Implicating Dendritic Cells In The Pathogenesis Of Anterior Uveitis 

Uveitis is a potentially blinding condition whereby inflammation may irreversibly damage the delicate intraocular structures. It can be associated with infections, other systemic autoimmune conditions, or may be idiopathic.

Anterior uveitis (AU), is the most common type and is defined as occurring within the anterior chamber of the eye. There is currently no one unifying hypothesis for the pathogenesis of AU. Dendritic cells (DC) are considered key initiators of inflammation through their role of antigen presentation and have thereby been suggested to play a role in many autoimmune diseases. The potential of DC manipulation in autoimmune disease has shown promise.

We investigated the role of DC in AU pathogenesis by examining DC in the circulation of AU patients. We also profiled the local microenvironment in AU by sampling inflamed aqueous humor (AqH). The effect of this inflamed local microenvironment on DC was tested in an ex vivo model by exposing DC to AqH and assessing the effect on co-cultured T cells. All patient samples were treatment naïve and compared to healthy control samples.

We found perturbations in the numbers of circulating DC, with AU samples showing decreased myeloid and plasmacytoid DC compared to healthy control samples. This would suggest that these antigen presenting cells are being recruited out of circulation to a more active site of inflammation. Alterations in DC numbers have been found in other autoimmune diseases with both increased and decreased numbers of circulating DC reported.

Healthy control AqH was completely devoid of any immune cells. Populations of CD4⁺ and CD8⁺ T cells, as well as a large CD15+ neutrophil population, were identified within the inflamed AqH samples from AU patients. HLA-DR⁺CD11c⁺ DC was also identified in the inflamed AqH. These DC had variable expression of CD14⁺, suggesting an inflammatory-type DC of monocyte origin as has been found in other autoimmune diseases. This is the first study, as far as we are aware, which profiles the complete cellular content of inflamed AqH which identifies the entire orchestra of infiltrating cells propagating the inflammation at this stage of the disease. The inflamed AqH contained abundant inflammatory cytokines and chemokines IFNy, IL10, IL1b, IL6, and IL8, as measured by ELISA. The local cytokine expression was significantly higher than that measured in paired AU patient serum samples highlighting this highly inflamed micro-environment within the eye.

Inflamed AU AqH activated a human DC model with a resultant expression of cell surface activation and maturation markers CD40 and CD80, as well as increased production of IL6 measured in the supernatant. This suggests that DC undergo a program of maturation on exposure to inflamed AqH within the anterior chamber of the eye. The functional effects of inflamed AqH on T cells through co-culture showed that these activated DC, in turn, activate CD4⁺ T cells with increased cellular proliferation and intracellular pro-inflammatory cytokines TNFa, IFNy, IL17a, and GM-CSF.

The findings of this study suggest that DC may recruit from circulation to the AqH in the anterior chamber of the eye during AU. We profiled this highly inflamed micro-environment containing abundant cytokines which drive inflammation as well as recruitment of neutrophils, T cells, and DC. We showed that inflamed AU AqH can activate a DC model which results in T cell proliferation and activation. By working with human samples obtained from patients during active disease, we hope our experiments interrogate the pathogenesis of this disease accurately. We would like to further profile the cells within the anterior chamber through cell sorting and potentially examine signaling pathways that are active within these cells. Converting these DC to a more tolerizing profile rather than pro-inflammatory offers a potential therapeutic window which we intend to further explore, which would offer a treatment to turn off the pro-inflammatory cascade and prevent disease recurrences.

These findings are described in the article entitled The pathogenic role of dendritic cells in non-infectious anterior uveitis, recently published in the journal Experimental Eye Research. This work was conducted by M. O’Rourke and C.C. Murphy from the Royal College of Surgeons in Ireland, U. Fearon, S.A. Basdeo, J.M. Fletcher, and M. Canavan from Trinity College Dublin, and C.M. Sweeney from St Vincent’s University Hospital.