Inhibition of Nitric Oxide Production in Activated Macrophages Caused by Toxoplasma gondii Infection Occurs by Distinct Mechanisms in Different Mouse Macrophage Cell Lines

Abstract

Toxoplasma gondii, the causative agent of toxoplasmosis, is a widespread intracellular parasite able to infect virtually any nucleated cell. T. gondii infection of activated macrophages inhibits nitric oxide (NO) production; however, parasite effectors responsible for this block have not been defined. Macrophage populations are extremely heterogeneous, responding differently to stimuli and to parasite infection. Here we evaluated the inhibition of NO production caused by T. gondii infection of J774-A1 and RAW 264.7 macrophages and assessed the role of several known parasite virulence factors in this phenotype. Infection of activated macrophages from both macrophage lines reduced NO production, however, the mechanism of this decrease was different. Consistent with previous reports, infected J774-A1 macrophages had reduced iNOS expression and lower number of iNOS positive cells. In contrast, T. gondii infection of RAW 264.7 macrophages did not alter iNOS expression or the number of iNOS positive cells, and yet it led to lower levels of NO production. Deletion of a number of previously defined virulence factors including ROP kinases that disrupt innate immune factors, TgIST which blocks STAT1 activation, as well as the secretory trafficking proteins ASP5 and MYR1, did not alter the phenotype of decreased NO production. Taken together our findings indicate that T. gondii infection inhibits NO production of activated macrophages by different mechanisms that involve reduction of iNOS expression vs. iNOS impairment, and suggest that a novel parasite effector is involved in modulating this important host defense pathway.

Cyclooxygenase (COX)-2 Inhibitors Reduce Toxoplasma gondii Infection and Upregulate the Pro-inflammatory Immune Response in Calomys callosus Rodents and Human Monocyte Cell Line

“…Thus, it is possible conclude that meloxicam and celecoxib induce a pro-inflammatory immune response, which triggers significant reduction in T. gondii infection. Many studies demonstrated the important protective role of IFN-γ, nitrite (Gazzinelli et al, 1994; Lang et al, 2007; Kemp et al, 2013; Koblansky et al, 2013; Behnke et al, 2017; Abreu-Cabral et al, 2018), IL-17A (Kelly et al, 2005), MIF (Ferro et al, 2008; Flores et al, 2008; Terrazas et al, 2010; Gomes et al, 2011, 2018; Barbosa et al, 2014), TNF and IL-6 (Castro et al, 2013; Barbosa et al, 2014, 2015) during infection by T. gondii . Our recent studies showed that IL-6, TNF and MIF are the most important cytokines involved in the immune response to T. gondii in human trophoblast cells, human explants from third trimester and murine maternal-fetal interface, allowing a significant reduction in the vertical transmission of the parasite (Barbosa et al, 2015; Silva et al, 2017; Gomes et al, 2018).…”

Immunobiotic and Paraprobiotic Potential Effect of Lactobacillus casei in a Systemic Toxoplasmosis Murine Model

“…However, it is known that T. gondii has the ability to evade the cytotoxic effect of nitric oxide by inhibiting the production of NO in mouse activated macrophages [27,28]. Cabral [29] suggest that inhibition of NO production in activated macrophages infected with T. gondii is a general phenomenon, but the suppression of iNOS varies depending on the macrophage cell line. The increase in the percentage of activated macrophages, as well as the production of intracellular nitric oxide in mice treated with immunobiotics, show that inhibition of NO production by T. gondii can be reversed after administration of viable Lc, thereby increasing the microbicidal capacity of activated macrophages.…”

Future of Probiotics and Prebiotics and the Implications for Early Career Researchers

“…Animal models are not strictly necessary for preclinical assessment of probiotics. While humanized animal models can be implemented (Table 1), it is highly challenging to develop ones that simulate microbe-host interaction in humans for niches demonstrating unique physiological features such as the lactobacilli-dominated vaginal niche characterized by a low pH (Miller et al, 2016). Human-based in vitro and ex vivo models followed by small studies with healthy volunteers and larger clinical intervention studies are invariably required to draw more precise and relevant conclusions on probiotic safety, action, and health benefits.…”