Charles O. Elson

Transforming growth factor-beta induces development of the T(H)17 lineage.

A new lineage of effector CD4+ T cells characterized by production of interleukin (IL)-17, the T-helper-17 (TH17) lineage, was recently described based on developmental and functional features distinct from those of classical TH1 and TH2 lineages. Like TH1 and TH2, TH17 cells almost certainly evolved to provide adaptive immunity tailored to specific classes of pathogens, such as extracellular bacteria. Aberrant TH17 responses have been implicated in a growing list of autoimmune disorders. TH17 development has been linked to IL-23, an IL-12 cytokine family member that shares with IL-12 a common subunit, IL-12p40 (ref. 8). The IL-23 and IL-12 receptors also share a subunit, IL-12Rβ1, that pairs with unique, inducible components, IL-23R and IL-12Rβ2, to confer receptor responsiveness. Here we identify transforming growth factor-β (TGF-β) as a cytokine critical for commitment to TH17 development. TGF-β acts to upregulate IL-23R expression, thereby conferring responsiveness to IL-23. Although dispensable for the development of IL-17-producing T cells in vitro and in vivo, IL-23 is required for host protection against a bacterial pathogen, Citrobacter rodentium. The action of TGF-β on naive T cells is antagonized by interferon-γ and IL-4, thus providing a mechanism for divergence of the TH1, TH2 and TH17 lineages.

Transforming growth factor-β induces development of the TH17 lineage

A new lineage of effector CD4+ T cells characterized by production of interleukin (IL)-17, the T-helper-17 (TH17) lineage, was recently described based on developmental and functional features distinct from those of classical TH1 and TH2 lineages. Like TH1 and TH2, TH17 cells almost certainly evolved to provide adaptive immunity tailored to specific classes of pathogens, such as extracellular bacteria. Aberrant TH17 responses have been implicated in a growing list of autoimmune disorders. TH17 development has been linked to IL-23, an IL-12 cytokine family member that shares with IL-12 a common subunit, IL-12p40 (ref. 8). The IL-23 and IL-12 receptors also share a subunit, IL-12Rβ1, that pairs with unique, inducible components, IL-23R and IL-12Rβ2, to confer receptor responsiveness. Here we identify transforming growth factor-β (TGF-β) as a cytokine critical for commitment to TH17 development. TGF-β acts to upregulate IL-23R expression, thereby conferring responsiveness to IL-23. Although dispensable for the development of IL-17-producing T cells in vitro and in vivo, IL-23 is required for host protection against a bacterial pathogen, Citrobacter rodentium. The action of TGF-β on naive T cells is antagonized by interferon-γ and IL-4, thus providing a mechanism for divergence of the TH1, TH2 and TH17 lineages.

Late Developmental Plasticity in the T Helper 17 Lineage

Development of T helper (Th) 17 cells requires transforming growth factor (TGF)-beta and interleukin (IL)-6 and is independent of the Th1 pathway. Although T cells that produce interferon (IFN)-gamma are a recognized feature of Th17 cell responses, mice deficient for STAT4 and T-bet-two prototypical Th1 transcription factors-are protected from autoimmunity associated with Th17 pathogenesis. To examine the fate and pathogenic potential of Th17 cells and origin of IFN-gamma-producing T cells that emerge during Th17 immunity, we developed IL-17F reporter mice that identify cells committed to expression of IL-17F and IL-17A. Th17 cells required TGF-beta for sustained expression of IL-17F and IL-17A. In the absence of TGF-beta, both IL-23 and IL-12 acted to suppress IL-17 and enhance IFN-gamma production in a STAT4- and T-bet-dependent manner, albeit with distinct efficiencies. These results support a model of late Th17 developmental plasticity with implications for autoimmunity and host defense.

Reciprocal interactions of the intestinal microbiota and immune system

The emergence of the adaptive immune system in vertebrates set the stage for evolution of an advanced symbiotic relationship with the intestinal microbiota. The defining features of specificity and memory that characterize adaptive immunity have afforded vertebrates the mechanisms for efficiently tailoring immune responses to diverse types of microbes, whether to promote mutualism or host defence. These same attributes can put the host at risk of immune-mediated diseases that are increasingly linked to the intestinal microbiota. Understanding how the adaptive immune system copes with the remarkable number and diversity of microbes that colonize the digestive tract, and how the system integrates with more primitive innate immune mechanisms to maintain immune homeostasis, holds considerable promise for new approaches to modulate immune networks to treat and prevent disease.

Dextran sulfate sodium-induced colitis occurs in severe combined immunodeficient mice.

BACKGROUND/AIMS Oral administration of dextran sulfate sodium (DSS) has been reported to induce colitis in mice. The purpose of this study was to determine whether the possible pathogenic mechanism involved the acquired immune system. METHODS Normal BALB/c and related C.B17 severe combined immunodeficient mice were fed 5% DSS (40 kilodaltons) in their drinking water for 7 days; controls were fed only water. Colons were scored for histological activity at various times. Cytokine production by cultures of colon and of draining lymph node cell was measured. The effect of DSS on the proliferation of the MCA-38 colonic epithelial cell line was assessed. RESULTS DSS feeding resulted in a very reproducible acute distal colitis in both BALB/c and C.B17 severe combined immunodeficient mice. The lesions of BALB/c mice had an increased production of macrophage-derived cytokines, such as interleukin (IL) 1 beta, IL-6, tumor necrosis factor, and granulocyte-macrophage colony-stimulating factor, but not the T-cell cytokines IL-3 or interferon gamma. Draining lymph node cells produced these cytokines plus interferon gamma and IL-3. DSS inhibited MCA-38 cells at doses that would be easily achieved in the distal colon. CONCLUSIONS Acute DSS-induced colitis does not require the presence of T cells or B cells because it occurred in C.B17 severe combined immunodeficient mice that lack these cells. Its induction may result from a toxicity of DSS for colonic epithelial cells.

The Intestinal Microbiota Modulates the Anticancer Immune Effects of Cyclophosphamide

The Microbiota Makes for Good Therapy The gut microbiota has been implicated in the development of some cancers, such as colorectal cancer, but—given the important role our intestinal habitants play in metabolism—they may also modulate the efficacy of certain cancer therapeutics. Iida et al. (p. 967) evaluated the impact of the microbiota on the efficacy of an immunotherapy [CpG (the cytosine, guanosine, phosphodiester link) oligonucleotides] and oxaliplatin, a platinum compound used as a chemotherapeutic. Both therapies were reduced in efficacy in tumor-bearing mice that lacked microbiota, with the microbiota important for activating the innate immune response against the tumors. Viaud et al. (p. 971) found a similar effect of the microbiota on tumor-bearing mice treated with cyclophosphamide, but in this case it appeared that the microbiota promoted an adaptive immune response against the tumors. The gut microbiota promote the efficacy of several antineoplastic agents in mice. Cyclophosphamide is one of several clinically important cancer drugs whose therapeutic efficacy is due in part to their ability to stimulate antitumor immune responses. Studying mouse models, we demonstrate that cyclophosphamide alters the composition of microbiota in the small intestine and induces the translocation of selected species of Gram-positive bacteria into secondary lymphoid organs. There, these bacteria stimulate the generation of a specific subset of “pathogenic” T helper 17 (pTH17) cells and memory TH1 immune responses. Tumor-bearing mice that were germ-free or that had been treated with antibiotics to kill Gram-positive bacteria showed a reduction in pTH17 responses, and their tumors were resistant to cyclophosphamide. Adoptive transfer of pTH17 cells partially restored the antitumor efficacy of cyclophosphamide. These results suggest that the gut microbiota help shape the anticancer immune response.

Experimental models of inflammatory bowel disease reveal innate, adaptive, and regulatory mechanisms of host dialogue with the microbiota

Summary:  There are now many experimental models of inflammatory bowel disease (IBD), most of which are due to induced mutations in mice that result in an impaired homeostasis with the intestinal microbiota. These models can be clustered into several broad categories that, in turn, define the crucial cellular and molecular mechanisms of host microbial interactions in the intestine. The first of these components is innate immunity defined broadly to include both myeloid and epithelial cell mechanisms. A second component is the effector response of the adaptive immune system, which, in most instances, comprises the CD4+ T cell and its relevant cytokines. The third component is regulation, which can involve multiple cell types, but again particularly involves CD4+ T cells. Severe impairment of a single component can result in disease, but many models demonstrate milder defects in more than one component. The same is true for both spontaneous models of IBD, C3H/HeJBir and SAMPI/Yit mice. The thesis is advanced that ‘multiple hits’ or defects in these interacting components is required for IBD to occur in both mouse and human.

Innate lymphoid cells regulate CD4 + T-cell responses to intestinal commensal bacteria

Innate lymphoid cells (ILCs) are a recently characterized family of immune cells that have critical roles in cytokine-mediated regulation of intestinal epithelial cell barrier integrity. Alterations in ILC responses are associated with multiple chronic human diseases, including inflammatory bowel disease, implicating a role for ILCs in disease pathogenesis. Owing to an inability to target ILCs selectively, experimental studies assessing ILC function have predominantly used mice lacking adaptive immune cells. However, in lymphocyte-sufficient hosts ILCs are vastly outnumbered by CD4+ T cells, which express similar profiles of effector cytokines. Therefore, the function of ILCs in the presence of adaptive immunity and their potential to influence adaptive immune cell responses remain unknown. To test this, we used genetic or antibody-mediated depletion strategies to target murine ILCs in the presence of an adaptive immune system. We show that loss of retinoic-acid-receptor-related orphan receptor-γt-positive (RORγt+) ILCs was associated with dysregulated adaptive immune cell responses against commensal bacteria and low-grade systemic inflammation. Remarkably, ILC-mediated regulation of adaptive immune cells occurred independently of interleukin (IL)-17A, IL-22 or IL-23. Genome-wide transcriptional profiling and functional analyses revealed that RORγt+ ILCs express major histocompatibility complex class II (MHCII) and can process and present antigen. However, rather than inducing T-cell proliferation, ILCs acted to limit commensal bacteria-specific CD4+ T-cell responses. Consistent with this, selective deletion of MHCII in murine RORγt+ ILCs resulted in dysregulated commensal bacteria-dependent CD4+ T-cell responses that promoted spontaneous intestinal inflammation. These data identify that ILCs maintain intestinal homeostasis through MHCII-dependent interactions with CD4+ T cells that limit pathological adaptive immune cell responses to commensal bacteria.

Differential susceptibility of inbred mouse strains to dextran sulfate sodium-induced colitis

Dextran sulfate sodium (DSS)-induced murine colitis represents an experimental model for human inflammatory bowel disease. The aim of this study was to screen various inbred strains of mice for genetically determined differences in susceptibility to DSS-induced colitis. Mice of strains C3H/HeJ, C3H/HeJBir, C57BL/6J, DBA/2J, NOD/LtJ, NOD/LtSz-Prkdc(scid)/Prkdc(scid), 129/SvPas, NON/LtJ, and NON.NOD-H2g7 were fed 3.5% DSS in drinking water for 5 days and necropsied 16 days later. Ceca and colons were scored for histological lesions based on severity, ulceration, hyperplasia, and area involved. Image analysis was used to quantitate the proportion of cecum ulcerated. Histological examination revealed significant differences among inbred strains for all parameters scored. In both cecum and colon, C3H/HeJ and a recently selected substrain, C3H/HeJBir, were highly DSS susceptible. NOD/LtJ, an autoimmune-prone strain, and NOD/LtSz-Prkdc(scid)/Prkdc(scid), a stock with multiple defects in innate and adoptive immunity, were also highly DSS susceptible. NON/LtJ, a strain closely related to NOD, was quite DSS resistant. The major histocompatibility (MHC) haplotype of NOD mice (H2g7), a major component of the NOD autoimmune susceptibility, was not crucial in determining DSS susceptibility, since NON mice congenic for this MHC haplotype retained resistance. C57BL/6J, 129/SvPas, and DBA/2J mice showed various degrees of susceptibility, depending upon the anatomical site. A greater male susceptibility to DSS-induced colonic but not cecal lesions was observed. In summary, this study demonstrates major differences in genetic susceptibility to DSS-induced colitis among inbred strains of mice. Knowledge of these strain differences in genetic responsiveness to acute inflammatory stress in the large intestine will permit design of genetic crosses to elucidate the genes involved.Dextran sulfate sodium (DSS)-induced murine colitis represents an experimental model for human inflammatory bowel disease. The aim of this study was to screen various inbred strains of mice for genetically determined differences in susceptibility to DSS-induced colitis. Mice of strains C3H/HeJ, C3H/HeJBir, C57BL/6J, DBA/2J, NOD/LtJ, NOD/LtSz- Prkdcscid/Prkdcscid , 129/SvPas, NON/LtJ, and NON.NOD- H2g7 were fed 3.5% DSS in drinking water for 5 days and necropsied 16 days later. Ceca and colons were scored for histological lesions based on severity, ulceration, hyperplasia, and area involved. Image analysis was used to quantitate the proportion of cecum ulcerated. Histological examination revealed significant differences among inbred strains for all parameters scored. In both cecum and colon, C3H/HeJ and a recently selected substrain, C3H/HeJBir, were highly DSS susceptible. NOD/LtJ, an autoimmune-prone strain, and NOD/LtSz- Prkdcscid/Prkdcscid , a stock with multiple defects in innate and adoptive immunity, were also highly DSS susceptible. NON/LtJ, a strain closely related to NOD, was quite DSS resistant. The major histocompatibility (MHC) haplotype of NOD mice ( H2g7 ), a major component of the NOD autoimmune susceptibility, was not crucial in determining DSS susceptibility, since NON mice congenic for this MHC haplotype retained resistance. C57BL/6J, 129/SvPas, and DBA/2J mice showed various degrees of susceptibility, depending upon the anatomical site. A greater male susceptibility to DSS-induced colonic but not cecal lesions was observed. In summary, this study demonstrates major differences in genetic susceptibility to DSS-induced colitis among inbred strains of mice. Knowledge of these strain differences in genetic responsiveness to acute inflammatory stress in the large intestine will permit design of genetic crosses to elucidate the genes involved.

A dominant, coordinated T regulatory cell-IgA response to the intestinal microbiota

A T cell receptor transgenic mouse line reactive to a microbiota flagellin, CBir1, was used to define mechanisms of host microbiota homeostasis. Intestinal IgA, but not serum IgA, was found to block mucosal flagellin uptake and systemic T cell activation in mice. Depletion of CD4+CD25+ Tregs decreased IgA+ B cells, total IgA, and CBir1-specific IgA in gut within days. Repletion of T cell-deficient mice with either CD4+CD25+ or CD4+foxp3+ Tregs restored intestinal IgA to a much greater extent than their reciprocal CD4+ subsets, indicating that Tregs are the major helper cells for IgA responses to microbiota antigens such as flagellin. We propose that the major role of this coordinated Treg-IgA response is to maintain commensalism with the microbiota.