Acanthamoeba castellanii (Genotype T4) Stimulates the Production of Interleukin-10 as well as Pro-inflammatory Cytokines in THP-1 Cells, Human Peripheral Blood Mononuclear Cells and Human Monocyte-Derived Macrophages

Free-living amoebae of the genus Acanthamoeba can cause severe and chronic infections in humans, mainly localized in immune privileged sites, as the brain and the eye. Monocytes/macrophages are thought to be involved in Acanthamoeba infections, but little is known about how these facultative parasites influence their functions. The aim of this work was to investigate the effects of Acanthamoeba on human monocytes/macrophages, during the early phase of infection. Herein, THP-1 cells, primary human monocytes isolated from peripheral blood and human monocyte-derived macrophages were either co-incubated with trophozoites of a clinical isolate of Acanthamoeba (genotype T4) or stimulated with amoeba-derived cell free conditioned medium. Production of pro-inflammatory cytokines (TNF-α, IL-6, IL-12), anti-inflammatory cytokine (IL-10) and chemokine (IL-8) was evaluated at specific hours post-stimulation (ranging from 1.30 h to 23 h). We showed that both Acanthamoeba trophozoites and soluble amoebic products induce an early anti-inflammatory monocyte-macrophage phenotype, characterized by a significant production of IL-10; furthermore, challenge with either trophozoites or their soluble metabolites stimulate both pro-inflammatory cytokines and chemokine production, suggesting that this protozoan infection may result from the early induction of coexisting, opposed immune responses. Results reported in this paper confirm that the production of pro-inflammatory cytokines and chemokines by monocytes and macrophages can play a role in the development of the inflammatory response during Acanthamoeba infections. Furthermore, we demonstrate for the first time that Acanthamoeba stimulates IL-10 production in human innate immune cells, which might both promote the immune evasion of Acanthamoeba and limit the induced inflammatory response.