CD4+CD25+Foxp3+ regulatory T cells prevent the development of Th1 immune response by inhibition of dendritic cell function during the early stage of Plasmodium yoelii infection in susceptible BALB/c mice

Attenuated T Cell Responses Are Associated With the Blockade of Cerebral Malaria Development by YOP1-Deficient Plasmodium berghei ANKA

Reticulon and the REEP family of proteins stabilize the high curvature of endoplasmic reticulum tubules. The REEP5 homolog in Plasmodium, Plasmodium berghei YOP1 (PbYOP1), plays an important role in the erythrocytic cycle of the P. berghei ANKA and the pathogenesis of experimental cerebral malaria (ECM), but the mechanisms are largely unknown. Here, we show that protection from ECM in Pbyop1Δ-infected mice is associated with reduced intracerebral Th1 accumulation, decreased expression of pro-inflammatory cytokines and chemokines, and attenuated pathologies in the brainstem, though the total number of CD4⁺ and CD8⁺ T cells sequestered in the brain are not reduced. Expression of adhesive molecules on brain endothelial cells, including ICAM-1, VCAM-1, and CD36, are decreased, particularly in the brainstem, where fatal pathology is always induced during ECM. Subsequently, CD8⁺ T cell-mediated cell apoptosis in the brain is compromised. These findings suggest that Pbyop1Δ parasites can be a useful tool for mechanistic investigation of cerebral malaria pathogenesis.

Plasmodium yoelii 17XL infection modified maturation and function of dendritic cells by skewing Tregs and amplificating Th17

Background

Emerging data has suggested that Tregs, Th17, Th1 and Th2 are correlated with early immune mechanisms by controlling Plasmodium infection. Plasmodium infection appeared to impair the antigen presentation and maturation of DCs, leading to attenuation of specific cellular immune response ultimately. Hence, in this study, we aim to evaluate the relevance between DCs and Tregs/Th17 populations in the process and outcomes of infection with Plasmodium yoelii 17XL (P.y17XL).

Methods

DCs detection/analysis dynamically was performed by Tregs depletion or Th17 neutralization in P.y17XL infected BALB/c mice via flow cytometry. Then the levels of cytokines production were detected using enzyme-linked mmunosorbent assay (ELISA).

Results

Our results indicated that Tregs depletion or Th17 neutralization in BALB/c mice infected with P.y17XL significantly up-regulated the percentages of mDC and pDC, increased the expressions of major histocompatibility complex (MHC) class II, CD80, CD86 on DCs and the levels of IL-10/IL-12 secreted by DCs, indicating that abnormal amplification of Tregs or Th17 may damage the maturation and function of DCs during the early stage of malaria infection. Interestingly, we also found that the abnormal amplification of Th17, as well as Tregs, could inhibit the maturation of DCs.

Conclusions

Tregs skewing or Th17 amplification during the early stage of malaria infection may inhibit the maturation and function of DCs by modifying the subsets of DCs, expressions of surface molecules on DCs and secretion mode of cytokines.

Oral administration of vitamin D and importance in prevention of cerebral malaria

Cerebral malaria (CM) is a serious and fatal malaria-associated syndrome caused by the development of an overwhelming proinflammatory response. Vitamin D (Vit.D; cholecalciferol) has regulatory functions associated with both innate and adaptive immune responses. Prevention is better than cure, in this experiment, we evaluated prophylactic oral Vit.D as a means of preventing CM presentation before infection of C57BL/6 mice with Plasmodium berghei ANKA (PbA) by modulating the host proinflammatory response. Mice that were supplemented with oral Vit.D has reduce death rate and ameliorated the integrity of the blood brain barrier. Prophylactic oral vitamin D relieved the symptoms of brain malaria and avoided death, gained valuable time for the diagnosis and treatment post infection. The robust Th1 response was attenuated in the Vit.D + PbA group. Furthermore, T-cell trafficking to the brain was diminished before PbA infection using Vit.D. The results suggest that Vit.D supplementation mediates the development of an anti-inflammatory environment that improves CM severity. In summary, the use of Vit.D as a nutritional supplement in malaria-endemic regions may help reduce the severity and mortality of CM.

Immunogenicity of glycosylphosphatidylinositol-anchored micronemal antigen in natural Plasmodium vivax exposure

Background

Plasmodium vivax is the most geographically widespread malaria species and codominates with Plasmodium falciparum, the deadliest form of the malaria parasite. For the last few years, the number of vivax malaria cases has increased, but vivax malaria is still considered a neglected disease. During the blood stages of their life cycle, P. vivax parasites export several hundred proteins into host red blood cells. Some of these exported proteins have been discovered and studied for use as a blood-stage malaria vaccine. The P. vivax glycosylphosphatidylinositol (GPI)-anchored micronemal antigen (PvGAMA) was identified in previous study, which plays an important role in parasite invasion. To support the hypothesis that PvGAMA can induce an immune response in natural exposure, the antibody responses and cellular immunity against this antigen was demonstrated during and post-infection.

Methods

The recombinant protein PvGAMA was expressed and purified by wheat germ cell-free (WGCF) system. The analysis of humoral and cellular immune responses to the PvGAMA antigen during infection and post-infection with the P. vivax parasite were done by enzyme-linked immunosorbent assay (ELISA) techniques.

Results

During P. vivax infection, 95% of patients showed significant antibody responses to PvGAMA antigen. The cytophilic IgG1 and IgG3 isotypes were the major isotypes produced in response to PvGAMA. A cross-sectional study of anti-PvGAMA responses during and post-infection with P. vivax found that the majority of individuals, approximately 54% of patients, were shown to maintain a positive anti-PvGAMA titre at 3 months post-infection, and some patients had the ability to maintain an antibody response for up to 12 months post-infection. Moreover, PvGAMA had the ability to stimulate a cellular immune response that was characterized by the production of the cytokines IL-2, IFN-γ and IL-10. The levels of the cytokines IFN-γ and IL-10 were significantly increased in PvGAMA-stimulated lymphocyte cultures.

Conclusions

Taken together, PvGAMA had potential to induce an immune response both humoral and cellular immunity in naturally acquired P. vivax infection individuals during infection and post-infection. Therefore, PvGAMA could be as a vaccine candidate to stimulate immune response against P. vivax infection.

Plasmacytoid dendritic cells appear inactive during sub-microscopic Plasmodium falciparum blood-stage infection, yet retain their ability to respond to TLR stimulation

Plasmacytoid dendritic cells (pDC) are activators of innate and adaptive immune responses that express HLA-DR, toll-like receptor (TLR) 7, TLR9 and produce type I interferons. The role of human pDC in malaria remains poorly characterised. pDC activation and cytokine production were assessed in 59 malaria-naive volunteers during experimental infection with 150 or 1,800 P. falciparum-parasitized red blood cells. Using RNA sequencing, longitudinal changes in pDC gene expression were examined in five adults before and at peak-infection. pDC responsiveness to TLR7 and TLR9 stimulation was assessed in-vitro. Circulating pDC remained transcriptionally stable with gene expression altered for 8 genes (FDR < 0.07). There was no upregulation of co-stimulatory molecules CD86, CD80, CD40, and reduced surface expression of HLA-DR and CD123 (IL-3R-α). pDC loss from the circulation was associated with active caspase-3, suggesting pDC apoptosis during primary infection. pDC remained responsive to TLR stimulation, producing IFN-α and upregulating HLA-DR, CD86, CD123 at peak-infection. In clinical malaria, pDC retained HLA-DR but reduced CD123 expression compared to convalescence. These data demonstrate pDC retain function during a first blood-stage P. falciparum exposure despite sub-microscopic parasitaemia downregulating HLA-DR. The lack of evident pDC activation in both early infection and malaria suggests little response of circulating pDC to infection.

Acanthamoeba castellanii Genotype T4 Stimulates the Production of Interleukin-10 as Well as Proinflammatory Cytokines in THP-1 Cells, Human Peripheral Blood Mononuclear Cells, and Human Monocyte-Derived Macrophages

Free-living amoebae of the genus Acanthamoeba can cause severe and chronic infections in humans, mainly localized in immune privileged sites, such as the brain and the eye. Monocytes/macrophages are thought to be involved in Acanthamoeba infections, but little is known about how these facultative parasites influence their functions. The aim of this work was to investigate the effects of Acanthamoeba on human monocytes/macrophages during the early phase of infection. Here, THP-1 cells, primary human monocytes isolated from peripheral blood, and human monocyte-derived macrophages were either coincubated with trophozoites of a clinical isolate of Acanthamoeba (genotype T4) or stimulated with amoeba-derived cell-free conditioned medium. Production of proinflammatory cytokines (tumor necrosis factor alpha [TNF-α], interleukin-6 [IL-6], and IL-12), anti-inflammatory cytokine (IL-10), and chemokine (IL-8) was evaluated at specific hours poststimulation (ranging from 1.5 h to 23 h). We showed that both Acanthamoeba trophozoites and soluble amoebic products induce an early anti-inflammatory monocyte-macrophage phenotype, characterized by significant production of IL-10; furthermore, challenge with either trophozoites or their soluble metabolites stimulate both proinflammatory cytokines and chemokine production, suggesting that this protozoan infection results from the early induction of coexisting, opposed immune responses. Results reported in this paper confirm that the production of proinflammatory cytokines and chemokines by monocytes and macrophages can play a role in the development of the inflammatory response during Acanthamoeba infections. Furthermore, we demonstrate for the first time that Acanthamoeba stimulates IL-10 production in human innate immune cells, which might both promote the immune evasion of Acanthamoeba and limit the induced inflammatory response.

Bacillus Calmette-Guérin-inoculation at different time points influences the outcome of C57BL/6 mice infected with Plasmodium chabaudi chabaudi AS

Bacillus Calmette-Guérin (BCG) is an attenuated Mycobacterium tuberculosis vaccine. We performed a series of co-infection experiments with BCG-Plasmodium chabaudi chabaudi Landau, 1965 AS using C57BL/6 mice to analyse whether BCG can affect the development of protective immunity to infection with Plasmodium spp. and the mechanism of this protection. We divided mice into four groups: BCG-inoculation 4 weeks prior to P. c. chabaudi AS infection (B-4w-Pc); simultaneous BCG-inoculation and P. c. chabaudi AS infection (Pc+B); BCG-inoculation 3 days post P. c. chabaudi AS (Pc-3-B) infection; and mono-P. c. chabaudi AS infection as control (Pc). The parasitemia level in the B-4w-Pc group was noticeably higher than control group at 6-19 days post infection (dpi). Compared with the control group, the proportion of CD4(+)CD69(+) T cells was significantly reduced 5, 8 and 12 dpi, but the proportion of CD4(+)CD25(+)Foxp3(+) Tregs was significantly increased in the B-4w-Pc group on 5 and 8 dpi. The B-4w-Pc group also demonstrated reduced levels of IFN-γ and TNF-α on 5 and 8 dpi and significantly elevated level of IL-10 on 12 dpi. There were significantly fewer mDCs (CD11c(+)CD11b(+)) and pDCs (CD11c(+)B220(+)) in the B-4w-Pc group than the control group at all the time points post infection and the expression of MHC II was noticeably reduced on day 8 pi. Our findings confirmed that BCG inoculation prior to Plasmodium infection resulted in excessive activation and proliferation of Tregs and upregulation of anti-inflammatory mediators, which inhibited establishment of a Th1-dominant immune response during the early stages of Plasmodium infection by inhibiting dendritive cells response. BCG inoculation prior to P. c. chabaudi AS infection may contribute to overgrowth of parasites as well as mortality in mice.

Improvement of the cytotoxic T lymphocyte response against hepatocellular carcinoma by transduction of cancer cells with an adeno-associated virus carrying the interferon-γ gene

Dendritic cell (DC)-based antigen-targeted immunotherapy may offer effective adjuvant therapy for hepatocellular carcinoma (HCC), in which cytotoxic T lymphocytes (CTLs) are key. However, in a number of cases, the activity of CTLs is completely inhibited due to the downregulated expression of major human leukocyte antigen (HLA) class I molecules by HCC cells. The aim of the present study was to overcome this issue. Hep3B cells were transduced by HCC‑specific recombinant adeno‑associated virus (rAAV) carrying human α‑fetoprotein promoter (AFPp) and the interferon‑γ (IFN‑γ) gene (rAAV/AFPp‑IFN‑γ). rAAV carrying the cytomegalovirus promoter (CMVp) and human α‑fetoprotein (AFP) gene (rAAV/CMVp‑AFP) was used to transduce professional antigen‑presenting DCs for the purpose of stimulating a CTL response. It was observed that transduction of DCs with rAAV/CMVp‑AFP resulted in: (i) AFP and interleukin‑12 expression; (ii) high expression levels of cluster of differentiation (CD)80, CD83, CD86, CD40, HLA‑death receptor and CD1a; (iii) T cell populations with marked IFN‑γ expression; (iv) a high percentage of CD69+/CD8+ T cells; and (v) the activity of CTLs against HLA‑A2‑expressing Hep3B cells. The transduction of Hep3B cells with rAAV/AFPp‑IFN‑γ resulted in: (i) IFN‑γ expression; (ii) upregulated expression of HLA‑A2; and (iii) an improved CTL response against HLA‑A2‑deficient Hep3B cells. rAAV/CMVp‑AFP‑transduced DCs elicited an AFP‑specific and HLA‑class I‑restricted CTL response against Hep3B cells. In conclusion, it was shown that the transduction of Hep3B with rAAV/AFPp-IFN-γ upregulated the expression of HLA-A2 and improved the sensitivity to CTL response.

The immunological balance between host and parasite in malaria

Coevolution of humans and malaria parasites has generated an intricate balance between the immune system of the host and virulence factors of the parasite, equilibrating maximal parasite transmission with limited host damage. Focusing on the blood stage of the disease, we discuss how the balance between anti-parasite immunity versus immunomodulatory and evasion mechanisms of the parasite may result in parasite clearance or chronic infection without major symptoms, whereas imbalances characterized by excessive parasite growth, exaggerated immune reactions or a combination of both cause severe pathology and death, which is detrimental for both parasite and host. A thorough understanding of the immunological balance of malaria and its relation to other physiological balances in the body is of crucial importance for developing effective interventions to reduce malaria-related morbidity and to diminish fatal outcomes due to severe complications. Therefore, we discuss in this review the detailed mechanisms of anti-malarial immunity, parasite virulence factors including immune evasion mechanisms and pathogenesis. Furthermore, we propose a comprehensive classification of malaria complications according to the different types of imbalances.

L-arginine exacerbates experimental cerebral malaria by enhancing pro-inflammatory responses

L-Arginine (L-Arg), the substrate for nitric oxide (NO) synthase, has been used to treat malaria to reverse endothelial dysfunction in adults. However, the safety and efficacy of L-Arg remains unknown in malaria patients under the age of five, who are at the greatest risk of developing cerebral malaria (CM), a severe malaria complication. Here, we tested effects of L-Arg treatment on the outcomes of CM using a mouse model. Experimental cerebral malaria (ECM) was induced in female C57BL/6 mice infected with Plasmodium berghei ANKA, and L-Arg was administrated either prophylactically or after parasite infection. Surprisingly, both types of L-Arg administration caused a decline in survival time and raised CM clinical scores. L-Arg treatment increased the population of CD4(+)T-bet(+)IFN-γ(+) Th1 cells and the activated macrophages (F4/80(+)CD36(+)) in the spleen. The levels of pro-inflammatory cytokines, IFN-γ and TNF-α, in splenocyte cultures were also increased by L-Arg treatment. The above changes were accompanied with a rise in the number of dendritic cells (DCs) and an increase in their maturation. However, L-Arg did not affect the population of regulatory T cells or the level of IL-10 in the spleen. Taken together, these data suggest that L-Arg may enhance the Th1 immune response, which is essential for a protective response in uncomplicated malaria but could be lethal in CM patients. Therefore, the prophylactic use of L-Arg to treat CM, based on the assumption that restoring the bioavailability of endothelial NO improves the outcome of CM, may need to be reconsidered especially for children.

Depletion of regulatory T cells decreases cardiac parasitosis and inflammation in experimental Chagas disease

Infection with the protozoan parasite Trypanosoma cruzi may lead to a potentially fatal cardiomyopathy known as Chagas heart disease. This disease is characterized by infiltration of the myocardium by mononuclear cells, including CD4+ T cells, together with edema, myofibrillary destruction, and fibrosis. A multifaceted systemic immune response develops that ultimately keeps parasitemia and tissue parasitosis low. T helper 1 and other pro-inflammatory T cell responses are effective at keeping levels of T. cruzi low in tissues and blood, but they may also lead to tissue inflammation when present chronically. The mechanism by which the inflammatory response is regulated in T. cruzi-infected individuals is complex, and the specific roles that Th17 and T regulatory (Treg) cells may play in that regulation are beginning to be elucidated. In this study, we found that depletion of Treg cells in T. cruzi-infected mice leads to reduced cardiac parasitosis and inflammation, accompanied by an augmented Th1 response early in the course of infection. This is followed by a downregulation of the Th1 response and increased Th17 response late in infection. The effect of Treg cell depletion on the Th1 and Th17 cells is not observed in mice immunized with T. cruzi in adjuvant. This suggests that Treg cells specifically regulate Th1 and Th17 cell responses during T. cruzi infection and may also be important for modulating parasite clearance and inflammation in the myocardium of T. cruzi-infected individuals.

Vitamin D inhibits the occurrence of experimental cerebral malaria in mice by suppressing the host inflammatory response

In animal models of experimental cerebral malaria (ECM), neuropathology is associated with an overwhelming inflammatory response and sequestration of leukocytes and parasite-infected RBCs in the brain. In this study, we explored the effect of vitamin D (VD; cholecalciferol) treatment on host immunity and outcome of ECM in C57BL/6 mice during Plasmodium berghei ANKA (PbA) infection. We observed that oral administration of VD both before and after PbA infection completely protected mice from ECM. VD administration significantly dampened the inducible systemic inflammatory responses with reduced circulating cytokines IFN-γ and TNF and decreased expression of these cytokines by the spleen cells. Meanwhile, VD also resulted in decreased expression of the chemokines CXCL9 and CXCL10 and cytoadhesion molecules (ICAM-1, VCAM-1, and CD36) in the brain, leading to reduced accumulation of pathogenic T cells in the brain and ultimately substantial improvement of the blood-brain barriers of PbA-infected mice. In addition, VD inhibited the differentiation, activation, and maturation of splenic dendritic cells. Meanwhile, regulatory T cells and IL-10 expression levels were upregulated upon VD treatment. These data collectively demonstrated the suppressive function of VD on host inflammatory responses, which provides significant survival benefits in the murine ECM model.

Erythropoietin protects against murine cerebral malaria through actions on host cellular immunity

Cerebral malaria (CM) is associated with excessive host proinflammatory responses and endothelial activation. The hematopoietic hormone erythropoietin (EPO) possesses neuroprotective functions in animal models of ischemic-hypoxic, traumatic, and inflammatory injuries. In the Plasmodium berghei ANKA model of experimental CM (ECM), recombinant human EPO (rhEPO) has shown evident protection against ECM. To elucidate the mechanism of EPO in this ECM model, we investigated the effect of rhEPO on host cellular immune responses. We demonstrated that improved survival of mice with ECM after rhEPO treatment was associated with reduced endothelial activation and improved integrity of the blood-brain barrier. Our results revealed that rhEPO downregulated the inflammatory responses by directly inhibiting the levels and functions of splenic dendritic cells. Conversely, rhEPO treatment led to significant expansion of regulatory T cells and increased expression of the receptor cytotoxic T lymphocyte antigen 4 (CTLA-4). The data presented here provide evidence of the direct effect of rhEPO on host cellular immunity during ECM.

Pre-existing Schistosoma japonicum infection alters the immune response to Plasmodium berghei infection in C57BL/6 mice

BACKGROUND

Since helminths and malaria parasites are often co-endemic, it is important to clarify the immunoregulatory mechanism that occurs during the process of co-infection. A previous study confirmed that dendritic cells (DCs) are involved in the establishment and regulation of the T-cell-mediated immune response to malaria infection. In the current study, distinct response profiles for splenic DCs and regulatory T cell (Treg) responses were assessed to evaluate the effects of a pre-existing Schistosoma japonicum infection on malaria infection.

METHODS

Malaria parasitaemia, survival rate, brain histopathology and clinical experimental cerebral malaria (ECM) were assessed in both Plasmodium berghei ANKA-mono-infected and S. japonicum-P. berghei ANKA-co-infected mice. Cell surface/intracellular staining and flow cytometry were used to analyse the level of splenic DC subpopulations, toll-like receptors (TLRs), DC surface molecules, Tregs (CD4⁺CD25⁺Foxp3⁺), IFN-γ/IL-10-secreting Tregs, and IFN-γ⁺/IL-10⁺-Foxp3⁻CD4⁺ T cells. IFN-γ, IL-4, IL-5, IL-10 and IL-13 levels were determined in splenocyte supernatants using enzyme-linked immunosorbent assay (ELISA).

RESULTS

The co-infected mice had significantly higher malaria parasitaemia, compared with the mono-infected mice, on days 2, 3, 7 and 8 after P. berghei ANKA infection. Mono-infected mice had a slightly lower survival rate, while clinical ECM symptoms, and brain pathology, were significantly more severe during the period of susceptibility to ECM. On days 5 and 8 post P. berghei ANKA infection, co-infected mice had significantly lower levels of CD11c⁺CD11b⁺, CD11c⁺CD45R/B220⁺, CD11c⁺TLR4⁺, CD11c⁺TLR9⁺, CD11c⁺MHCII⁺, CD11c⁺CD86⁺, IFN-γ-secreting Tregs, and IFN-γ⁺Foxp3⁻CD4⁺ T cells in single-cell suspensions of splenocytes when compared with P. berghei ANKA-mono-infected mice. Co-infected mice also had significantly lower levels of IFN-γ and higher levels of IL-4, IL-5, and IL-13 in splenocyte supernatants compared to mono-infected mice. There were no differences in the levels of IL-10-secreting Tregs or IL-10⁺Foxp3⁻CD4⁺ T cells between co-infected and mono-infected mice.

CONCLUSIONS

A Tregs-associated Th2 response plays an important role in protecting against ECM pathology. Pre-existing S. japonicum infection suppressed TLR ligand-induced DC maturation and had an anti-inflammatory effect during malaria infection not only by virtue of its ability to induce Th2 responses, but also by directly suppressing the ability of DC to produce pro-inflammatory mediators.

Molecular analysis of non-specific protection against murine malaria induced by BCG vaccination

Although the effectiveness of BCG vaccination in preventing adult pulmonary tuberculosis (TB) has been highly variable, epidemiologic studies have suggested that BCG provides other general health benefits to vaccinees including reducing the impact of asthma, leprosy, and possibly malaria. To further evaluate whether BCG immunization protects against malarial parasitemia and to define molecular correlates of this non-specific immunity, mice were vaccinated with BCG and then challenged 2 months later with asexual blood stage Plasmodium yoelii 17XNL (PyNL) parasites. Following challenge with PyNL, significant decreases in parasitemia were observed in BCG vaccinated mice relative to naïve controls. To identify immune molecules that may be associated with the BCG-induced protection, gene expression was evaluated by RT-PCR in i) naïve controls, ii) BCG-vaccinated mice, iii) PyNL infected mice and iv) BCG vaccinated/PyNL infected mice at 0, 1, 5, and 9 days after the P. yoelii infection. The expression results showed that i) BCG immunization induces the expression of at least 18 genes including the anti-microbial molecules lactoferrin, eosinophil peroxidase, eosinophil major basic protein and the cathelicidin-related antimicrobial peptide (CRAMP); ii) an active PyNL infection suppresses the expression of important immune response molecules; and iii) the extent of PyNL-induced suppression of specific genes is reduced in BCG-vaccinated/PyNL infected mice. To validate the gene expression data, we demonstrated that pre-treatment of malaria parasites with lactoferrin or the cathelicidin LL-37 peptide decreases the level of PyNL parasitemias in mice. Overall, our study suggests that BCG vaccination induces the expression of non-specific immune molecules including antimicrobial peptides which may provide an overall benefit to vaccinees by limiting infections of unrelated pathogens such as Plasmodium parasites.

Age-related CD4(+)CD25(+)Foxp3(+) regulatory T-cell responses during Plasmodium berghei ANKA infection in mice susceptible or resistant to cerebral malaria

Different functions have been attributed to CD4⁺CD25⁺Foxp3⁺ regulatory T-cells (Tregs) during malaria infection. Herein, we describe the disparity in Treg response and pro- and anti-inflammatory cytokines during infection with Plasmodium berghei ANKA between young (3-week-old) and middle-aged (8-month-old) C57BL/6 mice. Young mice were susceptible to cerebral malaria (CM), while the middle-aged mice were resistant to CM and succumbed to hyperparasitemia and severe anemia. The levels of pro-inflammatory cytokines, such as TNF-α, in young CM-susceptible mice were markedly higher than in middle-aged CM-resistant mice. An increased absolute number of Tregs 3-5 days post-inoculation, co-occurring with elevated IL-10 levels, was observed in middle-aged CM-resistant mice but not in young CM-susceptible mice. Our findings suggest that Treg proliferation might be associated with the suppression of excessive pro-inflammatory Th1 response during early malaria infection, leading to resistance to CM in the middle-aged mice, possibly in an IL-10-dependent manner.

Modulation of the immune and inflammatory responses by Plasmodium falciparum schizont extracts: role of myeloid dendritic cells in effector and regulatory functions of CD4+ lymphocytes

The optimal immune response to malaria infection comprises rapid induction of inflammatory responses promptly counteracted by regulatory mechanisms to prevent immunopathology. To evaluate the role of dendritic cells (DC) in the balance of parasite-induced inflammatory/anti-inflammatory mechanisms, we studied the activity of monocyte-derived dendritic cells (MDDC), previously exposed to soluble extracts of Plasmodium falciparum-infected red blood cells (PfSE), in the differentiation of CD4 cells isolated from donors never exposed to malaria infection. We show that MDDC exposed to PfSE are extremely efficient to induce a contemporary differentiation of TH1 effector cells and T regulatory (Treg) cells in CD4 T cells even when exposed to low concentrations of parasitic extracts. Treg cells induced by MDDC infected with PfSE (MDDC-PfSE) produce transforming growth factor beta (TGF-β) and interleukin 10 (IL-10) and are endowed with strong suppressive properties. They also show phenotypical and functional peculiarities, such as the contemporary expression of markers of Treg and TH1 differentiation and higher sensitivity to TLR4 ligands both inducing an increasing production of suppressive cytokines. On the whole, our data indicate that MDDC exposed to PfSE orchestrate a well-balanced immune response with timely differentiation of TH1 and Treg cells in CD4 cells from nonimmune donors and suggest that, during the infection, the role of MDCC could be particularly relevant in low-parasitemia conditions.

Supplement of L-Arg improves protective immunity during early-stage Plasmodium yoelii 17XL infection

L-arginine (L-Arg), the precursor of nitric oxide (NO), plays multiple important roles in nutrient metabolism and immune regulation. L-Arg supplement serves as a potential adjunctive therapy for severe malaria, because it improves NO bioavailability and reverses endothelial dysfunction in severe malaria patients. In this study, we investigated the effect of dietary L-Arg supplement on host immune responses during subsequent malaria infection using the Plasmodium yoelii 17XL - BALB/c mouse model. We have shown that pretreatment of mice with L-Arg significantly decreased parasitemia and prolonged the survival time of mice after infection. L-Arg supplement led to significant increases in activated CD4(+)T-bet(+)IFN-γ(+) T cells and F4/80(+)CD36(+) macrophages during early-stage infection, which were accompanied by enhanced synthesis of IFN-γ, TNF-α and NO by spleen cells. Moreover, L-Arg-pretreated mice developed more splenic myeloid and plasmacytoid dendritic cells with up-regulated expression of MHC II, CD86 and TLR9. In comparison, L-Arg treatment did not change the number of regulatory T cells and the level of anti-inflammatory cytokine IL-10. Taken together, our results showed that L-Arg pretreatment could improve the protective immune response in experimental malaria infection in mice, which underlines potential importance of L-Arg supplement in malaria-endemic human populations.

Recent insights into microbial triggers of interleukin-10 production in the host and the impact on infectious disease pathogenesis

Since its initial description as a Th2-cytokine antagonistic to interferon-alpha and granulocyte-macrophage colony-stimulating factor, many studies have shown various anti-inflammatory actions of interleukin-10 (IL-10), and its role in infection as a key regulator of innate immunity. Studies have shown that IL-10 induced in response to microorganisms and their products plays a central role in shaping pathogenesis. IL-10 appears to function as both sword and shield in the response to varied groups of microorganisms in its capacity to mediate protective immunity against some organisms but increase susceptibility to other infections. The nature of IL-10 as a pleiotropic modulator of host responses to microorganisms is explained, in part, by its potent and varied effects on different immune effector cells which influence antimicrobial activity. A new understanding of how microorganisms trigger IL-10 responses is emerging, along with recent discoveries of how IL-10 produced during disease might be harnessed for better protective or therapeutic strategies. In this review, we summarize studies from the past 5 years that have reported the induction of IL-10 by different classes of pathogenic microorganisms, including protozoa, nematodes, fungi, viruses and bacteria and discuss the impact of this induction on the persistence and/or clearance of microorganisms in the host.

Experimental study of the mechanism of tolerance induction in dexamethasone-treated dendritic cells

Background

The aim of this study was to investigate the mechanisms underlying tolerance induction of dexamethasone (Dex)-treated dendritic cells (DCs).

Material/Methods

Well-grown DC2.4 cells were randomly assigned to receive control, 50 μg/L, 100 μg/L, or 200 μg/L of dexamethasone and then were cultured for 6 days. The expressions of CD80, CD86, galectin-9, and PD-L1 on the surface of DC2.4 cells were analyzed with flow cytometry and the level of IL-12 secreted by DC2.4 cells was determined by ELISA. The stimulating activity of DC2.4 cells on allogeneic T cells was assessed with mixed lymphocyte reaction. Dexamethasone-treated DC2.4 cells were co-cultured with allogeneic splenic lymphocytes and the Foxp3 expression in naive T lymphocytes was determined with flow cytometry.

Results

Compared with the control group, the expressions of CD80, CD86, galectin-9, and PD-L1 on the surface of DC2.4 cells exposed to different doses of dexamethasone showed no significant changes; however, dexamethasone treatment significantly reduced IL-12 secretion and inhibited DC2.4’s stimulation on the proliferation of allogeneic T lymphocytes. Moreover, dexamethasone-treated DC2.4 cells effectively promoted FOXP3 expression in naive T lymphocytes.

Conclusions

DC2.4 is a stable cell line with high expressions of CD80, CD86, and PD-L1. Dexamethasone does not significantly change the cell phenotype of DC2.4 cells, but inhibits the secretion of IL-12 cytokine and attenuates DC2.4’s stimulation of the proliferation of allogeneic T cells. Dexamethasone-treated DC2.4 cells also effectively promote FOXP3 expression in naive T lymphocytes.

Stimulation of α7 nicotinic acetylcholine receptor by nicotine increases suppressive capacity of naturally occurring CD4+CD25+ regulatory T cells in mice in vitro

α7 Nicotinic acetylcholine receptor (α7 nAChR) has been found in several non-neuronal cells and is described as an important regulator of cellular function. Naturally occurring CD4(+)CD25(+) regulatory T cells (Tregs) are essential for the active suppression of autoimmunity. The present study investigated whether naturally occurring Tregs expressed α7 nAChR and investigated the functionary role of this receptor in controlling suppressive activity of these cells. We found that CD4(+)CD25(+) Tregs from naive C57BL/6J mice positively expressed α7 nAChR, and its activation by nicotine enhanced the suppressive capacity of Tregs. Nicotine stimulation up-regulated the expression of cytotoxic T-lymphocyte-associated antigen (CTLA)-4 and forkhead/winged helix transcription factor p3 (Foxp3) on Tregs but had no effect on the production of interleukin (IL)-10 and transforming growth factor-β1 by Tregs. In the supernatants of CD4(+)CD25(+) Tregs/CD4(+)CD25(-) T-cell cocultures, we observed a decrease in the concentration of IL-2 in nicotine-stimulated groups, but nicotine stimulation had no effect on the ratio of IL-4/interferon (IFN)-γ, which partially represented T-cell polarization. The above-mentioned effects of nicotine were reversed by a selective α7 nAChR antagonist, α-bungarotoxin. In addition, the ratio of IL-4/IFN-γ was increased by treatment with α-bungarotoxin. We conclude that nicotine might increase Treg-mediated immune suppression of lymphocytes via α7 nAChR. The effect is related to the up-regulation of CTLA-4 as well as Foxp3 expression and decreased IL-2 secretion in CD4(+)CD25(+) Tregs/CD4(+)CD25(-) T-cell coculture supernatants. α7 nAChR seems to be a critical regulator for immunosuppressive function of CD4(+)CD25(+) Tregs.

The female lower genital tract is a privileged compartment with IL-10 producing dendritic cells and poor Th1 immunity following Chlamydia trachomatis infection

While a primary genital tract infection with C. trachomatis stimulates partial-protection against re-infection, it may also result in severe inflammation and tissue destruction. Here we have dissected whether functional compartments exist in the genital tract that restrict Th1-mediated protective immunity. Apart from the Th1-subset, little is known about the role of other CD4⁺ T cell subsets in response to a genital tract chlamydial infection. Therefore, we investigated CD4⁺ T cell subset differentiation in the genital tract using RT-PCR for expression of critical transcription factors and cytokines in the upper (UGT) and lower genital tract (LGT) of female C57BL/6 mice in response to C. trachomatis serovar D infection. We found that the Th1 subset dominated the UGT, as IFN-γ and T-bet mRNA expression were high, while GATA-3 was low following genital infection with C. trachomatis serovar D. By contrast, IL-10 and GATA-3 mRNA dominated the LGT, suggesting the presence of Th2 cells. These functional compartments also attracted regulatory T cells (Tregs) differently as increased FoxP3 mRNA expression was seen primarily in the UGT. Although IL-17A mRNA was somewhat up-regulated in the LGT, no significant change in RORγ-t mRNA expression was observed, suggesting no involvement of Th17 cells. The dichotomy between the LGT and UGT was maintained during infection by IL-10 because in IL-10-deficient mice the distinction between the two compartments was completely lost and a dramatic shift to the predominance of Th1 cells in the LGT occurred. Unexpectedly, the major source of IL-10 was CD11c⁺ CD11b⁺ DC, probably creating an anti-inflammatory privileged site in the LGT.

The immune response to the genital tract pathogen C. trachomatis can result in a number of pathological outcomes including tubal scarring and consequently, infertility. CD4⁺ T helper 1 (Th1) cells are critical for host protection against infection, but may also contribute to immunopathology. Apart from the Th1 cells, little is known about the role of other CD4⁺ T cell subsets in response to a genital tract chlamydial infection. By tracking the development of T helper cells in the genital tract using RT-PCR for distinct transcription factors associated with these subsets, we found vastly different immune responses in the upper genital tract (UGT) compared to the lower genital tract (LGT) of female mice during infection. The LGT was dominated by anti-inflammatory IL-10 production from dendritic cells (DC) and the non-protective Th2 subset. In contrast, the upper genital tract was populated by protective-Th1 cells. In the absence of IL-10, though, the LGT and UGT were both dominated by Th1 cells, arguing that DC-derived IL-10 secures an anti-inflammatory privileged site in the LGT. These findings provide a break-through in our understanding of functional compartments in the genital tract immune system with potentially strong impact on vaccine development.

Characterization of immune responses to single or mixed infections with P. yoelii 17XL and P. chabaudi AS in different strains of mice

The outcome of Plasmodium yoelii 17XL (P.y17XL)-infected BALB/c and DBA/2 mice, ranging from death to spontaneous cure, depends largely on the establishment of effective Th1 and Th2 responses and a successful switch between Th1 and Th2 responses, as well as appropriate functioning of CD4(+)CD25(+)Foxp3(+)regulatory T cells (Tregs). The infection with another malaria-causing parasite, Plasmodium chabaudi AS (P.cAS), leads to a different outcome in BALB/c and DBA/2 mice compared to mice infected with P.y17XL alone. To understand the consequence of co-infection with P.y17XL and P.cAS, we determined the proliferation curve of parasites, pro-inflammatory/anti-inflammatory cytokine profiles, and the dynamic changes of the number of Tregs in DBA/2 and BALB/c mice with single or mixed-species infections. The infective mode in mixed-species infections was the same as single P.y17XL infections. The multiplication of P.y17XL parasites prevailed in BALB/c and DBA/2 mice with early mixed infections, as detected by RTQ-PCR. Subsequently, the multiplication of P.cAS parasites dominated in DBA/2 mice with mixed infections, while BALB/c mice succumbed to infection. In addition, the dynamic changes in IFN-gamma and IL-4 production in mice with mixed infections, used as a measure of Th1 and Th2 responsiveness, were consistent with P.y17XL-infected mice. Treg activation and the IL-10 level were also closely related to susceptibility to infection. Our findings demonstrate that the characteristics of the immune response during infections with mixed species are dependent on the mode of proliferation of different species of Plasmodium. Indeed, different species of Plasmodium can influence each other in the same host.