Intermediate (CD14⁺⁺CD16⁺) monocytes are expanded in non-infectious uveitis patients and have a reduced capacity to drive Th17 differentiation.

Abstract

Purpose: Human monocyte subsets are phenotypically distinct and differ in their ability to stimulate T cells. It is unclear whether the proportion and function of monocyte subsets is skewed under inflammatory conditions or influenced by glucocorticoid treatment, thereby promoting or regulating tissue inflammation. The purpose of this project was therefore to characterise human monocyte subsets in the context of non-infectious uveitis and to interrogate their effect on CD4⁺ T cell phenotype and response to glucocorticoids.

Methods: The proportion of classical (CD14⁺⁺CD16^-), non-classical (CD14^dimCD16⁺⁺) and intermediate monocyte (CD14⁺⁺CD16⁺) subsets in the peripheral blood (PB) of patients with non-infectious uveitis was determined by flow cytometry (n=98). As these patients were receiving immunosuppressive therapy, monocyte subsets were similarly assessed in treatment naïve alcoholic hepatitis patients as comparators (n=19). Classical and intermediate monocytes were isolated from the PB of healthy volunteers by fluorescent activated cell sorting (n=14). These subsets were co-cultured for 5 days with autologous memory CD4⁺CD45RO⁺ T cells, in the presence or absence of the synthetic glucocorticoid Dexamethasone (Dex). T cell proliferation and intracellular cytokine expression was then quantified.

Results: Analysis of monocyte subsets in the PB of patients showed that intermediate monocytes were enriched in both conditions. Following glucocorticoid treatment, intermediate monocytes were further expanded in non-infectious uveitis patients. During co-culture, intermediate monocytes induced less memory T cell proliferation (29% v 41%; p=0.003), less IL-17 expression (8% v 12%; p<0.001) but similar IFNγ production (27% v 26%) than classical monocytes. Dex-mediated suppression of T cell proliferation and IFNγ production was abrogated to a greater degree in intermediate monocyte co-cultures than in classical monocyte co-cultures. T cell proliferation and IL-17 production was also reduced in co-cultures containing both monocyte subsets compared with co-cultures containing classical monocytes alone.

Conclusions: Intermediate monocytes are expanded in the PB of patients with non-infectious uveitis and have a reduced capacity to drive memory T cell proliferation and IL-17 production. This is associated with enhanced T cell suppression by glucocorticoids.