Immunological mechanisms controlling chronic inflammatory diseases

Abstract

Autoimmune diseases (AID) are chronic inflammatory diseases (CID) mediated by self-reactive T and B cells and are generally the results of the breakdown of T cell tolerance to self-antigen and failure of peripheral regulatory mechanisms. In this thesis I studied different mechanisms controlling the development of CIDs. I investigated the initial events involved in the activation of self-reactive CD4+ T cells which mediate the destruction of the thyroid in a mouse model of spontaneous thyroiditis. TAZ10 transgenic mice express a human T cell receptor (TCR) specific for a cryptic epitope of thyroid peroxidise (TPO) generated upon endogenous processing by thyroid epithelial cells (TEC), and a naturally occurring antagonistic epitope presented by dendritic cells (DC) upon exogenous processing of TPO.I have characterized the function of myeloid derived suppressor cells (MDSCs) in TAZ10mice. MDSCs accumulate in lymphoid and non-lymphoid organs of TAZ10 mice during acute phases of inflammation and their number decrease as inflammation is fading. Despite their strong inhibitory function on T cell function and proliferation, MDSCs fail to prevent the activation of self-reactive T cells. I showed that the manipulation of MDSCs generated DCs that efficiently promoted the activation of T cells from TAZ10 mice. By contrast, peripheral T cells from patients with rheumatoid arthritis (RA) and lupus had a high proliferative activity compared to controls. Further analysis revealed that RA patients had reduced amounts of inhibitory MDSCs in peripheral blood.I showed that in TAZ10 mice TEC upregulate MHC class II molecules and present the cryptic epitope to TAZ10 T cells inducing their activation. I have demonstrated that DCs are responsible for the spreading of the TPO cryptic epitope from the thyroid to draining lymph nodes(DLN) resulting in the strong activation of transgenic T cells from TAZ10 mice. By adoptive transfer experiments, I showed that the activation of naive TAZ10 T cells occurs within days both in the thyroid and draining lymph-nodes (DLN) and resulted in the destruction of the thyroid. Altogether, this work shows for the first time that in a model devoid of any environmental insults, the normal turnover of TEC is sufficient to induce the activation of self-reactive T cells and the development of AID.In this thesis, I have highlighted the potential role of tissue transglutaminse 2 (TG2) in the treatment of CIDs. TG2 contributes to the pathogenesis of celiac disease and I have showed that TG2 activity promotes inflammation in patients with cystic fibrosis (CF). Mutation of the cystic fibrosis transmembrane regulator gene (CFTR) in CF patients is associated with increased TG2 expression and activity. In CF, TG2 promoted the crosslinking of the anti-inflammatory peroxisome proliferator-activated receptor (PPAR) into perinuclear agresomes. The functional sequestration of PPAR was leading to increased inflammation.The finding of this function of TG2 in CF was relevant in TAZ10 mice as in-vivo inhibition of TG2 downregulated common markers of inflammation