Modulation of Human Dendritic Cell Function by the Ocular Microenvironment

Abstract

Purpose: : One mechanism of ocular immune privilege is via the modulation of antigen–presenting cell function by the ocular microenvironment, primarily through the actions of TGFß2. Although well established in animal models, the effects on human antigen presenting cell function are less clear. We wished to determine the capacity of aqueous humour (AqH), or its components, to modulate the stimulatory functions of human dendritic cells.

Methods: : Monocytes were purified from the peripheral blood of normal healthy volunteers using CD14 magnetic beads. Immature monocyte–derived dendritic cells (iDC) were generated from these cells by culture in IL–4/GM–CSF for 6 days. iDC were cultured for a further 2 days with combinations of TGFß2 or non–inflammatory AqH and a cocktail of maturation cytokines (IL–1ß, TNFα, IL–6, PGE₂). The resulting iDC and mature DC (mDC) were cultured with CFSE–labelled allogeneic purified peripheral blood CD4⁺ T cells. Proliferation was determined at day 5 by flow cytometry.

Results: : mDC stimulated extensive CD4⁺ T cell proliferation, with iDC inducing only a small number of cells to divide, although the number of cell divisions was similar. The addition of TGFß2 to the iDC cultures did not significantly affect the capacity of these cells to induce T cell proliferation. A similar effect was observed with non–inflammatory AqH obtained from healthy subjects undergoing cataract surgery. Neither TGFß2 nor AqH were able to significantly modulate the effect of the maturation cytokines.

Conclusions: : Both TGFß2 and non–inflammatory AqH maintain human monocyte–derived DC in an immature state, consistent with animal studies. However, neither was able to affect the ability of a pro–inflammatory cytokine cocktail to induce DC maturation.

Keywords: immune tolerance/privilege • inflammation • aqueous