SLy2 controls the antibody response to pneumococcal vaccine through an IL‐5Rα‐dependent mechanism in B‐1 cells

The adaptor protein SLy2 (Src homology domain 3 lymphocyte protein 2) is located on human chromosome 21 and was reported to be among a group of genes amplified in Down's syndrome (DS) patients. DS patients characteristically show an impaired immunity to pneumococcal infections. However, molecular mechanisms linking gene amplifications with specific DS phenotypes remain elusive. To investigate the effect of SLy2 gene amplification on the mammalian immune system, we studied SLy2 overexpressing transgenic‐SLy2 (TG) mice. We found that baseline immunoglobulin M (IgM) levels as well as IgM responses following Pneumovax immunizations were reduced in TG mice. Moreover, B‐1 cells, the major natural IgM‐producing population in mice, were reduced in the peritoneal cavity of TG mice, while other immune cell compartments were unaltered. Mechanistically, SLy2 overexpression attenuated the expression of the IL‐5 receptor α chain on B‐1 cells, resulting in decreased B‐1 cell numbers and decreased differentiation into Ab‐secreting cells. Since B‐1 cells essentially contribute to immunity against Streptococcus pneumoniae, the present study provides a novel molecular link between SLy2 expression and pneumococcal‐specific IgM responses in vivo. These studies suggest that the adaptor protein SLy2 is a potential future target for immunomodulatory strategies for pneumococcal infections.     

Knockout of SLy1 decreases double-negative thymocyte proliferation and protects mice from p53-induced tumor formation

The lymphocyte-specific adapter protein SLy1 has previously been identified as indispensable for thymocyte development and T-cell proliferation and, recently, as a cause of X-linked combined immunodeficiency in humans that recapitulates many of the abnormalities reported in SLy1^KO and SLy1^d/d mice. As SLy1^KO NK cells show increased levels of p53, we focused our research on the interdependency of SLy1 and p53 for thymocyte development. Using RT-PCR and immunoblot analysis, we observed increased levels of p53 as well as DNA damage response proteins in SLy1^KO thymocytes. To test for rescue from SLy1-induced deficiencies in thymocyte development like reduced thymocyte numbers and reduced DN to DP progression, we generated a mouse model with T cell-specific p53-deficiency on an SLy1^KO background and analyzed lymphocyte populations in these mice and respective controls. Astonishingly, SLy1^KO-typical deficiencies were retained, showing that SLy1 is mechanistically independent of p53. Studies of apoptosis and proliferation in SLy1KO thymocytes revealed decreased proliferation in the DN3 subpopulation as a possible reason for the decreased thymocyte number. In mice with p53-deficient T cells, we observed tumor formation leading to reduced survival, preferentially in SLy1^WT mice. Thus, we suggest that a SLy1-deficiency reduces proliferation, resulting in less hematologic tumors initiated by the p53-deficiency.     

T‐bet regulates differentiation of forkhead box protein 3+ regulatory T cells in programmed cell death‐1‐deficient mice

Programmed cell death‐1 (PD‐1) plays an important role in peripheral T cell tolerance, but whether or not it affects the differentiation of helper T cell subsets remains elusive. Here we describe the importance of PD‐1 in the control of T helper type 1 (Th1) cell activation and development of forkhead box protein 3 (FoxP3⁺) regulatory T cells (T_regs). PD‐1‐deficient T cell‐specific T‐bet transgenic (P/T) mice showed growth retardation, and the majority died within 10 weeks. P/T mice showed T‐bet over‐expression, increased interferon (IFN)‐γ production by CD4⁺ T cells and significantly low FoxP3⁺ T_reg cell percentage. P/T mice developed systemic inflammation, which was probably induced by augmented Th1 response and low FoxP3⁺ T_reg count. The study identified a unique, previously undescribed role for PD‐1 in Th1 and T_reg differentiation, with potential implication in the development of Th1 cell‐targeted therapy.     

Contact sensitizers trigger human CD1‐autoreactive T‐cell responses

Allergic contact dermatitis is a primarily T‐cell‐mediated inflammatory skin disease induced by exposure to small molecular‐weight haptens, which covalently bind to proteins. The abundance of cutaneous T cells that recognize CD1a antigen‐presenting molecules raises the possibility that MHC‐independent antigen presentation may be relevant in some hapten‐driven immune responses. Here we examine the ability of contact sensitizers to influence CD1‐restricted immunity. Exposure of human antigen‐presenting cells such as monocyte‐derived dendritic cells and THP‐1 cells to the prototypical contact sensitizer dinitrochlorobenzene potentiated the response of CD1a‐ and CD1d‐autoreactive T cells, which released a vast array of cytokines in a CD1‐ and TCR‐dependent manner. The potentiating effects of dinitrochlorobenzene depended upon newly synthesized CD1 molecules and the presence of endogenous stimulatory lipids. Further examination of a broad panel of contact sensitizers revealed 1,4‐benzoquinone, resorcinol, isoeugenol, and cinnamaldehyde to activate the same type of CD1‐restricted responses. These findings provide a basis for the antigen‐specific activation of skin‐associated CD1‐restricted T cells by small molecules and may have implications for contact sensitizer‐induced inflammatory skin diseases.     

IL‐1‐dependent,IL‐1R1‐independent resistance to gastrointestinal nematodes

IL‐1 null mice are unable to expel the intestinal nematode Trichuris muris; whereas WT littermates exhibit sterile immunity. Intriguingly the essential signalling components IL‐1R1 and IL‐1R accessory protein (AcP) are dispensable for expulsion of this parasite. IL‐1 is thus critical for CD4⁺ Th2‐mediated immunity to T. muris; however, this action is independent of the established IL‐1 signalling receptor. We also present data demonstrating that both IL‐1α and IL‐1β induce measurable effects on T. muris primed cells isolated from IL‐1R1 or IL‐1R AcP null mice. MLN cells from these mice restimulated with parasite antigen proliferated at a greater rate and produced more cytokines in response to exogenous IL‐1. This ability to respond to IL‐1 was restricted to these parasite‐primed cells and importantly was not evident in cells from naïve gene null mice. These in vitro data are consistent with the observed ability of mice with compromised IL‐1 signalling to expel the parasite, bolstering the premise that an alternative IL‐1 signalling mechanism is accessible in the context of an intestinal helminth‐driven Th2 immune response.     

The adaptor ASC exacerbates lethal Listeria monocytogenes infection by mediating IL‐18 production in an inflammasome‐dependent and ‐independent manner

Listeria monocytogenes induces the formation of inflammasomes and subsequent caspase‐1 activation, and the adaptor apoptosis‐associated speck‐like protein containing a CARD (ASC) is crucial for this response. However, the role of ASC in L. monocytogenes infection in vivo is unclear. In this study, we demonstrate that ASC has a detrimental effect on host defense against L. monocytogenes infection at a lethal dose (10⁶ CFU), but not at a sublethal dose (10³ CFU). During lethal L. monocytogenes infection, serum levels of IL‐18 and IL‐10 were markedly elevated in WT mice, but not in ASC KO mice. IL‐18 KO mice were more resistant to lethal L. monocytogenes infection than WT mice and had lower levels of serum IL‐10. Furthermore, blockade of IL‐10 receptor resulted in a reduction in bacterial counts, suggesting that ASC and IL‐18 might exacerbate L. monocytogenes infection through induction of IL‐10. We noticed that maturation of IL‐18 during lethal infection was partially independent of caspase‐1, but was critically dependent on ASC. ASC was required for the elevation of serum neutrophil serine protease activity, which correlated with caspase‐1‐independent IL‐18 maturation and IL‐10 production. Collectively, these results suggest that ASC plays a detrimental role in lethal L. monocytogenes infection through IL‐18 production in an inflammasome‐dependent and ‐independent manner.     

Transcriptional repressor Blimp1 regulates follicular regulatory T‐cell homeostasis and function

The B‐lymphocyte‐induced maturation protein 1 (Blimp1) regulates T‐cell homeostasis and function. Loss of Blimp1 could double the proportion of follicular regulatory T (Tfr) cells. However, the effects that Blimp1 may have on the function of Tfr cells remain unknown. Here we document the function for Blimp1 in Tfr cells in vitro and in vivo. Data presented in this study demonstrate that Tfr cells indirectly inhibit the activation and differentiation of B cells by negatively regulating follicular helper T cells, so lowering the secretion of antibody. Lack of Blimp1 makes the immune suppression function of Tfr cells impaired in vitro. In the in vivo study, adoptive transfer of Tfr cells could reduce immune responses in germinal centres and relieve the muscle weakness symptoms of mice with experimental autoimmune myasthenia gravis. Blimp1 deficiency resulted in reduced suppressive ability of Tfr cells. This study identifies that Tfr cells are potent suppressors of immunity and are controlled by Blimp1.     

Globotriaosylceramide inhibits iNKT‐cell activation in a CD1d‐dependent manner

Globotriaosylceramide (Gb3) is a glycosphingolipid present in cellular membranes that progressively accumulates in Fabry disease. Invariant Natural Killer T (iNKT) cells are a population of lipid‐specific T cells that are phenotypically and functionally altered in Fabry disease. The mechanisms responsible for the iNKT‐cell alterations in Fabry disease are not well understood. Here, we analyzed the effect of Gb3 on CD1d‐mediated iNKT‐cell activation in vitro using human cells and in vivo in the mouse model. We found that Gb3 competes with endogenous and exogenous antigens for CD1d binding, thereby reducing the activation of iNKT cells. This effect was exerted by a reduction in the amount of stimulatory CD1d:α–GalCer complexes in the presence of Gb3 as demonstrated by using an mAb specific for the complex. We also found that administration of Gb3 delivered to the same APC as α‐GalCer, induces reduced iNKT‐cell activation in vivo. This work highlights the complexity of iNKT‐cell activation and the importance of nonantigenic glycosphingolipids in the modulation of this process.     

Tissue‐resident and memory properties of human T‐cell and NK‐cell subsets

Efficient immune responses to invading pathogens are the result of the complex but coordinated synergy between a variety of cell types from both the innate and adaptive arms of the immune system. While adaptive and innate immune responses are highly complementary, some cells types within these two systems perform similar functions, underscoring the need for redundancy and increased flexibility. In this review, we will discuss the striking shared features of immunological memory and tissue residency recently discovered between T cells, a component of the adaptive immune system, and natural killer (NK) cells, members generally assigned to the innate compartment. Specifically, we will focus on the T‐cell and NK‐cell diversity at the single‐cell level, on the discrete function of specific subsets, and on their anatomical location. Finally, we will discuss the implication of such diversity in the generation of long‐term memory.     

Chitin induces upregulation of B7‐H1 on macrophages and inhibits T‐cell proliferation

Chitin is a highly abundant glycopolymer, which serves as structural component in fungi, arthropods and crustaceans but is not synthesized by vertebrates. However, vertebrates express chitinases and chitinase‐like proteins, some of which are induced by infection with helminths suggesting that chitinous structures may be targets of the immune system. The chitin‐induced modulations of the innate and adaptive immune responses are not well understood. Here, we demonstrate that intranasal administration of OVA and chitin resulted in diminished T‐cell expansion and Th2 polarization as compared with OVA administration alone. Chitin did not promote nor attenuate Th2 polarization in vitro. Chitin‐exposed macrophages inhibited proliferation of CD4⁺ T cells in a cell–cell contact‐dependent manner. Chitin induced upregulation of the inhibitory ligand B7‐H1 (PD‐L1) on macrophages independently of MyD88, TRIF, TLR2, TLR3, TLR4 and Stat6. Inhibition of T‐cell proliferation was largely dependent on B7‐H1, as the effect was not observed in cocultures with cells from B7‐H1‐deficient mice.     

FBXL12 regulates T‐cell differentiation in a cell‐autonomous manner

Aldehyde dehydrogenase (ALDH) activity is a hallmark of stem cells including embryonic, adult tissue and cancer stem cells. The SCF^FBXL12 complex is an authentic ubiquitin ligase that targets ALDH3 for degradation. FBXL12 is essential for the differentiation of trophoblast stem cells into specific cell types in the placenta during mouse embryogenesis, but its physiological functions in adult tissues have remained unknown. We have now investigated the role of the FBXL12‐ALDH3 axis in the thymus, in which FBXL12 was most abundant among adult mouse tissues examined. During T‐cell differentiation, FBXL12 is most abundant in CD4⁺CD8⁺ (DP) cells, with its expression declining as these cells differentiate into CD4⁺CD8^? or CD4^?CD8⁺ (SP) cells. T cells of FBXL12‐null mice manifested a differentiation block at the DP–SP transition that was associated with ALDH3 accumulation in DP cells. This differentiation block was also apparent in wild‐type mouse recipients of FBXL12‐null bone marrow transplants as well as in FBXL12‐null fetal thymic organ culture, suggesting that it is a cell‐autonomous phenomenon in the thymus rather than an indirect effect of altered systemic conditions. Our results thus indicate that, in addition to its role in placental development, the FBXL12‐ALDH3 axis is required for maturation of undifferentiated thymocytes.     

Effector T‐cell differentiation during viral and bacterial infections: Role of direct IL‐12 signals for cell fate decision of CD8+ T cells

To study the role of IL‐12 as a third signal for T‐cell activation and differentiation in vivo, direct IL‐12 signaling to CD8⁺ T cells was analyzed in bacterial and viral infections using the P14 T‐cell adoptive transfer model with CD8⁺ T cells that lack the IL‐12 receptor. Results indicate that CD8⁺ T cells deficient in IL‐12 signaling were impaired in clonal expansion after Listeria monocytogenes infection but not after infection with lymphocytic choriomeningitis virus, vaccinia virus or vesicular stomatitis virus. Although limited in clonal expansion after Listeria infection, CD8⁺ T cells deficient in IL‐12 signaling exhibited normal degranulation activity, cytolytic functions, and secretion of IFN‐γ and TNF‐α. However, CD8⁺ T cells lacking IL‐12 signaling failed to up‐regulate KLRG1 and to down‐regulate CD127 in the context of Listeria but not viral infections. Thus, direct IL‐12 signaling to CD8⁺ T cells determines the cell fate decision between short‐lived effector cells and memory precursor effector cells, which is dependent on pathogen‐induced local cytokine milieu.     

Regulatory T‐cells in acute dengue viral infection

Although regulatory T‐cells (T_regs) have been shown to be expanded in acute dengue, their role in pathogenesis and their relationship to clinical disease severity and extent of viraemia have not been fully evaluated. The frequency of T_regs was assessed in 56 adult patients with acute dengue by determining the proportion of forkhead box protein 3 (FoxP3) expressing CD4⁺ CD25⁺T‐cells (FoxP3⁺ cells). Dengue virus (DENV) viral loads were measured by quantitative real‐time polymerase chain reaction (PCR) and DENV‐specific T‐cell responses were measured by ex‐vivo interferon (IFN)‐γ enzyme‐linked immunospot (ELISPOT) assays to overlapping peptide pools of DENV‐NS3, NS1 and NS5. CD45RA and CCR4 were used to phenotype different subsets of T‐cells and their suppressive potential was assessed by their expression of cytotoxic T lymphocyte‐antigen 4 (CTLA‐4) and Fas. While the frequency of FoxP3⁺ cells in patients was significantly higher (P < 0·0001) when compared to healthy individuals, they did not show any relationship with clinical disease severity or the degree of viraemia. The frequency of FoxP3⁺ cells did not correlate with either ex‐vivo IFN‐γ DENV‐NS3‐, NS5‐ or NS1‐specific T‐cell responses. FoxP3⁺ cells of patients with acute dengue were predominantly CD45RA⁺ FoxP3^low, followed by CD45RA‐FoxP3^low, with only a small proportion of FoxP3⁺ cells being of the highly suppressive effector Treg subtype. Expression of CCR4 was also low in the majority of T‐cells, with only CCR4 only being expressed at high levels in the effector T_reg population. Therefore, although FoxP3⁺ cells are expanded in acute dengue, they predominantly consist of naive T_regs, with poor suppressive capacity.