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

Abstract

Acanthamoeba castellanii is a ubiquitous free-living amoeba with a worldwide distribution that can occasionally infect humans, causing particularly severe infections in immunocompromised individuals. Dissecting the immunology of Acanthamoeba infections has been considered problematic due to the very low incidence of disease, despite the high exposure rates. While macrophages are acknowledged as playing a significant role in Acanthamoeba infections, little is known about how this facultative parasite influences macrophage activity. Therefore, in this study we investigated the effects of Acanthamoeba on the activation of resting macrophages. Consequently, murine bone marrow-derived macrophages were cocultured with trophozoites of either the laboratory Neff strain or a clinical isolate of A. castellanii. In vitro real-time imaging demonstrated that trophozoites of both strains often established evanescent contact with macrophages. Both Acanthamoeba strains induced a proinflammatory macrophage phenotype characterized by the significant production of interleukin-12 (IL-12) and IL-6. However, macrophages cocultured with the clinical isolate of Acanthamoeba produced significantly less IL-12 and IL-6 than the Neff strain. The utilization of macrophages derived from MyD88-, TRIF-, Toll-like receptor 2 (TLR2)-, TLR4-, and TLR2/4-deficient mice indicated that Acanthamoeba-induced proinflammatory cytokine production was through MyD88-dependent, TRIF-independent, TLR4-induced events. This study shows for the first time the involvement of TLRs expressed on macrophages in the recognition of and response to Acanthamoeba trophozoites. KEYWORDS Acanthamoeba, macrophagesA canthamoeba castellanii is a ubiquitous free-living amoeba that has been isolated from both outdoor and indoor environments. It exists as actively feeding, dividing trophozoites and the dormant environmentally resistant cyst. Despite its ability to proliferate and survive as a free-living organism, Acanthamoeba is also a facultative parasite of humans, most frequently causing a painful, potentially blinding infection of the eye, called Acanthamoeba keratitis (AK), in immunocompetent individuals. Acanthamoeba is also an opportunistic parasite, and in immunocompromised individuals it is responsible for an often fatal infection of the brain, named granulomatous amoebic encephalitis (GAE) (1). The ability of the vast majority of immunocompetent humans to resist infection coupled with the susceptibility of the immunocompromised demonstrates the importance of the immune system in resistance to infection. However, and

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 .…”

“…It is secreted in reaction to PAMPs, specifically to certain lipopolysaccharides recognized by TLR-4. 10,12 Thus, inflammatory cells positive to IL-1β indicate the presence of a pathogen or of cell damage in host tissues. 38 The current data show an increase in IL-1β-positive inflammatory cells at the beginning of the infection followed by a decrease in the later stages, which is in agreement with previous descriptions of the course of the inflammatory response resulting by an A griffini infection and detected by standard histological techniques.…”

“…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 …”

“…Macrophages are known to respond chemotactically to Acanthamoeba sp antigens (PAMPs) and are able to kill the trophozoites in vitro. [10][11][12] Previous research has used histological analysis to examine the chronic inflammation characteristic of AK 2,5 but not immunohistochemical analysis to identify the molecules of the innate immune response. The current contribution focused on determining the kinetics of acute histological damage to the cornea as well as the specific interleukins and an apoptosis factor involved in the innate immune response after infection with a T3 isolate (A griffini).…”

The Expression of TLR2 and TLR4 in the Kidneys and Heart of Mice Infected with Acanthamoeba Spp.

“…The recognition of these patterns by TLRs initiates the migration and aggregation of immunes cells at the site of infection, which in turn leads to the development of in ammation [15]. TLRs activate signaling pathways that lead to activation of the transcription factors NF-κB and IRFs, which control the expression of genes encoding proin ammatory cytokines, such as TNF-α, IL-8 and IFN-γ [16,17]. A lack of TLR2 and TLR4 on the immune cells leads to a delayed phagocytosis of pathogens, including bacteria such as Escherichia coli, Salmonella typhimurium and Staphylococcus aureus [18].…”