Aqueous Humour Suppression of Human Dendritic Cell Function Is Maintained During Active Uveitis

Abstract

Purpose: : Aqueous humour (AqH) has been shown to have significant immunosuppressive effects in animal models. We have previously presented data showing that in humans, AqH inhibits dendritic cell (DC) maturation and so prevents the activation of the acquired immune response. We hypothesise that in uveitis the ocular microenvironment is no longer immunosuppressive but rather enhances antigen presentation and T cell effector function.

Methods: : AqH was taken from patients with active idiopathic uveitis (untreated or topical glucocorticoid (GC) treated) and patients attending for routine cataract surgery (non-inflammatory). After centrifugation AqH supernatant was separated for DC culture experiments whilst the cellular infiltrate was stained for the presence of dendritic cells. Human monocyte-derived DC were cultured for 48h in 50% human AqH or medium alone with or without the addition of pro-inflammatory cytokines. DC were then washed and placed in culture with CFSE-labelled bead-purified naïve CD4+ T cells from a different donor in an allogeneic proliferation assay.

Results: : Non-inflammatory AqH downregulated DC expression of class I and II MHC, CD86, and CCR5, and reduced their capacity to induce proliferation of allogeneic naïve CD4+ T cells. Uveitic AqH resulted in a distinct DC profile with reduced MHC II, CD86, and consequent reduction of CD4+ T cell proliferation, but with IFNγ-dependent upregulation of MHC class I and CCR5. The levels of most cytokines in these co-cultures were reduced (cf DC cultured in medium alone), paralleling the lower levels of proliferation; Th2 cytokines were less affected. Treated uveitis AqH caused additional glucocorticoid-dependent suppression of CD86 which could be reversed by the addition of glucocorticoid-receptor antagonist, RU486. Ex vivo AqH-derived myeloid DC showed elevated class I and II MHC and CCR5, but reduced CD86 compared to matched peripheral blood DC.

Conclusions: : Human AqH was a powerful inhibitor of DC maturation, retaining this regulatory role during uveitis. Interestingly uveitis AqH induced a distinct IFNγ-dependent MHC I^hi CD86^lo DC phenotype. We are now investigating whether this permits uveitis AqH to differentially regulate the CD4+ and CD8+ arms of the immune system.

Keywords: uveitis-clinical/animal model • antigen presentation/processing • aqueous