Toxoplasma gondii excreted-secreted antigens suppress Foxp3 via PI3K-AKT-mTOR signaling pathway

Progress on H2B as a multifunctional protein related to pathogens

Histone H2B is a member of the core histones, which together with other histones form the nucleosome, the basic structural unit of chromosomes. As scientists delve deeper into histones, researchers gradually realize that histone H2B is not only an important part of nucleosomes, but also plays a momentous role in regulating gene transcription, acting as a receptor and antimicrobial action outside the nucleus. There are a variety of epigenetically modified sites in the H2B tail rich in arginine and lysine, which can occur in ubiquitination, phosphorylation, methylation, acetylation, etc. When stimulated by foreign factors such as bacteria, viruses or parasites, histone H2B can act as a receptor for the recognition of these pathogens, and induce an intrinsic immune response to enhance host defense. In addition, the extrachromosomal histone H2B is also an important anti-microorganism agent, which may be the key to the development of antibiotics in the future. This review aims to summarize the interaction between histone H2B and etiological agents and explore the role of H2B in epigenetic modifications, receptors and antimicrobial activity.

Memory regulatory T cells in pregnancy

Pregnancy requires the process of maternal immune tolerance to semi-allogeneic embryos. In contrast, an overreactive maternal immune system to embryo-specific antigens is likely to result in the rejection of embryos while damaging the invading placenta, such that the likelihood of adverse pregnancy outcomes can be increased. Regulatory T cells (Tregs) are capable of suppressing excessive immune responses and regulating immune homeostasis. When stimulating Tregs, specific antigens will differentiate into memory Tregs with long-term survival and rapid and powerful immune regulatory ability. Immunomodulatory effects mediated by memory Tregs at the maternal-fetal interface take on critical significance in a successful pregnancy. The impaired function of memory Tregs shows a correlation with various pregnancy complications (e.g., preeclampsia, gestational diabetes mellitus, and recurrent pregnancy losses). However, the differentiation process and characteristics of memory Tregs, especially their role in pregnancy, remain unclear. In this study, a review is presented in terms of memory Tregs differentiation and activation, the characteristics of memory Tregs and their role in pregnancy, and the correlation between memory Tregs and pregnancy complications. Furthermore, several potential therapeutic methods are investigated to restore the function of memory Tregs in accordance with immunopathologies arising from memory Tregs abnormalities and provide novel targets for diagnosing and treating pregnancy-associated diseases.

Regulation of phosphoinositide metabolism in Apicomplexan parasites

Phosphoinositides are a biologically essential class of phospholipids that contribute to organelle membrane identity, modulate membrane trafficking pathways, and are central components of major signal transduction pathways that operate on the cytosolic face of intracellular membranes in eukaryotes. Apicomplexans (such as Toxoplasma gondii and Plasmodium spp.) are obligate intracellular parasites that are important causative agents of disease in animals and humans. Recent advances in molecular and cell biology of Apicomplexan parasites reveal important roles for phosphoinositide signaling in key aspects of parasitosis. These include invasion of host cells, intracellular survival and replication, egress from host cells, and extracellular motility. As Apicomplexans have adapted to the organization of essential signaling pathways to accommodate their complex parasitic lifestyle, these organisms offer experimentally tractable systems for studying the evolution, conservation, and repurposing of phosphoinositide signaling. In this review, we describe the regulatory mechanisms that control the spatial and temporal regulation of phosphoinositides in the Apicomplexan parasites Plasmodium and T. gondii. We further discuss the similarities and differences presented by Apicomplexan phosphoinositide signaling relative to how these pathways are regulated in other eukaryotic organisms.

Anti-Toxoplasma gondii IgM Long Persistence: What Are the Underlying Mechanisms?

Diagnosis of Toxoplasma gondii acute infection was first attempted by detection of specific IgM antibodies, as for other infectious diseases. However, it was noted that this immunoglobulin declines slowly and may last for months or even years. Apart from the diagnostic problem imposed on clinical management, this phenomenon called our attention due to the underlying phenomena that may be causing it. We performed a systematic comparison of reports studying IgM antibody kinetics, and the data from the papers were used to construct comparative plots and other graph types. It became clear that this phenomenon is quite generalized, and it may also occur in animals. Moreover, this is not a technical issue, although some tests make more evident the prolonged IgM decay than others. We further investigated biological reasons for its occurrence, i.e., infection dynamics (micro-reactivation–encystment, reinfection and reactivation), parasite strain relevance, as well as host innate, natural B cell responses and Ig class-switch problems inflicted by the parasite. The outcomes of these inquiries are presented and discussed herein.

The role of IL-15 on vulvovaginal candidiasis in mice and related adverse pregnancy outcomes

Vulvovaginal candidiasis (VVC), a major gynecological disease with high recurrence rate, increases the risk of abortion, intrauterine infection, premature rupture of membranes, and premature birth in pregnancy. However, the exact pathogenesis of this disease has yet to be elucidated. To facilitate understanding of the pathogenesis of VVC in pregnancy, this study sought to establish an animal model of vaginal infection with Candida albicans in pregnant mice. Female mice were mated with male mice, and female mice were infected with C. albicans at E4.5 (embryonic day 4.5). The weight and abortion rate of pregnant mice at E0.5, E4.5, E8.5, E11.5, and E18.5 were recorded, respectively, as well as the weights of fetus and placenta on E18.5. Fetal weight at E18.5 and the weight growth rate in the experimental mice was lower than those in the control mice, but the placenta weight at E18.5 and the abortion rate in the experimental mice were increased with those of the control mice. Hematoxylin-eosin (H&E) staining, Gomori-Grocott staining and vaginal lavage culturing were conducted to verify that the experimental mice were infected with C. albicans. Differentially expressed gene IL-15 was screened out by polymerase chain reaction (PCR) array between the two groups. Enzyme-linked immunosorbent assay (ELISA) showed that IL-15 expression in plasma of the mice was decreased in the experimental group compared with the control group. RT-qPCR confirmed that IL-15 mRNA expression was increased in placental tissues, while mRNA expression of IL-15R/JAK1-JAK3/PI3K/PDK1/AKT/P70S6K-mTOR was decreased in placental tissues. In conclusion, this study demonstrated that VVC in BALB/c pregnant mice led to a series of adverse pregnancy outcomes that were related to changes in IL-15 and its downstream signaling pathways, which may indicate a potential therapy for VVC during pregnancy in humans.

The Role and Function of Regulatory T Cells in Toxoplasma gondii-Induced Adverse Pregnancy Outcomes

Infection with Toxoplasma gondii (T. gondii) during the pregnant period and its potentially miserable outcomes for the fetus, newborn, and even adult offspring continuously occur worldwide. People acquire infection through the consumption of infected and undercooked meat or contaminated food or water. T. gondii infection in pregnant women primarily during the gestation causes microcephaly, mental and psychomotor retardation, or death. Abnormal pregnancy outcomes are mainly associated with regulatory T cell (Treg) dysfunction. Tregs, a special subpopulation of T cells, function as a vital regulator in maintaining immune homeostasis. Tregs exert a critical effect on forming and maintaining maternal-fetal tolerance and promoting fetal development during the pregnancy period. Forkhead box P3 (Foxp3), a significant functional factor of Tregs, determines the status of Tregs. In this review, we summarize the effects of T. gondii infection on host Tregs and its critical transcriptional factor, Foxp3.

Toxoplasma gondii Infection Inhibits Histone Crotonylation to Regulate Immune Response of Porcine Alveolar Macrophages

Toxoplasma gondii (T. gondii) is an obligate intracellular parasite that can infect almost all warm-blooded animals, causing serious public health problems. Lysine crotonylation (Kcr) is a newly discovered posttranslational modification (PTM), which is first identified on histones and has been proved relevant to procreation regulation, transcription activation, and cell signaling pathway. However, the biological functions of histone crotonylation have not yet been reported in macrophages infected with T. gondii. As a result, a total of 1,286 Kcr sites distributed in 414 proteins were identified and quantified, demonstrating the existence of crotonylation in porcine alveolar macrophages. According to our results, identified histones were overall downregulated. HDAC2, a histone decrotonylase, was found to be significantly increased, which might be the executor of histone Kcr after parasite infection. In addition, T. gondii infection inhibited the crotonylation of H2B on K12, contributing on the suppression of epigenetic regulation and NF-κB activation. Nevertheless, the reduction of histone crotonylation induced by parasite infection could promote macrophage proliferation via activating PI3K/Akt signaling pathway. The present findings point to a comprehensive understanding of the biological functions of histone crotonylation in porcine alveolar macrophages, thereby providing a certain research basis for the mechanism research on the immune response of host cells against T. gondii infection.

The host mTOR pathway and parasitic diseases pathogenesis

The mechanistic (or mammalian) target of rapamycin (mTOR) is considered as a critical regulatory enzyme involved in essential signaling pathways affecting cell growth, cell proliferation, protein translation, regulation of cellular metabolism, and cytoskeletal structure. Also, mTOR signaling has crucial roles in cell homeostasis via processes such as autophagy. Autophagy prevents many pathogen infections and is involved on immunosurveillance and pathogenesis. Immune responses and autophagy are therefore key host responses and both are linked by complex mTOR regulatory mechanisms. In recent years, the mTOR pathway has been highlighted in different diseases such as diabetes, cancer, and infectious and parasitic diseases including leishmaniasis, toxoplasmosis, and malaria. The current review underlines the implications of mTOR signals and intricate networks on pathogen infections and the modulation of this master regulator by parasites. Parasitic infections are able to induce dynamic metabolic reprogramming leading to mTOR alterations in spite of many other ways impacting this regulatory network. Accordingly, the identification of parasite effects and interactions over such a complex modulation might reveal novel information regarding the biology of the abovementioned parasites and might allow the development of therapeutic strategies against parasitic diseases. In this sense, the effects of inhibiting the mTOR pathways are also considered in this context in the light of their potential for the prevention and treatment of parasitic diseases.

Toxoplasma gondii excreted-secreted antigens suppress Foxp3 promoter activity via a SP1-dependent mechanism

Toxoplasma gondii excreted-secreted antigens (ESA) could result in adverse outcomes of pregnancy including abortion, stillbirth, foetal infection or teratogenesis in mice during early stage of pregnancy. Defective generation or function of regulatory T cells (Tregs) may account for those adverse pregnancy outcomes. Forkhead box p3 (Foxp3), which is the key transcriptional factor of Tregs, modulates its development and maintains inhibitory function. We previously demonstrated that ESA inhibited Foxp3 expression by attenuating transforming growth factor β RII/Smad2/Smad3/Smad4 pathway. In this study, we propose to study the role of ESA on the activity of Foxp3 promoter and explore potential mechanisms. We demonstrated that ESA suppressed Foxp3 promoter activity using dual-luciferase reporter assay. ESA functioned at -443/-96 region of Foxp3 promoter to suppress its activity using truncated fragments of Foxp3 promoter. Further analysis revealed that suppressive role of ESA on Foxp3 promoter activity is related to specificity protein 1 (SP1). Transfection of expression plasmid of pcDNA3.1-SP1 could restore the down-regulation of Foxp3 induced by ESA. In conclusion, this study provides a new mechanism by which ESA could inhibit the Foxp3 promoter activity via SP1.