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NK cell-based immunotherapies have gained traction in the clinic for the treatment of cancer due to the ability of NK cells to directly lyse tumor cells. NK cells are being exploited in clinical trials using autologous and allogeneic NK cell infusion strategies alone or with hematopoietic stem cell transplantation. These strategies have rapidly evolved to exploit the therapeutic effects of NK cells transduced with chimeric antigen receptors and the utilization of IL-15 to induce NK cell persistence and expansion that seems to dominate current clinical trials. IL-15 is a member of the common receptor gamma chain (γc) family, which also includes IL-2, IL-4, IL-7, IL-9, and IL-21. This group of cytokines has a broad pleiotropic activity on both the innate and adaptive immune systems, with important therapeutic ramifications. The protein form of IL-15 contains two N-linked glycosylation sites at the C-terminus of the IL-15 protein, at N79 and N112, and disulfide bonds at positions C42-C88 and C35-C85, the former being homologous to the C C within IL-2. The IL-15 heterotrimeric receptor complex consists of a private IL-15 specific alpha subunit IL-15Rα (CD215), the IL-2/IL-15 receptor β (CD122), and the common γc receptor subunit (CD132) which are shared by the IL-2 receptor. The ability of IL-15 to stimulate NK cell responses, and its well-documented antitumor activity in preclinical models, support the development of clinical studies of IL-15 in cancer. IL-15 showed acceptable toxicity profiles in mouse and primate models and, thus, is increasingly recognized as a promising cytokine for the treatment of hematological and solid malignancies. IL-15 is currently being tested clinically in a number of formulations to enhance immunotherapy for several indications. Clinical studies of IL-15 or IL-15 superagonists, consisting of IL-15 linked to IL-15Rα portions, have been initiated; studies combining IL-15 with adoptive transfer of NK cells are ongoing in cancer patients. This review traces how our understanding of the complex regulation of IL-15 has evolved in time and how accumulated knowledge from the bench was translated in the clinic.

B6.SJL-Ptprca Pepcb/Boy (CD45.1) mice have been used in hundreds of congenic competitive transplants, with the presumption that they differ from C57BL/6 mice only at the CD45 locus. In this study, we describe a point mutation in the natural cytotoxicity receptor 1 (Ncr1) locus fortuitously identified in the CD45.1 strain. This point mutation was mapped at the 40th nucleotide of the Ncr1 locus causing a single amino acid mutation from cysteine to arginine at position 14 from the start codon, resulting in loss of NCR1 expression. We found that these mice were more resistant to CMV due to a hyper innate IFN-γ response in the absence of NCR1. In contrast, loss of NCR1 increased susceptibility to influenza virus, a result that is consistent with the role of NCR1 in the recognition of influenza Ag, hemagglutinin. This work sheds light on potential confounding experimental interpretation when this congenic strain is used as a tool for tracking lymphocyte development.

B6.SJL-Ptprc(a)Pepc(b)/Boy (CD45.1) mice have been used in hundreds of congenic competitive transplants, with the presumption that they differ from B6 mice only at the CD45 locus. In this study, we describe a point mutation in the Ncr1 locus fortuitously identified in the CD45.1 strain. This point mutation was mapped at the 40(th) nucleotide of the Ncr1 locus causing a single amino acid mutation from cysteine to arginine at position 14 from start codon, resulting in loss of NCR1 expression. We found that these mice were more resistant to cytomegalovirus due to a hyper innate IFNγ response in the absence of NCR1. In contrast, loss of NCR1 increased susceptibility to Influenza virus, a result which is consistent with the role of NCR1 in the recognition of influenza antigen, hemagglutinin. This work shed light on potential confounding experimental interpretation if this congenic strain is used as a tool for tracking lymphocyte development.

Invariant natural killer T (iNKT) cells to date represent the best example of cells known to have a hybrid function, representing both innate and adaptive immunity. Shared phenotypic similarities with NK cells together with a rapid response to a cytokine stimulus and a productive TCR engagement are the features that underline the hybrid nature of iNKT cells. Using these criteria, we provide molecular and functional evidence demonstrating that CD1d-independent (CD1d(ind)) NKT cells, a population of CD1d-unrestricted NKT cells, are endowed with a hybrid function far superior to that of iNKT cells: (i) an extensive shared program with NK cells, (ii) a closer Euclidian distance with NK cells, and (iii) the ability to respond to innate stimuli (Poly:IC) with cytotoxic potential in the same manner as NK cells identify a hybrid feature in CD1d(ind)NKT cells that truly fulfills the dual function of an NK and a T cell. Our finding that CD1d(ind)NKT cells are programmed to act like NK cells in response to innate signals while being capable of adaptive responses is unprecedented, and thus might reemphasize CD1d-unrestricted NKT cells as a subset of lymphocytes that could affect biological processes of antimicrobial and tumor immunity in a unique way.

BackgroundInteractions between host immune cells and gut microbiota are crucial for the integrity and function of the intestine. How these interactions regulate immune cell responses in the intestine remains a major gap in the field.AimWe have identified the signalling lymphocyte activation molecule family member 4 (SLAMF4) as an immunomodulator of the intestinal immunity. The aim is to determine how SLAMF4 is acquired in the gut and what its contribution to intestinal immunity is.MethodsExpression of SLAMF4 was assessed in mice and humans. The mechanism of induction was studied using GFPtgbone marrow chimaera mice, lymphotoxin α and TNLG8A-deficient mice, as well as gnotobiotic mice. Role in immune protection was revealed using oral infection withListeria monocytogenesandCytobacter rodentium.ResultsSLAMF4 is a selective marker of intestinal immune cells of mice and humans. SLAMF4 induction occurs directly in the intestinal mucosa without the involvement of the gut-associated lymphoid tissue. Gut bacterial products, particularly those of gut anaerobes, and gut-resident antigen-presenting cell (APC)TNLG8Aare key contributors of SLAMF4 induction in the intestine. Importantly, lack of SLAMF4 expression leads the increased susceptibility of mice to infection by oral pathogens culminating in their premature death.ConclusionsSLAMF4 is a marker of intestinal immune cells which contributes to the protection against enteric pathogens and whose expression is dependent on the presence of the gut microbiota. This discovery provides a possible mechanism for answering the long-standing question of how the intertwining of the host and gut microbial biology regulates immune cell responses in the gut.

Hematopoietic stem cell transplant therapy is limited by pulmonary infections. Mice with fully reconstituted hematopoietic compartments, including alveolar macrophages (AMs), after bone marrow transplantation (BMT) have impaired host defense against Gram-negative Pseudomonas aeruginosa. Impaired innate immunity is related to increased production of PGE2 by AMs. Cyclooxygenase (COX)-2 is the rate-limiting enzyme for synthesis of PGE2 from arachidonic acid, and COX-2 expression is elevated in AMs post-BMT. We hypothesized that epigenetic mechanisms may be responsible for upregulation of COX-2 in AMs. Using bisulfite sequencing, we observed the 5′-untranslated region and exon 1 of the COX-2 gene is hypomethylated in the AMs of BMT mice compared with control. COX-2 expression was increased in primary AMs and in the AM cell line (MHS) after treatment with 5-aza-2′-deoxycytidine (a methyltransferase inhibitor). Methylation by SssI methyltransferase of a 698-bp region of the COX-2 promoter including the beginning of exon 1 driving a luciferase reporter silenced luciferase expression. Because TGF-β1 is elevated in lungs post-BMT, we tested whether TGF-β1 could promote expression of COX-2 in a hypermethylated COX-2 vector, and observed TGF-β1–induced modest expression of COX-2, suggesting an ability to demethylate the promoter. Finally, BMTs performed with marrow from mice expressing a dominant-negative form of the TGF-βRII on CD11c-expressing cells (which includes AMs) demonstrated improved host defense and AM function. Our findings suggest impaired innate immunity and PGE2 elevation post-BMT are due to hypomethylation of the COX-2 gene, which is at least partly regulated by TGF-β1.

A large gap in our understanding of infant immunity is why natural killer (NK) cell responses are deficient, which makes infants more prone to viral infection. Here we demonstrate that transforming growth factor-β (TGF-β) was responsible for NK cell immaturity during infancy. We found more fully mature NK cells in CD11c(dnR) mice, whose NK cells lack TGF-β receptor (TGF-βR) signaling. Ontogenic maturation of NK cells progressed faster in the absence of TGF-β signaling, which results in the formation of a mature NK cell pool early in life. As a consequence, infant CD11c(dnR) mice efficiently controlled viral infections. These data thus demonstrate an unprecedented role for TGF-β in ontogeny that can explain why NK cell responses are deficient early in life.

Pulmonary infections and pneumonitis occur frequently after hematopoietic stem cell transplantation. Using a syngeneic mouse model of bone marrow transplantation (BMT), we have previously demonstrated that BMT mice are more susceptible to acute gammaherpesvirus 68 (MHV-68) replication at day 7 after infection. By day 21, the virus is latent in lungs of BMT and control mice, and there is no difference in viral load. Despite similar latent viral load, BMT mice develop severe pneumonitis associated with reduced oxygen saturation, fibrosis, peripheral inflammation, hyaline membranes, and foamy alveolar macrophages, a phenotype that persists for 7 weeks after infection. BMT mice demonstrate increased bronchoalveolar lavage (BAL) cells, and this population is enriched in neutrophils and T cells. Alternatively, activated macrophages appear earlier than do classically activated macrophages. BAL fluid from BMT mice at day 21 after infection contains increased levels of hydrogen peroxide, nitrite, and transforming growth factor–β (TGF-β). Mice expressing the dominant-negative transgene dn-TGFβRII in multiple cell types were used as BMT donors. BMT mice with T-cell dnTGFβRII are largely protected from the pneumonitis phenotype, whereas mice with CD11c-dnTGFβRII BMT mice are only modestly protected from pneumonitis. Protection in BMT mice with T-cell dnTGFβRII is associated with decreased TGF-β derived from parenchymal cells in the BAL fluid, lower nitrite levels, and reduced apoptosis, whereas alternatively activated macrophage markers are unchanged.

Natural Killer (NK) cells are crucial in early resistance to murine cytomegalovirus (MCMV) infection. In B6 mice, the activating Ly49H receptor recognizes the viral m157 glycoprotein on infected cells. Balb/c mice lacking LY49H are more susceptible to MCMV infection than B6 mice. Strikingly, CD11cdnR mice that lack TGFβR signaling in NK cells are protected from MCMV infection in both strains. It is established that unlicensed NK cells that are not inhibited by self-MHC class I can control viral infection more than licensed NK cells. We found that CD11cdnR mice have increased frequency of unlicensed (LY49G2+) NK cells and slightly decreased frequency of licensed (LY49C/I+) NK cells in B6 strain. Moreover, TGFβ-resistant NK cells showed more activated phenotypes such as increased granzyme B protein expression and more KLRG1+ expression than control NK cells in both licensed and unlicensed cells. Interestingly, in CD11cdnR mice even unlicensed NK cells have a significant capacity to produce IFN-γ when triggered by anti-NK1.1, but not in control mice. Our data suggest that inactivation of TGFβR signaling might have a critical role in the licensing of NK cell and lead to the resistance against MCMV infection.

Chronic allograft rejection (CR) is the main barrier to long-term transplant survival. CR is a progressive disease defined by interstitial fibrosis, vascular neointimal development, and graft dysfunction. The underlying mechanisms responsible for CR remain poorly defined. TGFβ has been implicated in promoting fibrotic diseases including CR, but is beneficial in the transplant setting due to its immunosuppressive activity. To assess the requirement for T cell TGFβ signaling in allograft acceptance and the progression of CR, we used mice with abrogated T cell TGFβ signaling as allograft recipients. We compared responses from recipients that were transiently depleted of CD4+ cells (that develop CR and express intragraft TGFβ) with responses from mice that received anti-CD40L mAb therapy (that do not develop CR and do not express intragraft TGFβ). Allograft acceptance and suppression of graft-reactive T and B cells were independent of T cell TGFβ signaling in mice treated with anti-CD40L mAb. In recipients transiently depleted of CD4+ T cells, T cell TGFβ signaling was required for the development of fibrosis associated with CR, long-term graft acceptance, and suppression of graft-reactive T and B cell responses. Furthermore, IL-17 was identified as a critical element in TGFβ-driven allograft fibrosis. Thus, IL-17 may provide a therapeutic target for preventing graft fibrosis, a measure of CR, while sparing the immunosuppressive activity of TGFβ.

One unresolved issue in immune tolerance is what prevents self-reactive T cells from activation. In this study, we used a transgenic mouse model of targeted functional inactivation of TGF-βR signaling in CD11c+cells (CD11cdnRmice) and showed a direct impact on the development of experimental autoimmune encephalomyelitis (EAE). We found that MOG35–55immunization of CD11cdnRmice results in strong inflammation of CNS, high frequency of T cells in CNS, increased levels of T helper 1 (TH1) and TH17 cytokines in the periphery, and lack of remission from EAE. Once crossed with mice prone to autoimmunity, double-transgenic CD11cdnRMogTCRmice revealed a spontaneous EAE-like disease characterized by early infiltration of activated myelin-specific T cells into CNS, activation of microglial cells, inflammation of CNS, dysfunction of locomotion, and premature death. We constructed chimeric mice and demonstrated that inactivation of TGF-βR signaling in dendritic cells (DCs) results in augmented EAE-associated T cell responses. Our data provide direct evidence that TGF-β can control autoimmunity via actions on DCs.

Alzheimer's disease is the most common dementia and is pathologically characterized by deposition of amyloid-beta peptide (Abeta) into beta-amyloid plaques, neuronal injury and low-level, chronic activation of brain immunity. Transforming growth factor-betas (TGF-betas) are pleiotropic cytokines that have key roles in immune cell activation, inflammation and repair after injury. We genetically interrupted TGF-beta and downstream Smad2/3 signaling (TGF-beta-Smad2/3) in innate immune cells by inducing expression of CD11c promoter-driven dominant-negative TGF-beta receptor type II in C57BL/6 mice (CD11c-DNR), crossed these mice with mice overexpressing mutant human amyloid precursor protein, the Tg2576 Alzheimer's disease mouse model, and evaluated Alzheimer's disease-like pathology. Aged double-transgenic mice showed complete mitigation of Tg2576-associated hyperactivity and partial mitigation of defective spatial working memory. Brain parenchymal and cerebrovascular beta-amyloid deposits and Abeta abundance were markedly (up to 90%) attenuated in Tg2576-CD11c-DNR mice. This was associated with increased infiltration of Abeta-containing peripheral macrophages around cerebral vessels and beta-amyloid plaques. In vitro, cultures of peripheral macrophages, but not microglia, from CD11c-DNR mice showed blockade of classical TGF-beta-activated Smad2/3 but also showed hyperactivation of alternative bone morphogenic protein-activated Smad1/5/8 signaling and increased Abeta phagocytosis. Similar effects were noted after pharmacological inhibition of activin-like kinase-5, a type I TGF-beta receptor. Taken together, our results suggest that blockade of TGF-beta-Smad2/3 signaling in peripheral macrophages represents a new therapeutic target for Alzheimer's disease.

Despite our knowledge of the protective role of antibodies passed to infants through breast milk, our understanding of immunity transfer via maternal leukocytes is still limited. To emulate the immunological interface between the mother and her infant while breast-feeding, we used murine pups fostered after birth onto MHC-matched and MHC-mismatched dams. Overall, data revealed that: 1) Survival of breast milk leukocytes in suckling infants is possible, but not significant after the foster-nursing ceases; 2) Most breast milk lymphocytes establish themselves in specific areas of the intestine termed Peyer's patches (PPs); 3) While most leukocytes in the milk bolus were myeloid cells, the majority of breast milk leukocytes localized to PPs were T lymphocytes, and cytotoxic T cells (CTLs) in particular; 4) These CTLs exhibit high levels of the gut-homing molecules α4β7 and CCR9, but a reduced expression of the systemic homing marker CD62L; 5) Under the same activation conditions, transferred CD8 T cells through breast milk have a superior capacity to produce potent cytolytic and inflammatory mediators when compared to those generated by the breastfed infant. It is therefore possible that maternal CTLs found in breast milk are directed to the PPs to compensate for the immature adaptive immune system of the infant in order to protect it against constant oral infectious risks during the postnatal phase.

A small pool of NK1.1+ CD8+ T cells is harbored among the conventional CD8+ T cell compartment. Conclusions drawn from the analysis of immune responses mediated by cytotoxic CD8+ T cells are often based on the total population, which includes these contaminating NK1.1+ CD8+ T cells. An unresolved question is whether NK1.1+ CD8+ cells are conventional T cells that acquire NK1.1 expression upon activation or delineation into memory phenotype or whether they are a distinct cell population that induces immune responses in a different manner than conventional T cells. To address this question, we used the Listeria monocytogenes model of infection and followed CD8+ NK1.1+ T cells and NK1.1− CD8+ T cells during each phase of the immune response: innate, effector, and memory. Our central finding is that CD8+ NK1.1+ cells and conventional NK1.1− CD8+ T cells both contribute to the adaptive immune response to Listeria, but only CD8+ NK1.1+ cells were equipped with the ability to provide a rapid innate immune response, as demonstrated by early and Ag-independent IFN-γ production, granzyme B expression, and degranulation. More importantly, purified conventional CD8+ T cells alone, in the absence of any contaminating CD8+ NK1.1+ cells, were not sufficient to provide early protection to lethally infected mice. These results highlight the role of CD8+ NK1.1+ T cells in mounting early innate responses that are important for host defense and support the therapeutic potential of this subset to improve the effectiveness of protective immunity.

The live attenuated yellow fever vaccine 17D (YF-17D) is one of the most effective vaccines available, with a 65-yr history of use in >400 million people globally. Despite this efficacy, there is presently no information about the immunological mechanisms by which YF-17D acts. Here, we present data that suggest that YF-17D activates multiple Toll-like receptors (TLRs) on dendritic cells (DCs) to elicit a broad spectrum of innate and adaptive immune responses. Specifically, YF-17D activates multiple DC subsets via TLRs 2, 7, 8, and 9 to elicit the proinflammatory cytokines interleukin (IL)-12p40, IL-6, and interferon-α. Interestingly, the resulting adaptive immune responses are characterized by a mixed T helper cell (Th)1/Th2 cytokine profile and antigen-specific CD8+ T cells. Furthermore, distinct TLRs appear to differentially control the Th1/Th2 balance; thus, whilst MyD88-deficient mice show a profound impairment of Th1 cytokines, TLR2-deficient mice show greatly enhanced Th1 and Tc1 responses to YF-17D. Together, these data enhance our understanding of the molecular mechanism of action of YF-17D, and highlight the potential of vaccination strategies that use combinations of different TLR ligands to stimulate polyvalent immune responses.

CD4+CD25+regulatory T cells are essential in the protection from organ-specific autoimmune diseases. In the pancreas, they inhibit actions of autoreactive T cells and thereby prevent diabetes progression. The signals that control the generation, the maintenance, or the expansion of regulatory T cell poolin vivoremain poorly understood. Here we show that a transient pulse of transforming growth factor β (TGF-β) in the islets during the priming phase of diabetes is sufficient to inhibit disease onset by promoting the expansion of intraislet CD4+CD25+T cell pool. Approximately 40–50% of intraislet CD4+T cells expressed the CD25 marker and exhibited characteristics of regulatory T cells including small size, high level of intracellular CTLA-4, expression of Foxp3, and transfer of protection against diabetes. Results fromin vivoincorporation of BrdUrd revealed that the generation of a high frequency of regulatory T cells in the islets is due toin situexpansion upon TGF-β expression. Thus, these findings demonstrate a previously uncharacterized mechanism by which TGF-β inhibits autoimmune diseases via regulation of the size of the CD4+CD25+regulatory T cell poolin vivo.

Immunosurveillance by Natural killer (NK) cells provides an efficient effector mechanism to eliminate tumor and virally infected cells. A well-defined characteristic of NK cells is their ability to lyse target cells deficient in MHC class I expression or target cells that express non-MHC ligands as a result of infection or transformation. This observation has been the basis for identification of a number of inhibitory and activatory NK cell receptors. Although the collective effort during the last decade shed light on the function of many NK cell receptors, the role of NCR1 in NK cell biology remains highly controversial. We have recently identified a spontaneous mutation of NCR1 in our C57BL/6 mouse colony. In this mutant, NCR1 expression was absent on conventional NK cells of all lymphoid organs as well as on innate lymphocytes (ILC3) of the gut lamina propria. Of note, NCR1 expression was absent on the surface as well as in the intracellular compartment of NK cells. Likewise, lack of NCR1 expression was confirmed in mixed BM chimera indicating a cell intrinsic phenotype. Only genetic backcrossing could correct the lack of NCR1 in these mice. ORF sequencing of NCR1 gene in mutant mice revealed a point mutation (C14R) in the region of signal peptide of NCR1 protein. However, while development and homeostasis of NK cells was not affected by the lack of NCR1, infection of NCR1C14R mutant mice with murine cytomegalovirus resulted in increased resistance, an advantage that correlated with NK cell hyperresponsive production of IFN-γ, but not cytotoxic activity. Moreover, NCR1 limits NK cell IFNγ response via regulation of Dok-1 phosphorylation and p38 activation. Collectively, our data reveal the role for NCR1 in IFNγ production of NK cell.

Hematopoietic stem cell transplantation (HSCT) is complicated by pulmonary infections that manifest posttransplantation. Despite engraftment, susceptibility to infections persists long after reconstitution. Previous work using a murine bone marrow transplant (BMT) model implicated increased cyclooxygenase-2 (COX-2) and prostaglandin E2(PGE2) in promoting impaired alveolar macrophage (AM) responses. However, mechanisms driving COX-2 overexpression remained elusive. Previously, transforming growth factor-β (TGF-β) signaling after BMT was shown to promote hypomethylation of the COX-2 gene. Here, we provide mechanistic insight into how this occurs and show that TGF-β induces microRNA (miR)-29b while decreasing DNA methyltransferases (DNMT)1, DNMT3a, and DNMT3b in AMs after BMT. De novo DNMT3a and DNMT3b were decreased upon transient transfection of miR-29b, resulting in decreased methylation of the COX-2 promoter and induction of COX-2. As a consequence, miR-29b-driven upregulation of COX-2 promoted AM dysfunction, and transfection of BMT AMs with a miR-29b inhibitor rescued the bacterial-killing defect. MiR-29b-mediated defects in BMT AMs were dependent on increased levels of PGE2, as miR-29b-transfected AMs treated with a novel E prostanoid receptor 2 antagonist abrogated the impaired bacterial killing. We also demonstrate that patients that have undergone HSCT exhibit increased miR-29b; thus these studies highlight miR-29b in driving defective AM responses and identify this miRNA as a potential therapeutic target.

Patients with idiopathic pulmonary fibrosis (IPF) often do worse following infection, but the cause of the decline is not fully understood. We previously demonstrated that infection with a murine gamma herpes virus (γHV-68) could exacerbate established lung fibrosis following administration of fluorescein isothiocyanate (McMillan et al. Am J Respir Crit Care Med 177: 771–780, 2008). In the present study, we anesthetized mice and injected saline or bleomycin intratracheally on day 0. On day 14, mice were anesthetized again and infected with either a Gram-negative bacteria ( Pseudomonas aeruginosa), or with H1N1 or γHV-68 viruses. Measurements were then made on days 15, 21, or 35. We demonstrate that infection with P. aeruginosa does not exacerbate extracellular matrix deposition post-bleomycin. Furthermore, fibrotic mice are effectively able to clear P. aeruginosa infection. In contrast, bleomycin-treated mice develop worse lung fibrosis when infected with γHV-68, but not when infected with H1N1. The differential ability of γHV-68 to cause increased collagen deposition could not be explained by differences in inflammatory cell recruitment or whole lung chemokine and cytokine responses. Alveolar epithelial cells from γHV-68-infected mice displayed increased expression of TGFβ receptor 1, increased SMAD3 phosphorylation, and evidence of apoptosis measured by cleaved poly-ADP ribose polymerase (PARP). The ability of γHV-68 to augment fibrosis required the ability of the virus to reactivate from latency. This property appears unique to γHV-68, as the β-herpes virus, cytomegalovirus, did not have the same effect.

Proliferation and differentiation of CD4 + T cells are often correlated, but it is not clear whether they are mechanistically linked. When antigen-specific T cells are present at high frequency in vivo, they all respond to antigenic peptide stimulation by expressing activation markers, but only a subset begins to proliferate. However, noncycling cells may synthesize the effector cytokine IFNγ even though their cell cycle is blocked in G1. These data show that proliferation and effector function are not rigidly linked in T cells. Instead, CD4 + T cells have the flexibility to engage in or bypass clonal expansion based on the integration of multiple signals, including the frequency of other responding T cells.

International audience; B lymphocyte generation in bone marrow (BM) compensates for cell loses. The Fas / Fas ligand (FasL) pathway has been implicated in apoptosis of various cell types. Abnormalities of the Fas receptor or of FasL expression are associated with excessive T cell proliferation and autoimmunity. To examine the role of the Fas / FasL system in B cell differentiation, we created double‐chimeric mice by transferring both C57BL / 6 (B6)‐Fas+ and lpr‐FasL+ BM cells into RAG‐2– / – hosts. Equal numbers of stem cells were co‐injected into sublethally irradiated recipients, and their progeny were studied by using antibodies directed against the B6‐Ly5.1+5.2+ and lpr‐Ly5.1–5.2+ populations. A longitudinal study lasting for up to 6 months revealed that cells of the lpr phenotype dominated the B6 phenotype in the BM, as a result of their active proliferation. Analysis of the B cell compartment showed more lpr than B6 cells among immature HSAhiB220lo populations. In contrast, the lpr and B6 phenotypes were equally represented among mature B cells. BM transfer to second hosts indicated that B6‐derived B cell progenitors were absent from the first host. These data suggest that activation of the Fas / FasL pathway disturbs the early steps of B cell development and might therefore contribute to the onset of autoimmune disorders.

International audience; Parkinson disease (PD) is a neurodegenerative disorder characterized by a loss of dopamine-containing neurons. Mounting evidence suggests that dopaminergic cell death is influenced by the innate immune system. However, the pathogenic role of the adaptive immune system in PD remains enigmatic. Here we showed that CD8+ and CD4+ T cells but not B cells had invaded the brain in both postmortem human PD specimens and in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD during the course of neuronal degeneration. We further demonstrated that MPTP-induced dopaminergic cell death was markedly attenuated in the absence of mature T lymphocytes in 2 different immunodeficient mouse strains (Rag1-/- and Tcrb-/- mice). Importantly, similar attenuation of MPTP-induced dopaminergic cell death was seen in mice lacking CD4 as well as in Rag1-/- mice reconstituted with FasL-deficient splenocytes. However, mice lacking CD8 and Rag1-/- mice reconstituted with IFN-gamma-deficient splenocytes were not protected. These data indicate that T cell-mediated dopaminergic toxicity is almost exclusively arbitrated by CD4+ T cells and requires the expression of FasL but not IFNgamma. Further, our data may provide a rationale for targeting the adaptive arm of the immune system as a therapeutic strategy in PD.

Increased extracellular pressure stimulates β1-integrin-dependent cancer cell adhesion. We asked whether pressure-induced adhesion is mediated by changes in β1-integrin binding affinity or avidity and whether these changes are phosphorylation dependent. We evaluated integrin affinity and clustering in human SW620 colon cancer cells by measuring differences in binding between soluble Arg-Gly-Asp (RGD)-Fc ligands and RGD-Fc-F(ab′)2multimeric complexes under ambient and 15-mmHg increased pressures. Phosphorylation of β1-integrin S785 and T788/9 residues in SW620 and primary malignant colonocytes was assessed in parallel. We further used GD25-β1-integrin-null murine fibroblasts stably transfected with either wild-type β1A-integrin, S785A, TT788/9AA, or T788D mutants to investigate the role of β1-integrin site-specific phosphorylation. SW620 binding of RGD-Fc-F(ab′)2multimeric complexes, but not soluble RGD-Fc ligands, was sensitive to integrin clustering. RGD-Fc ligand binding was significantly increased under elevated pressure, suggesting that pressure modulates β1-integrin affinity. Pressure stimulated both β1-integrin S785 and T788/9 phosphorylation. GD25-β1A-integrin wild-type and S785A cells displayed an increase in adhesion to fibronectin under elevated pressure, an effect absent in β1-integrin-null and TT788/9AA cells. T788D substitution significantly elevated basal cell adhesion but displayed no further increase under pressure. These results suggest pressure-induced cell adhesion is mediated by β1-integrin T788/9 phosphorylation-dependent changes in integrin binding affinity.

T cell homeostasis is required for normal immune responses and prevention of pathological responses. Transforming growth factor β (TGFβ) plays an essential role in that regulation. Owing to its broad expression and inhibitory effects on multiple immune cell types, TGFβ regulation is complex. Through recent advances in cell-specific targeting of TGFβ signaling in vivo, the role of TGFβ in T cell regulation is emerging. We demonstrated here a critical role for TGFβ in regulating effector vs regulatory T cell homeostasis.

Interferon-gamma and interleukin 12 produced by the innate arm of the immune system are important regulators of T helper type 1 (T(H)1) cell development, but signals that negatively regulate their expression remain controversial. Here we show that transforming growth factor-beta (TGF-beta) controlled T(H)1 differentiation through the regulation of interferon-gamma produced by natural killer (NK) cells. Blockade of TGF-beta signaling in NK cells caused the accumulation of a large pool of NK cells secreting copious interferon-gamma, responsible for T(H)1 differentiation and protection from leishmania infection. In contrast, blockade of TGF-beta signaling in dendritic cells did not affect dendritic cell homeostasis or interleukin 12 production, thus indicating a previously undescribed demarcation of the function of TGF-beta in NK cells versus dendritic cells.

The signals that control decisions of progenitor commitment involve the interplay of both cytokines and transcription factors. Flt3L has emerged as a potential regulator of dendritic cell (DC) development, but regulation of HSC commitment to the DC lineage remains poorly understood. Our central finding is the identification of STAT3 activation as a checkpoint of Flt3L-regulated DC development. Deletion of STAT3 caused profound deficiency in the DC compartment and abrogated Flt3L effects on DC development. DC derivation by Flt3L revealed a normal HSC pool, a 2- to 3-fold accumulation of CLP/CMP, but absence of common DC precursors as well as their DC progeny in STAT3-deficient mice. The formation of CMP and CLP represents the first decisive lineage commitment step, and in this regard we provide evidence that commitments of CLP/CMP to the DC lineage strictly depend on the interplay of both Flt3L and STAT3 activation.

Critical checkpoints controlling early thymic T-cell development and homeostasis are set by the proper signaling function of the interleukin 7 receptor (IL-7R) and the pre–T-cell antigen receptor. Although αβ T-cell development is observed in IL-7– and IL-7Rα–deficient mice, the number of thymocytes is significantly reduced, implying a role for the IL-7R in controlling the size of the thymic T-cell compartment. Here, we report the overexpression of IL-7Rα that occurs in the early T-cell compartment from AKR/J mice, animals that are highly susceptible to the spontaneous development of thymoma. Increased IL-7Rα was revealed by surface staining, and increased IL-7Rα mRNA was documented by using reverse transcriptase–polymerase chain reaction (RT-PCR). This resulted in increased survival of AKR/J early thymocytes, shown by the decreased frequency of TUNEL+ (terminal deoxynucleotidyl transferase mediated deoxyuridine triphosphate [dUTP]–fluorescein nick end labeling) cells. In an in vivo thymocyte repopulation model, AKR/J thymocytes had a selective advantage over healthy thymocytes. This advantage occurred at early stages of T-cell development. Our findings support the model that overexpression of growth factor receptors can contribute to proliferation and malignancy.

While the role of Transforming Growth Factor β (TGF-β) as an intrinsic pathway has been well established in driving de novo differentiation of Th17 cells, no study has directly assessed the capacity of TGF-β signaling initiated within dendritic cells (DCs) to regulate Th17 differentiation. The central finding of this study is the demonstration that Th17 cell fate during autoimmune inflammation is shaped by TGF-β extrinsic pathway via DCs. First, we provide evidence that TGF-β limits at the site of inflammation the differentiation of highly mature DCs as a means of restricting Th17 cell differentiation and controlling autoimmunity. Second, we demonstrate that TGF-β controls DC differentiation in the inflammatory site but not in the priming site. Third, we show that TGF-β controls DC numbers at a precursor level but not at a mature stage. While it is undisputable that TGF-β intrinsic pathway drives Th17 differentiation, our data provide the first evidence that TGF-β can restrict Th17 differentiation via DC suppression but such a control occurs in the site of inflammation, not at the site of priming. Such a demarcation of the role of TGF-β in DC lineage is unprecedented and holds serious implications vis-à-vis future DC-based therapeutic targets.

International audience; Fas‐mediated apoptosis is a form of cell death that operates through a Fas‐Fas ligand (FasL) interaction. In this study we investigated the role of the Fas system during development of normal and Fas‐mutated lymphocytes. Irradiated RAG2–/– recipients were reconstituted with bone marrow cells from B6 and lpr mice (Fas defective) or from B6 and gld mice (FasL defective), and analyzed for long‐term development. The results showed a primary role of the Fas system in peripheral cell death and thymic colonization. In the periphery, the interaction in vivo between Fas+ and Fas– T cell populations indicated that cellular homeostasis was defective. Indeed, we observed a FasL‐mediated cytotoxic effect on normal‐derived T cells, explaining the dominance of lpr T cells in the mixed chimeras. The Fas mutation affected neither cell activation nor cell proliferation, as the effector (Fas–) and target (Fas+) cells behaved similarly with regard to activation marker expression and cell cycle status. However, Fas– T cells failed to seed the periphery and the thymus in the long term. We suggest that this could be due to the fact that FasL is involved in the structural organization of the lymphoid compartment.

Au cours du developpement des lymphocytes T αβ, le processus de selection positive requiert l'interaction du recepteur de l'antigene (TCR) avec les molecules du complexe majeur d'histocompatibilite (CMH) exprimees a la surface des cellules epitheliales du cortex thymique. On s'est longtemps demande si l'interaction TCR-CMH est intrinsequement suffisante ou si les peptides du soi complexes aux molecules du CMH remplissent un role particulier lors de la selection positive. L'utilisation d'animaux genetiquement modifies, presentant des alterations des processus d'appretement et/ou de presentation de l'antigene a permis de montrer que la diversite des peptides du soi presentes par les molecules du CMH a un impact direct sur l'efficacite du developpement des lymphocytes CD4 + et CD8 + . L'ensemble de ces resultats experimentaux indique que le developpement intrathymique des lymphocytes T αβ, et par consequent l'elaboration du repertoire T fonctionnel, est fondee sur la reconnaissance des peptides du soi au cours du processus de selection positive.