The Journal of Immunology

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.

We previously described monophosphoryl lipid A (MPL) and synthetic cord factor, trehalose-6,6-dicorynomycolate (TDCM) significantly increases antibody (Ab) responses to T cell independent type 2 antigens (TI-2 Ags) in a manner dependent on B cell-intrinsic TLR4 expression as well as MyD88 and TRIF adapter proteins. Given the requirement for TRIF in optimal MPL/TDCM adjuvant effects and the capacity of MPL to drive type I IFN production, we aimed to investigate the extent to which adjuvant effects on TI-2 Ab responses depend on type I IFN receptor (IFNAR) signaling. We found IFNAR-/- mice had impaired early TI-2 Ag-induced B cell activation and expansion and that B cell-intrinsic type I IFN signaling on B cells was essential for normal antibody responses to TI-2 Ags, including haptenated Ficoll and the pneumococcal vaccine, Pneumovax23. However, MPL/TDCM significantly increased TI-2 IgM and IgG responses in IFNAR-/- mice. MPL/TDCM enhanced TI-2 Ab production primarily by activating innate B cells (B-1b and splenic CD23- B cells) as opposed to CD23+ enriched follicular B cells. In summary, our study highlights an important role for type I IFN in supporting early B cell responses to TI-2 Ags through B cell-expressed IFNAR, but nonetheless demonstrates an MPL/TDCM adjuvant significantly increases TI-2 Ab responses independently of type I IFN signaling and does so by predominantly supporting increased polysaccharide-specific Ab production by innate B cell populations. Key pointsO_LIB cell-intrinsic IFNAR expression promotes TI-2 Ab responses. C_LIO_LIMPL/TDCM adjuvant effects are independent of type 1 IFN. C_LIO_LIMPL/TDCM promotes TI-2 Ab responses by innate B cells. C_LI

The generation of antigen-specific CD8+ T cell responses is dictated by the affinity of the cognate antigen, the stimulatory capacity of antigen presenting cells (APCs), and the metabolic pathways required for rapid cell proliferation. The complexity of these pathways is a significant challenge in designing vaccines against diseases that require a protective CD8+ T cell response. To understand the mechanisms underlying CD8+ T cell responses, the STORE.2 model was developed to simulate the early events of T cell priming and expansion at the site of priming. STORE.2 is a mathematical, stochastic, and agent-based model based on first-principles that tracks every individual CD8+ T cell and APC. It allows for the simulation of different antigen affinity (Signal 1) as well as levels of costimulation (Signal 2) and inflammatory cytokines (Signal 3) provided by APCs. The impact of Signals 1-3 is translated to T cell responses via the transcription factor c-Myc, which supports T cell proliferation. Enhanced glycolysis during T cell activation results in a change in the metabolic environment that includes an increase in extracellular lactate concentration. STORE.2 models the role of lactate in the inhibition of T cell metabolism and proliferation as a negative feedback mechanism on c-Myc production. STORE.2 accurately recapitulated the CD8+ T cell response during in vitro T cell priming assays that control for Signals 1-3 as well as lactate concentration. Finally, application of STORE.2 to an in vivo response to immunization demonstrated that the model accurately simulates CD8+ T cell activation at the site of priming.

Mucosal Associated Invariant T cells (MAIT cells) are innate T cells that recognize bacterial metabolites and secrete cytokines and cytolytic enzymes to destroy infected target cells. This makes MAIT cells promising targets for immunotherapy to combat bacterial infections. Here, we analyzed the effects of an immunotherapeutic agent, the IL-15 superagonist N-803, on MAIT cell activation, trafficking, and cytolytic function in macaques. We found that N-803 could activate MAIT cells in vitro and increase their ability to produce IFN{gamma} in response to bacterial stimulation. To expand upon this, we examined the phenotypes and function of MAIT cells present in samples collected from PBMC, airways (BAL), and lymph nodes (LN) from rhesus macaques that were treated in vivo with N-803. N-803 treatment led to a transient 6-7 fold decrease in the total number of MAIT cells in the peripheral blood relative to pre N-803 timepoints. Concurrent with the decrease in cells in the peripheral blood, we observed a rapid decline in the frequency of CXCR3+CCR6+ MAITs. This corresponded with an increase in the frequency of CCR6+ MAITs in BAL, and higher frequencies of ki-67+ and granzyme B+ MAITs in blood, LN, and BAL. Finally, N-803 improved the ability of MAIT cells collected from PBMC and airways to produce IFN{gamma} in response to bacterial stimulation. Overall, N-803 shows the potential to transiently alter the trafficking and enhance the antibacterial activity of MAIT cells which could be combined with other strategies to combat bacterial infections.

T cell immunity depends on the precise coordination of signaling networks with actin cytoskeleton remodeling, yet the molecular regulators of these processes remain incompletely defined. Flightless-1 (FLII) is a gelsolin-family actin regulator with unique leucine-rich repeats that can couple cytoskeletal dynamics to diverse signaling pathways. Here, using conditional knockout mice, we identify essential roles for FLII in both CD8+ and regulatory T cells. Loss of FLII in CD8+ T cells caused a profound loss of naive cells from the spleen, impaired CCR7-dependent migration, and defective accumulation in the lung parenchyma during antigen-specific responses to respiratory vesicular stomatitis virus infection, despite largely preserved activation, effector differentiation, and cytotoxic function. FLII-deficient Foxp3+ regulatory T cells maintained normal numbers but exhibited diminished CD25 expression, defective IL-2 signaling, and failed to restrain spontaneous, tissue-specific autoimmunity. These findings identify FLII as a critical and previously unrecognized orchestrator of T cell trafficking and immune regulation, which may link chemokine receptor signaling to actin remodeling and is essential for proper T cell migration and function.

Tuberculosis (TB) caused by Mycobacterium tuberculosis (Mtb) is the leading infectious cause of death globally. Despite wide use of antiretroviral therapy (ART) by people living with HIV, the risk of TB remains increased. To understand immune interactions within lung granulomas, we compared spatial transcriptomics of Mtb and simian immunodeficiency virus (SIV) in co-infected macaques with or without ART as a model for HIV/Mtb co-infection. Spatially differentiated transcriptional profiles were observed in Mtb-only granulomas, with myeloid cells enriched in metabolic/antimicrobial pathways within the inner ring and T cell costimulatory/activation pathways enriched in the outer ring. These spatially distinct patterns were lost in SIV/Mtb granulomas with higher enrichment in type I IFN pathways compared to Mtb-only granulomas. SIV/ART/Mtb granulomas had an intermediate transcriptional pattern without restoration to Mtb-only granulomas, despite a lack of viral replication. Cell-cell communication was reduced among SIV/Mtb co-infected groups. These data suggest that HIV disrupts spatially organized immune functions of granulomas, which are not fully restored by ART.

Apolipoprotein A1 (ApoA1), the major constituent of the high-density lipoprotein (HDL) molecule, exhibits anti-inflammatory properties. Our laboratory has previously shown that ApoA1 protects against switching of regulatory T (Treg) cells to atherogenic T follicular helper cells in Western diet-fed mice. However, the role of ApoA1 in modulating Treg cell homeostasis in the absence of atherosclerosis remains uncharacterized. Here, we show that ApoA1 is required for normal Treg cell homeostasis and functioning at steady state. Specifically, lack of ApoA1 decreased the numbers of both natural and induced Treg cells and also lowered Treg cell-based homeostatic proliferation and suppressive functions. Importantly, these changes occurred without affecting other T cell populations. Finally, we determined that the observed phenotypes were caused by changes to cholesterol content and reduced interleukin-2 (IL-2) receptor signaling in ApoA1-deficient Treg cells. Overall, our results show that ApoA1-HDL is necessary for Treg cell homeostasis and functioning.

Tuberculosis remains a critical infectious disease world-wide. The development of novel therapeutic strategies requires greater understanding of host factors that contribute to disease susceptibility. A major unknown in TB pathogenesis is the mechanism of necrosis in TB granulomas that leads to the massive lung tissue damage and cavity formation necessary for the pathogen transmission. In humans, TB progression has been linked to hyperactivity of type I IFN (IFN-I) pathway, the primary cause of which remains elusive. We studied the mechanistic drivers of pulmonary TB progression using a unique model B6J.C3-Sst1C3HeB/Fej Krmn mice that develop human-like necrotic TB granulomas and IFN-I hyperactivity. We established that IFN{beta} super-induction occurred in the susceptible macrophages in response to continuous TNF stimulation in the context of a dysregulated antioxidant defense. We observed that unresolving oxidative stress amplified the induction of IFN{beta} through JNK activation and induced the Integrated Stress Response via PKR activation as a compensatory pathway. Subsequently, PKR amplifies IFN{beta} upregulation, forming a positive feedback loop, maintaining the hyperinflammatory state in susceptible macrophages and leading to mitochondrial dysfunction. Thus, within the inflammatory milieu, a cell-intrinsic mechanism of chronic regulatory dysfunction and unresolved stress gradually weakens the macrophage and ultimately promotes the necrotization of TB granulomas. The aberrant macrophage response to TNF can be prevented by an iron chelator and inhibitor of lipid peroxidation, ferrostatin-1. Moreover, ferrostatin treatment increased macrophage survival and boosted bacterial control in the TNF-stimulated macrophages infected with virulent Mtb. These findings identify targets for host-directed therapeutics to interrupt necrotization in TB granulomas.

Disruption in homeostasis of interleukin-15 (IL-15) is linked to poor maternal and fetal outcomes during pregnancy. The only cells described to respond to IL-15 at the early maternal-fetal interface have been natural killer (NK) cells. We now show a novel population of macrophages, evident in several organs but enriched in the uterus of mice and humans, expressing the {beta} chain of the IL-15 receptor complex (CD122) and responding to IL-15. CD122+ macrophages (CD122+Macs) are morphologic, phenotypic, and transcriptomic macrophages that can derive from bone marrow monocytes. CD122+Macs develop in the uterus and placenta with kinetics that mirror interferon (IFN) activity at the maternal-fetal interface. Macrophage colony-stimulating factor (M-CSF) permits macrophages to express CD122, and IFNs are sufficient to drive expression of CD122 on macrophages. Neither Type-I nor Type-II IFNs are required to generate CD122+Macs, however. In response to IL-15, CD122+Macs activate the ERK signaling cascade and enhance production of proinflammatory cytokines after stimulation with the Toll-like receptor 9 agonist CpG. Finally, we provide evidence of human cells that phenocopy murine CD122+Macs in secretory phase endometrium during the implantation window and in first-trimester uterine decidua. Our data support a model wherein IFNs local to the maternal-fetal interface direct novel IL-15-responsive macrophages with the potential to mediate IL-15 signals critical for optimal outcomes of pregnancy. The microarray data presented in this article have been submitted to the Gene Expression Omnibus (http://www.ncbi.nlm.nih.gov/geo/) under accession number GSE132353.

BackgroundHLA-DR-expressing fibroblast-like synoviocytes (FLS) are a prominent cell type in synovial tissue in chronic inflammatory forms of arthritis. We recently showed that peptides from several extracellular matrix (ECM) proteins, including fibronectin-1 (FN1), contained immunogenic CD4+ T cell epitopes in patients with postinfectious Lyme arthritis (LA). However, the role of FLS in presentation of these T cell epitopes remains uncertain. MethodsPrimary LA FLS and primary murine FLS stimulated with interferon gamma (IFN{gamma}), Borrelia burgdorferi, and/or B. burgdorferi peptidoglycan (PG) were assessed for properties associated with antigen presentation. HLA-DR-presented peptides from stimulated LA FLS were identified by immunopeptidomics analysis. OT-II T cells were cocultured with stimulated murine FLS in the presence of cognate ovalbumin antigen to determine the potential of FLS to act as inducible antigen presenting cells (APC). ResultsFLS expressed HLA-DR molecules within inflamed synovial tissue and tendons from patients with post-infectious LA patients in situ. MHC class II and costimulatory molecules were expressed by FLS following in vitro stimulation with IFN{gamma} and B. burgdorferi and presented both foreign and self MHC-II peptides, including T cell epitopes derived from two Lyme autoantigens fibronectin-1 (FN1) and endothelial cell growth factor (ECGF). Stimulated murine FLS induced proliferation of naive OT-II CD4+ T cells, particularly when FLS were stimulated with both IFN{gamma} and PG. ConclusionsMHC-II+ FLS are inducible APCs that can induce CD4+ T cell activation and can present Lyme autoantigens derived from ECM proteins, thereby amplifying tissue-localized autoimmune CD4+ T cell responses in LA. AUTHORS SUMMARYThis study demonstrates that IFN{gamma}-activated MHC-II+ fibroblast-like synoviocytes (FLS) stimulated with Borrelia burgdorferi present foreign and self MHC-II antigens, including Lyme autoantigens. Furthermore, IFN{gamma}-activated MHC-II+ FLS stimulated with B. burgdorferi peptidoglycan can induce activation and proliferation of naive CD4+ T cells in an MHC-II antigen-dependent manner, demonstrating that activated MHC-II+ FLS are inducible antigen presenting cells.

Interleukin-21 receptor engagement initiates a Janus Kinase (JAK) - signal transducer and activator of transcription (STAT) signalling cascade that activates several STAT proteins that drive the germinal center response. However, the relative effects of IL-21 on individual STAT proteins during the differentiation of T follicular helper cells and germinal center B cells has been difficult to distinguish. Here, we characterise a novel mutation in the interleukin-21 receptor (IL-21REINS) that creates a unique defect in the activation of STAT1. Our findings provide evidence that IL-21 mediated activation of STAT1 has a nonredundant role in the differentiation of T follicular (Tfh) cells following T dependent immunisation. IL-21REINS Tfh cells were even more impaired than Tfh cells genetically deficient in IL-21R, questioning our current understanding of the role of IL-21 derived from protein knockout mice. The observation that functional compensation fails in the presence of the IL-21R hypomorph provides insight into how underlying compensation can impact our interpretation of a complex biological system.

High levels of serum CD138, a heparan sulfate-bearing proteoglycan, correlates with increased disease activity in systemic lupus erythematosus (SLE) patients. Mechanisms responsible for serum CD138 production and its biological function in SLE disease remain poorly understood. In this study, corroborating patient data, we detected an increase in serum CD138 in MRL/Lpr mice parallel to disease activity. Although TCR{beta}+CD138+ T cells expand in MRL/Lpr mice as the disease progresses, surprisingly, TCR{beta}+CD138- cells were the primary source of circulating CD138 as the transfer of TCR{beta}+CD138- cells to young MRL/Lpr mice, but not TCR{beta}+CD138+ cells, resulted with higher serum CD138 in the recipient mice. We found that elevated trypsin, expressed by TCR{beta}+CD138- cells, was able to cleave CD138 from T cells. Moreover, suggesting the contribution of cleaved CD138 to the increase in blood CD138, trypsin inhibitors defined trypsin inhibitor (DTI) or leupeptin increased CD138 expression on TCR{beta}+CD138- cells. Furthermore, soluble CD138 was able to bind a proliferation inducing ligand (APRIL) and enhanced APRIL-mediated plasma cell generation and autoreactive antibody production through the phosphorylation of extracellular-signal-regulated kinase (ERK) in B cells. APRIL receptor, transmembrane activator, calcium modulator, and cyclophilin ligand interactor (TACI) was involved in the enhancement of APRIL activity by CD138, as the synergistic effect of APRIL and CD138 was ablated on TACI deficient B cells. These findings indicate a regulatory role for soluble CD138 in B cell differentiation and autoreactive antibody secretion in SLE disease.

The purinergic receptor P2X7 (P2X7R) is important in inflammasome activation and generally considered to favor proinflammatory Th17 immune responses. However, several studies utilizing P2rx7-/- mice did not observe impaired inflammation, on the contrary, these reports demonstrate that P2rx7-/- mice can have more sever inflammation compared to WT controls. To begin to clarify this discrepancy, the impact of P2X7R signaling on primary Th17 and Th1 cell responses was examined. Initially, utilizing a global knockout approach, we found that P2rx7-/- mice develop comparable Th17 and Th1 responses to those of WT mice. However, indepth in vitro and in vivo investigations revealed differences in the immune response outcome depending on which cell type expresses P2X7R. In this regard, DC-specific P2X7R deficient chimeras demonstrate a comparable Th17 differentiation pattern with that of WT chimeras but display a significantly enhanced Th1 response. However, P2rx7-/- T cells have a suppressed Th17 differentiation profile while developing a similarly enhanced Th1 response as observed in DC-specific P2X7R deficient chimeras. Finally, P2X7R expression induces more T cell death in vivo, attributed to its cytotoxicity, which results in a similar total number of WT Th17 and P2rx7-/- Th17 cells and remarkably higher amounts of P2rx7-/- Th1 cells. Collectively, our findings establish that P2X7R expression on CD4+ T cells is necessary for Th17 differentiation while inhibiting Th1 development.

The immune regulatory gene PTPN22 is expressed in all immune cells and encodes Lyp in humans and the ortholog PEP in mice. The PTPN22 alternative allele, 1858C>T, is expressed in 5-15% of the North American population and is strongly associated with the development of autoimmune disease while simultaneously capable of providing protection during virus infection and cancer. In murine models, significant progress has been made in elucidating the molecular mechanisms that PEP and its pro-autoimmune variant (PEP-R619W) modulate T cell function, yet their influence on non-T cell pathways, such as antigen presenting cell cytokine production, remains less defined. Previously, it was reported that PEP promotes type I interferon (IFN-I) production in dendritic cells (DCs) and macrophages following TLR4 stimulus. Here, we show that contrary to previous results, both PEP-WT and the PEP-R619W variant do not promote IFN-I production in DCs and macrophages following exposure to LPS, 3p-hpRNA, or coronavirus MHV A59. We attribute the prior findings to mouse strain-specific differences and conclude that factors independent of PEP may be regulating IFN-I production in these studies. We further show that PEP and its R619W variant distinctly modulate the production of TNF, IL-12 and IL-2 in DCs following LPS stimulus. Taken together, our results challenge the current understanding of the role of PEP during inflammation while providing new insight into how the PEP-R619W variant may alter myeloid cell function during disease.

The immune response to Mycobacterium tuberculosis infection determines tuberculosis disease outcomes, yet we have an incomplete understanding of what immune factors contribute to a protective immune response. Neutrophilic inflammation has been associated with poor disease prognosis in humans and in animal models during M. tuberculosis infection and, therefore, must be tightly regulated. ATG5 is an essential autophagy protein that is required in innate immune cells to control neutrophil-dominated inflammation and promote survival during M. tuberculosis infection, however, the mechanistic basis for how ATG5 regulates neutrophil recruitment is unknown. To interrogate what innate immune cells require ATG5 to control neutrophil recruitment during M. tuberculosis infection, we used different mouse strains that conditionally delete Atg5 in specific cell types. We found that ATG5 is required in CD11c+ cells (lung macrophages and dendritic cells) to control the production of proinflammatory cytokines and chemokines during M. tuberculosis infection, which would otherwise promote neutrophil recruitment. This role for ATG5 is autophagy-dependent, but independent of mitophagy, LC3-associated phagocytosis, and inflammasome activation, which are the most well-characterized ways that autophagy proteins regulate inflammation. In addition to the increase in proinflammatory cytokine production during M. tuberculosis infection, loss of ATG5 in innate immune cells also results in an early induction of TH17 responses. Despite prior published in vitro cell culture experiments supporting a role for autophagy in controlling M. tuberculosis replication in macrophages, loss of autophagy does not affect M. tuberculosis burden in macrophages in vivo and, therefore, the effects of autophagy on inflammatory responses occur without changes in pathogen numbers. These findings reveal new roles for autophagy proteins in lung resident macrophages and dendritic cells that are required to suppress inflammatory responses that are associated with poor control of M. tuberculosis infection.

Marginal zone (MZ) B cells are considered to be innate-like immune cells, and follicular (FO) B cells are considered to be adaptive immune B cells. Yet, the proliferative response of MZ and FO B cells to different innate stimuli remains unclear. Here, we investigated cell growth, division, and death to determine the collective proliferative response of MZ and FO B cells in response to innate stimuli, LPS and CpG. We show that the growth rate of FO B cells is higher than that of MZ B cells in response to CpG, though MZ B cells acquire a higher mass at division, whereas both the growth rate and mass at division for MZ and FO B cells remain similar in response to LPS stimulation. We show that MZ B cells divide faster and induce a higher cRel expression in response to both CpG and LPS stimulation than FO B cells. A higher proportion of MZ B cells enter first division in response to LPS stimulation, not in response to CpG stimulation, than FO B cells. Interestingly, CpG stimulation, not LPS stimulation, leads to higher cell death in MZ B cells than FO B cells. In response to LPS stimulation, MZ B cells show a higher cell number at early time and a reduced/ similar cell number at late time, whereas in response to CpG stimulation, MZ B cells show a lower cell number at both early and late time. Our study suggests that LPS and CpG stimulation impact cell growth, division, and death differently, which in turn regulate different proliferative responses of MZ and FO B cells. Thus, our study offers a new perspective that different innate stimuli regulate different features of proliferative responses.

The balance of pro-inflammatory T helper type 17 (Th17) and anti-inflammatory T regulatory (Treg) cells is crucial in maintaining immune homeostasis in health and disease conditions. Differentiation of naive CD4+ T cells into Th17/Treg cells is dependent upon T cell receptor (TCR) activation and cytokine signaling, which includes the kinase ITK. Signals from ITK can regulate the differentiation of Th17 and Treg cell fate choice, however, the mechanism remains to be fully understood. We report here that in the absence of ITK activity, instead of developing into Th17 cells under Th17 conditions, naive CD4+ T cells switch to cells expressing the Treg marker Foxp3 (Forkhead box P3). These switched Foxp3+ Treg like cells retain suppressive function and resemble differentiated induced Tregs in their transcriptomic profile, although their chromatin accessibility profiles are intermediate between Th17 and induced Tregs cells. Generation of the switched Foxp3+ Treg like cells was associated with reduced expression of molecules involved in mitochondrial oxidative phosphorylation and glycolysis, with reduced activation of the mTOR signaling pathway, and reduced expression of BATF. This ITK dependent switch between Th17 and Treg cells was reversed by increasing intracellular calcium. These findings suggest potential strategies for fine tune the TCR signal strength via ITK to regulate the balance of Th17/Treg cells.

Akt1 and Akt2, isoforms of the serine threonine kinase Akt, are essential for T cell development. However, their role in peripheral T cell differentiation remains undefined. Using mice with germline deletions of either Akt1 or Akt2, we found that both isoforms are important for Th17 differentiation, although Akt2 loss had a greater impact than loss of Akt1. In contrast to defective IL-17 production, Akt2-/- T cells exhibited enhanced IL-4 production in vitro under Th2 polarizing conditions. In vivo, Akt2-/- mice displayed significantly diminished IL-17A and GM-CSF production following immunization with myelin oligodendrocyte glycoprotein (MOG). This dampened response was associated with further alterations in Th cell differentiation including decreased IFN{gamma} production but preserved IL-4 production, and preferential expansion of regulatory T cells compared to non-regulatory CD4 T cells. Taken together, we identify Akt2 as an important signaling molecule in regulating peripheral CD4 T cell responses.

RAG1/RAG2 (RAG) endonuclease-mediated assembly of diverse lymphocyte antigen receptor genes by V(D)J recombination is critical for the development and immune function of T and B cells. However, this process creates highly self-reactive cells that must be properly selected to suppress autoimmunity. The RAG1 protein contains a ubiquitin ligase domain that stabilizes RAG1 and stimulates RAG endonuclease activity in vitro. We report that mice with a mutation that inactivates the RAG1 ubiquitin ligase in vitro exhibit modestly reduced thymic cellularity, decreased assembly and altered repertoires of T cell receptor (TCR) {beta} and genes in thymocytes, and impaired thymocyte developmental transitions that require the assembly of TCR{beta} or genes and signaling by their proteins. These RAG1 mutant mice also exhibit less efficient positive selection and superantigen-mediated negative selection of conventional {beta} T cells, 2) impaired differentiation of iNKT lineage {beta} T cells, and 3) CD4+ {beta} T cells with elevated autoimmune potential. Our findings demonstrate that the RAG1 ubiquitin ligase domain functions in vivo to stimulate the assembly and selection of TCR{beta} and TCR genes, thereby establishing replete diversity of {beta} TCRs and {beta} T cell lineages while restraining the inherent autoimmune hazard of generating diverse antigen specificities.

Soil-transmitted helminths are one of the most common infections globally, yet how to promote effective gut-associated humoral responses is not well understood. We identify the histone methyltransferase MLL1 as a key target to promote IgA-driven responses. Mll1 was increased in germinal center B cells in gut-associated lymphoid tissues, and Mll1-deficiency led to changes in the histone modification H3K4me3 on key B cell and immune-regulatory genes. Correspondingly, MLL1-deficient B cells had defective germinal centers and IgG1 in response to the helminth Trichuris muris. Yet, Mll1f/fCd23cre/+ mice expelled worms more rapidly compared to control mice. Accelerated worm clearance correlated with elevated IgA+ plasma cells, as well as both serum and fecal IgA. RNA-sequencing identified CCR9 as a key MLL1-regulated molecule. As such, Mll1f/fCd23cre/+ mice infected with T. muris had increased IgA+CCR9+ PC localized in the large intestine. Regulation of IgA by MLL1 was confirmed beyond T. muris infection. In vitro cultures confirmed Mll1-deficiency increased IgA+ plasma cells in a B cell-intrinsic manner, and IgA production was also increased in Mll1f/fCd23cre/+ mice infected with the bacterium C. rodentium. This study reveals MLL1 as a key target to promote IgA responses to gut-associated infections.