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The pathogenicity of disease-associated microbes varies widely between individuals. In this issue of Cell HostMicrobe, Rice et al. demonstrate that interactions between intestinal commensals reciprocally modulate the host immune response to each microbe, ameliorating the inflammation caused by one and dampening antibody responses to the other.

Atypical T cells take a different path Conventional T cells recognize peptides that are presented by polymorphic major histocompatibility complexes (MHCs). By contrast, many tissue-resident T cells, such as mucosal-associated invariant T cells, invariant natural killer T cells, and γδ T cells, respond to modified peptides and small molecules presented by conserved MHC-like molecules. Unconventional T cells are important for host defense and tissue repair and seed tissues during critical early-life windows of development. Constantinides and Belkaid review recent advances describing how unconventional T cell subsets compete for early-life signals, including those from the microbiota, which instruct their development and have enduring consequences for the health of the host. —STS

How defined microbes influence the skin immune system remains poorly understood. Here we demonstrate that Corynebacteria, dominant members of the skin microbiota, promote a dramatic increase in the number and activation of a defined subset of γδ T cells. This effect is long-lasting, occurs independently of other microbes, and is, in part, mediated by interleukin (IL)-23. Under steady-state conditions, the impact of Corynebacterium is discrete and noninflammatory. However, when applied to the skin of a host fed a high-fat diet, Corynebacterium accolens alone promotes inflammation in an IL-23–dependent manner. Such effect is highly conserved among species of Corynebacterium and dependent on the expression of a dominant component of the cell envelope, mycolic acid. Our data uncover a mode of communication between the immune system and a dominant genus of the skin microbiota and reveal that the functional impact of canonical skin microbial determinants is contextually controlled by the inflammatory and metabolic state of the host.

The microbiota, which consists of commensal bacteria, fungi, and viruses, limits the colonization of pathogens at barrier tissues and promotes immune homeostasis. The latter is accomplished through the induction and regulation of both innate and adaptive immune responses. Innate lymphocytes, which include the type-1 innate lymphoid cell (ILC1), NK cell, type-2 innate lymphoid cell (ILC2), type-3 innate lymphoid cell (ILC3), and lymphoid tissue inducer (LTi) cell populations, and innate-like lymphocytes, such as NKT cells, mucosal-associated invariant T (MAIT) cells, and γδ T cells, are uniquely capable of responding to the microbiota due to their tissue localization and rapid primary responses. In turn, through their effector functions, these lymphocyte populations modulate the composition of the microbiota and maintain the segregation of commensals. This review will focus on how innate and innate-like lymphocytes mediate the crosstalk with the microbiome.

Summary The microbiota plays a fundamental role in regulating host immunity. However, the processes involved in the initiation and regulation of immunity to the microbiota remain largely unknown. Here, we show that the skin microbiota promotes the discrete expression of defined endogenous retroviruses (ERVs). Keratinocyte-intrinsic responses to ERVs depended on cyclic GMP-AMP synthase (cGAS)/stimulator of interferon genes protein (STING) signaling and promoted the induction of commensal-specific T cells. Inhibition of ERV reverse transcription significantly impacted these responses, resulting in impaired immunity to the microbiota and its associated tissue repair function. Conversely, a lipid-enriched diet primed the skin for heightened ERV- expression in response to commensal colonization, leading to increased immune responses and tissue inflammation. Together, our results support the idea that the host may have co-opted its endogenous virome as a means to communicate with the exogenous microbiota, resulting in a multi-kingdom dialog that controls both tissue homeostasis and inflammation., Graphical abstract, Highlights • Endogenous retrovirus sensing is required for commensal-specific immunity • Reverse transcription inhibition impairs commensal-induced immunity in the skin • cGAS/STING signaling in keratinocytes is required for skin immunity to the microbiota • Enhanced endogenous retrovirus expression promotes microbiota-induced inflammation, The host immune system uses the endogenous virome to communicate with the exogenous microbiota in a multi-kingdom interaction that modulates tissue repair or inflammation.

The cross-talk between the microbiota and the immune system plays a fundamental role in the control of host physiology. However, the tissue-specific factors controlling this dialogue remain poorly understood. Here we demonstrate that T cell responses to commensal colonization are associated with the development of organized cellular clusters within the skin epithelium. These organized lymphocyte clusters are surrounded by keratinocytes expressing a discrete program associated with antigen presentation and antimicrobial defense. Notably, IL-22–mediated keratinocyte-intrinsic MHC class II expression was required for the selective accumulation of commensal-induced IFN-γ, but not IL-17A–producing CD4 + T cells within the skin. Taking these data together, this work uncovers an unexpected role for MHC class II expression by keratinocytes in the control of homeostatic type 1 responses to the microbiota. Our findings have important implications for the understanding of the tissue-specific rules governing the dialogue between a host and its microbiota.

Commensals rule the MAITrix Mucosal-associated invariant T (MAIT) cells play an important role in mucosal homeostasis. MAIT cells recognize microbial small molecules presented by the major histocompatibility complex class Ib molecule MR1. MAIT cells are absent in germ-free mice, and the mechanisms by which microbiota control MAIT cell development are unknown (see the Perspective by Oh and Unutmaz). Legoux et al. show that, in mice, development of MAIT cells within the thymus is governed by the bacterial product 5-(2-oxopropylideneamino)-6- d -ribitylaminouracil, which rapidly traffics from the mucosa to the thymus, where it is captured by MR1 and presented to developing MAIT cells. Constantinides et al. report that MAIT cell induction only occurs during a limited, early-life window and requires exposure to defined microbes that produce riboflavin derivatives. Continual interactions between MAIT cells and commensals in the skin modulates tissue repair functions. Together, these papers highlight how the microbiota can direct immune cell development and subsequent function at mucosal sites by secreting compounds that act like self-antigens. Science , this issue p. 494 , p. eaax6624 ; see also p. 419

International audience; The precise lineage relationship between innate lymphoid cells (ILCs) and lymphoid tissue-inducer (LTi) cells is poorly understood. Using single-cell multiplex transcriptional analysis of 100 lymphoid genes and single-cell cultures of fetal liver precursor cells, we identified the common proximal precursor to these lineages and found that its bifurcation was marked by differential induction of the transcription factors PLZF and TCF1. Acquisition of individual effector programs specific to the ILC subsets ILC1, ILC2 and ILC3 was initiated later, at the common ILC precursor stage, by transient expression of mixed ILC1, ILC2 and ILC3 transcriptional patterns, whereas, in contrast, the development of LTi cells did not go through multilineage priming. Our findings provide insight into the divergent mechanisms of the differentiation of the ILC lineage and LTi cell lineage and establish a high-resolution 'blueprint' of their development.

Bcl6 and E3 ligase cullin 3 complexes mediate negative feedback regulation during thymocyte development and T cell activation to restrain exaggerated Tfh responses., Induction of Bcl6 (B cell lymphoma 6) is essential for T follicular helper (Tfh) cell differentiation of antigen-stimulated CD4+ T cells. Intriguingly, we found that Bcl6 was also highly and transiently expressed during the CD4+CD8+ (double positive [DP]) stage of T cell development, in association with the E3 ligase cullin 3 (Cul3), a novel binding partner of Bcl6 which ubiquitinates histone proteins. DP stage–specific deletion of the E3 ligase Cul3, or of Bcl6, induced the derepression of the Bcl6 target genes Batf (basic leucine zipper transcription factor, ATF-like) and Bcl6, in part through epigenetic modifications of CD4+ single-positive thymocytes. Although they maintained an apparently normal phenotype after emigration, they expressed increased amounts of Batf and Bcl6 at basal state and produced explosive and prolonged Tfh responses upon subsequent antigen encounter. Ablation of Cul3 in mature CD4+ splenocytes also resulted in dramatically exaggerated Tfh responses. Thus, although previous studies have emphasized the essential role of Bcl6 in inducing Tfh responses, our findings reveal that Bcl6–Cul3 complexes also provide essential negative feedback regulation during both thymocyte development and T cell activation to restrain excessive Tfh responses.

Innate lymphoid cells (ILCs) specialize in the rapid secretion of polarized sets of cytokines and chemokines to combat infection and promote tissue repair at mucosal barriers. Their diversity and similarities with previously characterized natural killer (NK) cells and lymphoid tissue inducers (LTi) have prompted a provisional classification of all innate lymphocytes into groups 1, 2 and 3 solely on the basis of cytokine properties, but their developmental pathways and lineage relationships remain elusive. Here we identify and characterize a novel subset of lymphoid precursors in mouse fetal liver and adult bone marrow that transiently express high amounts of PLZF, a transcription factor previously associated with NK T cell development, by using lineage tracing and transfer studies. PLZF(high) cells were committed ILC progenitors with multiple ILC1, ILC2 and ILC3 potential at the clonal level. They excluded classical LTi and NK cells, but included a peculiar subset of NK1.1(+)DX5(-) 'NK-like' cells residing in the liver. Deletion of PLZF markedly altered the development of several ILC subsets, but not LTi or NK cells. PLZF(high) precursors also expressed high amounts of ID2 and GATA3, as well as TOX, a known regulator of PLZF-independent NK and LTi lineages. These findings establish novel lineage relationships between ILC, NK and LTi cells, and identify the common precursor to ILCs, termed ILCP. They also reveal the broad, defining role of PLZF in the differentiation of innate lymphocytes.

Infectious agents are estimated to cause approximately 18% of cancers worldwide, supporting a link between microbial products and carcinogenesis. The diverse array of commensal microorganisms that reside at barrier sites of the human body, collectively termed the microbiome, provide the primary source of constitutive microbial stimulation and promote immune homeostasis through their release of microbial products, including derivatives of vitamin synthesis. Mucosal-associated invariant T (MAIT) cells are unconventional T-cells that recognize microbial-derived metabolites and provide an initial defense to pathogens through their rapid production of type-1 or type-17 cytokines. While MAIT-cells have been shown to infiltrate colorectal tumors, it remains to be determined how MAIT-cells contribute to tumorigenesis and whether commensals regulate MAIT-cell function. Here we show that MAIT-cells are a substantial skin-resident population capable of producing IL-17A. IL-23 signaling promotes the accumulation of cutaneous MAIT-cells and skin commensals induce local MAIT-cell proliferation and IL-1-dependent IL-17A production. In the absence of commensals, MAIT-cells are dramatically decreased, indicating that the microbiota is necessary for the development of this population. Utilizing MAIT-cell-deficient mice, we demonstrate that cutaneous MAIT-cells promote wound healing and inhibit the colonization of pathogens. 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. Since IL-17A promotes tumor vascularization and neutrophil recruitment, the high frequency of MAIT-cells in human skin suggests that modulation of the skin-resident bacteria may have clinical applications for the progression of melanoma, and current studies are exploring this possibility using the B16 melanoma model in mice.This work was supported by the NIH Intramural Research Program. MGC is a Cancer Research Institute Irvington Fellow supported by the Cancer Research Institute. Citation Format: Michael G. Constantinides, Samira Tamoutounour, Jonathan L. Linehan, Shurjo Sen, Jahangheer Shaik, Sobhan Roy, Erin J. Adams, Yasmine Belkaid. Mucosal-associated invariant T-cells respond to the cutaneous microbiota and promote skin immunity [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr PR16.

The transcription factor PLZF [promyelocytic leukemia zinc finger, encoded by zinc finger BTB domain containing 16 (Zbtb16)] is induced during the development of innate and innate-like lymphocytes to direct their acquisition of a T-helper effector program, but the molecular mechanisms involved are poorly understood. Using biotinylation-based ChIP-seq and microarray analysis of both natural killer T (NKT) cells and PLZF-transgenic thymocytes, we identified several layers of regulation of the innate-like NKT effector program. First, PLZF bound and regulated genes encoding cytokine receptors as well as homing and adhesion receptors; second, PLZF bound and activated T-helper–specific transcription factor genes that in turn control T-helper–specific programs; finally, PLZF bound and suppressed the transcription of Bach2, a potent general repressor of effector differentiation in naive T cells. These findings reveal the multilayered architecture of the transcriptional program recruited by PLZF and elucidate how a single transcription factor can drive the developmental acquisition of a broad effector program.

The discovery of tissue-resident innate lymphoid cell populations effecting different forms of type 1, 2, and 3 immunity; tissue repair; and immune regulation has transformed our understanding of mucosal immunity and allergy. The emerging complexity of these populations along with compounding issues of redundancy and plasticity raise intriguing questions about their precise lineage relationship. Here we review advances in mapping the emergence of these lineages from early lymphoid precursors. We discuss the identification of a common innate lymphoid cell precursor characterized by transient expression of the transcription factor PLZF, and the lineage relationships of innate lymphoid cells with conventional natural killer cells and lymphoid tissue inducer cells. We also review the rapidly growing understanding of the network of transcription factors that direct the development of these lineages.

Rare CD1d-α-galactosylceramide–specific T cells that do not express the invariant Vα24 chain of human NKT cells were recently identified after expansion in vitro with the lipid Ag, but their phenotype and frequency in vivo and lineage relationship with NKT cells could not be elucidated. By using a CD1d tetramer-based method to enrich these cells from fresh peripheral blood, we demonstrated their naive-like CD62LhighCD45RO−CD4+ phenotype and relatively high frequency of ∼10−5 in several healthy individuals. Notably, these cells expressed the NKT lineage-specific transcription promyelocytic leukemia zinc finger (PLZF), indicating a developmental relationship with NKT cells and ruling out the possibility that they were conventional MHC-restricted T cells cross-reacting against CD1d-α-galactosylceramide. Although PLZF is known to direct the effector program of NKT cells, we show in this study that the naive-like cells expressed it at a significantly lower amount than NKT cells. Further, we present mouse studies demonstrating a sharp PLZF expression threshold requirement for induction of the effector phenotype. These findings directly demonstrate in vivo the existence of naive-like CD1d-restricted human T cells marked by intermediate levels of PLZF.

Thymocytes expressing the NKT cell semi-invariant αβ TCR are thought to undergo agonist interactions with CD1d ligands prior to expressing promyelocytic leukemia zinc finger (PLZF), a broad complex, tramtrack, bric-a-brac, poxvirus, and zinc finger transcription factor that directs acquisition of the effector program of these innate-like T cells. Whether PLZF can mediate this effector conversion independently of agonist signaling has not been investigated. We demonstrated that transgenic (Tg) expression of PLZF under the CD4 promoter induced the innate effector program in two different MHC class II-restricted TCR-Tg Rag1−/− models examined. In CD4 thymocytes expressing a fixed Tg TCR β-chain, the associated TCRα sequences in wild-type and PLZF-Tg mice overlapped extensively, further demonstrating that PLZF could induce the effector program in most CD4 T cells that would normally be selected as naive cells. In contrast, PLZF altered the negative selection of thymocytes expressing TCR β-chains reactive against several retroviral superantigens. Thus, PLZF is remarkable in that it is a transcription factor capable of inducing an effector program in the absence of T cell agonist interactions or cell division. Its expression may also enhance the survival of agonist-signaled thymocytes.

PLZF-expressing NKT cells establish residence at intravascular locations, failing to enter the circulation because of constitutive interactions with LFA-1 and ICAM-1., Innate-like NKT cells conspicuously accumulate within the liver microvasculature of healthy mice, crawling on the luminal side of endothelial cells, but their general recirculation pattern and the mechanism of their intravascular behavior have not been elucidated. Using parabiotic mice, we demonstrated that, despite their intravascular location, most liver NKT cells failed to recirculate. Antibody blocking experiments established that they were retained locally through constitutive LFA-1–intercellular adhesion molecule (ICAM) 1 interactions. This unprecedented lifelong intravascular residence could be induced in conventional CD4 T cells by the sole expression of promyelocytic leukemia zinc finger (PLZF), a transcription factor specifically expressed in the NKT lineage. These findings reveal the unique genetic and biochemical pathway that underlies the innate intravascular surveillance program of NKT cells.

Highly-ordered, three-dimensional superlattices were self-assembled from dodecanethiol-ligated gold nanocrystals using a simple drop-drying technique. The superlattices had the shape of truncated pyramids (frustums) and reached lateral dimensions of several micrometers. The formation and thermal stability were studied by grazing-incidence small-angle x-ray scattering. We found that the superlattice frustums adopt a hcp packing structure. When annealed above 50 °C in vacuum, the lattices started to disorder and the average lattice spacing was observed to decrease. This could be associated with the onset of ligand melting transition as well as the continuous desorption of ligand in vacuum.

Among the variety of tissue-resident NK-like populations recently distinguished from recirculating classical NK (cNK) cells, liver innate lymphoid cells (ILC) type 1 (ILC1s) have been shown to represent a distinct lineage that originates from a novel promyelocytic leukaemia zinc finger (PLZF)-expressing ILC precursor (ILCP) strictly committed to the ILC1, ILC2, and ILC3 lineages. Here, using PLZF-reporter mice and cell transfer assays, we studied the developmental progression of ILC1s and demonstrated substantial overlap with stages previously ascribed to the cNK lineage, including pre–pro-NK, pre-NK precursor (pre-NKP), refined NKP (rNKP), and immature NK (iNK). Although they originated from different precursors, the ILC1 and cNK lineages followed a parallel progression at early stages and diverged later at the iNK stage, with a striking predominance of ILC1s over cNKs early in ontogeny. Although a limited set of ILC1 genes depended on PLZF for expression, characteristically including Il7r, most of these genes were also differentially expressed between ILC1s and cNKs, indicating that PLZF together with other, yet to be defined, factors contribute to the divergence between these lineages.

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.

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.

Summary Cancer cells must evade immune responses at distant sites to establish metastases. The lung is a frequent site for metastasis. We hypothesized that lung-specific immunoregulatory mechanisms create an immunologically permissive environment for tumor colonization. We found that T-cell-intrinsic expression of the oxygen-sensing prolyl-hydroxylase (PHD) proteins is required to maintain local tolerance against innocuous antigens in the lung but powerfully licenses colonization by circulating tumor cells. PHD proteins limit pulmonary type helper (Th)-1 responses, promote CD4 + -regulatory T (T reg ) cell induction, and restrain CD8 + T cell effector function. Tumor colonization is accompanied by PHD-protein-dependent induction of pulmonary T reg cells and suppression of IFN-γ-dependent tumor clearance. T-cell-intrinsic deletion or pharmacological inhibition of PHD proteins limits tumor colonization of the lung and improves the efficacy of adoptive cell transfer immunotherapy. Collectively, PHD proteins function in T cells to coordinate distinct immunoregulatory programs within the lung that are permissive to cancer metastasis. PaperClip

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.”

Background The transcription factor promyelocytic leukemia zinc finger (PLZF) is transiently expressed during development of type 2 innate lymphoid cells (ILC2s) but is not present at the mature stage. We hypothesized that PLZF-deficient ILC2s have functional defects in the innate allergic response and represent a tool for studying innate immunity in a mouse with a functional adaptive immune response. Objective We determined the consequences of PLZF deficiency on ILC2 function in response to innate and adaptive immune stimuli by using PLZF −/− mice and mixed wild-type:PLZF −/− bone marrow chimeras. Methods PLZF −/− mice, wild-type littermates, or mixed bone marrow chimeras were treated with the protease allergen papain or the cytokines IL-25 and IL-33 or infected with the helminth Nippostrongylus brasiliensis to induce innate type 2 allergic responses. Mice were sensitized with intraperitoneal ovalbumin-alum, followed by intranasal challenge with ovalbumin alone, to induce adaptive T H 2 responses. Lungs were analyzed for immune cell subsets, and alveolar lavage fluid was analyzed for ILC2-derived cytokines. In addition, ILC2s were stimulated ex vivo for their capacity to release type 2 cytokines. Results PLZF-deficient lung ILC2s exhibit a cell-intrinsic defect in the secretion of IL-5 and IL-13 in response to innate stimuli, resulting in defective recruitment of eosinophils and goblet cell hyperplasia. In contrast, the adaptive allergic inflammatory response to ovalbumin and alum was unimpaired. Conclusions PLZF expression at the innate lymphoid cell precursor stage has a long-range effect on the functional properties of mature ILC2s and highlights the importance of these cells for innate allergic responses in otherwise immunocompetent mice.

How expression of canonical semi-invariant TCRs leads to innate-like effector differentiation is a central enigma of NKT cell development. NKT thymic precursors undergo elevated TCR signals leading to increased Egr2, which directly induces their signature transcription factor, PLZF. PLZF is necessary and sufficient to induce a multipotent, unbiased effector program that precedes terminal differentiation into T-bet(high) NK1.1(+) (NKT1) cells and recently identified NKT2 and NKT17 sublineages. Major variations in polarized NKT sublineages have been uncovered in different mouse strains and in several mutants, with direct impact on NKT cell function but also, unexpectedly, on the development and function of conventional T cells.

The differentiation of several T- and B-cell effector programs in the immune system is directed by signature transcription factors that induce rapid epigenetic remodelling. Here we report that promyelocytic leukaemia zinc finger (PLZF), the BTB-zinc finger (BTB-ZF) transcription factor directing the innate-like effector program of natural killer T-cell thymocytes, is prominently associated with cullin 3 (CUL3), an E3 ubiquitin ligase previously shown to use BTB domain-containing proteins as adaptors for substrate binding. PLZF transports CUL3 to the nucleus, where the two proteins are associated within a chromatin-modifying complex. Furthermore, PLZF expression results in selective ubiquitination changes of several components of this complex. CUL3 was also found associated with the BTB-ZF transcription factor BCL6, which directs the germinal-centre B cell and follicular T-helper cell programs. Conditional CUL3 deletion in mice demonstrated an essential role for CUL3 in the development of PLZF- and BCL6-dependent lineages. We conclude that distinct lineage-specific BTB-ZF transcription factors recruit CUL3 to alter the ubiquitination pattern of their associated chromatin-modifying complex. We propose that this new function is essential to direct the differentiation of several T- and B-cell effector programs, and may also be involved in the oncogenic role of PLZF and BCL6 in leukaemias and lymphomas.

Distinct lineages of natural killer T cells arise in the thymus and are characterized by the signature transcription factors T-bet, GATA-3 or RORγt.

The transcriptional control of CD1d-restricted NKT cell development has remained elusive. We report that PLZF (promyelocytic leukemia zinc finger; Zbtb16), a member of the BTB/POZ-ZF family of transcription factors which includes the CD4 lineage-specific c-Krox (Th-POK, Zbtb7b), is exquisitely specific to CD1d-restricted NKT cells and human MR1-specific MAIT cells. PLZF was induced immediately after positive selection of NKT cell precursors and PLZF-deficient NKT cells failed to undergo the intrathymic expansion and effector differentiation that characterize their lineage. Instead, they preserved a naïve phenotype and were directed to lymph nodes. Conversely, transgenic expression of PLZF induced CD4 thymocytes to acquire effector differentiation and migrate to non-lymphoid tissues. We suggest that PLZF is a transcriptional signature of NKT cells that directs their innate-like effector differentiation during thymic development.