Mucosal-associated invariant T cells respond to cutaneous microbiota

The microbiome consists of a diverse array of commensal microorganisms that reside at barrier sites of the body and promote immune homeostasis through the release of microbial products, including derivatives of vitamin synthesis. Mucosal-associated invariant T (MAIT) cells are unconventional T cells that recognize vitamin B2 (riboflavin) derivatives presented by the major histocompatibility class I-like molecule, MR1. MAIT cells are predominantly located in barrier tissues, where they represent a substantial population of non-classical T cells and provide an initial defense to pathogens through their rapid production of either IL-17A or IFNg. However, it remains to be determined whether commensals regulate the development and function of MAIT cells. Here we show that MAIT cells are present in murine skin at a high frequency and their homeostasis requires the microbiota, as these lymphocytes are nearly absent in germ-free animals. Furthermore, application of distinct human commensal bacteria to the skin of mice induces the proliferation of IL-17A-producing MAIT cells that exhibit a unique transcriptional profile. The induction of these cells occurs in a manner that is partially dependent on both antigen presentation and IL-23 signaling. Additionally, MAIT cells stimulated by the cutaneous microbiota provide heterologous protection against subsequent pathogenic challenges. This work identifies MAIT cells as the only cell population that is entirely dependent on the microbiota and reveals the mechanism by which these cells respond to the commensal microbial community. Due to the high frequency of MAIT cells in human skin, these observations suggest that modulation of the skin-resident bacteria may have clinical applications.

Candida albicans colonization exacerbates skin inflammation in a murine model of psoriasis

In addition to being a primary site of exposure to pathogens, the skin is also home to a complex microbiota that modulate skin immune homeostasis. Notably, our previous work revealed that defined microbes differentially regulate the skin immune landscape. In clinical settings, shifts in skin microbiota composition have been shown in the context of skin inflammatory disorders, such as atopic dermatitis, acne vulgaris and psoriasis. However, the precise role of cutaneous microbiota in the initiation, control or promotion of skin inflammatory states remains unclear. To clarify the mechanisms by which the skin microbiota influence host immunity under inflammatory conditions, we focused on psoriasis, a common inflammatory skin disorder mediated by both innate and adaptive immune systems.

Murine studies have shown that topical application of imiquimod, a TLR7 agonist, can induce psoriasis-like skin inflammation, mediated by the IL-23/IL-17 axis. Using this experimental model, we found that previous skin association of mice with C.albicans but not other skin microbes (e.g., S.aureus), significantly enhanced skin inflammation. Notably, C.albicans topical association promoted IL-17A production from CD4+ effector T cells in the skin and skin draining lymph nodes. Our work currently explores how adaptive immunity directed against C.albicans could contribute to the etiology of this important skin disorder. This work aims to define the causative association between defined microbes and the development of skin inflammatory disorders and may allow for the development of tailored clinical interventions aiming at controlling skin microbiota and/or aberrant responses to these microbes.

Dendritic cells expressing immunoreceptor CD300f are critical for controlling chronic gut inflammation

Proinflammatory cytokine overproduction and excessive cell death, coupled with impaired clearance of apoptotic cells, have been implicated as causes of failure to resolve gut inflammation in inflammatory bowel diseases. Here we have found that dendritic cells expressing the apoptotic cell-recognizing receptor CD300f play a crucial role in regulating gut inflammatory responses in a murine model of colonic inflammation. CD300f-deficient mice failed to resolve dextran sulfate sodium-induced colonic inflammation as a result of defects in dendritic cell function that were associated with abnormal accumulation of apoptotic cells in the gut. CD300f-deficient dendritic cells displayed hyperactive phagocytosis of apoptotic cells, which stimulated excessive TNF-α secretion predominantly from dendritic cells. This, in turn, induced secondary IFN-γ overproduction by colonic T cells, leading to prolonged gut inflammation. Our data highlight a previously unappreciated role for dendritic cells in controlling gut homeostasis and show that CD300f-dependent regulation of apoptotic cell uptake is essential for suppressing overactive dendritic cell-mediated inflammatory responses, thereby controlling the development of chronic gut inflammation.

Host-Protozoan Interactions Protect from Mucosal Infections through Activation of the Inflammasome

While conventional pathogenic protists have been extensively studied, there is an underappreciated constitutive protist microbiota that is an integral part of the vertebrate microbiome. The impact of these species on the host and their potential contributions to mucosal immune homeostasis remain poorly studied. Here, we show that the protozoan Tritrichomonas musculis activates the host epithelial inflammasome to induce IL-18 release. Epithelial-derived IL-18 promotes dendritic cell-driven Th1 and Th17 immunity and confers dramatic protection from mucosal bacterial infections. Along with its role as a "protistic" antibiotic, colonization with T. musculis exacerbates the development of T-cell-driven colitis and sporadic colorectal tumors. Our findings demonstrate a novel mutualistic host-protozoan interaction that increases mucosal host defenses at the cost of an increased risk of inflammatory disease.

On-going Mechanical Damage from Mastication Drives Homeostatic Th17 Cell Responses at the Oral Barrier

Immuno-surveillance networks operating at barrier sites are tuned by local tissue cues to ensure effective immunity. Site-specific commensal bacteria provide key signals ensuring host defense in the skin and gut. However, how the oral microbiome and tissue-specific signals balance immunity and regulation at the gingiva, a key oral barrier, remains minimally explored. In contrast to the skin and gut, we demonstrate that gingiva-resident T helper 17 (Th17) cells developed via a commensal colonization-independent mechanism. Accumulation of Th17 cells at the gingiva was driven in response to the physiological barrier damage that occurs during mastication. Physiological mechanical damage, via induction of interleukin 6 (IL-6) from epithelial cells, tailored effector T cell function, promoting increases in gingival Th17 cell numbers. These data highlight that diverse tissue-specific mechanisms govern education of Th17 cell responses and demonstrate that mechanical damage helps define the immune tone of this important oral barrier.

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Distinct signals shape the Th17 cell network at the oral barrier

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Oral barrier Th17 cells develop independently of commensal microbe colonization

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Physiologic damage through mastication promotes the generation of oral Th17 cells

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Barrier damage triggers oral Th17-cell-mediated protective immunity and inflammation

Linking the Microbiota, Chronic Disease, and the Immune System

Chronic inflammatory diseases (CIDs) are the most important causes of mortality in the world today and are on the rise. We now know that immune-driven inflammation is critical in the etiology of these diseases, though the environmental triggers and cellular mechanisms that lead to their development are still mysterious. Many CIDs are associated with significant shifts in the microbiota toward inflammatory configurations, which can affect the host both by inducing local and systemic inflammation and by alterations in microbiota-derived metabolites. This review discusses recent findings suggesting that shifts in the microbiota may contribute to chronic disease via effects on the immune system.

Abstract A076: Cutaneous microbiota drive the accumulation of IL-17A-producing T cells within the lungs

Infectious agents are estimated to cause approximately 18% of cancers worldwide, supporting a link between microbial products and carcinogenesis. The microbiome consists of a diverse array of commensal microorganisms that reside at barrier sites of the human body and promote local immune homeostasis, but also provide the primary source of constitutive microbial stimulation. While recent work has demonstrated that intestinal commensals can influence immunity throughout the body, the distal effects of other microbial communities have not been fully explored. Here we show that application of distinct human commensals to the skin of mice induces the accumulation of IL-17A-producing T cells in the lungs. The induction of these cells occurs in a manner that is partially dependent on both antigen presentation and IL-23 signaling. Response kinetics and adoptive transfer experiments suggest that the T cells migrate from the skin-draining lymph nodes, while transcriptional analysis has identified specific chemokine receptors that facilitate trafficking to the lungs. Furthermore, in the context of a pulmonary challenge, cutaneous application of commensals promotes the production of IL-17A and recruitment of neutrophils to the lungs. This work demonstrates that the skin microbiome can enhance pulmonary immunity, but also has the potential to cause pro-oncogenic inflammation. Since IL-17A promotes tumor vascularization and neutrophils can contribute to the establishment of metastases, specific microbes at distal sites such as the skin may exacerbate the progression of lung cancer.

Citation Format: Michael G. Constantinides, Vanessa K. Ridaura, Yasmine Belkaid. Cutaneous microbiota drive the accumulation of IL-17A-producing T cells within the lungs [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr A076.

Abstract A078: Cutaneous microbiota in development of endogenous anti-melanocyte immunity

Despite major advances in immunotherapeutic approaches designed to bolster endogenous immune responses against tumors, metastatic melanoma remains associated with high mortality and rapid progression. Development of novel approaches toward enhancing endogenous immune responses against melanoma constitutes a critical step toward the management of disease. Of note, initiating immune responses against non-mutated melanocyte-specific protein antigens has shown efficacy in augmenting immunotherapies. Vitiligo is an autoimmune disease characterized by immune-mediated destruction of melanocytes, though the etiology of this disease remains poorly understood. Microbes have been recently found to have a profound effect on immune processes of the skin, including those that are associated with vitiligo progression. Identifying skin-resident microbes that initiate or exacerbate anti-melanocyte immunity, as well as the precise pathways that mediate these processes, may provide a novel framework for the development of immunotherapies to augment anti-tumor immune responses and efficacy of existing therapies. Thus, we have recruited a cohort of individuals with vitiligo and profiled their skin microbiomes at various body sites. We have isolated numerous vitiligo-associated bacteria and have adapted a mouse model of vitiligo in order to understand mechanisms of host-microbiome interaction in this setting. Interrogation of such a relationship between the microbiome and autoimmune destruction of melanocytes in vitiligo may lead to the identification of novel targets and pathways by which to augment melanoma immunotherapies.

Citation Format: Ivan Vujkovic-Cvijin, Jacquice Davis, Rasnik Singh, Kristina Lee, Zhiya Yu, Nicholas Restifo, Maria Wei, Yasmine Belkaid. Cutaneous microbiota in development of endogenous anti-melanocyte immunity [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr A078.

Critical role of fatty acid metabolism in ILC2-mediated barrier protection during malnutrition and helminth infection

Belkaid et al. show that type 2 innate lymphoid cells rely predominately on fatty acid metabolism during helminth infection and malnutrition.

Innate lymphoid cells (ILC) play an important role in many immune processes, including control of infections, inflammation, and tissue repair. To date, little is known about the metabolism of ILC and whether these cells can metabolically adapt in response to environmental signals. Here we show that type 2 innate lymphoid cells (ILC2), important mediators of barrier immunity, predominantly depend on fatty acid (FA) metabolism during helminth infection. Further, in situations where an essential nutrient, such as vitamin A, is limited, ILC2 sustain their function and selectively maintain interleukin 13 (IL-13) production via increased acquisition and utilization of FA. Together, these results reveal that ILC2 preferentially use FAs to maintain their function in the context of helminth infection or malnutrition and propose that enhanced FA usage and FA-dependent IL-13 production by ILC2 could represent a host adaptation to maintain barrier immunity under dietary restriction.

Abstract 4881: CD300f-regulated efferocytosis by dendritic cells and macrophages controls the initiation and resolution of experimental colitis

Phagocytic clearance of apoptotic cells (efferocytosis) is critical for resolution of inflammation and prevention of chronic inflammatory disorders, including inflammatory bowel diseases, and inflammation-associated cancer. CD300f (CLM-1), a cell surface receptor that recognizes phosphatidylserine exposed on apoptotic cells, has been shown to promote efferocytosis by macrophages. In the present study, we found that CD300f plays a critical role in controlling the severity and duration of dextran sulfate sodium (DSS)-induced colitis, and CD300f-expressing macrophages and dendritic cells (DC) were identified as key players controlling disease pathogenesis. Compared to Cd300f+/+ mice, Cd300f-/- mice showed increased susceptibility to DSS-induced colitis and impaired resolution of inflammation. In Cd300f-/- mice, macrophage-mediated efferocytosis was reduced, resulting in apoptotic cell accumulation in the gut mucosa. In contrast, Cd300f-/- DC engulfed apoptotic cells more efficiently than Cd300f+/+ DC. CD300f-deficient DC transfer exacerbated DSS-induced inflammation and delayed its resolution, whereas CD300f-expressing macrophage transfer attenuated DSS-induced inflammation. Hyperactive efferocytosis by CD300f-deficient gut DC resulted in excessive tumor necrosis factor-á (TNF-á) secretion, which induced secondary interferon-ã (IFN-ã) over-production, both of which impaired the resolution of colitis. TNF-á neutralization resulted in decreased levels of gut pro-inflammatory cytokines and significant disease amelioration. Collectively, these results suggest that CD300f is important for preventing chronic inflammation by enhancing macrophage efferocytosis and inhibiting TNF-á production induced by DC efferocytosis. From these findings, it is conceivable that increasing macrophage-mediated efferocytosis and suppressing DC-mediated efferocytosis through upregulation of CD300f expression would provide a new therapeutic strategy for inflammatory bowel disease patients.

Citation Format: Ha-Na Lee, Linjie Tian, Jacquice Davis, Mariam Quinones, Yasmine Belkaid, Konrad Krzewski, John E. Coligan. CD300f-regulated efferocytosis by dendritic cells and macrophages controls the initiation and resolution of experimental colitis. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4881.

The GARP/Latent TGF-β1 complex on Treg cells modulates the induction of peripherally derived Treg cells during oral tolerance

Treg cells can secrete latent TGF-β1 (LTGF-β1), but can also utilize an alternative pathway for transport and expression of LTGF-β1 on the cell surface in which LTGF-β1 is coupled to a distinct LTGF-β binding protein termed glycoprotein A repetitions predominant (GARP)/LRRC32. The function of the GARP/LTGF-β1 complex has remained elusive. Here, we examine in vivo the roles of GARP and TGF-β1 in the induction of oral tolerance. When Foxp3(-) OT-II T cells were transferred to wild-type recipient mice followed by OVA feeding, the conversion of Foxp3(-) to Foxp3(+) OT-II cells was dependent on recipient Treg cells. Neutralization of IL-2 in the recipient mice also abrogated this conversion. The GARP/LTGF-β1 complex on recipient Treg cells, but not dendritic cell-derived TGF-β1, was required for efficient induction of Foxp3(+) T cells and for the suppression of delayed hypersensitivity. Expression of the integrin αvβ8 by Treg cells (or T cells) in the recipients was dispensable for induction of Foxp3 expression. Transient depletion of the bacterial flora enhanced the development of oral tolerance by expanding Treg cells with enhanced expression of the GARP/LTGF-β1 complex.

Cutaneous microbiota drive the accumulation of IL-17A-producing T cells within the lungs

The microbiome consists of a diverse array of commensal microorganisms that reside at barrier sites of the human body and promote local immune homeostasis. While recent work has demonstrated that intestinal commensals can influence immunity throughout the body, the distal effects of other microbial communities have not been fully explored. Here we show that application of distinct human commensals to the skin of mice induces the accumulation of IL-17A-producing T cells in the lungs. The induction of these cells occurs in a manner that is partially dependent on both antigen presentation and IL-23 signaling. Response kinetics and adoptive transfer experiments suggest that the T cells migrate from the skin-draining lymph nodes, while transcriptional analysis has identified specific chemokine receptors that may facilitate trafficking to the lungs. Furthermore, in the context of pulmonary infection, cutaneous application of commensals promotes the production of IL-17A and recruitment of neutrophils to the lungs. This work demonstrates that the skin microbiome can enhance pulmonary immunity, but also has the potential to exacerbate inflammation through the production of IL-17A, thus providing a possible mechanism for why children with atopic dermatitis have an increased propensity to develop asthma, a progression commonly referred to as the “atopic march.”

Commensal-dendritic-cell interaction specifies a unique protective skin immune signature

The skin represents the body’s primary interface with the environment, acting as the first line of physical and immunological defense. This organ is also home to trillions of microbes (bacteria, fungi and viruses) that play an important role in tissue homeostasis and local immunity. Skin microbial communities are highly diverse and can be remodeled over time or in response to environmental challenges. How in the context of this complexity, individual commensals may differentially modulate skin immunity and what the consequences of these responses for tissue physiology are remain unclear. Here, we demonstrate that defined commensals dominantly impact skin immunity and identify the cellular mediators involved in this specification. In particular, colonization with Staphylococcus epidermidis induces IL-17A+CD8+T cells that home to the epidermis, enhance innate barrier immunity and limit pathogen invasion. These commensal-specific T cell responses result from the coordinated action of skin resident dendritic cell subsets and are not associated with inflammation, revealing that tissue resident cells are poised to sense and respond to alterations in microbial communities. This dialogue may represent an evolutionary means by which the skin immune system uses fluctuating commensal clues to calibrate barrier immunity and provide heterologous protection against invasive pathogens. Altogether these findings reveal that the skin immune landscape is a highly dynamic environment that can be rapidly and specifically remodeled by encounters with defined commensals, findings that have profound implications for our understanding of tissue specific immunity and pathologies.

Group 3 innate lymphoid cells continuously require the transcription factor GATA-3 after commitment

We have previously reported that the transcription factor GATA-3 is critical for the development of all interleukin 7 receptor α-chain (IL-7Rα)-expressing innate lymphoid cells (ILCs) from their progenitor. After ILC lineage commitment, GATA-3 is essential for the maintenance and function of group 2 ILCs (ILC2 cells). Moreover, GATA-3 also maintains low expression in other mature ILCs, such as ILC3 cells, but its function is still elusive. We found that GATA-3 regulated the homeostasis of ILC3 cells by controlling IL-7Rα expression. In addition, GATA-3 served an indispensable function for the further development of the NKp46+ ILC3 subset. GATA-3 bound directly to the Rorc locus in ILC3 cells, repressed RORγt expression, and, thus, regulated the balance between the transcription factors T-bet and RORγt during NKp46+ ILC3 development. Whole transcriptome comparison of CCR6+ lymphoid tissue-inducer (LTi) ILC3 and NKp46+ ILC3 subsets from Gata3 sufficient and deficient mice showed that, among NKp46+ ILC3 cells, GATA-3 not only positively regulated genes specific to the NKp46+ ILC3 subset, but also negatively regulated genes specific to LTi ILC3 cells. Furthermore, GATA-3 also bound to the Il22 promoter locus and was required for IL-22 production in both ILC3 subsets. Mice deficient for Gata3 in ILC3 cells succumbed to Citrobacter rodentium infection due to defective IL-22 production. In conclusion, despite its low expression, GATA-3 was required for the homeostasis, development and function of ILC3 subsets.

Zbtb-1 controls NKp46+RORgammat+ innate lymphoid cell (ILC3) development

Innate lymphoid cells (ILCs) play a central role in conferring protective immunity at the mucosal frontier. We identified a new function of the transcription factor Zbtb1 for the development of RORgammat+ ILCs (ILC3s). Zbtb1-deficient mice lacked NKp46+ ILC3 cells in the lamina propria of the small intestine and colon, which was consequence of impaired development of its RORgammat+ CCR6−NKp46− progenitors. This requirement of Zbtb1 was cell intrinsic as it was observed in in vitro developmental co-cultures with OP9-DL1 stroma and in vivo in bone marrow chimeras. The ILC3 developmental defect correlated with inefficient upregulation of T-bet expression and, as consequence, ILC3 cells from Zbtb1-deficient mice failed to acquire IFN-γ and repress IL-22 production upon development into NKp46+ cells. In correlation with a lack of NKp46+ILC3 cells, Zbtb1-deficient mice presented increased susceptibility to C.Rodentium infections. Altogether, these results establish that Zbtb1 is essential for the development of NKp46+ ILC3 cells.

NOD1 ligand administration restores optimal steady-state hematopoiesis in germ-free mice

The microbiota is required for optimal hematopoiesis. When compared to specific-pathogen free (SPF) mice, germ free (GF) animals display decreased numbers of hematopoietic stem cells (HSC), common myeloid progenitors (CMP) and common lymphoid progenitors (CLP) in bone marrow. Muropeptides produced by both gram-negative and gram-positive bacteria are important agonists of the innate immune response and are recognized by the intracellular pattern-recognition receptors NOD1 and NOD2. In the present study, we examined both direct and indirect effects of NOD signaling on hematopoietic homeostasis. While stimulation with NOD1 or NOD2 ligands had no effect on survival/proliferation of HSC, CMP and CLP in vitro, exposure of bone marrow-derived stroma cells (BMSC) to NOD1, but not NOD2, ligand induced expression of the differentiation factors SCF, IL-7, IL-3, Thpo and IL-6. Interestingly LPS, which is known to act directly on hematopoietic precursors, selectively induced only IL-6 in BMSC. To test the effects of NOD1 ligand in vivo, we compared groups of GF animals with and without peroral NOD1 ligand administration. NOD1 ligand treatment restored to normal levels serum concentrations of SCF, Thpo and IL-6, as well as the numbers of HSC, CMP and CLP in bone marrow. Taken together, these findings demonstrate that NOD1 ligand induces BMSC to produce cytokines that regulate the size of the major hematopoietic precursor pools. Thus, NOD1 signaling appears to be a major factor underlying the requirement for the microbiota in the maintenance of steady-state hematopoiesis.

This work was supported by the Intramural Research Program of the National Institute of Allergy and Infectious diseases.

Group 3 innate lymphoid cells continuously require the transcription factor GATA-3 after commitment

The transcription factor GATA-3 is indispensable for the development of all innate lymphoid cells (ILCs) that express the interleukin 7 receptor α-chain (IL-7Rα). However, the function of low GATA-3 expression in committed group 3 ILCs (ILC3 cells) has not been identified. We found that GATA-3 regulated the homeostasis of ILC3 cells by controlling IL-7Rα expression. In addition, GATA-3 served a critical function in the development of the NKp46(+) ILC3 subset by regulating the balance between the transcription factors T-bet and RORγt. Among NKp46(+) ILC3 cells, although GATA-3 positively regulated genes specific to the NKp46(+) ILC3 subset, it negatively regulated genes specific to lymphoid tissue-inducer (LTi) or LTi-like ILC3 cells. Furthermore, GATA-3 was required for IL-22 production in both ILC3 subsets. Thus, despite its low expression, GATA-3 was critical for the homeostasis, development and function of ILC3 subsets.

Microbiota-Dependent Sequelae of Acute Infection Compromise Tissue-Specific Immunity

Infections have been proposed as initiating factors for inflammatory disorders; however, identifying associations between defined infectious agents and the initiation of chronic disease has remained elusive. Here, we report that a single acute infection can have dramatic and long-term consequences for tissue-specific immunity. Following clearance of Yersinia pseudotuberculosis, sustained inflammation and associated lymphatic leakage in the mesenteric adipose tissue deviates migratory dendritic cells to the adipose compartment, thereby preventing their accumulation in the mesenteric lymph node. As a consequence, canonical mucosal immune functions, including tolerance and protective immunity, are persistently compromised. Post-resolution of infection, signals derived from the microbiota maintain inflammatory mesentery remodeling and consequently, transient ablation of the microbiota restores mucosal immunity. Our results indicate that persistent disruption of communication between tissues and the immune system following clearance of an acute infection represents an inflection point beyond which tissue homeostasis and immunity is compromised for the long-term. VIDEO ABSTRACT.

In Vitro Analyses of T Cell Effector Differentiation

In vitro culture is an important complement, or substitute, to in vivo approaches in order to study T cell effector differentiation. Here, we describe culture conditions that generate specific effector cell types by exposing naïve T cells to appropriate cytokine signals.

Antibiotics in neonatal life increase murine susceptibility to experimental psoriasis

Psoriasis is an inflammatory skin disease affecting ∼2% of the world's population, but the aetiology remains incompletely understood. Recently, microbiota have been shown to differentially regulate the development of autoimmune diseases, but their influence on psoriasis is incompletely understood. We show here that adult mice treated with antibiotics that target Gram-negative and Gram-positive bacteria develop ameliorated psoriasiform dermatitis induced by imiquimod, with decreased pro-inflammatory IL-17- and IL-22-producing T cells. Surprisingly, mice treated neonatally with these antibiotics develop exacerbated psoriasis induced by imiquimod or recombinant IL-23 injection when challenged as adults, with increased IL-22-producing γδ(+) T cells. 16S rRNA gene compositional analysis reveals that neonatal antibiotic-treatment dysregulates gut and skin microbiota in adults, which is associated with increased susceptibility to experimental psoriasis. This link between neonatal antibiotic-mediated imbalance in microbiota and development of experimental psoriasis provides precedence for further investigation of its specific aetiology as it relates to human psoriasis.

Enhanced T-cell activation and differentiation in lymphocytes from transgenic mice expressing ubiquitination-resistant 2KR LAT molecules

Linker for activation of T cells (LAT) is critical for the propagation of T-cell signals upon T-cell receptor (TCR) activation. Previous studies demonstrated that substitution of LAT lysines with arginines (2KR LAT) resulted in decreased LAT ubiquitination and elevated T-cell signaling, indicating that LAT ubiquitination is a molecular checkpoint for attenuation of T-cell signaling. To investigate the role of LAT ubiquitination in vivo, we have generated transgenic mice expressing WT and ubiquitin-defective 2KR LAT. On TCR stimulation of T cells from these mice, proximal signaling and cytokine production was elevated in 2KR versus wild-type (WT) LAT mice. Enhanced cytolytic activity as well as T-helper responses were observed on LAT expression, which were further elevated by 2KR LAT expression. Despite greater T-effector function, WT or 2KR LAT expression did not have any effect on clearance of certain pathogens or tumors. Our data support the model that lack of tumor clearance is due to increased differentiation and acquisition of effector phenotype that is associated with suboptimal immunity in an immunotherapy model. Thus, our data further reinforce the role of LAT ubiquitination in TCR signaling and uncovers a novel role for LAT in driving T-cell differentiation.

Bone-Marrow-Resident NK Cells Prime Monocytes for Regulatory Function during Infection

Tissue-infiltrating Ly6C(hi) monocytes play diverse roles in immunity, ranging from pathogen killing to immune regulation. How and where this diversity of function is imposed remains poorly understood. Here we show that during acute gastrointestinal infection, priming of monocytes for regulatory function preceded systemic inflammation and was initiated prior to bone marrow egress. Notably, natural killer (NK) cell-derived IFN-γ promoted a regulatory program in monocyte progenitors during development. Early bone marrow NK cell activation was controlled by systemic interleukin-12 (IL-12) produced by Batf3-dependent dendritic cells (DCs) in the mucosal-associated lymphoid tissue (MALT). This work challenges the paradigm that monocyte function is dominantly imposed by local signals after tissue recruitment, and instead proposes a sequential model of differentiation in which monocytes are pre-emptively educated during development in the bone marrow to promote their tissue-specific function.