Role of toxoplasma gondii DegP, a rhoptry serine protease, on microbicidal effects of THP-1 cell lines

Abstract

Toxoplasma gondii, the causative agent of toxoplasmosis, is an obligate intracellular protozoan parasite that infects approximatively 30% of the worlds human population. While the disease is asymptomatic in immunocompetent individuals, it can be life threatening in immunocompromised patients and in infected pregnant women. T. gondii has the ability to infect all nucleated cells including macrophages. Its replication seems to be dependent from the downregulation of ROS production by these cells. Nox-4 is an enzyme involved in the generation of ROS in different cells. Macrophage Nox4-dependent ROS production is crucial for the upregulation of MIF that is required to control parasite growth. DegP is a serine protease that cleaves and refolds unfolding proteins functioning in the periplasmic space of the Gram-negative bacteria. It is a highly conserved family of proteins functioning in all living organisms and assist in resistance of microorganisms in stress conditions. In T. gondii, a DegP-like serine protease was identified and was demonstrated to play an essential role in the virulence of the parasite. Our study aimed to decipher the molecular dictating the virulence of TgDegP. For these reasons, macrophage derived from THP-1 monocytes were infected with Pru and KO-DegPII. The transcript levels of Nox-4, MIF and iNOS were assessed by real time PCR. Reactive Oxygen Species (ROS) production was measured using flow cytometer. The levels of pro-inflammatory cytokines (IL-1β, IL-6, MCP-1, IL-12 and TNF-α, INF-γ) and anti-inflammatory cytokines (IL-10 and TGF-β) produced by the macrophages upon infection with KO-DegPII or its control Pru strain were also assessed by real-time PCR and ELISA. Our study demonstrated that TgDegP did not show a well-defined role on pro-inflammatory cytokines and whether it is involved in the repression of these cytokines production. On the other hand, TgDegP might have a potential role in repressing IL-1β transcription. In addition, TgDegP did not show a difference in mRNA level of MIF, Nox-4 and iNOS and did not affect ROS production. Therefore, it will be of high interest to elaborate more researches especially in vivo studies where all physiological conditions are met in order to establish a clear correlation of TgDegP with the microbicidal effects of cells of the immune system.