Uveitis is underappreciated as a sight-threatening cause of blindness. There are two broad causative classes of uveitis: infectious and non-infectious. Non-infectious uveitis is considered a prototypical autoimmune disorder based mainly on data from experimental models in the mouse. Several different experimental models exist that reflect the different types of uveitis in man (anterior, intermediate, and posterior uveitis). These models have demonstrated that uveitis is predominantly a Th1/Th17 mediated disease, although innate immune cells play a significant role both in induction of disease and in tissue damage. Most experimental models of uveitis rely on activation of the innate immune system by use of adjuvants that activate a range of pathogen recognition receptors (PRRs). This begs the question of the underlying role of initial and/or persistent infection, including latent infection, in immune-mediated uveitis in which active infection cannot be demonstrated. This further raises the possibility of pathogenic mechanisms such as antigenic cross-reactivity and molecular mimicry. Alternatively, residual/latent antigen from infectious agents may act as "endogenous" adjuvants for induction of immune reactions to damaged/altered self antigen, suggesting a commonality in pathogenesis for both infectious and non-infectious uveitis in man.

SummaryExposure 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.

Dendritic cells (DC) are the major antigen-presenting cells bridging innate and adaptive immunity, a function they perform by converting quiescent DC to active, mature DC with the capacity to activate naïve T cells. They do this by migrating from the tissues to the T cell area of the secondary lymphoid tissues. Here, we demonstrate that myeloid cell-specific genetic deletion of PTP1B (LysM PTP1B) leads to defects in lipopolysaccharide-driven bone marrow-derived DC (BMDC) activation associated with increased levels of phosphorylated Stat3. We show that myeloid cell-specific PTP1B deletion also causes decreased migratory capacity of epidermal DC, as well as reduced CCR7 expression and chemotaxis to CCL19 by BMDC. PTP1B deficiency in BMDC also impairs their migration in vivo. Further, immature LysM PTP1B BMDC display fewer podosomes, increased levels of phosphorylated Src at tyrosine 527, and loss of Src localization to podosome puncta. In co-culture with T cells, LysM PTP1B BMDC establish fewer and shorter contacts than control BMDC. Finally, LysM PTP1B BMDC fail to present antigen to T cells as efficiently as control BMDC. These data provide first evidence for a key regulatory role for PTP1B in mediating a central DC function of initiating adaptive immune responses in response to innate immune cell activation.

We specify the clinical features of a spontaneous experimental autoimmune uveitis (EAU) model, in which foreign hen-egg lysozyme (HEL) is expressed in the retina, controlled by the promoter for interphotoreceptor retinol binding protein (IRBP). We previously reported 100% P21 (post-partum day) IRBP:HEL single transgenic (sTg) mice, when crossed to transgenic T cell receptor mice (3A9) generating the double transgenic (dTg) genotype, develop EAU despite profound lymphopenia (thymic HEL-specific T cell deletion). In this work, we characterized the immune component of this model and found conventional dTg CD4+ T cells were less anergic than those from 3A9 controls. Furthermore, prior in vitro HEL-activation of 3A9 anergic T cells (T an) rendered them uveitogenic upon adoptive transfer (Tx) to sTg mice, while antigen-experienced (AgX, dTg), but not naïve (3A9) T cells halted disease in P21 dTg mice. Flow cytometric analysis of the AgX cells elucidated the underlying pathology: FoxP3+CD25 hi CD4+ T regulatory cells (T reg) comprised ∼18%, while FR4+CD73+FoxP3-CD25 lo/− CD4+ T an comprised ∼1.2% of total cells. Further T reg-enrichment (∼80%) of the AgX population indicated FoxP3+CD25 hi CD4+ T reg played a key role in EAU-suppression while FoxP3-CD25 lo/− CD4+ T cells did not. Here we present the novel concept of dual immunological tolerance where spontaneous EAU is due to escape from anergy with consequent failure of T reg induction and subsequent imbalance in the [T reg :T effector ] cell ratio. The reduced numbers of T an , normally sustaining T reg to prevent autoimmunity, are the trigger for disease, while immune homeostasis can be restored by supplementation with AgX, but not naïve, antigen-specific T reg .