ICOS signaling promotes a secondary humoral response after re-challenge with Plasmodium chabaudi chabaudi AS.
ABSTRACT: The co-stimulatory molecule ICOS is associated with the induction and regulation of T helper cell responses, including the differentiation of follicular helper T (Tfh) cells and the formation and maintenance of memory T cells. However, the role of ICOS signaling in secondary immune responses is largely unexplored. Here we show that memory T cell formation and maintenance are influenced by persistent infection with P. chabaudi chabaudi AS infection, as memory T cell numbers decline in wild-type and Icos-/- mice after drug-clearance. Following drug-clearance Icos-/- mice display a relapsing parasitemia that occurs more frequently and with higher peaks compared to wild-type mice after re-challenge. The secondary immune response in Icos-/- mice is characterized by significant impairment in the expansion of effector cells with a Tfh-like phenotype, which is associated with a diminished and delayed parasite-specific Ab response and the absence of germinal centers. Similarly, the administration of an anti-ICOSL antagonizing antibody to wild-type mice before and after reinfection with P. c. chabaudi AS leads to an early defect in Tfh cell expansion and parasite-specific antibody production, confirming a need for ICOS-ICOSL interactions to promote memory B cell responses. Furthermore, adoptive transfer of central memory T (TCM) cells from wild-type and Icos-/- mice into tcrb-/- mice to directly evaluate the ability of TCM cells to give rise to Tfh cells revealed that TCM cells from wild-type mice acquire a mixed Th1- and Tfh-like phenotype after P. c. chabaudi AS infection. While TCM cells from Icos-/- mice expand and display markers of activation to a similar degree as their WT counterparts, they displayed a reduced capacity to upregulate markers indicative of a Tfh cell phenotype, resulting in a diminished humoral response. Together these findings verify that ICOS signaling in memory T cells plays an integral role in promoting T cell effector responses during secondary infection with P. c. chabaudi AS.
Project description:Blood-stage Plasmodium chabaudi chabaudi AS infection requires cell- and Ab-mediated immunity to control acute and persistent infection, respectively. ICOS regulates CD4(+) T cell activation and promotes the induction of follicular Th (TFH) cells, CD4(+) T cells that support B cell affinity maturation within germinal centers (GCs), resulting in the production of high-affinity Abs. In this article, we demonstrate that, in response to P. c. chabaudi AS infection, the absence of ICOS resulted in an enhanced Th1 immune response that reduced peak parasitemia. Despite the absence of ICOS, CD4(+) T cells were capable of expressing PD-1, B cell lymphoma 6, and CXCR5 during early infection, indicating TFH development was not impaired. However, by day 21 postinfection, Icos(-/-) mice accumulated fewer splenic TFHs compared with Icos(+/+) mice, leading to substantially fewer GC B cells and a decrease in affinity, but not production, of parasite-specific isotype-switched Abs. Moreover, treatment of mice with anti-ICOS ligand Abs to modulate ICOS-ICOS ligand signaling revealed a requirement for ICOS in TFH differentiation only after day 6 postinfection. Ultimately, the quality and quantity of isotype-switched Abs produced in Icos(-/-) mice declined over time, resulting in impaired control of persistent parasitemia. Collectively, these data suggest ICOS is not required for TFH induction during P. c. chabaudi AS infection or production of isotype-switched Abs, but it is necessary for maintenance of a sustained high-affinity, protective Ab response.
Project description:Interactions between ICOS and ICOS ligand (ICOSL) are essential for the development of T follicular helper (Tfh) cells and thus the formation and maintenance of GC reactions. Given the conflicting reports on the requirement of other CD4(+) T-cell populations for ICOS signals, we have employed a range of in vivo approaches to dissect requirements for ICOS signals in mice during an endogenous CD4(+) T-cell response and contrasted this with CD28 signals. Genetic absence of ICOSL only modestly reduced the total number of antigen-specific CD4(+) T cells at the peak of the primary response, but resulted in a severely diminished number of both T central memory and T effector memory cells. Treatment with blocking anti-ICOS mAb during the primary response recapitulated these effects and caused a more substantial reduction than blocking CD28 signals with CTLA4Ig. During the memory phase of the response further signals through ICOS or CD28 were not required for survival. However, upon secondary challenge only Tfh cell expansion remained heavily ICOS-dependent, while CD28 signals were required for optimal expansion of all subsets. These data demonstrate the importance of ICOS signals specifically for memory CD4(+) T-cell formation, while highlighting the potential of therapeutically targeting this pathway.
Project description:CD4 T cells are required to fight malaria infection by promoting both phagocytic activity and B cell responses for parasite clearance. In Plasmodium chabaudi infection, one specific CD4 T cell subset generates anti-parasitic IFN-? and the antibody-promoting cytokine, IL-21. To determine the lineage of these multifunctional T cells, we followed IFN-?+ effector T cells (Teff) into the memory phase using Ifng-reporter mice. While Ifng+ Teff expanded, the level of the Th1 lineage-determining transcription factor T-bet only peaked briefly. Ifng+ Teff also co-express ICOS, the B cell area homing molecule CXCR5, and other Tfh lineage-associated molecules including Bcl6, the transcription factor required for germinal center (GC) T follicular helper cells (Tfh) differentiation. Because Bcl6 and T-bet co-localize to the nucleus of Ifng+ Teff, we hypothesized that Bcl6 controls the Tfh-like phenotype of Ifng+ Teff cells in P. chabaudi infection. We first transferred Bcl6-deficient T cells into wildtype hosts. Bcl6-deficient T cells did not develop into GC Tfh, but they still generated CXCR5+ IFN-?+ IL-21+ IL-10+ Teff, suggesting that this predominant population is not of the Tfh-lineage. IL-10 deficient mice, which have increased IFN-? and T-bet expression, demonstrated expansion of both IFN-?+ IL-21+ CXCR5+ cells and IFN-?+ GC Tfh cells, suggesting a Th1 lineage for the former. In the memory phase, all Ifng+ T cells produced IL-21, but only a small percentage of highly proliferative Ifng+ T cells maintained a T-bethi phenotype. In chronic malaria infection, serum IFN-? correlates with increased protection, and our observation suggests Ifng+ T cells are maintained by cellular division. In summary, we found that Ifng+ T cells are not strictly Tfh derived during malaria infection. T cells provide the host with a survival advantage when facing this well-equipped pathogen, therefore, understanding the lineage of pivotal T cell players will aid in the rational design of an effective malaria vaccine.
Project description:Tight control of T follicular helper (Tfh) cells is required for optimal maturation of the germinal centre (GC) response. The molecular mechanisms controlling Tfh-cell differentiation remain incompletely understood. Here we show that microRNA-146a (miR-146a) is highly expressed in Tfh cells and peak miR-146a expression marks the decline of the Tfh response after immunization. Loss of miR-146a causes cell-intrinsic accumulation of Tfh and GC B cells. MiR-146a represses several Tfh-cell-expressed messenger RNAs, and of these, ICOS is the most strongly cell autonomously upregulated target in miR-146a-deficient T cells. In addition, miR-146a deficiency leads to increased ICOSL expression on GC B cells and antigen-presenting cells. Partial blockade of ICOS signalling, either by injections of low dose of ICOSL blocking antibody or by halving the gene dose of Icos in miR-146a-deficient T cells, prevents the Tfh and GC B-cell accumulation. Collectively, miR-146a emerges as a post-transcriptional brake to limit Tfh cells and GC responses.
Project description:The proper regulation of ICOS and ICOS ligand (ICOSL) has been shown to be essential for maintaining proper immune homeostasis. Loss of either protein results in defective humoral immunity, and overexpression of ICOS results in aberrant Ab production resembling lupus. How ICOSL is regulated in response to ICOS interaction is still unclear. We demonstrate that a disintegrin and metalloproteinase (ADAM)10 is the primary physiological sheddase of ICOSL in mice and humans. Using an in vivo system in which ADAM10 is deleted only on B cells, elevated levels of ICOSL were seen. This increase is also seen when ADAM10 is deleted from human B cell lines. Identification of the primary sheddase has allowed the characterization of a novel mechanism of ICOS regulation. In wild-type mice, interaction of ICOS/ICOSL results in ADAM10-induced shedding of ICOSL on B cells and moderate ICOS internalization on T cells. When this shedding is blocked, excessive ICOS internalization occurs. This results in severe defects in T follicular helper development and TH2 polarization, as seen in a house dust mite exposure model. In addition, enhanced TH1 and TH17 immune responses are seen in experimental autoimmune encephalomyelitis. Blockade of ICOSL rescues T cell ICOS surface expression and rescues, at least in part, T follicular helper numbers and the abnormal Ab production previously reported in these mice. Overall, we propose a novel regulation of the ICOS/ICOSL axis, with ADAM10 playing a direct role in regulating ICOSL, as well as indirectly regulating ICOS, thus controlling ICOS/ICOSL-dependent responses.
Project description:Cognate interactions between T follicular helper (Tfh) cells and B cells are essential for promoting protective Ab responses. Whereas costimulatory receptors such as ICOS are accepted as being important for the induction of Tfh cell fate decision, other molecules may play key roles in amplifying or maintaining the Tfh phenotype. In this study, with vaccinia virus infection in mice, we show that OX40 was expressed on Tfh cells that accumulated at the T/B borders in the white pulp of the spleen and that OX40-dependent signals directly shaped the magnitude and quality of the their response to viral Ags. OX40 deficiency in Tfh cells profoundly impaired the acquisition of germinal center (GC) B cell phenotype, plasma cell generation, and virus-specific Ab responses. Most significantly, we found that sustained interactions between OX40 and its ligand, OX40L, beyond the time of initial encounter with dendritic cells were required for the persistence of high numbers of Tfh and GC B cells. Interestingly, OX40 was coexpressed with ICOS on Tfh cells in and around the GC, and ICOS-ICOSL interactions were similarly crucial at late times for maintenance of the Tfh and GC B cells. Thus, OX40 and ICOS act in a cooperative, nonredundant manner to maximize and prolong the Tfh response that is generated after acute virus infection.
Project description:Abrogation of ICOS/ICOS ligand (ICOSL) costimulation prevents the onset of diabetes in the non-obese diabetic (NOD) mouse but, remarkably, yields to the development of a spontaneous autoimmune neuromyopathy. At the pathological level, ICOSL-/- NOD mice show stronger protection from insulitis than their ICOS-/- counterparts. Also, the ICOSL-/- NOD model carries a limited C57BL/6 region containing the Icosl nul mutation, but, in contrast to ICOS-/- NOD mice, no gene variant previously reported as associated to NOD diabetes. Therefore, we aimed at providing a detailed characterization of the ICOSL-/- NOD model. The phenotype observed in ICOSL-/- NOD mice is globally similar to that observed in ICOS-/- and ICOS-/-ICOSL-/- double-knockout NOD mice, manifested by a progressive locomotor disability first affecting the front paws as observed by catwalk analysis and a decrease in grip test performance. The pathology remains limited to peripheral nerve and striated muscle. The muscle disease is characterized by myofiber necrosis/regeneration and an inflammatory infiltrate composed of CD4+ T-cells, CD8+ T-cells, and myeloid cells, resembling human myositis. Autoimmune neuromyopathy can be transferred to NOD.scid recipients by CD4+ but not by CD8+ T-cells isolated from 40-week-old female ICOSL-/- NOD mice. The predominant role of CD4+ T-cells is further demonstrated by the observation that neuromyopathy does not develop in CIITA-/-ICOSL-/- NOD in contrast to ?2microglobulin-/-ICOSL-/- NOD mice. Also, the cytokine profile of CD4+ T-cells infiltrating muscle and nerve of ICOSL-/- NOD mice is biased toward a Th1 pattern. Finally, adoptive transfer experiments show that diabetes development requires expression of ICOSL, in contrast to neuromyopathy. Altogether, the deviation of autoimmunity from the pancreas to skeletal muscles in the absence of ICOS/ICOSL signaling in NOD mice is strictly dependent on CD4+ T-cells, leads to myofiber necrosis and regeneration. It provides the first mouse model of spontaneous autoimmune myopathy akin to human myositis.
Project description:<h4>Background</h4>Granulomatous and fibrosing inflammation in response to parasite eggs is the main pathology that occurs during infection with Schistosoma spp. CD4+ T cells play critical roles in both host immune responses against parasitic infection and immunopathology in schistosomiasis,and coordinate many types of immune cells that contribute to fibrosis. ICOSL plays an important role in controlling specific aspects of T cell activation, differentiation, and function. Previous work has suggested that ICOS is essential for Th17 cell development. However, the immunopathogenesis of this pathway in schistosomiasis fibrosisis still unclear.<h4>Methodology/principal findings</h4>Using models of schistosomiasis in ICOSL KO and the C57BL/6 WT mice, we studied the role of the ICOSL/ICOS interaction in the mediation of the Th17 response in host granulomatous inflammation, particularly in liver fibrosis during S. japonicum infection, and investigated the immune responses and pathology of ICOSL KO mice in these models. The results showed that ICOSL KO mice exhibited improved survival, reduced liver granulomatous inflammation around parasite eggs, markedly inhibited hepatic fibrosis development, lower levels of Th17-related cytokines (IL-17/IL-21), Th2-related cytokines (IL-4/IL-6/IL-10), a pro-fibrotic cytokine (IL-13), and TGF-?1, but higher level of Th1-related cytokine (IFN-?) compared to wild-type (WT) mice. The reduced progression of fibrogenesis was correlated with the down-regulation of Th17 and Th2 and the elimination of ICOSL/ICOS interactions.<h4>Conclusions/significance</h4>Our findings suggest that IL-17-producing cells contribute to the hepatic granulomatous inflammation and subsequent fibrosis. Importantly, there was a clearly positive correlation between the presence of IL-17-producing cells and ICOS expression in ICOSL KO mice, and additional results indicated that Th17 was involved in the pathological tissue remodeling in liver fibrosis induced by schistosomiasis.
Project description:A complete understanding of the mechanisms underlying the acquisition of protective immunity is crucial to improve vaccine strategies to eradicate malaria. However, it is still unclear whether recognition of damage signals influences the immune response to Plasmodium infection. Adenosine triphosphate (ATP) accumulates in infected erythrocytes and is released into the extracellular milieu through ion channels in the erythrocyte membrane or upon erythrocyte rupture. The P2X7 receptor senses extracellular ATP and induces CD4 T cell activation and death. Here we show that P2X7 receptor promotes T helper 1 (Th1) cell differentiation to the detriment of follicular T helper (Tfh) cells during blood-stage Plasmodium chabaudi malaria. The P2X7 receptor was activated in CD4 T cells following the rupture of infected erythrocytes and these cells became highly responsive to ATP during acute infection. Moreover, mice lacking the P2X7 receptor had increased susceptibility to infection, which correlated with impaired Th1 cell differentiation. Accordingly, IL-2 and IFN? secretion, as well as T-bet expression, critically depended on P2X7 signaling in CD4 T cells. Additionally, P2X7 receptor controlled the splenic Tfh cell population in infected mice by promoting apoptotic-like cell death. Finally, the P2X7 receptor was required to generate a balanced Th1/Tfh cell population with an improved ability to transfer parasite protection to CD4-deficient mice. This study provides a new insight into malaria immunology by showing the importance of P2X7 receptor in controlling the fine-tuning between Th1 and Tfh cell differentiation during P. chabaudi infection and thus in disease outcome.
Project description:The role of ICOS and its ligand (ICOSL) have both been shown to be essential for proper humoral responses as well as autoimmune Ab development in mouse models of lupus. In this paper, we report a specific role for the metalloprotease ADAM10 on B cells in regulating both ICOSL and ICOS in a mouse model of increased humoral immunity using B6mir146a-/- mice and a model of lymphoproliferative disease using the well-characterized lpr model. B6lpr mice lacking ADAM10 on B cells (A10Blpr) have decreased nodal proliferation and T cell accumulation compared with control B6lpr mice. Additionally, A10Blpr mice have a drastic reduction in autoimmune anti-dsDNA Ab production. In line with this, we found a significant reduction in follicular helper T cells and germinal center B cells in these mice. We also show that lymphoproliferation in this model is closely tied to elevated ICOS levels and decreased ICOSL levels. Overall, our data not only show a role of B cell ADAM10 in control autoimmunity but also increase our understanding of the regulation of ICOS and ICOSL in the context of autoimmunity.