, neuroinflammation, and demyelination of the central nervous system (CNS). Emerging evidence links gut microbiota to disease pathogenesis, but the microbial factors that regulate pathogenic microRNA (miRNA) programs are largely unknown. Here, using experimental autoimmune encephalomyelitis (EAE, a MS mouse model), we investigated whether gut microbiota exacerbate EAE pathogenesis by modulating host miRNA expression. Antibiotic-induced depletion of the gut microbiota markedly attenuated EAE scores and reduced circulating inflammatory miRNAs, with miR-21 emerging as the dominant pathogenic candidate. Functional inhibition of miR-21 significantly ameliorated disease severity and reduced CNS T-cell infiltration. Mechanistically, miR-21 enhanced IL-17 and GM-CSF production by CD4 T cells and promoted immune-cell entry into the CNS through endothelial activation and blood-brain barrier dysfunction. We identified a transient expansion of Akkermansia muciniphila during the prodromal phase of EAE that positively correlated with circulating miR-21 levels. Colonization of antibiotic-treated mice with A. muciniphila exacerbated EAE and increased serum miR-21, whereas monocolonization of germ-free mice was insufficient to induce systemic miR-21, indicating a requirement for an inflammatory host environment. Further analyses revealed that atypical lipopolysaccharides (LPS) derived from A. muciniphila induce epithelial miR-21 production through coordinated TLR2/TLR4 signaling. Circulating miR-21 subsequently promoted endothelial dysfunction through the TIMP3-ADAM17 pathway, facilitating pathogenic T-cell migration into the CNS. Importantly, circulating miR-21 was also elevated in patients with MS. Collectively, these findings identify a previously unrecognized A. muciniphila-LPS-miR-21 axis linking gut dysbiosis to neuroinflammation and suggest that host-derived miRNAs function as systemic mediators through which microbial signals influence CNS autoimmunity.

Elastin degradation during chronic lung inflammation generates elastin peptides (EPs) with immunomodulatory properties. Because elastin is abundant in the lung, its breakdown in diseases such as chronic obstructive pulmonary disease (COPD) and asthma produces high EPs levels that may influence local immune responses. Here, we investigated the impact of EPs on group 2 innate lymphoid cells (ILC2) using mouse models of EP-induced emphysema and house dust mite (HDM)-induced asthma. EPs instillation reduced lung ILC2 numbers without affecting Th2 cells. In patients with COPD, we observed decreased CCL20 expression in lung immune cells and an inverse correlation between serum CCL20 levels and clinical indicators of elevated EPs burden. We also showed that EPs instillation during HDM-induced lung inflammation directly decreased CCL20 expression. These findings identify EPs as regulators of ILC2 trafficking through CCL20 downregulation, revealing a direct link between extracellular matrix (ECM) degradation and the chemokine networks orchestrating type 2 immunity. One Sentence SummaryElastin-derived peptides reshape type 2 immunity by blocking CCL20-driven ILC2 recruitment during lung inflammation.

The IFN-I (type I interferon) signaling pathway is the first line of defence against foreign pathogens. Stringent control of signalling pathways is necessary to maintain host immune responses and homeostasis. However, the underlying mechanism for its tight regulation is yet completely understood. In this study, we demonstrated that the TRIM family protein tripartite motif-containing 52 (TRIM52) is a novel negative regulator of IFN-{beta} production. Ectopically expressed TRIM52 markedly inhibited the activation of the IFN-{beta} promoter by ectopic expression of cGAS/STING, RIG-IN, or TRIF, MAVS, STING, and TBK1 but not by IRF3/5D, indicating that TRIM52 targets TBK1. TRIM52 also significantly inhibited the IFN-{beta}, ISG54, and ISG56 production, the dimerization of IRF3 and the nuclear localization of IRF3-YFP induced by ectopic expression of TBK1. Co-immunoprecipitation experiment revealed that TRIM52 specifically interacted with TBK1. Furthermore, the TBK1 protein, but not its mRNA, decreased considerably with increasing expression of TRIM52, and TRIM52 did not decrease the expression of the cGAS, STING, or IRF3 proteins. In addition, proteasome inhibitor MG-132 blocked the reduced TBK1 induced by TRIM52, indicating that TRIM52 caused TBK1 degradation via the proteasome pathway. Co-IP and ubiquitination assays demonstrated that TRIM52 promotion of K48-linked ubiquitination of TBK1, which depends on its E3 ubiquitin ligase. Collectively, our findings identify a previously unrecognized role of TRIM52 in regulating the IFN-I signalling pathway through targeting TBK1 for polyubiquitination and degradation.

Chronic infections require mechanisms that limit tissue damage while preserving pathogen control, yet the contribution of regulatory T (Treg) cells to this balance remains unclear. In this study, we characterized Treg cell responses during a chronic parasitic infection using experimental Trypanosoma cruzi infection as a model of persistent low-level parasitism and chronic tissue inflammation. We found that, although Treg cell numbers decline in the spleen, they accumulate in parasite-affected tissues such as skeletal muscle, where they adopt a combined Th1-associated and tissue-repair program. Systemic Treg cell depletion had limited impact on immune and disease-associated parameters, whereas local depletion in skeletal muscle exacerbated tissue damage and increased parasite burden. Moreover, transient systemic perturbation of Treg cells during the acute phase impaired their long-term accumulation in skeletal muscle, resulting in increased tissue damage and parasite burden during chronic infection. Additionally, accumulation of reparative Treg cells in skeletal muscle was impaired in the absence of ST2. Together, these findings identify a tissue-adapted Treg cell population that integrates inflammatory and reparative programs to preserve skeletal muscle integrity during chronic parasitic infection.

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.

Abstract Background: The Chikungunya virus (CHIKV), a re-emerging mosquito-borne alphavirus, is responsible for acute febrile illness and severe polyarthralgia. Although both innate and adaptive immune responses influence the disease outcomes, the detailed cellular immunopathogenesis of CHIKV in peripheral blood is not yet fully elucidated. Methods: We conducted single-cell RNA sequencing (scRNA-seq) on peripheral blood mononuclear cells (PBMCs) obtained from patients acutely infected with CHIKV and from healthy control subjects. Cellular interactions were inferred, and the transcriptomic results were orthogonally validated through quantitative real-time PCR (qPCR) and Enzyme-Linked Immunosorbent Assay (ELISA) to assess systemic interferon-stimulated responses. Furthermore, a comparative analysis was performed using publicly available single-cell data from Dengue virus (DENV) infections. Results: CHIKV infection significantly altered the immune system, increasing monocytes and dendritic cells while reducing T and B lymphocytes. Monocytes and NK cells showed strong activation of interferon-stimulated genes (ISGs). Monocytes were identified as key in driving inflammatory and immune responses. In adaptive immunity, CHIKV led B cells to become plasmablasts with antiviral immunoglobulins and caused T cells and NK-like T cells to show signs of cytotoxicity and exhaustion. Validation showed increased levels of IFN-{gamma}, IFN-{beta}1, MX1, and ISG15. CHIKV triggered a more intense, monocyte-driven interferon response than DENV. Conclusions: Acute CHIKV infection induces a systemic interferon response predominantly centered on monocytes, accompanied by significant alterations in adaptive immunity. Circulating ISG products, including MX1 and ISG15, reflect the transcriptomic activation and may serve as potential biomarkers for assessing the early intensity of innate antiviral responses.

Type I interferons (IFN-I) and IFN{gamma} exert divergent effects during tuberculosis, but the mechanisms that determine whether macrophage activation promotes host defense or inflammatory pathology remain incompletely understood. Here, we dissect the interplay between IFN-I and IFN{gamma} in macrophage activation using genetically susceptible B6.Sst1S macrophages. We show that, during tumor necrosis factor (TNF) stimulation, susceptible macrophages enter a persistent pathological activation state (pPAS) characterized by sustained lipid peroxidation and super-induction of IFN-I responses. This pathological state is maintained by autocrine IFN-I signaling. In contrast, IFN{gamma} priming prevents pPAS development by enhancing macrophage resilience to oxidative stress, in part through regulation of iron metabolism and induction of ferritin expression. Computational cell state transition assessment and regulation (cSTAR) analysis identified pathways and small molecules predicted to promote the transition of susceptible macrophages toward an IFN{gamma}-induced, Mtb-resistant state. Consistent with these predictions, the CDK4/6 inhibitor trilaciclib reduced lipid peroxidation by regulating iron metabolism, whereas retinoic acid signaling enhanced GPX4 expression and lipid biosynthesis programs. Combined CDK4/6 inhibition and retinoic acid receptor activation efficiently prevented the pathological activation state. Together, these findings delineate a mechanism of IFN-I/IFN{gamma} crosstalk during macrophage activation and identify pharmacologic strategies to prevent IFN-I-dominant, lipid peroxidation-driven macrophage pathology.

SIGLECs remain poorly defined in human B-cell biology beyond SIGLEC-2/CD22 and SIGLEC-10. Here, we identify a previously unrecognized regulatory pathway involving the paired receptors SIGLEC-5 and SIGLEC-14 at the human B-T-cell interface. We show that activated B-cells differentially regulate these receptors: SIGLEC-5 is predominantly surface-expressed and induced by CD40 engagement, whereas SIGLEC-14 is primarily secreted and upregulated after both CD40 and TLR9 stimulation. We further identify EBP (elastin binding protein) and CTSA (cathepsin A) components of the elastin receptor complex (ERC), expressed by activated T-cells, as a novel ligand for both SIGLEC-5 and SIGLEC-14. Functionally, ERC-associated engagement of SIGLEC-5 on B-cells suppresses T-cell IFN-g; and IL-17 expression, establishing SIGLEC-5 as a B-cell-expressed inhibitory SIGLEC that restrains inflammatory T-cell cytokine responses. SIGLEC-14 does not alter this suppression, as SIGLEC-5+ B-cells from SIGLEC-14-sufficient and -null individuals show comparable inhibitory activity. These findings broaden SIGLEC-mediated adaptive immune regulation, with relevance to inflammatory and autoimmune disease.

Dimeric immunoglobulin A (dIgA) is generated from IgA monomers (mIgA) via JCHAIN-dependent polymerization. DIgA is transported across epithelial barriers by the poly Ig receptor (PIGR) and confers mucosal protection, while serum contains substantial amounts of IgA monomers. Distinct plasma cell subsets have been proposed to produce either monomeric or dimeric IgA, with bone marrow plasma cells as a primary source of mIgA. Here, we addressed whether IgA plasma cell populations segregate based on mIgA or dIgA production. Flow cytometric analysis of antibody-secreting cells from bone marrow, lymphoid and mucosal tissues revealed universal intracellular JCHAIN expression across isotypes and failed to identify a discrete JCHAIN-negative IgA plasma cell population. To detect polymeric IgA, we generated a recombinant soluble PIGR that selectively bound JCHAIN-containing dIgA in Western blot, ELISA, and flow cytometry. Soluble PIGR binding was detected in all IgA plasma cells irrespective of tissue origin, arguing against a dedicated mIgA-producing plasma cell subset incapable of dIgA formation. Ex vivo cultures and single-cell DropMap secretion assays demonstrated that bone marrow and lamina propria IgA antibody-secreting cells co-secrete mIgA and dIgA. These findings suggest that dIgA assembly and secretion are general properties of IgA plasma cells and disfavor a dedicated mIgA-producing population.

Invasive pulmonary aspergillosis poses a life-threatening complication in immunocompromised individuals, including recipients of allogeneic hematopoietic cell transplantation (allo-HCT). By contrast, immunocompetent individuals are usually protected against infection with Aspergillus fumigatus, the causative agent of aspergillosis. The mechanisms underlying pulmonary innate immune protection remain poorly understood. Here, we identify alveolar macrophages (AMs) as key players in pulmonary antifungal defense. In immunocompromised mice, AMs conferred protection against lethal invasive aspergillosis by day 6, but not day 4 post-allo-HCT. To enhance AM function at the earlier time point, we tested cytokine-based interventions and showed that M-CSF, but not IL-34, which both bind to the CSF-1 receptor, promotes migratory activity, phagolysosomal function and fungal killing in both mouse and human primary tissue-resident AMs. In allo-HCT recipient mice, M-CSF treatment preserved lung tissue integrity, suppressed pro-inflammatory cytokines, and protected mice from lethal invasive aspergillosis. The M-CSF-driven protective effect was abrogated upon AM depletion. Our findings demonstrate a critical role of tissue-resident AMs in pulmonary antifungal immunity and suggest that therapeutic modulation of AM activity via M-CSF may offer a promising strategy to combat severe fungal infections in immunocompromised patients.

The central nervous system interprets inflammatory signals in the body and directs the modulation of inflammatory responses by reflexively engaging peripheral sympathetic neurons. This includes sympathetic neurons that innervate the spleen, which can regulate immune functions and modulate inflammation. Yet, it is unclear if neuroimmune interactions involve specialised immunoregulatory sympathetic neurons, and if the immune system can reciprocally regulate peripheral sympathetic neurons to control these responses. Using retrograde tracing and single-cell transcriptomics, we find that spleen-innervating neurons are heterogeneous but do not exhibit a distinct transcriptional program indicative of specialisation for immune communication. However, we report that immune responses induced by pathogens can regulate postganglionic sympathetic neuron functions. Cytokines produced by immune cells downregulate expression of the neurotrophin nerve growth factor in spleen mesenchymal cells, leading to organ-specific sympathetic nerve retraction from the spleen. Concurrently, splenic type I interferon signalling induces inflammatory gene expression in neurons and suppresses neuron excitability. Chemogenetic activation of sympathetic neurons demonstrates an impaired anti-inflammatory capacity in the spleen during infection. These results reveal regulation of sympathetic neuronal functions by the immune system, which could support optimal generation of immune responses against pathogens.

Transforming growth factor-{beta} (TGF-{beta}) regulates CD4 T cell quiescence, activation, and regulatory T cell differentiation, but its role in T cell iron metabolism is poorly defined. Here, we investigated whether TGF-{beta} regulates iron homeostasis and how iron overload alters TGF-{beta} responsiveness. During T cell activation, TGF-{beta} enhanced survival but markedly reduced proliferation. These effects were accompanied by decreased CD71 expression and cytosolic iron availability, as well as increased mitochondrial iron accumulation. Genetic deletion of TGF{beta}R1 reversed these changes, demonstrating that TGF-{beta} regulates CD4 T cell iron homeostasis through TGF{beta}R1-dependent signaling. Iron-overloaded CD4 T cells lacking the heme exporter FLVCR1 exhibit hypersensitivity to TGF-{beta}, increased TGF-{beta} secretion, and sustained TGF{beta}R1 expression upon activation. Pharmacologic inhibition of TGF{beta}R1restored proliferation, CD71 expression, and iron levels in FLVCR1-deficient cells. Although TGF-{beta} selectively induced total and mitochondrial ROS levels in FLVCR1-deficient cells, antioxidant treatment or Nox2 inhibition did not rescue this phenotype, suggesting that ROS is associated with, but not sufficient to explain, TGF-{beta} hypersensitivity. Acute FeSO4-induced iron overload partially recapitulated the phenotype of FLVCR1-deficient cells, although TGF{beta}R1 expression and TGF-{beta} production differed. Finally, regulatory T cells generated in vitro in the presence of TGF-{beta} displayed reduced iron acquisition, and excess iron impaired FoxP3 induction. Together, this work identifies TGF-{beta} as a context-dependent regulator of CD4 T cell iron homeostasis.

RNA-binding protein LARP4 plays an important role in T cell activation and differentiation, but its role in B cell biology and the pathogenesis of systemic lupus erythematosus (SLE) remains unclear. This study found that LARP4 was specifically highly expressed in B cells of SLE patients and was positively correlated with disease activity. By constructing T cell-specific and B cell-specific conditional knockout mice, we found that deletion of LARP4 in B cells, but not in T cells, significantly alleviated pristane-induced and Bm12-induced lupus nephritis. Further analysis showed that LARP4 deletion selectively inhibited B cell differentiation into plasma cells, but did not affect germinal center B cell formation. Integrated transcriptomic and metabolomics analyses revealed that this effect is due to reduced phosphatidic acid synthesis and decreased mTORC1 activity caused by mitochondrial oxidative phosphorylation dysfunction. Furthermore, we used LIPEP, a LARP4 inhibitory peptide that effectively mimicked the therapeutic effects of LARP4 gene knockout in the MRL/lpr spontaneous lupus model and outperformed cyclophosphamide in reducing glomerular immune complex deposition and improving extrarenal dermatitis. These results indicates that LARP4 is a key metabolic checkpoint regulating B cell differentiation into Plasma cells and suggest that it may be a potential therapeutic target for SLE.

Contagious bovine pleuropneumonia (CBPP), caused by Mycoplasma mycoides subsp. mycoides (Mmm), remains a major burden to cattle health and the agricultural industry. Mmm is an atypical bacterial pathogen that appears to lack classical virulence factors that cause direct tissue injury (i.e. toxins), and little is known about the mechanisms driving its pathogenicity. The host immune response is believed to be implicated in CBPP pathology, though the molecular mechanisms underlying lesion initiation, progression and chronicity are poorly defined. Classical pathology describes a continuum of lung lesions starting from early inflammation to more mature necrotic lesions and formation of fibrotic sequestra. However, the host transcriptional response driving this potentially immunopathological progression during Mmm infection has never been resolved in vivo. Here, we performed lesion-stage-resolved transcriptomic profiling of pathological lung tissue collected from experimentally infected animals and compared to healthy lung tissue collected from unchallenged controls. Differential gene expression and functional enrichment analyses were used to identify biological pathways relevant to Mmm infection and pathological lesion formation. Early infection was dominated by interferon-stimulated genes and cytokine-responsive pathways, creating a primarily antiviral-like response environment despite the bacterial etiology. Red hepatization showed strong induction of neutrophil chemoattractants, epithelial remodeling markers, and early matrix-remodeling enzymes. Consolidation, spanning red and grey stages, was enriched for innate immune activation, leukocyte adhesion, extracellular matrix organization, and persistent interferon signaling. Grey hepatization reflected late-stage consolidation with heightened neutrophil effector activity, oxidative and proteolytic injury, and macrophage and fibroblast-linked collagen processing. Necrosis/Sequestra lesions showed reduced inflammatory signaling, robust extracellular matrix organization, adhesion, and morphogenetic pathways consistent with encapsulation and sequestrum formation. Our data indicate that the dynamic continuum of CBPP lung pathology is initiated by interferon-primed myeloid recruitment and amplified by neutrophil-driven injury and macrophage- and fibroblast-mediated matrix remodeling. These data further substantiate the role of dysregulated immunity in the development of disease during Mmm infection.