P2X7 receptor mediates NLRP3-dependent IL-1β secretion and parasite proliferation in Toxoplasma gondii-infected human small intestinal epithelial cells

Abstract

Background Toxoplasma gondii can invade and replicate in all nucleated cells in a wide range of host species, and infection induces IL-1β production. IL-1β plays central roles in the stimulation of the innate immune system and inflammation. However, little is known of the innate immune responses in human fetal small intestinal epithelial cells (FHs 74 Int cells) after T. gondii infection.MethodsFHs 74 Int cells were infected with the T. gondii GFP-RH strain. Then, IL-1β production and its mechanisms of action were evaluated using ELISA, MTT cell viability assays, Western blotting, immunofluorescence, quantitative real-time polymerase chain reaction (qRT-PCR), and gene-specific small interfering RNA (siRNA) transfection.ResultsInfection of FHs 74 Int cells by T. gondii triggered significant time- and dose-dependent IL-1β production. Although T. gondii activated NLRP1, NLRP3, NLRC4 and AIM2 inflammasomes in FHs 74 Int cells, NLRP3 levels were consistently and significantly time-dependently increased, while the other inflammasomes were not. Transfection with siRNA targeting NLRP3, cleaved caspase-1 (Casp-1) or ASC significantly reduced T. gondii-induced IL-1β production, whereas T. gondii proliferation was markedly increased. Toxoplasma gondii infection activated P2X7 receptor (P2X7R) levels in FHs 74 Int cells in a time-dependent manner; however, transfection with siRNA targeting P2X7R significantly reduced T. gondii-induced IL-1β secretion and substantially increased T. gondii proliferation, which is mediated by decreased protein expression levels of NLRP3, cleaved Casp-1 and ASC. Collectively, NLRP3-dependent IL-1β secretion is mediated by P2X7R in small intestinal epithelial cells in response to T. gondii infection, thereby controlling parasite proliferation.ConclusionsThis study revealed that the P2X7R/NLRP3 pathway plays important roles in IL-1β secretion and inhibition of T. gondii proliferation in small intestinal epithelial cells. These results not only contribute to our understanding of the mucosal immune mechanisms of T. gondii infection but also offer new insight into the identification of innate resistance in the gut epithelium.Electronic supplementary materialThe online version of this article (10.1186/s13071-017-2573-y) contains supplementary material, which is available to authorized users.

Analytical and Clinical Assessment of a Portable, Isothermal Recombinase Polymerase Amplification (RPA) Assay for the Molecular Diagnosis of Urogenital Schistosomiasis

“…In adopting this strategy, significant gains have been made in reducing the overall burden of disease throughout many areas of sub-Saharan Africa [ 16 , 17 ]. As the number of individuals infected, as well as the intensity of infection within those infected individuals, is diminished, however, a sharp decline in transurinal egg output causes great difficulty in reliably detecting individuals with low levels of infection using standard diagnostic methods—urine-egg microscopy and haematuria-detecting lateral-flow strips [ 18 , 19 , 20 , 21 ].…”

Treatment of mice with IL2-complex enhances inflammasome-driven IFN-γ production and prevents lethal toxoplasmosis

“…It is likely that this divergence highlights the evolutionary complexity of parasites and suggests that more highly evolved organisms have developed a more complex inflammasome-dependent interplay with their hosts. In line with this hypothesis, it was shown recently in vitro that T. gondii also activates the NLRC4 and AIM2 inflammasomes in human fetal small epithelial cells [47], as well as the expression of NLRP6, NLRP8 and NLRP13 in THP-1 macrophages [48]. Due to the diverse expression of different internalization receptors and the abundance of inflammasome components, various myeloid cells seem to be endowed with unique abilities to interact with T. gondii.…”

“…Toxoplasma gondii appears to activate both NLRP1 and NLRP3 [24], yet the specificity of this activation remains elusive. While the activation of NLRP3 in response to T. gondii appears to be influenced by P2X7 receptor-dependent potassium efflux and the induction of reactive oxygen species [47,[49][50][51], the exact mechanisms of how T. gondii activates multiple inflammasomes remain enigmatic. In this context it is also interesting to note that in vitro infection of mouse macrophages and human monocytes with T. gondii only leads to the secretion of IL-1β, but not IL-18 [24,52].…”

Intestinal epithelial cells: at the interface of the microbiota and mucosal immunity

“…Although PRR‐mediated mechanisms of sensing microbial products are the most extensively studied, IECs also use a number of other pathways. For example, inflammasomes have been shown to play an important role in IEC‐sensing of microbial stimuli and damage‐associated molecular patterns and in triggering protective barrier responses . The NAIP‐NLRC4 inflammasome has recently been implicated in the IEC response to Salmonella infection in vivo , enabling pro‐inflammatory programmes that result in production of cytokines and the hormone‐like eicosanoid prostaglandin E 2 , as well as lytic cell death and the expulsion of infected IECs .…”

“…For example, inflammasomes have been shown to play an important role in IEC-sensing of microbial stimuli and damage-associated molecular patterns and in triggering protective barrier responses. [18][19][20][21] The NAIP-NLRC4 inflammasome has recently been implicated in the IEC response to Salmonella infection in vivo, enabling pro-inflammatory programmes that result in production of cytokines and the hormone-like eicosanoid prostaglandin E 2 , as well as lytic cell death and the expulsion of infected IECs. 22 The autophagy pathway has also been shown to be critical for maintaining intestinal epithelial integrity in response to microbes, and a recent study demonstrated that release of lysozyme by Paneth cells during bacterial infection is mediated through an autophagy-based alternative secretion pathway.…”