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B27 modulation of LPS response

ABSTRACT: Objectives How HLA-B27 contributes towards arthritis susceptibility is still unclear, but effects on the response to bacteria unrelated to the classical antigen presenting role of B27 have been suggested. This study investigated whether HLA-B27 modulates the innate response to LPS, a component shared between all Gram –ve bacteria that can trigger reactive arthritis. Methods Pools of U937 transfectants expressing either HLA-B27, HLA-A2, or the expression plasmid alone were differentiated with PMA and stimulated with LPS. Supernatants were analysed for TNF-alpha secretion and the gene expression profiles of unstimulated and LPS stimulated cells were determined by microarray analysis. Changes in gene expression that are indicative of an unfolded protein response were also analysed by quantitative PCR. Results TNF-alpha secretion, a biological marker of the inflammatory response to LPS, was not significantly different between U937-B27 and U937-control. No differences in gene expression between unstimulated U937- B27 and U937-control lines were detected. Both U937-control and U937-B27 exhibited a stereotypic response to LPS. Only 1 gene, OAS2, was differentially expressed by these cell lines, and this was confirmed by quantitative PCR. Analysis of XBP-1 splicing suggested that a small increase in the unfolded protein response is induced following LPS stimulation, but this increase was seen in all transfectants. Conclusions The expression of B27 does not profoundly alter gene expression following LPS stimulation. Therefore, additional signals, such as those provided by cytokines or intracellular infection, may be required to reveal any influence of B27 expression on the inflammatory response. Keywords: antigen response

ORGANISM(S): Homo sapiens

PROVIDER: GSE4579 | GEO | 2006/04/10

SECONDARY ACCESSION(S): PRJNA94421

REPOSITORIES: GEO

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Project description:Background The striking association of HLA-B27 with spondyloarthritis (SpA) has been known for 50 years. However, its pathophysiological significance remains incompletely understood. In the HLA-B27/human-β2 microglobulin (hβ2m) transgenic rat (B27 rat) that spontaneously develops inflammatory phenotype characteristic of SpA, myeloid cells expressing the HLA-B27/h2m transgene are critical for disease induction and functionally impaired. Recently, we produced HLA-B27/hβ2m transgenic Drosophila to study non-canonical effects of HLA-B27. We showed that HLA-B27/h2m expressed in Drosophila wing imaginal disc deregulated BMP pathway by interacting physically with the type I bone morphogenetic protein (BMP) receptor (BMPR1) Saxophone (Sax), leading to a loss of crossveins. Methods Genetic interaction was studied between the activin/TGF pathway and HLA-B27/hβ2m in transgenic Drosophila wings. The HLA-B27-bound peptidome was characterized in wing imaginal discs from transgenic Drosophila by high-performance liquid chromatography and mass spectrometry of the peptide fraction eluted from affinity purified HLA-B27. In mesenteric lymph node (mLN) T cells from B27 rats, physical interaction between HLA-B27 and activin receptor-like kinase-2 (ALK2), ALK3 and ALK5 BMPR1s was assessed by proximity ligation assay and phosphorylation of SMADs and proteins of the non-canonical BMP/TGF pathway induced by its ligands was assessed by flow cytometry. Transcript level of several target genes of the TGF pathway was evaluated by real-time quantitative polymerase chain reaction in mLN subsets of T cells from B27 and control nontransgenic rats, with and without treatment by TGF. Results We showed that, in addition to the BMP pathway, inappropriate signaling through the activin/transforming growth factor β (TGFβ) pathway, involving Baboon (Babo) BMPR1, also contributed to the crossveinless wing phenotype. We identified a set of peptides bound to HLA-B27 with canonical binding motif in HLA-B27/hβ2m transgenic Drosophila wing imaginal disc, despite the lack of peptide loading complex. We then demonstrated specific physical interaction, between HLA-B27/h2m and both mammalian orthologues of Sax and Babo, i.e. ALK2 and ALK5 (i.e. TGF receptor I), in the mLN cells from B27 rat. The magnitude of phosphorylation of SMAD2/3 in response to TGFβ1 was increased in T cells from adult and premorbid B27 rats, showing evidence for deregulated TGF pathway. Accordingly, expression of several target genes of the pathway was increased in T cells from B27 rats, in basal conditions and/or after TGFexposure, including Foxp3, Rorc, Runx1 and Maf. Interestingly. Tgfb1 expression was reduced in naïve T cells from B27 rats, even premorbid, an observation consistent with a pro-inflammatory pattern. Conclusions This study highlights a complex interplay between HLA-B27 and the BMP/TGFβ pathways in both Drosophila and B27 rat. Given the importance of the TGF pathway in CD4+ T cells differenciation and regulation, the disturbance caused by HLA-B27 could contribute to the abnormal expansion of pro-inflammatory T helper 17 cells and the altered regulatory T cell phenotype observed in B27 rat.

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B27 modulation of LPS response

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