Development and functional specialization of CD103+ dendritic cells

Summary: CD103 (α_E) integrin expression distinguishes a population of dendritic cells (DCs) that can be found in many if not all lymphoid and non-lymphoid organs. CD103⁺ DCs display distinct functional activities. Migratory CD103⁺ DCs derived from skin, lung, and intestine efficiently present exogenous antigens in their corresponding draining lymph nodes to specific CD8⁺ T cells through a mechanism known as cross-presentation. On the T cells they prime, intestinal CD103⁺ DCs can drive the induction of the chemokine receptor CCR9 and α₄β₇ integrin, both known as gut-homing receptors. CD103⁺ DCs also contribute to control inflammatory responses and intestinal homeostasis by fostering the conversion of naive T cells into induced Foxp3⁺ regulatory T cells, a mechanism that relies on transforming growth factor-β and retinoic acid signaling. This review discusses recent findings that identify murine CD103⁺ DCs as important regulators of the immune response.     

Intestinal CD103− dendritic cells migrate in lymph and prime effector T cells

Intestinal dendritic cells (DCs) continuously migrate through lymphatics to mesenteric lymph nodes where they initiate immunity or tolerance. Recent research has focused on populations of intestinal DCs expressing CD103. Here we demonstrate, for the first time, the presence of two distinct CD103⁻ DC subsets in intestinal lymph. Similar to CD103⁺ DCs, these intestine-derived CD103⁻ DCs are responsive to Flt3 and they efficiently prime and confer a gut-homing phenotype to naive T cells. However, uniquely among intestinal DCs, CD103⁻ CD11b⁺ CX₃CR1^int lymph DCs induce the differentiation of both interferon-γ and interleukin-17-producing effector T cells, even in the absence of overt stimulation. Priming by CD103⁻ CD11b⁺ DCs represents a novel mechanism for the rapid generation of effector T-cell responses in the gut. Therefore, these cells may prove to be valuable targets for the treatment of intestinal inflammation or in the development of effective oral vaccines.     

Optimal stimulation for CD70 induction on human monocyte‐derived dendritic cells and the importance of CD70 in naive CD4+ T‐cell differentiation

Studies in mice have shown that CD70 on dendritic cells (DCs) is sufficient to convert T‐cell tolerance into immunity and hence induce anti‐tumour immune responses. Therefore, it is important to investigate (i) optimal stimuli to induce CD70 on human monocyte‐derived DCs (MoDCs), which are widely used for tumour immunotherapy, and (ii) the role of CD70 in functional differentiation of naive CD4⁺ and CD8⁺ T cells stimulated with MoDCs. We show that interferon‐α (IFN‐α) is a key cytokine to differentiate monocytes into DCs with the capacity to express CD70 upon maturation. CD70 expression on IFN‐α‐induced MoDCs was elicited by different categories of maturation‐inducing factors (Toll‐like receptor ligands, CD40 ligand and pro‐inflammatory mediators), among which prostaglandin E₂ was most effective. Naive T cells stimulated with MoDCs also expressed CD70. Stimulation with MoDCs promoted naive CD4⁺ T cells to acquire the ability to produce T helper type 1 and 2 cytokines in a CD70‐dependent manner. In contrast, the CD70–CD27 interaction diminished the production of an immunoregulatory cytokine IL‐10. The CD27 signal did not play a dominant role in the induction of effector molecules in naive CD8⁺ T cells during the stimulation with MoDCs. This study adds a novel function to the versatile cytokines, type I IFNs, that is, the induction of CD70 on MoDCs. CD70 promotes naive CD4⁺ T cells to acquire immunostimulatory activity through the DC–T‐cell and T‐cell–T‐cell interactions during the stimulation with MoDCs. Hence, the CD70–CD27 interaction may play an important role in inducing effective immune responses in DC‐based immunotherapy.     

Functional specialization of intestinal dendritic cell subsets during Th2 helminth infection in mice

Dendritic cells (DCs) are essential in dictating the nature and effectiveness of immune responses. In the intestine DCs can be separated into discrete subsets, defined by expression of CD11b and CD103, each with different developmental requirements and distinct functional potential. Recent evidence has shown that different intestinal DC subsets are involved in the induction of T helper (Th)17 and regulatory T cell responses, but the cells that initiate Th2 immune responses are still incompletely understood. We show that in the Th2 response to an intestinal helminth in mice, only CD11b⁺ and not CD11b^? DCs accumulate in the local lymph node, upregulate PDL2 and express markers of alternative activation. An enteric Th1 response instead activated both CD11b⁺ and CD11b^? DCs without eliciting alternative activation in either population. Functionally, only CD11b⁺ DCs activated during helminth infection supported Th2 differentiation in naive CD4⁺ T cells. Together our data demonstrate that the ability to prime Th2 cells during intestinal helminth infection, is a selective and inducible characteristic of CD11b⁺ DCs.     

Retinoic acid primes human dendritic cells to induce gut-homing,IL-10-producing regulatory T cells

The vitamin A metabolite all-trans retinoic acid (RA) is an important determinant of intestinal immunity. RA primes dendritic cells (DCs) to express CD103 and produce RA themselves, which induces the gut-homing receptors α4β7 and CCR9 on T cells and amplifies transforming growth factor (TGF)-β-mediated development of Foxp3⁺ regulatory T (Treg) cells. Here we investigated the effect of RA on human DCs and subsequent development of T cells. We report a novel role of RA in immune regulation by showing that RA-conditioned human DCs did not substantially enhance Foxp3 but induced α4β7⁺ CCR9⁺ T cells expressing high levels of interleukin (IL)-10, which were functional suppressive Treg cells. IL-10 production was dependent on DC-derived RA and was maintained when DCs were stimulated with toll-like receptor ligands. Furthermore, the presence of TGF-β during RA-DC-driven T-cell priming favored the induction of Foxp3⁺ Treg cells over IL-10⁺ Treg cells. Experiments with naive CD4⁺ T cells stimulated by anti-CD3 and anti-CD28 antibodies in the absence of DCs emphasized that RA induces IL-10 in face of inflammatory mediators. The data thus show for the first time that RA induces IL-10-producing Treg cells and postulates a novel mechanism for IL-10 in maintaining tolerance to the intestinal microbiome.     

Colonic tolerance develops in the iliac lymph nodes and can be established independent of CD103+ dendritic cells

Tolerance to harmless exogenous antigens is the default immune response in the gastrointestinal tract. Although extensive studies have demonstrated the importance of the mesenteric lymph nodes (MLNs) and intestinal CD103⁺ dendritic cells (DCs) in driving small intestinal tolerance to protein antigen, the structural and immunological basis of colonic tolerance remain poorly understood. We show here that the caudal and iliac lymph nodes (ILNs) are inductive sites for distal colonic immune responses and that colonic T cell-mediated tolerance induction to protein antigen is initiated in these draining lymph nodes and not in MLNs. In agreement, colonic tolerance induction was not altered by mesenteric lymphadenectomy. Despite tolerance development, CD103⁺CD11b⁺ DCs, which are the major migratory DC population in the MLNs, and the tolerance-related retinoic acid-generating enzyme RALDH2 were virtually absent from the ILNs. Administration of ovalbumin (OVA) to the distal colon did increase the number of CD11c⁺MHCII^hi migratory CD103⁻CD11b⁺ and CD103⁺CD11b⁻ DCs in the ILNs. Strikingly, colonic tolerance was intact in Batf3-deficient mice specifically lacking CD103⁺CD11b⁻ DCs, suggesting that CD103⁻ DCs in the ILNs are sufficient to drive tolerance induction after protein antigen encounter in the distal colon. Altogether, we identify different inductive sites for small intestinal and colonic T-cell responses and reveal that distinct cellular mechanisms are operative to maintain tolerance at these sites.     

Retinoic acid prevents mesenteric lymph node dendritic cells from inducing IL-13-producing inflammatory Th2 cells

The vitamin A (VA) metabolite retinoic acid (RA) affects the properties of T cells and dendritic cells (DCs). In VA-deficient mice, we observed that mesenteric lymph node (MLN)-DCs induce a distinct inflammatory T helper type 2 (Th2)-cell subset that particularly produces high levels of interleukin (IL)-13 and tumor necrosis factor-α (TNF-α). This subset expressed homing receptors for skin and inflammatory sites, and was mainly induced by B220⁻CD8α⁻CD11b⁺CD103⁻ MLN-DCs in an IL-6- and OX40 ligand-dependent manner, whereas RA inhibited this induction. The corresponding MLN-DC subset of VA-sufficient mice induced a similar T-cell subset in the presence of RA receptor antagonists. IL-6 induced this subset differentiation from naive CD4⁺ T cells upon activation with antibodies against CD3 and CD28. Transforming growth factor-β inhibited this induction, and reciprocally enhanced Th17 induction. Treatment with an agonistic anti-OX40 antibody and normal MLN-DCs enhanced the induction of general inflammatory Th2 cells. In VA-deficient mice, proximal colon epithelial cells produced TNF-α that may have enhanced OX40 ligand expression in MLN-DCs. The repeated oral administrations of a T cell-dependent antigen primed VA-deficient mice for IL-13-dependent strong immunoglobulin G1 (IgG1) responses and IgE responses that caused skin allergy. These results suggest that RA inhibits allergic responses to oral antigens by preventing MLN-DCs from inducing IL-13-producing inflammatory Th2 cells.     

Dendritic cells,T cells and their interaction in rheumatoid arthritis

Dendritic cells (DCs) are the key professional antigen-presenting cells which bridge innate and adaptive immune responses, inducing the priming and differentiation of naive to effector CD4⁺ T cells, the cross-priming of CD8⁺ T cells and the promotion of B cell antibody responses. DCs also play a critical role in the maintenance of immune homeostasis and tolerance. DC–T cell interactions underpin the generation of an autoimmune response in rheumatoid arthritis (RA). Here we describe the function of DCs and review evidence for DC and T cell involvement in RA pathogenesis, in particular through the presentation of self-peptide by DCs that triggers differentiation and activation of autoreactive T cells. Finally, we discuss the emerging field of targeting the DC–T cell interaction for antigen-specific immunotherapy of RA.     

CX3CR1+ cells facilitate the activation of CD4 T cells in the colonic lamina propria during antigen-driven colitis

Dendritic cells (DCs) and macrophages populate the intestinal lamina propria to initiate immune responses required for the maintenance of intestinal homeostasis. To investigate whether CX₃CR1⁺ phagocytes communicate with CD4 T cells during the development of transfer colitis, we established an antigen-driven colitis model induced by the adoptive transfer of DsRed OT-II cells in CX₃CR1^GFP/+ × RAG^−/− recipients challenged with Escherichia coli expressing ovalbumin (OVA) fused to a cyan fluorescent protein (CFP). After colonization of CX₃CR1^GFP/+ × RAG^−/− animals with red fluorescent E. coli pCherry-OVA, colonic CX₃CR1⁺ cells but not CD103⁺ DCs phagocytosed E. coli pCherry-OVA. Degraded bacterial-derived antigens are transported by CD103⁺ DCs to mesenteric lymph nodes (MLNs), where CD103⁺ DCs prime naive T cells. In RAG^−/− recipients reconstituted with OT II cells and gavaged with OVA-expressing E. coli, colonic CX₃CR1⁺ phagocytes are in close contact with CD4 T cells and presented bacterial-derived antigens to CD4 T cells to activate and expand effector T cells.     

Neutrophil-dependent tumor rejection and priming of tumoricidal CD8+ T cell response induced by dendritic cells overexpressing CD95L

Overexpression of CD95 (Fas/Apo-1) ligand (CD95L) has been shown to induce T cell tolerance but also, neutrophilic inflammation and rejection of allogeneic tissue. We explored the capacity of dendritic cells (DCs) genetically engineered to overexpress CD95L to induce an antitumor response. We first found that DCs overexpressing CD95L, in addition to MHC class I-restricted OVA peptides (CD95L-OVA-DCs), induced increased antigen-specific CD8(+) T cell responses as compared with DCs overexpressing OVA peptides alone. The enhanced T cell responses were associated with improved regression of a tumor expressing OVA, allowing survival of all animals. When DCs overexpressing CD95L (CD95L-DCs) were injected with the tumor expressing OVA, in vivo tumor proliferation was strikingly inhibited. A strong cellular apoptosis and a massive neutrophilic infiltrate developed in this setting. Neutrophil depletion prevented tumor regression as well as enhanced IFN-gamma production induced by CD95L-OVA-DCs. Furthermore, the CD8(+) T cell response induced by the coadministration of tumor cells and CD95L-DCs led to rejection of a tumor implanted at a distance from the DC injection site. In summary, DCs expressing CD95L promote tumor rejection involving neutrophil-mediated innate immunity and CD8(+) T cell-dependent adaptative immune responses.     

A profile of TNFR2+ regulatory T cells and CD103+ dendritic cells in the peripheral blood of patients with asthma

The interaction of tolerogenic CD103⁺ dendritic cells (DCs) with regulatory T (Tregs) cells modulates immune responses by inducing immune tolerance. Hence, we determined the proportion of these cells in the peripheral blood mononuclear cells (PBMC) of asthmatic patients. We observed lower trends of CD11b^-CD103⁺ DCs and CD86 within CD11b^-CD103⁺ DCs, while increased levels of Foxp3 expressing CD25^+/-TNFR2⁺ cells in asthmatics. There was a positive correlation in the expression of Foxp3 within CD3⁺CD4⁺CD25⁺TNFR2⁺ Tregs and CD11b^-CD103⁺ as well as the expression of CD86 within HLA-DR⁺CD11c⁺CD11b^-CD103⁺ DCs. In conclusion, we suggest that the increased levels of Tregs in blood could continuously suppress the T helper 2 (Th2) cells activation in the circulation which is also supported by the increase of anti-inflammatory cytokines IL-10 and TNF. Overall, functional immunoregulation of the regulatory cells, particularly Tregs, exhibit immune suppression and induce immune tolerance linked with the immune activation by the antigen presenting cells (APC).     

Synergy between intraepithelial lymphocytes and lamina propria T cells drives intestinal inflammation during infection

Oral infection of C57BL/6 mice with Toxoplasma gondii triggers severe necrosis in the ileum within 7–10 days of infection. Lesion development is mediated by Th-1 cytokines, CD4⁺ T cells, and subepithelial bacterial translocation. As such, these features share similarity to Crohn's disease. Recently, we uncovered a role for intraepithelial lymphocytes (IELs) in mediating pathology after Toxoplasma infection. We show here that αβ and not γδ T-cell IELs mediate intestinal damage. By adoptive transfer of mucosal T cells into naive Rag1^−/− mice, we demonstrate that IELs do not function alone to cause inflammatory lesions, but act with CD4⁺ T lymphocytes from the lamina propria (LP). Furthermore, recipient mice pretreated with broad-spectrum antibiotics to eliminate intestinal flora resisted intestinal disease after transfer of IELs and LP lymphocytes. Our data provide valuable new insights into the mechanisms of intestinal inflammation, findings that have important implications for understanding human inflammatory bowel disease.     

Tolerogenic effect of mouse fibroblasts on dendritic cells

There is controversy about the immunomodulatory effect of fibroblasts on dendritic cells (DCs). To clarify this issue, in this study, we have evaluated different features of fibroblast‐primed DCs including their ability to express co‐inhibitory and co‐stimulatory molecules, pro‐inflammatory and anti‐inflammatory cytokines and their ability to induce T‐cell proliferation. We also examined migratory capacity of DCs to lymphatic tissues and present fibroblast‐derived antigens after encountering fibroblasts. The results of our in vitro study showed that both co‐inhibitory (programmed death ligand 1 and ligand 2 and B7H4) and co‐stimulatory (CD86) molecules were up‐regulated when DCs were co‐cultured with fibroblasts. In an animal model, we showed that intra‐ peritoneal injection (IP) of both syngeneic and allogeneic fibroblasts significantly increased both total DC count and expression level of co‐inhibitory and co‐stimulatory molecules on DCs. Priming of DCs with syngeneic and allogeneic fibroblasts reduced the proliferation of CD4⁺ and CD8⁺ T cells. Even activation of fibroblast‐ primed DCs failed to restore their ability to induce T‐cell proliferation. Likewise, priming of DCs with fibroblasts blocked the ability of ovalbumin‐pulsed DCs to induce proliferation of ovalbumin‐specific CD4⁺ T cells. Compared with non‐activated DCs, fibroblast‐primed DCs had significantly higher expression levels of interleukin‐10 and indoleamine 2, 3 dioxygenase. Fibroblast‐primed DCs had a significantly reduced interleukin‐12 expression level compared with that of activated DCs. After priming with fibroblasts, DCs were able to migrate to lymphatic tissues and present fibroblast‐derived antigens (ovalbumin). In conclusion, after priming with fibroblasts, DCs gain tolerogenic features. This finding suggests the potential role of fibroblasts in the maintenance of immune tolerance.     

Suppression of Th1 and Th17, but not Th2, responses in a CD8+ T cell-mediated model of oral tolerance

The role of CD8⁺ T cells in oral tolerance remains unclear. To address this, we developed a model to induce CD8⁺ Tregs by feeding the major histocompatibility complex class I immunodominant epitope of OVA, OVA_(257–264). OVA_(257–264) feeding induced tolerance similar to that observed in OVA protein-fed mice, capable of suppressing the production of Th1 and Th17 cytokines and inhibiting a Th1-driven delayed-type hypersensitivity response following immunization with whole OVA (wOVA) protein. OVA_(257–264) peptide-induced suppression could be transferred to naive mice with CD8⁺ cells, but not CD8-depleted cells, isolated from mesenteric lymph nodes of peptide-fed mice. Interestingly, while capable of inhibiting Th1 and Th17 responses, OVA_(257–264) feeding could not suppress any feature of a Th2 inflammatory response, though OVA protein feeding could, suggesting that these cells function through a different mechanism than their CD4⁺ counterparts generated in response to feeding with wOVA. Thus, CD8⁺ T cells are functionally capable of mediating tolerance to Th1 and Th17 responses.     

Neonatal lung immune responses show a shift of cytokines and transcription factors toward Th2 and a deficit in conventional and plasmacytoid dendritic cells

The high incidence of lung‐damaging life‐threatening respiratory infections in infants may be related to the immaturity of their immune systems. To determine whether lung immune features differ in early life compared with those in adulthood, whole lung as well as lung T lymphocyte and DC responses were investigated in BALB/c neonates versus adults. Higher expression of GATA‐3 and rapid and sustained production of type 2 cytokines by lung explants after in vitro exposure to anti‐CD3 was the hallmark of the neonatal period, suggestive of a Th2 bias. Neonatal lung GATA‐3‐producing cells were identified as CD3⁺, CD4 and CD8 double‐negative T lymphocytes, a subset found at a higher frequency in neonatal than adult lung. The neonatal lungs contained fewer conventional DCs, with a lower ratio of CD103⁺ to CD11b⁺ DCs, and a much lower number of plasmacytoid DCs in comparison with adult lungs. Yet, when stimulated in vivo by BCG, neonatal lung DCs matured and primed adult naïve CD4⁺ T cells toward Th1 as efficiently as adult BCG‐primed lung DCs. Conversely, both adult and neonatal BCG‐primed lung DCs induced a Th2 cytokine response from neonatal naïve lymph node T cells, suggestive of an intrinsic feature of neonatal T lymphocytes.     

Lymph-borne CD8α+ dendritic cells are uniquely able to cross-prime CD8+ T cells with antigen acquired from intestinal epithelial cells

Cross-presentation of cellular antigens is crucial for priming CD8⁺ T cells, and generating immunity to intracellular pathogens—particularly viruses. It is unclear which intestinal phagocytes perform this function in vivo. To address this, we examined dendritic cells (DCs) from the intestinal lymph of IFABP-tOVA 232-4 mice, which express ovalbumin in small intestinal epithelial cells (IECs). Among lymph DCs (LDCs) only CD103⁺ CD11b⁻ CD8α⁺ DCs cross-present IEC-derived ovalbumin to CD8⁺ OT-I T cells. Similarly, in the mesenteric lymph nodes (MLNs), cross-presentation of IEC–ovalbumin was limited to the CD11c⁺ MHCII^hi CD8α⁺ migratory DCs, but absent from all other subsets, including the resident CD8α^hi DCs. Crucially, delivery of purified CD8α⁺ LDCs, but not other LDC subsets, into the MLN subcapsular lymphatic sinus induced proliferation of ovalbumin-specific, gut-tropic CD8⁺ T cells in vivo. Finally, in 232-4 mice treated with R848, CD8α⁺ LDCs were uniquely able to cross-prime interferon γ-producing CD8⁺ T cells and drive their migration to the intestine. Our results clearly demonstrate that migrating CD8α⁺ intestinal DCs are indispensable for cross-presentation of cellular antigens and, in conditions of inflammation, for the initial differentiation of effector CD8⁺ T cells. They may therefore represent an important target for the development of antiviral vaccinations.     

1,25‐dihydroxyvitamin D3‐induced dendritic cells suppress experimental autoimmune encephalomyelitis by increasing proportions of the regulatory lymphocytes and reducing T helper type 1 and type 17 cells

Dendritic cells (DCs), a bridge for innate and adaptive immune responses, play a key role in the development of multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE), an animal model for MS. Administration of tolerogenic DCs has been used as an immunotherapy in autoimmune diseases. Deficiency of vitamin D is an environmental risk factor of MS. In this study, we induced tolerogenic DCs by 1,25‐dihydroxyvitamin D₃ and transferred the tolerogenic DCs (VD₃‐DCs) into EAE mice by adoptive transfer. We found that VD₃‐DCs inhibited the infiltrations of T helper type 1 (Th1) and Th17 cells into spinal cord and increased the proportions of regulatory T cells (CD4⁺ CD25⁺ Foxp3⁺), CD4⁺ IL‐10⁺ T cells and regulatory B cells (CD19⁺ CD5⁺ CD1d⁺) in peripheral immune organs, which resulted in attenuated EAE. However, the proportions of T helper type 1 (Th1) and Th17 cells in spleen and lymph nodes and the levels of pro‐inflammatory cytokines and IgG in serum also increased after transfer of VD₃‐DCs. We conclude that transfer of VD₃‐DCs suppressed EAE by increasing proportions of regulatory T cells, CD4⁺ IL‐10⁺ T cells and regulatory B cells in spleen and reducing infiltration of Th1 and Th17 cells into spinal cord, which suggests a possible immunotherapy method using VD₃‐DCs in MS.     

Mapping of the lingual immune system reveals the presence of both regulatory and effector CD4+ T cells

Background Sublingual immunotherapy (SLIT) is safe and reduces both symptoms and medication requirements in patients with type I respiratory allergies. Nonetheless, immune mechanisms underlying SLIT need to be further documented. Objective A detailed characterization of the lingual immune system was undertaken in mice, to investigate the presence of tolerogenic and pro‐inflammatory mechanisms. Methods Immune cells were characterized in lingual tissues from BALB/c mice using immunohistology and flow cytometry. Resident CD4⁺ T cells were sorted and toll‐like receptor (TLR) expression profiles as well as functional characterization were assessed by RT‐PCR, T cell suppressive assays and cytokine gene expression, respectively. Results Eosinophils and mast cells were only detected in submucosal tissues. No NK, NK‐T, γ/δ, CD8⁺ T cells, nor B‐lymphocytes were detected. Potential antigen presenting cells include various subsets of dendritic cells (CD207⁺ Langerhans cells, CD11b⁺CD11c⁺ myeloid cells and 120G8⁺ plasmacytoid DCs) together with F4/80⁺ macrophages. Noteworthy, both CD103^? and CD103⁺ CD4⁺ T cells expressing TLR2 and TLR4 receptors are present along the lamina propria, in vicinity of myeloid CD11b⁺CD11c^± dendritic cells. Such resident lingual CD4⁺ T lymphocytes comprise both suppressive T cells as well as cells with memory/effector functions (i.e. expressing IFNγ, IL4, IL10 and IL17 genes following stimulation), irrespective of the presence of the mucosal addressing marker CD103. Conclusion The sublingual route is pertinent to induce antigen‐specific tolerance, due to (i) limited numbers of pro‐inflammatory cells, rather located in submucosal tissues, (ii) co‐localization of APCs and resident CD4⁺ T cells with regulatory functions. Since the oral immune system can also elicit pro‐inflammatory effector responses, the cytokine milieu in which allergens are presented by sublingual APCs needs to be controlled during immunotherapy (e.g. with adjuvants) in order to favour tolerance over inflammation.     

IL-36 cytokines imprint a colitogenic phenotype on CD4+ T helper cells

IL-36 cytokines are emerging as potent orchestrators of intestinal inflammation and are being implicated in the pathogenesis of inflammatory bowel diseases (IBD). However, the mechanisms through which these cytokines mediate these effects remain to be fully uncovered. Here, we report specifically elevated expression of IL-36α, and not IL-36β or IL-36γ in the serum of newly diagnosed, treatment naïve, paediatric IBD patients and identify T cells as primary cellular mediators of IL-36 responses in the inflamed gut. IL-36R expression on CD4⁺ T cells was found to promote intestinal pathology in a murine model of colitis. Consistent with these effects, IL-36R can act as a potent instructor of CD4⁺ T cell differentiation in vivo, enhancing Th1 responses, while inhibiting the generation of Tregs. In addition, loss of IL-36 responsiveness significantly reduced the migration of pathogenic CD4⁺ T cells towards intestinal tissues and IL-36 was found to act, uniquely among IL-1 family members, to induce the expression of gut homing receptors in proinflammatory murine and human CD4⁺ T cells. These data reveal an important role for IL-36 cytokines in driving the colitogenic potential of CD4⁺ T cells and identify a new mechanism through which they may contribute to disease pathogenesis.