Acanthamoeba castellanii Genotype T4 Stimulates the Production of Interleukin-10 as Well as Proinflammatory Cytokines in THP-1 Cells, Human Peripheral Blood Mononuclear Cells, and Human Monocyte-Derived Macrophages

Abstract

Free-living amoebae of the genus Acanthamoeba can cause severe and chronic infections in humans, mainly localized in immune privileged sites, such 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. Here, THP-1 cells, primary human monocytes isolated from peripheral blood, and human monocyte-derived macrophages were either coincubated with trophozoites of a clinical isolate of Acanthamoeba (genotype T4) or stimulated with amoeba-derived cell-free conditioned medium. Production of proinflammatory cytokines (tumor necrosis factor alpha [TNF-α], interleukin-6 [IL-6], and IL-12), anti-inflammatory cytokine (IL-10), and chemokine (IL-8) was evaluated at specific hours poststimulation (ranging from 1.5 h to 23 h). We showed that both Acanthamoeba trophozoites and soluble amoebic products induce an early anti-inflammatory monocyte-macrophage phenotype, characterized by significant production of IL-10; furthermore, challenge with either trophozoites or their soluble metabolites stimulate both proinflammatory cytokines and chemokine production, suggesting that this protozoan infection results from the early induction of coexisting, opposed immune responses. Results reported in this paper confirm that the production of proinflammatory 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.

Experimental keratitis in rats caused by Acanthamoeba griffini: A kinetic histopathological study

“…IL‐1β appears whenever cellular activation against a pathogen occurs in a host tissue. It is secreted in reaction to PAMPs, specifically to certain lipopolysaccharides recognized by TLR‐4 . Thus, inflammatory cells positive to IL‐1β indicate the presence of a pathogen or of cell damage in host tissues .…”

“…At 4 and 8 weeks, there were other cells positive to the same cytokine, including those of the outer part of the corneal epithelium. Mattana et al reported the secretion of IL‐10 by macrophages in vitro in response to contact with A castellanii . The anti‐inflammatory element during the inflammatory response of the host probably has the purpose of limiting damage caused by pro‐inflammatory molecules.…”

“…Upon recognizing the lipophosphoglycan of Acanthamoeba sp, TLR‐4 triggers the production of MYD88, which by activating NF‐κB leads to the secretion of cytokines IL‐8, TNF‐α and IFN‐γ in human corneal cells. Macrophages are known to respond chemotactically to Acanthamoeba sp antigens (PAMPs) and are able to kill the trophozoites in vitro …”

Acanthamoeba Activates Macrophages Predominantly through Toll-Like Receptor 4- and MyD88-Dependent Mechanisms To Induce Interleukin-12 (IL-12) and IL-6

“…This discrepancy could be explained by differences between murine and human cells or the experimental techniques optimized for each cell type. This would include differences in the numbers of trophozoites used in the coincubation models, as well as the time of observations, each of which was optimized to allow coculture with minimal cell death but with a sufficient interaction to induce measurable levels of cytokines (30). In addition, we also investigated whether conditioned medium derived from Acanthamoeba cultures could mimic some of the effects observed on human cells (30,31), but we found conditioned medium to be less effective with murine cells.…”

“…This would include differences in the numbers of trophozoites used in the coincubation models, as well as the time of observations, each of which was optimized to allow coculture with minimal cell death but with a sufficient interaction to induce measurable levels of cytokines (30). In addition, we also investigated whether conditioned medium derived from Acanthamoeba cultures could mimic some of the effects observed on human cells (30,31), but we found conditioned medium to be less effective with murine cells. These differences could be species dependent or due to differences in culture conditions, including medium components, such as the concentration of heat-inactivated fetal bovine serum.…”