CXCL4 is a novel inducer of human Th17 cells and correlates with IL‐17 and IL‐22 in psoriatic arthritis

CXCL4 regulates multiple facets of the immune response and is highly upregulated in various Th17‐associated rheumatic diseases. However, whether CXCL4 plays a direct role in the induction of IL‐17 production by human CD4⁺ T cells is currently unclear. Here, we demonstrated that CXCL4 induced human CD4⁺ T cells to secrete IL‐17 that co‐expressed IFN‐γ and IL‐22, and differentiated naïve CD4⁺ T cells to become Th17‐cytokine producing cells. In a co‐culture system of human CD4⁺ T cells with monocytes or myeloid dendritic cells, CXCL4 induced IL‐17 production upon triggering by superantigen. Moreover, when monocyte‐derived dendritic cells were differentiated in the presence of CXCL4, they orchestrated increased levels of IL‐17, IFN‐γ, and proliferation by CD4⁺ T cells. Furthermore, the CXCL4 levels in synovial fluid from psoriatic arthritis patients strongly correlated with IL‐17 and IL‐22 levels. A similar response to CXCL4 of enhanced IL‐17 production by CD4⁺ T cells was also observed in patients with psoriatic arthritis. Altogether, we demonstrate that CXCL4 boosts pro‐inflammatory cytokine production especially IL‐17 by human CD4⁺ T cells, either by acting directly or indirectly via myeloid antigen presenting cells, implicating a role for CXCL4 in PsA pathology.     

Emergence of a distinct HIV‐specific IL‐10‐producing CD8+ T‐cell subset with immunomodulatory functions during chronic HIV‐1 infection

Interleukin‐10 (IL‐10) plays a key role in regulating proinflammatory immune responses to infection but can interfere with pathogen clearance. Although IL‐10 is upregulated throughout HIV‐1 infection in multiple cell subsets, whether this is a viral immune evasion strategy or an appropriate response to immune activation is unresolved. Analysis of IL‐10 production at the single cell level in 51 chronically infected subjects (31 antiretroviral (ART) naïve and 20 ART treated) showed that a subset of CD8⁺ T cells with a CD25^neg FoxP3^neg phenotype contributes substantially to IL‐10 production in response to HIV‐1 gag stimulation. The frequencies of gag‐specific IL‐10‐ and IFN‐γ‐producing T cells in ART‐naïve subjects were strongly correlated and the majority of these IL‐10⁺ CD8⁺ T cells co‐produced IFN‐γ; however, patients with a predominant IL‐10⁺/IFN‐γ^neg profile showed better control of viraemia. Depletion of HIV‐specific CD8⁺ IL‐10⁺ cells from PBMCs led to upregulation of CD38 on CD14⁺ monocytes together with increased IL‐6 production, in response to gag stimulation. Increased CD38 expression was positively correlated with the frequency of the IL‐10⁺ population and was also induced by exposure of monocytes to HIV‐1 in vitro. Production of IL‐10 by HIV‐specific CD8⁺ T cells may represent an adaptive regulatory response to monocyte activation during chronic infection.     

Mycobacterium tuberculosis RpfE promotes simultaneous Th1‐ and Th17‐type T‐cell immunity via TLR4‐dependent maturation of dendritic cells

Reciprocal induction of the Th1 and Th17 immune responses is essential for optimal protection against Mycobacterium tuberculosis (Mtb); however, only a few Mtb antigens are known to fulfill this task. A functional role for resuscitation‐promoting factor (Rpf) E, a latency‐associated member of the Rpf family, in promoting naïve CD4⁺ T‐cell differentiation toward both Th1 and Th17 cell fates through interaction with dendritic cells (DCs) was identified in this study. RpfE induces DC maturation by increasing expression of surface molecules and the production of IL‐6, IL‐1β, IL‐23p19, IL‐12p70, and TNF‐α but not IL‐10. This induction is mediated through TLR4 binding and subsequent activation of ERK, p38 MAPKs, and NF‐κB signaling. RpfE‐treated DCs effectively caused naïve CD4⁺ T cells to secrete IFN‐γ, IL‐2, and IL‐17A, which resulted in reciprocal expansions of the Th1 and Th17 cell response along with activation of T‐bet and RORγt but not GATA‐3. Furthermore, lung and spleen cells from Mtb‐infected WT mice but not from TLR4^?/? mice exhibited Th1 and Th17 polarization upon RpfE stimulation. Taken together, our data suggest that RpfE has the potential to be an effective Mtb vaccine because of its ability to activate DCs that simultaneously induce both Th1‐ and Th17‐polarized T‐cell expansion.     

T‐bet is essential for Th1‐mediated,but not Th17‐mediated,CNS autoimmune disease

T cells that produce both IL‐17 and IFN‐γ, and co‐express ROR‐γt and T‐bet, are often found at sites of autoimmune inflammation. However, it is unknown whether this co‐expression of T‐bet with ROR‐γt is a prerequisite for immunopathology. We show here that T‐bet is not required for the development of Th17‐driven experimental autoimmune encephalomyelitis (EAE). The disease was not impaired in T‐bet^?/? mice and was associated with low IFN‐γ production and elevated IL‐17 production among central nervous system (CNS) infiltrating CD4⁺ T cells. T‐bet^?/? Th17 cells generated in the presence of IL‐6/TGF‐β/IL‐1 and IL‐23 produced GM‐CSF and high levels of IL‐17 and induced disease upon transfer to naïve mice. Unlike their WT counterparts, these T‐bet^?/– Th17 cells did not exhibit an IL‐17→IFN‐γ switch upon reencounter with antigen in the CNS, indicating that this functional change is not critical to disease development. In contrast, T‐bet was absolutely required for the pathogenicity of myelin‐responsive Th1 cells. T‐bet‐deficient Th1 cells failed to accumulate in the CNS upon transfer, despite being able to produce GM‐CSF. Therefore, T‐bet is essential for establishing Th1‐mediated inflammation but is not required to drive IL‐23‐induced GM‐CSF production, or Th17‐mediated autoimmune inflammation.     

Induction, function and regulation of IL-17-producing T cells

Recent reports have provided convincing evidence that IL‐17‐producing T cells play a key role in the pathogenesis of organ‐specific autoimmune diseases, a function previously attributed exclusively to IFN‐γ‐secreting Th1 cells. Furthermore, it appears that IL‐17‐producing T cells can also function with Th1 cells to mediate protective immunity to pathogens. Although much of the focus has been on IL‐17‐secreting CD4⁺ T cells, termed Th17 cells, CD8⁺ T cells, γδ T cells and NKT cells are also capable of secreting IL‐17. The differentiation of Th17 cells from naïve T cells appears to involve signals from TGF‐β, IL‐6, IL‐21, IL‐1β and IL‐23. Furthermore, IL‐1α or IL‐1β in synergy with IL‐23 can promote IL‐17 secretion from memory T cells. The induction or function of Th17 cells is regulated by cytokines secreted by the other major subtypes of T cells, including IFN‐γ, IL‐4, IL‐10 and at high concentrations, TGF‐β. The main function of IL‐17‐secreting T cells is to mediate inflammation, by stimulating production of inflammatory cytokines, such as TNF‐α, IL‐1β and IL‐6, and inflammatory chemokines that promote the recruitment of neutrophils and macrophages.     

IFN‐γ‐producing NKT cells exacerbate sepsis by enhancing C5a generation via IL‐10‐mediated inhibition of CD55 expression on neutrophils

A role for NKT cells has been implicated in sepsis, but the mechanism by which NKT cells contribute to sepsis remains unclear. Here, we examined WT and NKT‐cell‐deficient mice of C57BL/6 background during cecal ligation and puncture‐induced sepsis. The levels of C5a, IFN‐γ, and IL‐10 were higher in the serum and peritoneal fluid of WT mice than in those of CD1d^?/? mice, while the mortality rate was lower in CD1d^?/? mice than in WT mice. C5a blockade decreased mortality of WT mice during sepsis, whereas it did not alter that of CD1d^?/? mice. As assessed by intracellular staining, NKT cells expressed IFN‐γ, while neutrophils expressed IL‐10. Upon coculture, IL‐10‐deficient NKT cells enhanced IL‐10 production by WT, but not IFN‐γR‐deficient, neutrophils. Meanwhile, CD1d^?/? mice exhibited high CD55 expression on neutrophils during sepsis, whereas those cells from WT mice expressed minimal levels of CD55. Recombinant IL‐10 administration into CD1d^?/? mice reduced CD55 expression on neutrophils. Furthermore, adoptive transfer of sorted WT, but not IFN‐γ‐deficient, NKT cells into CD1d^?/? mice suppressed CD55 expression on neutrophils, but increased IL‐10 and C5a levels. Taken together, IFN‐γ‐producing NKT cells enhance C5a generation via IL‐10‐mediated inhibition of CD55 expression on neutrophils, thereby exacerbating sepsis.     

mTORC2 regulates multiple aspects of NKT‐cell development and function

Invariant NKT (iNKT) cells bridge innate and adaptive immunity by rapidly secreting cytokines and lysing targets following TCR recognition of lipid antigens. Based on their ability to secrete IFN‐γ, IL‐4 and IL‐17A, iNKT‐cells are classified as NKT‐1, NKT‐2, and NKT‐17 subsets, respectively. The molecular pathways regulating iNKT‐cell fate are not fully defined. Recent studies implicate Rictor, a required component of mTORC2, in the development of select iNKT‐cell subsets, however these reports are conflicting. To resolve these questions, we used Rictor^fl/fl CD4cre⁺ mice and found that Rictor is required for NKT‐17 cell development and normal iNKT‐cell cytolytic function. Conversely, Rictor is not absolutely required for IL‐4 and IFN‐γ production as peripheral iNKT‐cells make copious amounts of these cytokines. Overall iNKT‐cell numbers are dramatically reduced in the absence of Rictor. We provide data indicating Rictor regulates cell survival as well as proliferation of developing and mature iNKT‐cells. Thus, mTORC2 regulates multiple aspects of iNKT‐cell development and function.     

ICOS cooperates with CD28, IL-2, and IFN-gamma and modulates activation of human naïve CD4+ T cells

Several sets of data indicate that ICOS regulates cytokine production in activated T cells, but is less effective on naïve T cells. This work evaluates ICOS function in human naïve CD4⁺ T cells through an assessment of the effect of soluble forms of the ICOS and CD28 physiological ligands on activation driven by anti‐CD3 mAb. ICOS strikingly potentiated secretion of IL‐2, IFN‐γ, IL‐10, and TNF‐α, but not IL‐4, promoted by optimal stimulation of CD3+CD28, and it was the key switching‐factor of activation when cells received suboptimal stimulation of CD3+CD28 or stimulation of CD3 alone in the presence of exogenous IL‐2. In these conditions, blockade of IL‐2 and IFN‐γ showed that ICOS builds up a positive feedback loop with IFN‐γ, which required IL‐2 and was inhibited by IL‐4. By contrast, in the absence of CD28 triggering or exogenous IL‐2, ICOS‐induced costimulation mainly supported expression of TGF‐β1 and FoxP3 and differentiation of regulatory T cells capable to inhibit proliferation of naïve CD4⁺ T cells driven by allogeneic cells. These data suggest that ICOS favors differentiation of Th effector cells when cooperates with appropriate activation stimuli such as CD3+CD28 or CD3+IL‐2, whereas it supports differentiation of regulatory T cells when costimulatory signals are insufficient.     

Antigen-activated T cells induce IL-12p75 production from dendritic cells in an IFN-γ-independent manner

The addition of IL‐12p75 to naïve CD4⁺ T cells promotes their differentiation towards a T_H1‐type cytokine pattern. Dendritic cells stimulated by LPS generate IL‐12p75, but only if the environment also contains IFN‐γ. Thus, it appears that IFN‐γ is needed to start the response that will result in further production of IFN‐γ. We previously reported that paradoxically DCs produce IL‐12p75 only after engaging primed, but not naïve T cells. This study examines the mechanism by which primed T cells trigger IL‐12p75 secretion and asks whether this induction is also dependent on the presence of IFN‐γ. Here, we show that, in contrast to LPS, primed T cells induce IL‐12p75 in an IFN‐γ‐independent manner. Addition of rIFN‐γ to cocultures of naïve T cells with DCs did not induce IL‐12p75. Moreover, antigen‐activated CD4⁺ T cells from wild type or IFN‐γ‐deficient mice both initiated IL‐12p75 production from DCs. Surprisingly, we found that synergies between three T‐cell‐derived factors – CD40 Ligand, IL‐4 and GM‐CSF – were necessary and sufficient for IL‐12p75 production. These results suggest that there are at least two distinct pathways for IL‐12p75 production in vivo. Furthermore, the T‐cell‐dependent pathway of IL‐12p75 production employs molecules that are not classically associated with a T_H1‐type response.     

Type I cytokine profiles of human naïve and memory B lymphocytes: a potential for memory cells to impact polarization

B cells bifurcating along ‘type 1’ or ‘type 2’ pathways under the influence of polarizing cytokines can, in turn, influence the direction of an immune response. Here, we compare the capacity of human B cells residing within naïve and memory compartments to participate in type 1 polarizing responses. B‐cell receptor (BCR) engagement provided the main signal for interleukin (IL)‐12Rβ1 expression in the two subsets: this was potentiated by CD154 together with interferon‐γ (IFN‐γ) but inhibited by IL‐12. IL‐12Rβ2 could be induced on a minority of B cells by the same signals, and also by IFN‐γ alone. WSX‐1, a receptor for IL‐27, was expressed in both subsets with no evidence for its regulation by the signals studied. While neither subset was capable of secreting much IL‐12 p70, memory B cells could produce a small amount of IL‐12 p40 on CD40 ligation. Memory B cells also, exclusively, expressed IL‐23 p19 mRNA on BCR triggering. Importantly, products of appropriately stimulated memory – but not naive – B cells were shown to promote the synthesis of IFN‐γ in uncommitted T‐helper cells. The data indicate an equal capacity for naïve and memory B cells to respond within a type 1 polarizing environment. Although poorly equipped for initiating type 1 responses, B cells – by virtue of the memory subset – reveal a capacity for their maintenance and amplification following T‐dependent signalling.     

Th17‐related cytokines contribute to recall‐like expansion/effector function of HMBPP‐specific Vγ2Vδ2 T cells after Mycobacterium tuberculosis infection or vaccination

Whether cytokines can influence the adaptive immune response by antigen‐specific γδ T cells during infections or vaccinations remains unknown. We previously demonstrated that, during BCG/Mycobacterium tuberculosis (Mtb) infections, Th17‐related cytokines markedly upregulated when phosphoantigen‐specific Vγ2Vδ2 T cells expanded. In this study, we examined the involvement of Th17‐related cytokines in the recall‐like responses of Vγ2Vδ2 T cells following Mtb infection or vaccination against TB. Treatment with IL‐17A/IL‐17F or IL‐22 expanded phosphoantigen 4‐hydroxy‐3‐methyl‐but‐enyl pyrophosphate (HMBPP)‐stimulated Vγ2Vδ2 T cells from BCG‐vaccinated macaques but not from naïve animals, and IL‐23 induced greater expansion than the other Th17‐related cytokines. Consistently, Mtb infection of macaques also enhanced the ability of IL‐17/IL‐22 or IL‐23 to expand HMBPP‐stimulated Vγ2Vδ2 T cells. When evaluating IL‐23 signaling as a prototype, we found that HMBPP/IL‐23‐expanded Vγ2Vδ2 T cells from macaques infected with Mtb or vaccinated with BCG or Listeria ΔactA prfA*‐ESAT6/Ag85B produced IL‐17, IL‐22, IL‐2, and IFN‐γ. Interestingly, HMBPP/IL‐23‐induced production of IFN‐γ in turn facilitated IL‐23‐induced expansion of HMBPP‐activated Vγ2Vδ2 T cells. Furthermore, HMBPP/IL‐23‐induced proliferation of Vγ2Vδ2 T cells appeared to require APC contact and involve the conventional and novel protein kinase C signaling pathways. These findings suggest that Th17‐related cytokines can contribute to recall‐like expansion and effector function of Ag‐specific γδ T cells after infection or vaccination.     

Cytokine‐dependent regulation of dendritic cell differentiation in the splenic microenvironment

The DC‐derived chemokine CCL17, a ligand of CCR4, has been shown to promote various inflammatory diseases such as atopic dermatitis, atherosclerosis, and inflammatory bowel disease. Under steady‐state conditions, and even after systemic stimulation with LPS, CCL17 is not expressed in resident splenic DCs as opposed to CD8α^?CD11b⁺ LN DCs, which produce large amounts of CCL17 in particular after maturation. Upon systemic NKT cell activation through α‐galactosylceramide stimulation however, CCL17 can be upregulated in both CD8α^? and CD8α⁺ splenic DC subsets and enhances cross‐presentation of exogenous antigens. Based on genome‐wide expression profiling, we now show that splenic CD11b⁺ DCs are susceptible to IFN‐γ‐mediated suppression of CCL17, whereas LN CD11b⁺CCL17⁺ DCs downregulate the IFN‐γR and are much less responsive to IFN‐γ. Under inflammatory conditions, particularly in the absence of IFN‐γ signaling in IFN‐γRKO mice, CCL17 expression is strongly induced in a major proportion of splenic DCs by the action of GM‐CSF in concert with IL‐4. Our findings demonstrate that the local cytokine milieu and differential cytokine responsiveness of DC subsets regulate lymphoid organ specific immune responses at the level of chemokine expression.     

IL‐33 attenuates the development of experimental autoimmune uveitis

Interleukin‐33 (IL‐33) is associated with several important immune‐mediated disorders. However, its role in uveitis, an important eye inflammatory disease, is unknown. Here, we investigated the function of IL‐33 in the development of experimental autoimmune uveitis (EAU). IL‐33 and IL‐33 receptor (ST2) were expressed in murine retinal pigment epithelial (RPE) cells in culture, and IL‐33 increased the expression of Il33 and Mcp1 mRNA in RPE cells. In situ, IL‐33 was highly expressed in the inner nuclear cells of the retina of naïve mice, and its expression was elevated in EAU mice. ST2‐deficient mice developed exacerbated EAU compared with WT mice, and administration of IL‐33 to WT mice significantly reduced EAU severity. The attenuated EAU in IL‐33‐treated mice was accompanied by decreased frequency of IFN‐γ⁺ and IL‐17⁺ CD4⁺ T cells and reduced IFN‐γ and IL‐17 production but with increased frequency of IL‐5⁺ and IL‐4⁺ CD4 T cells and IL‐5 production in the draining lymph node and spleen. Macrophages from the IL‐33‐treated mice show a significantly higher polarization toward an alternatively activated macrophage phenotype. Our results therefore demonstrate that the endogenous IL‐33/ST2 pathway plays an important role in EAU, and suggest that IL‐33 represents a potential option for treatment of uveitis.     

TGF‐β indirectly favors the development of human Th17 cells by inhibiting Th1 cells

Human Th17 clones and circulating Th17 cells showed lower susceptibility to the anti‐proliferative effect of TGF‐β than Th1 and Th2 clones or circulating Th1‐oriented T cells, respectively. Accordingly, human Th17 cells exhibited lower expression of clusterin, and higher Bcl‐2 expression and reduced apoptosis in the presence of TGF‐β, in comparison with Th1 cells. Umbilical cord blood naïve CD161⁺CD4⁺ T cells, which contain the precursors of human Th17 cells, differentiated into IL‐17A‐producing cells only in response to IL‐1β plus IL‐23, even in serum‐free cultures. TGF‐β had no effect on constitutive RORγt expression by umbilical cord blood CD161⁺ T cells but it increased the relative proportions of CD161⁺ T cells differentiating into Th17 cells in response to IL‐1β plus IL‐23, whereas under the same conditions it inhibited both T‐bet expression and Th1 development. These data suggest that TGF‐β is not critical for the differentiation of human Th17 cells, but indirectly favors their expansion because Th17 cells are poorly susceptible to its suppressive effects.     

Enrichment of IL‐17A+IFN‐γ+ and IL‐22+IFN‐γ+ T cell subsets is associated with reduction of NKp44+ILC3s in the terminal ileum of Crohn's disease patients

Crohn's disease (CD) is a chronic inflammatory condition of the human gastrointestinal tract whose aetiology remains largely unknown. Dysregulated adaptive immune responses and defective innate immunity both contribute to this process. In this study, we demonstrated that the interleukin (IL)‐17A⁺interferon (IFN)‐γ⁺ and IL‐22⁺IFN‐γ⁺ T cell subsets accumulated specifically in the inflamed terminal ileum of CD patients. These cells had higher expression of Ki‐67 and were active cytokine producers. In addition, their proportions within both the IL‐17A‐producer and IL‐22‐producer populations were increased significantly. These data suggest that IL‐17A⁺IFN‐γ⁺ and IL‐22⁺IFN‐γ⁺ T cell subsets might represent the pathogenic T helper type 17 (Th17) population in the context of intestinal inflammation for CD patients. In the innate immunity compartment we detected a dramatic alteration of both phenotype and function of the intestinal innate lymphoid cells (ILCs), that play an important role in the maintenance of mucosal homeostasis. In the inflamed gut the frequency of the NKp44^–CD117^–ILC1s subset was increased significantly, while the frequency of NKp44⁺ILC3s was reduced. Furthermore, the frequency of human leucocyte antigen D‐related (HLA‐DR)‐expressing‐NKp44⁺ILC3s was also reduced significantly. Interestingly, the decrease in the NKp44⁺ILC3s population was associated with an increase of pathogenic IL‐17A⁺IFN‐γ⁺ and IL‐22⁺IFN‐γ⁺ T cell subsets in the adaptive compartment. This might suggest a potential link between NKp44⁺ILC3s and the IL‐17A⁺IFN‐γ⁺ and IL‐22⁺IFN‐γ⁺ T cell subsets in the terminal ileum of CD patients.     

BJ‐2266 ameliorates experimental autoimmune encephalomyelitis through down‐regulation of the JAK/STAT signaling pathway

CD4⁺ T cells differentiate into distinct effector subsets upon antigenic stimulation. Cytokines, and micro‐environmental factors present during T‐cell priming, direct differentiation of naïve CD4⁺ T cells into pro‐inflammatory Th1 and Th17 cells. From extensive screening of 2,4,5‐trimethylpyridin‐3‐ol derivatives with various functional groups at C(6)‐position, BJ‐2266, a 6‐thioureido‐derivative, showed potent inhibitory activity on in vitro T helper (Th)‐cell differentiation. This compound inhibited IFN‐γ and IL‐17 production from polyclonal CD4⁺ T cells and ovalbumin (OVA)‐specific CD4⁺ T cells that were activated by T‐cell receptor (TCR) engagement. We assessed the inhibitory effect of BJ‐2266 in experimental autoimmune encephalomyelitis (EAE). Our results suggest that BJ‐2266 treatment significantly suppresses EAE disease progression with reduced generation of Th1 and Th17 cells. Notably, Th‐cell differentiation was significantly suppressed by BJ‐2266 treatment with no effect on apoptosis, activation and proliferation of activated T cells. Furthermore, adoptive transfer of BJ‐2266 treated MOG‐reactive Th1 and Th17 cells led to a lower EAE disease score and better clinical recovery from EAE. The underlying mechanism of BJ‐2266 effect involved the inhibition of JAK/STAT phosphorylation that is critical for Th‐cell differentiation. We conclude that BJ‐2266 regulates the JAK/STAT pathway in response to cytokine signals and subsequently suppresses the differentiation of Th‐cell responses.