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Cerebral malaria (CM) is a complex parasitic disease caused by Plasmodium sp. Failure to establish an appropriate balance between pro- and anti-inflammatory immune responses is believed to contribute to the development of cerebral pathology. Using the blood-stage PbA (Plasmodium berghei ANKA) model of infection, we show here that administration of the pro-Th2 cytokine, IL-33, prevents the development of experimental cerebral malaria (ECM) in C57BL/6 mice and reduces the production of inflammatory mediators IFN-γ, IL-12 and TNF-α. IL-33 drives the expansion of type-2 innate lymphoid cells (ILC2) that produce Type-2 cytokines (IL-4, IL-5 and IL-13), leading to the polarization of the anti-inflammatory M2 macrophages, which in turn expand Foxp3 regulatory T cells (Tregs). PbA-infected mice adoptively transferred with ILC2 have elevated frequency of M2 and Tregs and are protected from ECM. Importantly, IL-33-treated mice deleted of Tregs (DEREG mice) are no longer able to resist ECM. Our data therefore provide evidence that IL-33 can prevent the development of ECM by orchestrating a protective immune response via ILC2, M2 macrophages and Tregs.

The term macrophage activation syndrome (MAS) defines a severe, potentially fatal disorder characterized by overwhelming inflammation and multiorgan involvement. Interleukin-18 (IL-18) is a proinflammatory cytokine belonging to the IL-1 family, the activity of which is regulated by its endogenous inhibitor IL-18 binding protein (IL-18BP). Elevated IL-18 levels have been reported in patients with MAS. Herein, we show that on repeated toll-like receptor 9 (TLR9) stimulation with unmethylated cytosine guanine dinucleotide containing single-stranded DNA (CpG), mice display severe MAS manifestations, including increased weight loss, splenomegaly, anemia, thrombocytopenia, hyperferritinemia, and bone marrow hemophagocytosis as compared with wild-type mice. Serum-free IL-18 was detected in CpG-treated mice only. Levels of interferon-γ (IFN-γ) and of IFN-γ signature genes, such as the chemokine or the transcription factor, were significantly increased in mice. Blocking IL-18 receptor signaling attenuated the severity of MAS and IFN-γ responses in mice. Blocking IFN-γ had comparable effects to IL-18 inhibition on most MAS manifestations. Our data indicate that endogenous IL-18BP exerts a protective role in CpG-induced MAS and that IL-18, which acts upstream of IFN-γ, is involved in the severity of MAS.

Cerebral malaria (CM) is associated with a high mortality rate and long-term neurocognitive impairment in survivors. The murine model of experimental cerebral malaria (ECM) induced by Plasmodium berghei ANKA (PbA)-infection reproduces several of these features. We reported recently increased levels of IL-33 protein in brain undergoing ECM and the involvement of IL-33/ST2 pathway in ECM development. Here we show that PbA-infection induced early short term and spatial memory defects, prior to blood brain barrier (BBB) disruption, in wild-type mice, while ST2-deficient mice did not develop cognitive defects. PbA-induced neuroinflammation was reduced in ST2-deficient mice with low Ifng, Tnfa, Il1b, Il6, CXCL9, CXCL10 and Cd8a expression, associated with an absence of neurogenesis defects in hippocampus. PbA-infection triggered a dramatic increase of IL-33 expression by oligodendrocytes, through ST2 pathway. In vitro, IL-33/ST2 pathway induced microglia expression of IL-1β which in turn stimulated IL-33 expression by oligodendrocytes. These results highlight the IL-33/ST2 pathway ability to orchestrate microglia and oligodendrocytes responses at an early stage of PbA-infection, with an amplification loop between IL-1β and IL-33, responsible for an exacerbated neuroinflammation context and associated neurological and cognitive defects.

Cerebral malaria is a severe complication ofEur. J. Immunol. 2013Immunol. . 43: 2683Immunol. -2695 Plasmodium falciparum-infected children and young adults [1]. Cerebral malaria pathophysiology is still poorly understood, combining cerebral vascular obstruction, and exacerbated immune responses. Indeed, investigations in humans and mice documented the sequestration of erythrocytes, parasitized or not, platelets and leucocytes in cerebral blood vessels with an increased proinflammatory cytokine expression [1][2][3]. The specific role of T cells in cerebral malaria pathogenesis has been difficult to address in humans. In mice however, T-cell sequestration and activation in the brain are crucial steps for experimental cerebral malaria (ECM) development after Plasmodium berghei ANKA (PbA) infection [4][5][6][7]. In particular, αβ-CD8 + T cells sequestrated in the brain play a pathogenic, effector role for ECM development [6], and we showed recently a role for protein kinase C-θ (PKC-θ) in PbAinduced ECM pathogenesis [8]. Besides being a critical regulator of TCR signaling and T-cell activation, PKC-θ is involved in interferon type I/II signaling in human T cells [9]. Type II IFN-γ is essential for PbA-induced ECM development [10][11][12], promoting CD8 + T-cell accumulation in the brain [7,[12][13][14]. Type IIFNs are induced during viral infection but they also contribute to the antibacterial immune response. ResultsThe IFN-γ pathway is essential for ECM development upon sporozoite PbA infectionThe IFN-γ pathway is central for ECM development after bloodstage PbA infection. We first assessed the role of this pathway in preerythrocytic/intrahepatic stage infection by investigating ECM neurological signs development in IFN-γR1 −/− mice. Following the injection of 1000 sporozoites, 60% of the WT control mice developed typical ECM neurological symptoms, such as ataxia, loss of grip strength, progressive paralysis, and coma, and succumbed within 8-9 days, as previously described [22]. In contrast, IFN-γR1 −/− mice were fully resistant to the same challenge, surviving 30 days with no ECM neurological signs (Fig. 1A). Therefore, type II IFN-γ pathway is essential for ECM development after PbA sporozoite infection.Hampered ECM development in the absence of IFN-α/β pathway upon hepatic or blood-stage PbA infectionThe role of type I IFN-α/β versus type II IFN-γ pathways in ECM development after infection with hepatic or blood-stage PbA was then assessed in mice deficient for either IFNAR1 or IFN-γR1. IFNAR1 −/− mice were partially protected against ECM following sporozoite-initiated infection, only 20% dying before day 10, and 40% eventually developing typical ECM neurological symptoms, which reflected a delayed ECM development after infection with sporozoites ( Fig. 1A), as compared with WT control mice, 60% of which developed ECM and died before day 10, and IFN-γR1-deficient mice, which were fully resistant to PbA challenge. After injection of PbA-parasited red blood cells (10 5 pRBC/ mouse), WT mice succumbed within 7-...

A Th1 response is required for the development of Plasmodium berghei ANKA (PbA)-induced experimental cerebral malaria (ECM). The role of pro-Th1 IL-12 in malaria is complex and controversial. In this study, we addressed the role of IL-12Rβ2 in ECM development. C57BL/6 mice deficient for IL-12Rβ2, IL-12p40, or IL-12p35 were analyzed for ECM development after blood-stage PbA infection in terms of ischemia and blood flow by noninvasive magnetic resonance imaging and angiography, T cell recruitment, and gene expression. Without IL-12Rβ2, no neurologic sign of ECM developed upon PbA infection. Although wild-type mice developed distinct brain microvascular pathology, ECM-resistant, IL-12Rβ2–deficient mice showed unaltered cerebral microcirculation and the absence of ischemia after PbA infection. In contrast, mice deficient for IL-12p40 or IL-12p35 were sensitive to ECM development. The resistance of IL-12Rβ2–deficient mice to ECM correlated with reduced recruitment of activated T cells and impaired overexpression of lymphotoxin-α, TNF-α, and IFN-γ in the brain after PbA infection. Therefore, IL-12Rβ2 signaling is essential for ECM development but independent from IL-12p40 and IL-12p35. We document a novel link between IL-12Rβ2 and lymphotoxin-α, TNF-α, and IFN-γ expression, key cytokines for ECM pathogenesis.

were not affected in the absence of functional ST2 pathway, the local expression of ICAM-1, CXCR3, and LT-α, crucial for ECM development, was strongly reduced, and this may explain the diminished pathogenic T-cell recruitment and resistance to ECM. Therefore, IL-33 is induced in PbA sporozoite infection, and the pathogenic T-cell responses with local microvascular pathology are dependent on IL-33/ST2 signaling, identifying IL-33 as a new actor in ECM development. Keywords:Experimental cerebral malaria r IL-33 r Plasmodium berghei ANKA r Sporozoite r ST2Additional supporting information may be found in the online version of this article at the publisher's web-site IntroductionMalaria is the most common parasitosis in the world, leading to around 650 000 deaths in 2012, especially African children [1]. Plasmodium falciparum is responsible for the major and oftenCorrespondence: Dr. Valérie F. J. Quesniaux e-mail: quesniaux@cnrs-orleans.fr fatal cerebral malaria complication [2]. The pathophysiology of cerebral malaria, which remains poorly understood, is associated with microvessel obstruction and excessive inflammation in the brain. Indeed, studies in humans and mice have shown that cerebral malaria correlates with the sequestration of RBCs, * These authors contributed equally to this work. The contribution of the innate response in ECM development has remained more elusive. Indeed, although MyD88-deficient mice show protection against ECM upon PbA sporozoite infection ([11] and our unpublished data), little contribution of the TLRs pathways was reported [12,13]. MyD88 adaptor is also used by receptors of the IL-1 family, but both IL-1β and IL-18 seem dispensable for induction of ECM [11]. MyD88 is further shared by more recently characterized members of the IL-1 family such as IL-33 and IL-36. We were interested in studying the implication of IL-33, a modulator of T H 2 responses, in ECM development since the T H 1/T H 2 balance has been shown to modulate ECM [10,14]. IL-33, essential in innate and epithelial immune response [15,16], activates T H 2 T-cell differentiation and release of T H 2 cytokines and chemokines. IL-33 is overexpressed in clinical or experimental visceral leishmaniasis and it suppresses T H 1 responses in mice infected with Leishmania donovani [17]. IL-33 levels are increased in the plasma of infants with severe malaria, as compared with infection-free controls [18]. In addition, IL-33 has been associated with some cerebral diseases. IL-33 is implicated in Toxoplasma gondii induced encephalitis in mice, and was shown to attenuate EAE by suppressing IL-17 and IFN-γ production [19,20]. IL-33 is expressed within CNS by brain endothelial cells and astrocytes, LPS upregulating IL-33 expression by astrocytes [21]. In view of IL-33 implication in CNS pathologies and its role in modulating the T H 2/T H 1 balance, we investigated the role of IL-33 pathway in ECM development.Here, ECM development in response to PbA infection was investigated in mice deficient for IL-33 receptor, ST2. We show that br...

The IL-1 cytokine family includes eleven members, among which Il-36α, β and γ, IL-36Ra and IL-38. The IL-36 cytokines are involved in the pathogenesis of psoriasis. IL-38 is also expressed in the skin and was previously proposed to act as an IL-36 antagonist. In this study, we thus examined expression and function of Il-38 in a mouse model of imiquimod (IMQ)-induced skin inflammation. Il-38 mRNA was detected in the epidermis and in primary mouse keratinocytes, but not in dermal fibroblasts. At the peak of IMQ-induced inflammation, skin Il-38 mRNA levels were reduced, whereas Il-36ra mRNA expression increased. The severity of IMQ-induced skin inflammation, as assessed by recording ear thickness and histological changes, was similar in Il-38 KO and WT littermate control mice, while, in contrast, Il-36ra-deficient mice displayed more severe skin pathology than their WT littermates. Il-38-deficiency had no impact on IMQ-induced expression of proinflammatory mediators in the skin in vivo, on the basal expression of various cytokines or chemokines by cultured primary keratinocytes and dermal fibroblasts in vitro, or on the response of these cells to Il-36β. Finally, after cessation of topical IMQ application, the resolution of skin inflammation was also not altered in Il-38 KO mice. In conclusion, Il-38-deficiency did not impact the development or resolution of IMQ-induced skin inflammation. Our observations further suggest that endogenous Il-38 does not exert Il-36 inhibitory activity in this model, or in cultured skin cells. A potential anti-inflammatory function of Il-38 in mouse skin thus still remains to be demonstrated.