Lipopolysaccharide-primed heterotolerant dendritic cells suppress experimental autoimmune uveoretinitis by multiple mechanisms

Exposure of bone-marrow-derived dendritic cells (BMDC) to high-dose ultrapure lipopolysaccharide for 24 hr (LPS-primed BMDC) enhances their potency in preventing inter-photoreceptor retinoid binding protein: complete Freund's adjuvant-induced experimental autoimmune uveoretinitis (EAU). LPS-primed BMDC are refractory to further exposure to LPS (= endotoxin tolerance), evidenced here by decreased phosphorylation of TANK-binding kinase 1, interferon regulatory factor 3 (IRF3), c-Jun N-terminal kinase and p38 mitogen-activated protein kinase as well as impaired nuclear translocation of nuclear factor κB (NF-κB) and IRF3, resulting in reduced tumour necrosis factor-α (TNF-α), interleukin-6 (IL-6), IL-12 and interferon-β secretion. LPS-primed BMDC also show reduced surface expression of Toll-like receptor-4 and up-regulation of CD14, followed by increased apoptosis, mediated via nuclear factor of activated T cells (NFATc)-2 signalling. LPS-primed BMDC are not only homotolerant to LPS but are heterotolerant to alternative pathogen-associated molecular pattern ligands, such as mycobacterial protein extract (Mycobacterium tuberculosis). Specifically, while M. tuberculosis protein extract induces secretion of IL-1β, TNF-α and IL-6 in unprimed BMDC, LPS-primed BMDC fail to secrete these cytokines in response to M. tuberculosis. We propose that LPS priming of BMDC, by exposure to high doses of LPS for 24 hr, stabilizes their tolerogenicity rather than promoting immunogenicity, and does so by multiple mechanisms, namely (i) generation of tolerogenic apoptotic BMDC through CD14:NFATc signalling; (ii) reduction of NF-κB and IRF3 signalling and downstream pro-inflammatory cytokine production; and (iii) blockade of inflammasome activation

Colitis in a transgenic mouse model of autoimmune uveitis may be induced by neoantigen presentation in the bowel

Undifferentiated uveitis (intraocular inflammation, IOI) is an idiopathic sight-threatening, presumed autoimmune disease, accountable for ~ 10% of all blindness in the developed world. We have investigated the association of uveitis with inflammatory bowel disease (IBD) using a mouse model of spontaneous experimental autoimmune uveoretinitis (EAU). Mice expressing the transgene (Tg) hen egg lysozyme (HEL) in the retina crossed with 3A9 mice expressing a transgenic HEL-specific TCR spontaneously develop uveoretinitis at post-partum day (P)20/21. Double transgenic (dTg TCR/HEL) mice also spontaneously develop clinical signs of colitis at ~ P30 with diarrhoea, bowel shortening, oedema and lamina propria (LP) inflammatory cell infiltration. Single (s)Tg TCR (3A9) mice also show increased histological LP cell infiltration but no bowel shortening and diarrhoea. dTg TCR/HEL mice are profoundly lymphopenic at weaning. In addition, dTg TCR/HEL mice contain myeloid cells which express MHC Class II-HEL peptide complexes (MHCII-HEL), not only in the inflamed retina but also in the colon and have the potential for antigen presentation. In this model the lymphopenia and reduction in the absolute Treg numbers in dTg TCR/HEL mice is sufficient to initiate eye disease. We suggest that cell-associated antigen released from the inflamed eye can activate colonic HEL-specific T cells which, in a microbial micro-environment, not only cause colitis but feedback to amplify IOI