Molecular mechanisms of T helper 1 and T helper 2 cell development: differential signalling in response to Interleukin-12

Interleukin-12, a heterodimeric cytokine produced by activated monocytes and dendritic cells, plays a crucial role in regulating IFN-ү production and in the generation of IFN-ү producing T helper 1 cells. Here is shown that the IL-12Rß2 subunit, a recently cloned binding and signal transducing component of the IL- 12R, is expressed on human Thl but not Th2 clones, and is induced during differentiation of human naive T cells along the Thl but not the Th2 pathway. IL- 12 and IFN-a but not IFN-ү induce expression of the IL-12Rß2 chain during in vitro T cell differentiation following antigen receptor triggering, whereas IL-4 inhibits IL-12Rß2 transcription. Conversely, IFN-ү but not IFN-ɑ can rescue IL-12Rß2 mRNA expression and restore IL-12 responsiveness in early developing mouse Th2 cells. IFN-ɑ activity in humans is mediated by Stat4. The DNase Hypersensitive Site analysis allowed the characterisation of chromatin structure and accessibility of the IL-12Rß2 locus. Naive T cells as well as Th2 cells show a relative “closed” chromatin configuration, whereas Thl cells displayed an accessible chromatin configuration with a complex pattern of DNase Hypersensitivity. The characterisation of the DH sites selectively present in Thl cells allowed the identification of: i) a TATA-less, CpG rich, IL-12Rß2 minimal promoter ii) IL-12 and IFN-ɑ responsive enhancer regions. These regions contain GAS binding sites that not only bind Stat4, but also that are transcriptionally active. These data provide strong evidence that Stat4 plays a key role in the regulation of the Thl-specific expression of IL-12Rß2. Furthermore, the IL-12RP2 GAS. sites display a binding selectivity and do not efficiently bind Stat1. Thus, the week effects exerted by IFN-ү in humans on IL-12Rß2 gene regulation, and the consequent failure to induce Thl development, can be explained by the inefficient binding of the IFN-ү-induced Stat1 to the IL-12Rß2 GAS sites

Bacterial sensor triggering receptor expressed on myeloid cells-2 regulates the mucosal inflammatory response

BACKGROUND AND AIMS: Triggering receptor expressed on myeloid cells (TREM)-2 is a surface receptor detected on macrophages, dendritic cells, and microglia that binds repeated anionic motifs on yeast and Gram-positive and Gram-negative bacteria. Little is known about TREM-2 expression and function in the intestine or its role in inflammatory bowel disease (IBD). We investigated the expression of TREM-2 in the intestinal lamina propria and its role in the development of colonic inflammation. METHODS: We measured levels of TREM-2 in lamina propria mononuclear cells from surgical specimens collected from patients with IBD or cancer (controls). We analyzed the development of colitis in TREM-2 knockout and wild-type mice. Colon samples were isolated from mice and analyzed for cytokine expression, phagocytosis of bacteria, proliferation in colonic crypts, lamina propria mononuclear cell function, and T-cell activation by ovalbumin. RESULTS: TREM-2 was virtually absent from colon samples of control patients, but levels were significantly higher in within the inflamed mucosa of patients with IBD; it was mainly expressed by CD11c(+) cells. Levels of TREM-2 increased as acute or chronic colitis was induced in mice. TREM-2 knockout mice developed less severe colitis than wild-type mice; the knockout mice lost less body weight, had a lower disease activity index, and had smaller mucosal lesions in endoscopic analysis. Colon dendritic cells from TREM-2 knockout mice produced lower levels of inflammatory cytokines and had reduced levels of bacterial killing and T-cell activation than cells from wild-type mice. CONCLUSIONS: TREM-2 contributes to mucosal inflammation during development of colitis in mice. Levels of TREM-2 are increased within the inflamed mucosa of patients with IBD, indicating its potential as a therapeutic target

Identification of soluble TREM-2 in the cerebrospinal fluid and its association with multiple sclerosis and CNS inflammation

Triggering receptor expressed on myeloid cells 2 (TREM-2) is a membrane-bound receptor expressed by microglia and macrophages. Engagement of TREM-2 on these cells has been reported to reduce inflammatory responses and, in microglial cells, to promote phagocytosis. TREM-2 function is critical within the CNS, as its genetic deficiency in humans causes neurodegeneration with myelin and axonal loss. Blockade of TREM-2 worsened the mouse model for multiple sclerosis. In the present study, a soluble form of TREM-2 protein has been identified by immunoprecipitation and by ELISA. Soluble TREM-2 protein (sTREM-2) was detected in human CSF, and was compared among subjects with relapsing-remitting multiple sclerosis (RR-MS; n = 52), primary progressive multiple sclerosis (PP-MS; n = 21), other inflammatory neurologic diseases (OIND; n = 19), and non-inflammatory neurologic diseases (NIND; n = 41). Compared to NIND subjects, CSF sTREM-2 levels were significantly higher in RR-MS (P = 0.004 by ANOVA) and PP-MS (P < 0.001) subjects, as well as in OIND (P < 0.001) subjects. In contrast, levels of sTREM-2 in blood did not differ among the groups. Furthermore, TREM-2 was detected on a subset of CSF monocytes by flow cytometry, and was also highly expressed on myelin-laden macrophages in eight active demyelinating lesions from four autopsied multiple sclerosis subjects. The elevated levels of sTREM-2 in CSF of multiple sclerosis patients may inhibit the anti-inflammatory function of the membrane-bound receptor suggesting sTREM-2 to be a possible target for future therapies

Chromatin remodeling by the SWI/SNF-like BAF complex and STAT4 activation synergistically induce IL-12Rbeta2 expression during human Th1 cell differentiation.

Interleukin-12 (IL-12) is a key cytokine for the development of T helper type 1 (Th1) responses; however, naive CD4(+) T cells do not express IL-12Rbeta2, and are therefore unresponsive to IL-12. We have examined the mechanisms that control Th1-specific expression of the human IL-12Rbeta2 gene at early time points after T-cell stimulation. We have identified a Th1-specific enhancer element that binds signal transducer and activator of transcription 4 (STAT4) in vivo in developing Th1 but not Th2 cells. T-cell receptor (TCR) signaling induced histone hyperacetylation and recruitment of BRG1, the ATPase subunit of the SWI/SNF-like BAF chromatin remodeling complex, to the IL-12Rbeta2 regulatory regions and was associated with low-level gene transcription at the IL-12Rbeta2 locus. However, high-level IL-12Rbeta2 expression required TCR triggering in the presence of IL-12. Our results indicate a synergistic role of TCR-induced chromatin remodeling and cytokine-induced STAT4 activation to direct IL-12Rbeta2 expression during Th1 cell development