Regulation of Dendritic Cell Function in the Human Eye: The Immunosuppressive Role of Aqueous Humour in Health and Disease

Abstract

Purpose: : Aqueous humour (AqH) has been shown to have significant immunosuppressive effects in animal models. Our hypothesis was that in humans, AqH may inhibit dendritic cell (DC) maturation and so prevent the activation of the acquired immune response, but that in uveitis (intraocular inflammation) this inhibitory effect is overcome. The aim of this study was to establish whether this immunoregulatory phenomenon occurs in the human eye, and to investigate its underlying mechanism.

Methods: : Human monocyte-derived DC were cultured for 48h in 50% human AqH (non-inflammatory, untreated uveitis or topical glucorticoid (GC) treated uveitis) or medium alone with or without the addition of pro-inflammatory cytokines (IL-1β, IL-6, TNFα and PGE2). Naïve CD4+ T cells were isolated from the peripheral blood of allogeneic donors, labelled with CFSE and cultured for 4d with each DC population in an allogeneic proliferation assay.

Results: : Non-inflammatory AqH significantly inhibited the capacity of DC to induce proliferation of allogeneic naïve CD4+ T cells. Culture with inflammatory AqH also inhibited DC induced proliferation, with GC treated uveitis AqH having the strongest inhibitory effect. Flow cytometric analysis of relevant DC surface molecules showed that control AqH was associated with a reduction in MHC class I and II, CD86 and CCR5, an increase in DC-SIGN, and no significant change in CD80 or CCR7. Untreated uveitis AqH was associated with a reduction in class II MHC, CD86, CCR5 and DC-SIGN, but no significant change in MHC class I, CD80 or CCR7. Conversely treated uveitis AqH was associated with higher MHC class I, but reduced MHC class II and CD86 and no significant change in CD80, CCR5, CCR7 or DC-SIGN. The level of expression of the costimulatory molecule CD86 was strongly predictive of DC capacity to induce proliferation of allogeneic naïve CD4+ T cells.

Conclusions: : Non-inflammatory human AqH can significantly inhibit DC maturation, and this effect is largely retained even in the presence of uveitis. Inflammatory AqH does however differentially affect the DC in terms of its surface molecules. GC treatment appears to augment the inhibitory effect of AqH. We are now investigating whether these changes are in turn associated with other aspects of DC function such as skewing of T cell phenotype.

Keywords: immunomodulation/immunoregulation • aqueous • uveitis-clinical/animal model