Expression profiles of NOD-like receptors and regulation of NLRP3 inflammasome activation in Toxoplasma gondii-infected human small intestinal epithelial cells

Jia-Qi Chu,Weiyun Wu,Cong Huang,Young-Ha Lee,Juan-Hua Quan,Fei Fei Gao,Sang Hyuk Lee,Zhaobin Pan,Chunchao Li,Jinhui Sun,Hao Wang

doi:10.1186/s13071-021-04666-w

Abstract

BackgroundToxoplasma gondii is a parasite that primarily infects through the oral route. Nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) play crucial roles in the immune responses generated during parasitic infection and also drive the inflammatory response against invading parasites. However, little is known about the regulation of NLRs and inflammasome activation in T. gondii-infected human small intestinal epithelial (FHs 74 Int) cells.MethodsFHs 74 Int cells infected with T. gondii were subsequently evaluated for morphological changes, cytotoxicity, expression profiles of NLRs, inflammasome components, caspase-cleaved interleukins (ILs), and the mechanisms of NLRP3 and NLRP6 inflammasome activation. Immunocytochemistry, lactate dehydrogenase assay, reverse transcription polymerase chain reaction (RT-PCR), real-time quantitative RT-PCR, and western blotting techniques were utilized for analysis.ResultsUnder normal and T. gondii-infected conditions, members of the NLRs, inflammasome components and caspase-cleaved ILs were expressed in the FHs Int 74 cells, except for NLRC3, NLRP5, and NLRP9. Among the NLRs, mRNA expression of NOD2, NLRP3, NLRP6, and NAIP1 was significantly increased in T. gondii-infected cells, whereas that of NLRP2, NLRP7, and CIITA mRNAs decreased significantly in a time-dependent manner. In addition, T. gondii infection induced NLRP3, NLRP6 and NLRC4 inflammasome activation and production of IL-1β, IL-18, and IL-33 in FHs 74 Int cells. T. gondii-induced NLRP3 inflammasome activation was strongly associated with the phosphorylation of p38 MAPK; however, JNK1/2 had a weak effect. NLRP6 inflammasome activation was not related to the MAPK pathway in FHs 74 Int cells.ConclusionsThis study highlighted the expression profiles of NLRs and unraveled the underlying mechanisms of NLRP3 inflammasome activation in T. gondii-infected FHs 74 Int cells. These findings may contribute to understanding of the mucosal and innate immune responses induced by the NLRs and inflammasomes during T. gondii infection in FHs 74 Int cells.Graphical

Highlights

Toxoplasma gondii is a parasite that primarily infects through the oral route
Chu et al Parasites Vectors (2021) 14:153 of the mucosal and innate immune responses induced by the Nucleotide-binding oligomerization domain-like recep‐ tors (NLRs) and inflammasomes during T. gondii infection in FHs 74 Int cells
Our results indicated that the majority of the NLR family members, including NOD1, NOD2, NLRC4, NLRC5, NLRP1, NLRP2, NLRP3, NLRP4, NLRP6, NLRP7, NLRP8, NLRP10, NLRP11, NLRP12, NLRP13, NLRP14, NAIP1, CIITA, and NLRX1 were expressed in these cells under normal conditions (Fig. 1a)

Summary

Introduction

Toxoplasma gondii is a parasite that primarily infects through the oral route. Nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) play crucial roles in the immune responses generated during parasitic infection and drive the inflammatory response against invading parasites. Intestinal epithelial cells can sense and respond to the invading microbial stimuli to reinforce their barrier function They participate in the coordination of appropriate immune responses [3]. The innate immune system plays a significant role in sensing pathogens and triggering biological mechanisms to control infection and eliminate pathogens [4, 5]. It is activated when pattern recognition receptor proteins, such as Toll-like receptors (TLRs) or nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs), detect the presence of pathogens, their products, or the danger signals [5,6,7]

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