Natural regulatory (CD4+CD25+FOXP+) T cells control the production of pro-inflammatory cytokines during Plasmodium chabaudi adami infection and do not contribute to immune evasion

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Abstract

Different functions have been attributed to natural regulatory CD4+CD25+FOXP+ (Treg) cells during malaria infection. Herein, we assessed the role for Treg cells during infections with lethal (DS) and non-lethal (DK) Plasmodium chabaudi adami parasites, comparing the levels of parasitemia, inflammation and anaemia. Independent of parasite virulence, the population of splenic Treg cells expanded during infection, and the absolute numbers of activated CD69+ Treg cells were higher in DS-infected mice. In vivo depletion of CD25+ T cells, which eliminated 80% of CD4+FOXP3+CD25+ T cells and 60–70% of CD4+FOXP3+ T cells, significantly decreased the number of CD69+ Treg cells in mice with lethal malaria. As a result, higher parasite burden and morbidity were measured in the latter, whereas the kinetics of infection with non-lethal parasites remained unaffected. In the absence of Treg cells, parasite-specific IFN-γ responses by CD4+ T cells increased significantly, both in mice with lethal and non-lethal infections, whereas IL-2 production was only stimulated in mice with non-lethal malaria. Following the depletion of CD25+ T cells, the production of IL-10 by CD90 cells was also enhanced in infected mice. Interestingly, a potent induction of TNF-α and IFN-γ production by CD4+ and CD90 lymphocytes was measured in DS-infected mice, which also suffered severe anaemia earlier than non-depleted infected controls. Taken together, our data suggest that the expansion and activation of natural Treg cells represent a counter-regulatory response to the overwhelming inflammation associated with lethal P.c. adami. This response to infection involves TH1 lymphocytes as well as cells from the innate immune system.

Introduction

Natural Treg cells represent a population of CD4+CD45RBlow T cells constitutively expressing the α chain of the IL-2 receptor (CD25) (Schwartz, 2005) and which, in mice, comprise more than 85% of the cells expressing the Fork Head BOX P3 transcriptional factor (FOXP3) (Khattri et al., 2003, Fontenot et al., 2005). These cells play determinant roles in the preservation of self-tolerance and in the control of graft and tumor rejection and inflammation, and their abrogation leads to autoimmunity and inflammatory diseases in several experimental models (Fontenot et al., 2005, Schwartz, 2005).

In addition to their function in self-tolerance, Treg cells participate in the control of overwhelming responses to infectious agents such as viruses, bacteria and protozoan parasites (Raghavan and Holmgren, 2005, Belkaid et al., 2006, Demengeot et al., 2006, Suvas and Rouse, 2006). In malaria, Treg cells expand during infection with the Plasmodium berghei ANKA strain (Nie et al., 2007, Vigario et al., 2007) and have been shown to inhibit the development of pathogenic TH1 cells, responsible for cerebral disease in resistant BALB/c mice (Nie et al., 2007). These results contrast with the detrimental effects associated with Treg cells during P. berghei ANKA infection in susceptible C57BL/6 mice (Amante et al., 2007). In this infection model, depletion of Treg cells results in a significant increase in survival, a minor but significant reduction in blood parasitemia and an important reduction in parasite load in the brain and vasculature. A comparable delay in the onset of peak parasitemia has been reported during P. berghei NK65 infection in mice depleted of Treg cells (Long et al., 2003) and in the Plasmodium yoelii 17XL infection model, elimination of Treg cells allows BALB/c mice to control otherwise lethal infections (Hisaeda et al., 2004). Moreover, data provided by Plasmodium falciparum infections in humans correlates the expansion of natural Treg cells and the production of transforming growth factor-β (TGF-β) with higher parasite multiplication rates (Walther et al., 2005). Altogether, these observations attribute contrasting functions to natural Treg cells during Plasmodium infections.

Herein, the role of natural Treg cells in the lethality associated with Plasmodium chabaudi adami infection has been evaluated using two parasite strains with contrasting virulence, sustained by distinct parasite multiplication rates, and by the severity of inflammation and anaemia generated. Our results indicate that during P.c. adami infection, Treg cells contribute to the control of overwhelming inflammatory responses and do not impair protective immune responses.

Section snippets

Parasites, mice and infections

The P.c. adami DS (lethal) and DK (non-lethal) strains derive from two different isolates (Killick-Kendrick and Peters, 1978). Female BALB/c mice, 4–6 weeks old (Charles River), were infected with 105 parasitised red blood cells (PRBC) by the i.p. route. Parasitemia was measured daily in methanol fixed tail blood smears stained with a 10% Giemsa solution in PBS.

Cell purification

Single-cell suspensions of splenocytes from naïve and P.c. adami-infected mice (peak parasitemia) were prepared. In experiments

Pro-inflammatory cytokines responses are enhanced during lethal P.c. adami infection

In BALB/c mice and in other inbred and outbred mouse strains, inoculation of P.c. adami DS PRBCs resulted in elevated parasitemia (45–65%) and 100% mortality (Scorza et al., 2005; and unpublished results) (Fig. 1a). In contrast, similar infective doses with DK parasites resulted in moderate infection (13–20% parasitemia) that resolved 12–13 days later in BALB/c mice (Fig. 1a).

We compared the levels of TNF-α, IFN-γ and IL-10 in 72 h culture supernatants of splenic cells from BALB/c mice with DS

Discussion

In the present study, we show that the population of natural Treg cells significantly expands during lethal P.c. adami DS infections. In this malaria infection model, Treg cells contribute to down-regulation of the severe inflammatory response but fail to protect the mice from the development of lethal anaemia and death.

Regulatory T cells participate in the attenuation of overwhelming inflammatory responses during infections with protozoa and helminths (Belkaid et al., 2006). In BALB/c mice,

Acknowledgements

This work was supported by the Natural Sciences and Engineering Research Council of Canada and Le Programme d’aide à la Recherche PAFARC. M. Cambos is recipient of a FARE scholarship. The study was conducted in compliance with the regulations from the Animal Committee of the University of Quebec in Montreal (Protocol 0705-R1-508-0706).

References (40)

  • M. Walther et al.

    Upregulation of TGF-beta, FOXP3, and CD4+CD25+ regulatory T cells correlates with more rapid parasite growth in human malaria infection

    Immunity

    (2005)
  • Amante, F.H., Stanley, A.C., Randall, L.M., Zhou, Y., Haque, A., McSweeney, K., Waters, A.P., Janse, C.J., Good, M.F.,...
  • I.A. Clark et al.

    Human malarial disease: a consequence of inflammatory cytokine release

    Malar. J.

    (2006)
  • C.L. Day et al.

    PD-1 expression on HIV-specific T cells is associated with T-cell exhaustion and disease progression

    Nature

    (2006)
  • J. Demengeot et al.

    Regulatory T cells in microbial infection

    Springer Semin. Immunopathol.

    (2006)
  • F. Eddahri et al.

    CD4+CD25+ regulatory T cells control the magnitude of T-dependent humoral immune responses to exogenous antigens

    Eur. J. Immunol.

    (2006)
  • J.R. Fakey et al.

    Rapid multiplication rate, rather than immunosuppression, causes the death of mice infected with lethal Plasmodium yoelii

    Infect. Immunol.

    (1987)
  • P.B. Falanga et al.

    Acute lethal infection with Plasmodium chabaudi does not impair the generation of a protective immune response

    Parasite Immunol.

    (1989)
  • H. Hisaeda et al.

    Escape of malaria parasites from host immunity requires CD4+CD25+ regulatory T cells

    Natl. Med.

    (2004)
  • R. Khattri et al.

    An essential role for Scurfin in CD4+CD25+ Tregulatory cells

    Natl. Immunol.

    (2003)
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