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

Toll-like receptor 4 (TLR4) deficiency impedes Toxoplasma gondii excreted-secreted antigens (ESA)-induced abortion

INTRODUCTION

Toxoplasma gondii is an opportunistic intracellular parasite that is a major pathogenic factor in miscarriage, especially when it occurs early in pregnancy. We have previously demonstrated that the regulation of forkhead box transcription factor (Foxp3) is associated with abortion in early pregnancy caused by excretory-secretory antigen (ESA) of strain China 1. We aimed to reveal the underlying mechanism of miscarriage caused by ESA.

METHODS

A TLR4-/- pregnant mouse model was successfully constructed. Pregnant mice at gestational day 5 (G5) were injected with ESA. All animals were sacrificed on G13, pregnancy outcomes were observed, and abortion rates were calculated. Placental status observed by Hematoxylin-eosin staining; gene expression was measured by IHC; flow cytometry analysis was used to determine the number and function of regulatory T cells. In EL4 cells, real-time PCR and Western blot were used to evaluate gene expression and cytokines assay.

RESULTS

In vivo studies revealed that ESA injection caused 83% abortion in pregnant mice but only 35% abortion in TLR4-/- pregnant mice. In addition, ESA attenuated the number and function of regulatory T cells, further suppressed Foxp3, FOXO1 levels, and upregulated CD127 expression. TLR4-/- mice partially reversed this inhibitory effect on regulatory T cells. Furthermore, in vitro studies revealed that ESA inhibited TLR4/NF-κB signaling pathway expression and that TLR4 agonists significantly restored the ESA-induced decrease in Foxp3.

DISCUSSION

These findings suggest that ESA suppresses Foxp3 expression by blocking TLR4/NF-κB signaling, resulting in miscarriage. More importantly, the results indicated that miscarriage caused by ESA is TLR4 dependent.

Inhibition of Foxp3 expression in the placenta of mice infected intraperitoneally by toxoplasma gondii tachyzoites: insights into the PPARγ/miR-7b-5p/Sp1 signaling pathway

BACKGROUND

Toxoplasma gondii, an obligate intracellular parasitic protozoa, infects approximately 30% of the global population. Contracting T. gondii at the primary infection of the mother can result in neonatal microcephaly, chorioretinitis, hydrocephalus, or mortality. Our previous study indicated that pregnant mice infected with T. gondii displayed a decrease in both the number and the suppressive ability of regulatory T cells, accompanied by the reduced Forkhead box P3 (Foxp3). Numerous studies have proved that microRNAs (miRNAs) are implicated in T. gondii infection, but there is meager evidence on the relationship between alterations of miRNAs and downregulation of Foxp3 induced by T. gondii.

METHODS

Quantitative reverse transcription polymerase chain reaction was utilized to detect the transcriptions of miRNAs and Foxp3. Protein blotting and immunofluorescence were used to detect the expressions of Foxp3 and related transcription factors. The structure of mouse placenta was observed by hematoxylin and eosin (HE) staining. To examine the activity of miR-7b promoter and whether miR-7b-5p targets Sp1 to suppress Foxp3 expression, we constructed recombinant plasmids containing the full-length/truncated/mutant miR-7b promoter sequence or wildtype/mutant of Sp1 3' untranslated region (3' UTR) to detect the fluorescence activity in EL4 cells.

RESULTS

In T. gondii-infected mice, miR-7b transcription was significantly elevated, while Foxp3 expression was decreased in the placenta. In vitro, miR-7b mimics downregulated Foxp3 expression, whereas its inhibitors significantly upregulated Foxp3 expression. miR-7b promoter activity was elevated upon the stimulation of T. gondii antigens, which was mitigated by co-transfection of mutant miR-7b promoter lacking peroxisome proliferator-activated receptor γ (PPARγ) target sites. Additionally, miR-7b mimics diminished Sp1 expression, while miR-7b inhibitors elevated its expression. miR-7b mimics deceased the fluorescence activity of Sp1 3' untranslated region (3' UTR), but it failed to impact the fluorescence activity upon the co-transfection of mutant Sp1 3' UTR lacking miR-7b target site.

CONCLUSIONS

T. gondii infection and antigens promote miR-7b transcription but inhibit Foxp3 protein and gene levels. T. gondii antigens promote miR-7b promoter activity by a PPARγ-dependent mechanism. miR-7b directly binds to Sp1 3' UTR to repress Sp1 expression. Understanding the regulatory functions by which T. gondii-induced miR-7b suppresses Foxp3 expression can provide new perspectives for the possible therapeutic avenue of T. gondii-induced adverse pregnancy outcomes.

The Decreased Treg Cells Number Associated with Retinal Lesion Size in Ocular Toxoplasmosis

Introduction

The imbalance of the immune response is an important factor contributing to the incidence of ocular toxoplasmosis (OT). Regulatory T cells (Treg) play a key role in maintaining the balance between Th1 and Th17 immune responses, while interleukin-27 (IL-27) levels are related to the differentiation of Th17 cells. This study analyzes the differences in the number of Treg cells and the level of IL-27 between OT patients and seropositive individuals without ocular lesions and its correlation with retinal lesion size.

Methods

This analytic observational study, conducted for 8 months, involved 11 OT patients and 10 seropositive individuals without ocular lesions. All subjects underwent a comprehensive ophthalmological examination. Retinal lesions were documented by fundus photographs and the size was measured using Digimizer 4.2.2.0 software. Isolation of peripheral blood mononuclear cells (PBMC) was performed to measure the number of Treg cells using flow cytometry and interleukin-27 levels were assessed using the Sandwich enzyme-linked immunosorbent assay (ELISA) technique. Data were analyzed with SPSS.

Result

The number of Treg cells in the OT group (47.16 ± 15.66%) was lower than in the seropositive group without the ocular lesions (62.86 ± 17.08%) (p = 0.029). The serum IL-27 levels in the OT group were not significantly different from the seropositive group without the ocular lesions (p = 0.360). The number of Treg cells was significantly related to retinal lesion size (p = 0.043), with a correlation coefficient of -0.648, indicating a strong and inverse correlation. There was no significant correlation between serum IL-27 levels and retinal lesion size (p = 0.556).

Conclusion

Ocular toxoplasmosis patients have a low number of Treg cells that are inversely related to the retinal lesion size. The size of the retinal lesion increases as the number of Treg cells decreases.

Regulatory T cells in parasite infections: susceptibility, specificity and specialisation

Regulatory T cells (Tregs) are essential to control immune system responses to innocuous self-specificities, intestinal and environmental antigens. However, they may also interfere with immunity to parasites, particularly in chronic infection. Susceptibility to many parasite infections is, to a greater or lesser extent, controlled by Tregs, but often they play a more prominent role in moderating the immunopathological consequences of parasitism, and dampening bystander reactions in an antigen-nonspecific manner. More recently, Treg subtypes have been defined which may preferentially act in different contexts; we also discuss the degree to which this specialisation is now being mapped onto how Tregs maintain the delicate balance between tolerance, immunity, and pathology in infection.

From the immune system to mood disorders especially induced by Toxoplasma gondii: CD4+ T cell as a bridge

Toxoplasma gondii (T. gondii), a ubiquitous and obligatory intracellular protozoa, not only alters peripheral immune status, but crosses the blood-brain barrier to trigger brain parenchymal injury and central neuroinflammation to establish latent cerebral infection in humans and other vertebrates. Recent findings underscore the strong correlation between alterations in the peripheral and central immune environment and mood disorders. Th17 and Th1 cells are important pro-inflammatory cells that can drive the pathology of mood disorders by promoting neuroinflammation. As opposed to Th17 and Th1, regulatory T cells have inhibitory inflammatory and neuroprotective functions that can ameliorate mood disorders. T. gondii induces neuroinflammation, which can be mediated by CD4+ T cells (such as Tregs, Th17, Th1, and Th2). Though the pathophysiology and treatment of mood disorder have been currently studied, emerging evidence points to unique role of CD4+ T cells in mood disorder, especially those caused by T. gondii infection. In this review, we explore some recent studies that extend our understanding of the relationship between mood disorders and T. gondii.

Involvement of chemokine receptor CXCR3 in the defense mechanism against Neospora caninum infection in C57BL/6 mice

C-X-C motif chemokine receptor 3 (CXCR3) is an important receptor controlling the migration of leukocytes, although there is no report regarding its role in Neospora caninum infection. Herein, we investigated the relevance of CXCR3 in the resistance mechanism to N. caninum infection in mice. Wild-type (WT) C57BL/6 mice and CXCR3-knockout (CXCR3KO) mice were used in all experiments. WT mice displayed a high survival rate (100%), while 80% of CXCR3KO mice succumbed to N. caninum infection within 50 days. Compared with WT mice, CXCR3KO mice exhibited significantly lower body weights and higher clinical scores at the subacute stage of infection. Flow cytometric analysis revealed CXCR3KO mice as having significantly increased proportions and numbers of CD11c-positive cells compared with WT mice at 5 days post infection (dpi). However, levels of interleukin-6 and interferon-γ in serum and ascites were similar in all groups at 5 dpi. Furthermore, no differences in parasite load were detected in brain, spleen, lungs or liver tissue of CXCR3KO and WT mice at 5 and 21 dpi. mRNA analysis of brain tissue collected from infected mice at 30 dpi revealed no changes in expression levels of inflammatory response genes. Nevertheless, the brain tissue of infected CXCR3KO mice displayed significant necrosis and microglial activation compared with that of WT mice at 21 dpi. Interestingly, the brain tissue of CXCR3KO mice displayed significantly lower numbers of FoxP3⁺ cells compared with the brain tissue of WT mice at 30 dpi. Accordingly, our study suggests that the lack of active regulatory T cells in brain tissue of infected CXCR3KO mice is the main cause of these mice having severe necrosis and lower survival compared with WT mice. Thus, CXCR3⁺ regulatory T cells may play a crucial role in control of neosporosis.

Immune responses to Toxoplasma gondii

Toxoplasma gondii is an obligate intracellular parasite that can cause severe complications in the newborn and immunocompromised individuals. The parasite evokes a strong innate immune response in the infected hosts which is followed by a robust adaptive immunity. In the last few years, importance of innate immune mechanisms dependent on the role of MyD-88 independent pathways, inflammatory monocytes and innate lymphocyte have been identified. However, notwithstanding the strong immune response to the parasite, the chronic infection persists in the host. The inability to prevent chronic infection can be attributed to aberration in the memory CD8 T cell response caused by an increased expression of inhibitory receptors that leads to their dysfunctionality.