Differential control of CD4+ T‐cell subsets by the PD‐1/PD‐L1 axis in a mouse model of allergic asthma

Studies examining the role of PD‐1 family members in allergic asthma have yielded conflicting results. Using a mouse model of allergic asthma, we demonstrate that blockade of PD‐1/PD‐L1 has distinct influences on different CD4⁺ T‐cell subsets. PD‐1/PD‐L1 blockade enhances airway hyperreactivity (AHR), not by altering the magnitude of the underlying Th2‐type immune response, but by allowing the development of a concomitant Th17‐type immune response. Supporting differential CD4⁺ T‐cell responsiveness to PD‐1‐mediated inhibition, naïve PD‐1^?/? mice displayed elevated Th1 and Th17 levels, but diminished Th2 cytokine levels, and ligation of PD‐1 in WT cells limited cytokine production by in vitro polarized Th1 and Th17 cells, but slightly enhanced cytokine production by in vitro polarized Th2 cells. Furthermore, PD‐1 ligation enhanced Th2 cytokine production by naïve T cells cultured under nonpolarizing conditions. These data demonstrate that different CD4⁺ T‐cell subsets respond differentially to PD‐1 ligation and may explain some of the variable results observed in control of allergic asthma by the PD‐1 family members. As the PD‐1/PD‐L1 axis limits asthma severity by constraining Th17 cell activity, this suggests that severe allergic asthma may be associated with a defective PD‐1/PD‐L1 regulatory axis in some individuals.     

HIV‐1 impairs in vitro priming of naïve T cells and gives rise to contact‐dependent suppressor T cells

Priming of T cells in lymphoid tissues of HIV‐infected individuals occurs in the presence of HIV‐1. DC in this milieu activate T cells and disseminate HIV‐1 to newly activated T cells, the outcome of which may have serious implications in the development of optimal antiviral responses. We investigated the effects of HIV‐1 on DC–naïve T‐cell interactions using an allogeneic in vitro system. Our data demonstrate a dramatic decrease in the primary expansion of naïve T cells when cultured with HIV‐1‐exposed DC. CD4⁺ and CD8⁺ T cells showed enhanced expression of PD‐1 and TRAIL, whereas CTLA‐4 expression was observed on CD4⁺ T cells. It is worth noting that T cells primed in the presence of HIV‐1 suppressed priming of other naïve T cells in a contact‐dependent manner. We identified PD‐1, CTLA‐4, and TRAIL pathways as responsible for this suppresion, as blocking these negative molecules restored T‐cell proliferation to a higher degree. In conclusion, the presence of HIV‐1 during DC priming produced cells with inhibitory effects on T‐cell activation and proliferation, i.e. suppressor T cells, a mechanism that could contribute to the enhancement of HIV‐1 pathogenesis.     

Programmed death (PD)‐1 molecule and its ligand PD‐L1 distribution among memory CD4 and CD8 T cell subsets in human immunodeficiency virus‐1‐infected individuals

Human immunodeficiency virus (HIV)‐1 causes T cell anergy and affects T cell maturation. Various mechanisms are responsible for impaired anti‐HIV‐1‐specific responses: programmed death (PD)‐1 molecule and its ligand PD‐L1 are negative regulators of T cell activity and their expression is increased during HIV‐1 infection. This study examines correlations between T cell maturation, expression of PD‐1 and PD‐L1, and the effects of their blockade. Peripheral blood mononuclear cells (PBMC) from 24 HIV‐1⁺ and 17 uninfected individuals were phenotyped for PD‐1 and PD‐L1 expression on CD4⁺ and CD8⁺ T cell subsets. The effect of PD‐1 and PD‐L1 blockade on proliferation and interferon (IFN)‐γ production was tested on eight HIV‐1⁺ patients. Naive (CCR7⁺CD45RA⁺) CD8⁺ T cells were reduced in HIV‐1 aviraemic (P = 0·0065) and viraemic patients (P = 0·0130); CD8 T effector memory subsets [CCR7^‐CD45RA^–(T_EM)] were increased in HIV‐1⁺ aviraemic (P = 0·0122) and viraemic (P = 0·0023) individuals versus controls. PD‐1 expression was increased in CD4 naive (P = 0·0496), central memory [CCR7⁺CD45RA^– (T_CM); P = 0·0116], T_EM (P = 0·0037) and CD8 naive T cells (P = 0·0133) of aviraemic HIV‐1⁺versus controls. PD‐L1 was increased in CD4 T_EMRA (CCR7^‐CD45RA⁺, P = 0·0119), CD8 T_EM (P = 0·0494) and CD8 T_EMRA (P = 0·0282) of aviraemic HIV‐1⁺versus controls. PD‐1 blockade increased HIV‐1‐specific proliferative responses in one of eight patients, whereas PD‐L1 blockade restored responses in four of eight patients, but did not increase IFN‐γ‐production. Alteration of T cell subsets, accompanied by increased PD‐1 and PD‐L1 expression in HIV‐1 infection contributes to anergy and impaired anti‐HIV‐1‐specific responses which are not rescued when PD‐1 is blocked, in contrast to when PD‐L1 is blocked, due possibly to an ability to bind to receptors other than PD‐1.     

Mineralocorticoid receptor signaling reduces numbers of circulating human naïve T cells and increases their CD62L,CCR7, and CXCR4 expression

The role of mineralocorticoid receptors (MRs) in human T‐cell migration is not yet understood. We have recently shown that the MR antagonist spironolactone selectively increases the numbers of circulating naïve and central memory T cells during early sleep, which is the time period in the 24 h cycle hallmarked by predominant MR activation. To investigate whether this effect is specific to spironolactone's blockade of MRs and to study the underlying molecular mechanisms, healthy humans were given the selective MR‐agonist fludrocortisone or placebo and numbers of eight T‐cell subsets and their CD62L and CXCR4 expression were analyzed. Fludrocortisone selectively reduced counts of naïve CD4⁺, central memory CD4⁺, and naïve CD8⁺ T cells and increased CXCR4 expression on the naïve subsets. In complementing in vitro studies, fludrocortisone enhanced CXCR4 and CD62L expression, which was counteracted by spironolactone. Incubation of naïve T cells with spironolactone alone reduced CD62L and CCR7 expression. Our results indicate a regulatory influence of MR signaling on human T‐cell migration and suggest a role for endogenous aldosterone in the redistribution of T‐cell subsets to lymph nodes, involving CD62L, CCR7, and CXCR4. Facilitation of T‐cell homing following sleep‐dependent aldosterone release might thus essentially contribute to sleep's well‐known role in supporting adaptive immunity.     

Cardiolipin activates antigen‐presenting cells via TLR2‐PI3K‐PKN1‐AKT/p38‐NF‐kB signaling to prime antigen‐specific naïve T cells in mice

Mitochondrial defects and antimitochondrial cardiolipin (CL) antibodies are frequently detected in autoimmune disease patients. CL from dysregulated mitochondria activates various pattern recognition receptors, such as NLRP3. However, the mechanism by which mitochondrial CL activates APCs as a damage‐associated molecular pattern to prime antigen‐specific naïve T cells, which is crucial for T‐cell‐dependent anticardiolipin IgG antibody production in autoimmune diseases is unelucidated. Here, we show that CL increases the expression of costimulatory molecules in CD11c⁺ APCs both in vitro and in vivo. CL activates CD11c⁺ APCs via TLR2‐PI3K‐PKN1‐AKT/p38MAPK‐NF‐κB signaling. CD11c⁺ APCs that have been activated by CL are sufficient to prime H‐Y peptide‐specific naïve CD4⁺ T cells and OVA‐specific naïve CD8⁺ T cells. TLR2 is necessary for anti‐CL IgG antibody responses in vivo. Intraperitoneal injection of CL does not activate CD11c⁺ APCs in CD14 KO mice to the same extent as in wild‐type mice. CL binds to CD14 (Kd = 7 × 10^?7 M). CD14, but not MD2, plays a role in NF‐kB activation by CL, suggesting that CD14⁺ macrophages contribute to recognizing CL. In summary, CL activates signaling pathways in CD11c⁺ APCs through a mechanism similar to gram (+) bacteria and plays a crucial role in priming antigen‐specific naïve T cells.     

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.     

DC expressing transgene Foxp3 are regulatory APC

Tolerogenic DC and suppressive Foxp3⁺ Treg play important roles in preventing autoimmunity and allograft rejection. We report that (adenovirus mediated) ectopic expression of Foxp3 in human DC (i.e. DC.Foxp3) yields an APC that severely limits T‐cell proliferation and type‐1 immune responses from the naïve, but not memory, pool of responder T cells in vitro. In marked contrast, the frequencies of type‐2 and Treg responses were dramatically increased after stimulation of naïve T cells with DC.Foxp3 versus control DC. DC.Foxp3‐induced CD4⁺CD25⁺ Treg cells potently suppressed the proliferation of, and IFN‐γ production from, CD4⁺ and CD8⁺ responder T cells. Notably, the immunosuppressive biology of DC.Foxp3 was effectively normalized by addition of 1‐methyl‐tryptophan or neutralizing anti‐TGF‐β1 Ab during the period of T‐cell priming. These data suggest the potential utility of regulatory DC.Foxp3 and/or DC.Foxp3‐induced CD4⁺CD25⁺ Treg as translational agents for the amelioration or prevention of pathology in the setting of allograft transplantation and/or autoimmunity.     

IFN‐γ‐receptor signaling ameliorates transplant vasculopathy through attenuation of CD8+ T‐cell‐mediated injury of vascular endothelial cells

Occlusive transplant vasculopathy (TV) is the major cause for chronic graft rejection. Since endothelial cells (EC) are the first graft cells encountered by activated host lymphocytes, it is important to delineate the molecular mechanisms that coordinate the interaction of EC with activated T cells. Here, the interaction of CD8⁺ T cells with Ag‐presenting EC in vivo was examined using a transgenic heart transplantation model with β‐galactosidase (β‐gal) expression exclusively in EC (Tie2‐LacZ hearts). We found that priming with β‐gal peptide‐loaded DC failed to generate a strong systemic IFN‐γ response, but elicited pronounced TV in both IFN‐γ receptor (IFNGR)‐competent, and ifngr^?/? Tie2‐LacZ hearts. In contrast, stimulation of EC‐specific CD8⁺ T cells with β‐gal‐recombinant mouse cytomegalovirus (MCMV‐LacZ) in recipients of ifngr^+/+ Tie2‐LacZ hearts did not precipitate significant TV. However, MCMV‐LacZ infection of recipients of ifngr^?/? Tie2‐LacZ hearts led to massive activation of β‐gal‐specific CD8 T cells, and led to development of fulminant TV. Further analyses revealed that the strong systemic IFN‐γ “storm” associated with MCMV infection induced upregulation of programmed death‐1 ligand 1 (PD‐L1) on EC, and subsequent attenuation of programmed death‐1 (PD‐1)‐expressing EC‐specific CD8⁺ T cells. Thus, IFNGR signaling in ECs activates a potent peripheral negative feedback circuit that protects vascularized grafts from occlusive TV.     

Increased circulating Tfh17 and PD-1+Tfh cells are associated with autoantibodies in Hashimoto’s thyroiditis

Abstract

Objective: Hashimoto’s thyroiditis (HT) is characterized by autoantibodies targeting the thyroid. Abnormal CD4⁺CXCR5⁺T cell levels were previously shown to be associated with HT. However, Tfh cells consist of heterogeneous subpopulations, and which T follicular helper (Tfh) cell subpopulation participates in the pathogenesis of HT remains poorly understood.

Methods: Thirty healthy controls (HCs) and 52 HT patients were enrolled in the study. The percentages of Tfh, ICOS⁺Tfh, PD1⁺Tfh, Tfh1, Tfh2, Tfh17, effector Tfh, resting Tfh, effector memory Tfh, central memory Tfh, and naïve Tfh cells in the peripheral blood were all determined via flow cytometry, and the associations between the percentages of these cells and thyroid function indices were also investigated.

Results: The percentage of Tfh cells was significantly higher in HT patients than in HCs. Examination of the Tfh cell subsets revealed that the percentages of Tfh1, Tfh2, and resting Tfh cells were significantly decreased, while those of the ICOS⁺Tfh, PD1⁺Tfh, Tfh17, and effector Tfh cells were significantly increased in HT patients. No significant differences in effector memory, central memory or naïve Tfh cell percentages were noted between the HC and HT groups. Furthermore, the percentage of PD1⁺Tfh cells was positively correlated with anti-thyroglobulin antibody levels. Most importantly, only Tfh17 cell percentages were positively correlated with anti-thyroglobulin and anti-thyroid peroxidase antibody levels and were negatively correlated serum free T3 and free T4 levels in HT patients.

Conclusions: Increased circulating Tfh17 cell and PD1⁺Tfh percentages are associated with higher autoantibody levels in HT patients, which imply that Tfh17 or PD1⁺Tfh cells may play a pathogenic role in the development of HT.     

Human rhinoviruses induce IL‐35‐producing Treg via induction of B7‐H1 (CD274) and sialoadhesin (CD169) on DC

IL‐35 is a heterodimer of EBV‐induced gene 3 and of the p35 subunit of IL‐12, and recently identified as an inhibitory cytokine produced by natural Treg in mice, but not in humans. Here we demonstrate that DC activated by human rhinoviruses (R‐DC) induce IL‐35 production and release, as well as a suppressor function in CD4⁺ and CD8⁺ T cells derived from human peripheral blood but not in naïve T cells from cord blood. The induction of IL‐35‐producing T cells by R‐DC was FOXP3‐independent, but blocking of B7‐H1 (CD274) and sialoadhesin (CD169) on R‐DC with mAb against both receptors prevented the induction of IL‐35. Thus, the combinatorial signal delivered by R‐DC to T cells via B7‐H1 and sialoadhesin is crucial for the induction of human IL‐35⁺ Treg. These results demonstrate a novel pathway and its components for the induction of immune‐inhibitory T cells.     

Tumor‐specific CD4+ T cells maintain effector and memory tumor‐specific CD8+ T cells

Immunotherapies that augment antitumor T cells have had recent success for treating patients with cancer. Here we examined whether tumor‐specific CD4⁺ T cells enhance CD8⁺ T‐cell adoptive immunotherapy in a lymphopenic environment. Our model employed physiological doses of tyrosinase‐related protein 1‐specific CD4⁺ transgenic T cells‐CD4⁺ T cells and pmel‐CD8⁺ T cells that when transferred individually were subtherapeutic; however, when transferred together provided significant (p ≤ 0.001) therapeutic efficacy. Therapeutic efficacy correlated with increased numbers of effector and memory CD8⁺ T cells with tumor‐specific cytokine expression. When combined with CD4⁺ T cells, transfer of total (naïve and effector) or effector CD8⁺ T cells were highly effective, suggesting CD4⁺ T cells can help mediate therapeutic effects by maintaining function of activated CD8⁺ T cells. In addition, CD4⁺ T cells had a pronounced effect in the early posttransfer period, as their elimination within the first 3 days significantly (p < 0.001) reduced therapeutic efficacy. The CD8⁺ T cells recovered from mice treated with both CD8⁺ and CD4⁺ T cells had decreased expression of PD‐1 and PD‐1‐blockade enhanced the therapeutic efficacy of pmel‐CD8 alone, suggesting that CD4⁺ T cells help reduce CD8⁺ T‐cell exhaustion. These data support combining immunotherapies that elicit both tumor‐specific CD4⁺ and CD8⁺ T cells for treatment of patients with cancer.     

Terminal complement complex C5b-9-treated human monocyte-derived dendritic cells undergo maturation and induce Th1 polarization

Sublytic C5b‐9 has been described as a pro‐inflammatory mediator that triggers cell activation rather than inducing cell death. Dendritic cells (DC) play a critical role in controlling antigen‐specific immune responses. Although DC maturation induced by various stimuli has been well characterized, the role of C5b‐9 in DC function has not been described. In this report, we use in vitro assembled functional C5b‐9 based on purified distal complement protein to show that DC maturation is promoted by sublytic C5b‐9. This was demonstrated by up‐regulation of CD83, HLA‐antigens and costimulatory molecules, including CD80, D86, B7‐H1, B7‐H3, B7‐H4 and BTLA. In addition, secretion of cytokines such as interleukin (IL)‐12 and tumor necrosis factor‐α was increased while the capacity for antigen uptake (FITC‐Dextran and Lucifer Yellow) was reduced in C5b‐9‐treated DC. Mixed lymphocyte reactions indicated that C5b‐9‐activated DC acted as stimulators that significantly promoted CD4⁺ T cell activation and elicited production of cytokines, including interferon‐γ and IL‐2. Interestingly, C5b‐9‐treated DC also orient CD4⁺CD45RA⁺ naïve T cells toward Th1 polarization. Our results are the first to report that DC are potential immunoregulatory targets of C5b‐9, suggesting that C5b‐9 bridges innate and acquired immunity by inducing DC maturation.     

Efficient and versatile manipulation of the peripheral CD4+ T‐cell compartment by antigen targeting to DNGR‐1/CLEC9A

DC NK lectin group receptor‐1 (DNGR‐1, also known as CLEC9A) is a C‐type lectin receptor expressed by mouse CD8α⁺ DC and by their putative equivalents in human. DNGR‐1 senses necrosis and regulates CD8⁺ T‐cell cross‐priming to dead‐cell‐associated antigens. In addition, DNGR‐1 is a target for selective in vivo delivery of antigens to DC and the induction of CD8⁺ T‐cell and Ab responses. In this study, we evaluated whether DNGR‐1 targeting can be additionally used to manipulate antigen‐specific CD4⁺ T lymphocytes. Injection of small amounts of antigen‐coupled anti‐DNGR‐1 mAb into mice promoted MHC class II antigen presentation selectively by CD8α⁺ DC. In the steady state, this was sufficient to induce proliferation of antigen‐specific naïve CD4⁺ T cells and to drive their differentiation into Foxp3⁺ regulatory lymphocytes. Co‐administration of adjuvants prevented this induction of tolerance and promoted immunity. Notably, distinct adjuvants allowed qualitative modulation of CD4⁺ T‐cell behavior: poly I:C induced a strong IL‐12‐independent Th1 response, whereas curdlan led to the priming of Th17 cells. Thus, antigen targeting to DNGR‐1 is a versatile approach for inducing functionally distinct CD4⁺ T‐cell responses. Given the restricted pattern of expression of DNGR‐1 across species, this strategy could prove useful for developing immunotherapy protocols in humans.     

Targeted loss of SHP1 in murine thymocytes dampens TCR signaling late in selection

SHP1 is a tyrosine phosphatase critical to proximal regulation of TCR signaling. Here, analysis of CD4‐Cre SHP1^fl/fl conditional knockout thymocytes using CD53, TCRβ, CD69, CD4, and CD8α expression demonstrates the importance of SHP1 in the survival of post selection (CD53⁺), single‐positive thymocytes. Using Ca²⁺ flux to assess the intensity of TCR signaling demonstrated that SHP1 dampens the signal strength of these same mature, postselection thymocytes. Consistent with its dampening effect, TCR signal strength was also probed functionally using peptides that can mediate selection of the OT‐I TCR, to reveal increased negative selection mediated by lower‐affinity ligand in the absence of SHP1. Our data show that SHP1 is required for the survival of mature thymocytes and the generation of the functional T‐cell repertoire, as its absence leads to a reduction in the numbers of CD4⁺ and CD8⁺ naïve T cells in the peripheral lymphoid compartments.     

Mesenteric lymph node CD11b− CD103+ PD‐L1High dendritic cells highly induce regulatory T cells

Dendritic cells (DCs) in mesenteric lymph nodes (MLNs) induce Foxp3⁺ regulatory T cells to regulate immune responses to beneficial or non‐harmful agents in the intestine, such as commensal bacteria and foods. Several studies in MLN DCs have revealed that the CD103⁺ DC subset highly induces regulatory T cells, and another study has reported that MLN DCs from programmed death ligand 1 (PD‐L1) ‐deficient mice could not induce regulatory T cells. Hence, the present study investigated the expression of these molecules on MLN CD11c⁺ cells. Four distinct subsets expressing CD103 and/or PD‐L1 were identified, namely CD11b⁺ CD103⁺ PD‐L1^High, CD11b⁻ CD103⁺ PD‐L1^High, CD11b⁻ CD103⁺ PD‐L1^Low and CD11b⁺ CD103⁻ PD‐L1^Int. Among them, the CD11b⁻ CD103⁺ PD‐L1^High DC subset highly induced Foxp3⁺ T cells. This subset expressed Aldh1a2 and Itgb8 genes, which are involved in retinoic acid metabolism and transforming growth factor‐β (TGF‐β) activation, respectively. Exogenous TGF‐β supplementation equalized the level of Foxp3⁺ T‐cell induction by the four subsets whereas retinoic acid did not, which suggests that high ability to activate TGF‐β is determinant for the high Foxp3⁺ T‐cell induction by CD11b⁻ CD103⁺ PD‐L1^High DC subset. Finally, this subset exhibited a migratory DC phenotype and could take up and present orally administered antigens. Collectively, the MLN CD11b⁻ CD103⁺ PD‐L1^High DC subset probably takes up luminal antigens in the intestine, migrates to MLNs, and highly induces regulatory T cells through TGF‐β activation.     

CD40 is necessary for activation of naïve T cells by a dendritic cell line in vivo but not in vitro

The importance of CD40–CD40L interactions during CD4⁺ T‐cell activation has been extensively investigated over the years; however, it still remains questionable whether the interaction is a prerequisite for dendritic cell (DC)‐mediated antigen‐specific priming in vivo. Naïve CD4⁺ T cells require two signals for proper activation and induction of differentiation: signal 1 is provided by peptide antigens in the context of the major histocompatibility complex (MHC) class II, while signal 2 is delivered by costimulatory molecules such as CD80 or CD86 present on the antigen‐presenting cell (APC). It is well known that the expression of CD80/CD86 is upregulated after interaction between CD40 on APCs and CD40L expressed by at least partly activated T cells. We used a DC line, JawsII, to compare the importance of CD40 expression and downstream signalling in vitro and in vivo. JawsII cells represent pre‐immature bone marrow‐derived DCs expressing low levels of MHC molecules, low levels of B7 molecules and no CD40. We have previously shown that JawsII cells, despite the lack of CD40 expression, are capable of priming naïve allogeneic T cells in vitro. In correlation with the current literature, we present data showing that constitutive expression of CD40 significantly increases the priming capacity of JawsII cells in vitro. In addition, we show that CD40 expression is required for JawsII cell‐dependent T‐cell priming in vivo.     

Mitochondrial and cytosolic roles of PINK1 shape induced regulatory T‐cell development and function

Mutations in PTEN‐induced kinase 1 (PINK1), a serine/threonine kinase linked to familial early‐onset Parkinsonism, compromise mitochondrial integrity and metabolism and impair AKT signaling. As the activation of a naïve T cell requires an AKT‐dependent reorganization of a cell's metabolic machinery, we sought to determine if PINK1‐deficient T cells lack the ability to undergo activation and differentiation. We show that CD4⁺ T cells from PINK1 knockout mice fail to properly phosphorylate AKT upon activation, resulting in reduced expression of the IL‐2 receptor subunit CD25. Following, deficient IL‐2 signaling mutes the activation‐induced increase in respiratory capacity and mitochondrial membrane potential. Under polarization conditions favoring the development of induced regulatory T cells, PINK1^?/? T cells exhibit a reduced ability to suppress bystander T‐cell proliferation despite normal FoxP3 expression kinetics. Our results describe a critical role for PINK1 in integrating extracellular signals with metabolic state during T‐cell fate determination, and may have implications for the understanding of altered T‐cell populations and immunity during the progression of active Parkinson's disease or other immunopathologies.     

IL‐33 promotes DC development in BM culture by triggering GM‐CSF production

Short‐term DC cultures generated with GM‐CSF and other cytokines have markedly improved our ability to study the immunobiology of DC. Here, we tested 65 cytokines individually for their potential to promote the generation of CD11c⁺ cells in a murine BM culture system. In addition to several cytokines known to promote DC survival and/or growth, IL‐33 was found to augment DC development time‐ and dose‐dependently. Although the resulting CD11c⁺ cells generated in the presence of IL‐33 exhibited a typical dendritic morphology, they expressed MHC class II molecules only at modest levels, showed negligible responses to TLR ligands, produced no detectable IL‐12 p70, displayed PD‐L1 and PD‐L2 on the surface, and failed to activate immunologically naïve T cells efficiently. IL‐33‐induced expansion of CD11c⁺ cells was completely blocked by anti‐GM‐CSF mAb, and GM‐CSF mRNA and protein expression in BM culture was markedly elevated by added IL‐33, indicating that IL‐33 promotes in vitro DC generation indirectly by a GM‐CSF‐dependent manner. With regard to the cellular source, IL‐33‐dependent GM‐CSF production was observed exclusively within the CD45⁺/FcεRI⁺ BM population. Not only do our results reinforce the notion that GM‐CSF serves as a primary DC growth factor, but they also reveal a previously unrecognized mechanism supporting DC development.