Chikako Shimokawa

Involvement of CD8+ T cells in protective immunity against murine blood-stage infection with Plasmodium yoelii 17XL strain

When developing malaria vaccines, the most crucial step is to elucidate the mechanisms involved in protective immunity against the parasites. We found that CD8+ T cells contribute to protective immunity against infection with blood‐stage parasites of Plasmodium yoelii. Infection of C57BL/6 mice with P. yoelii 17XL was lethal, while all mice infected with a low‐virulence strain of the parasite 17XNL acquired complete resistance against re‐infection with P. yoelii 17XL. However, the host mice transferred with CD8+ T cells from mice primed only with P. yoelii 17XNL failed to acquire protective immunity. On the other hand, the irradiated host mice were completely resistant to P. yoelii 17XL infection, showing no grade of parasitemia when adoptively transferred with CD8+ T cells from immune mice that survived infection with both P. yoelii XNL and, subsequently, P. yoelii 17XL. These protective CD8+ T cells from immune WT mice had the potential to generate IFN‐γ, perforin (PFN) and granzyme B. When mice deficient in IFN‐γ were used as donor mice for CD8+ T cells, protective immunity in the host mice was fully abrogated, and the immunity was profoundly attenuated in PFN‐deficient mice. Thus, CD8+ T cells producing IFN‐γ and PFN appear to be involved in protective immunity against infection with blood‐stage malaria.

Entamoeba moshkovskii Is Associated With Diarrhea in Infants and Causes Diarrhea and Colitis in Mice

BACKGROUND Entamoeba moshkovskii is prevalent in developing countries and morphologically indistinguishable from pathogenic Entamoeba histolytica and nonpathogenic Entamoeba dispar. It is not known if E. moshkovskii is pathogenic. METHODS Mice were intracecally challenged with the trophozoites of each Entamoeba spp. to test the ability to cause diarrhea, and infants in Bangladesh were prospectively observed to see if newly acquired E. moshkovskii infection was associated with diarrhea. RESULTS E. moshkovskii and E. histolytica caused diarrhea and weight loss in susceptible mice. E. dispar infected none of the mouse strains tested. In Mirpur, Dhaka, Bangladesh, E. moshkovskii, E. histolytica, and E. dispar were identified in 42 (2.95%), 66 (4.63%), and 5 (0.35%), respectively, of 1426 diarrheal episodes in 385 children followed prospectively from birth to one year of age. Diarrhea occurred temporally with acquisition of a new E. moshkovskii infection: in the 2 months preceding E. moshkvskii-associated diarrhea, 86% (36 of 42) of monthly surveillance stool samples were negative for E. moshkovskii. CONCLUSIONS E. moshkovskii was found to be pathogenic in mice. In children, the acquisition of E. moshkovskii infection was associated with diarrhea. These data are consistent with E. moshkovskii causing disease, indicating that it is important to reexamine its pathogenicity.

Mast Cells Are Crucial for Induction of Group 2 Innate Lymphoid Cells and Clearance of Helminth Infections

Summary Mast cells are important for eradication of intestinal nematodes; however, their precise mechanisms of action have remained elusive, especially in the early phase of infection. We found that Spi‐B‐deficient mice had increased numbers of mast cells and rapidly expelled the Heligmosomoides polygyrus (Hp) nematode. This was accompanied by induction of interleukin‐13 (IL‐13)‐producing group 2 innate lymphoid cells (ILC2) and goblet cell hyperplasia. Immediately after Hp infection, mast cells were rapidly activated to produce IL‐33 in response to ATP released from apoptotic intestinal epithelial cells. In vivo inhibition of the P2X7 ATP receptor rendered the Spi‐B‐deficient mice susceptible to Hp, concomitant with elimination of mast cell activation and IL‐13‐producing ILC2 induction. These results uncover a previously unknown role for mast cells in innate immunity in that activation of mast cells by ATP orchestrates the development of a protective type 2 immune response, in part by producing IL‐33, which contributes to ILC2 activation. Graphical Abstract Figure. No Caption available. HighlightsSpi‐B‐deficient mice are resistant to intestinal helminth infectionMyeloid differentiation is regulated by the Ets transcription factor Spi‐BMast cells are a potent source of IL‐33 and can activate ILC2The production of IL‐33 by mast cells requires their activation through ATP‐P2X7 &NA; Mast cells are supposed to contribute to protection against helminthic infection in the later phase. Shimokawa and colleagues demonstrate that mast cells play a critical role for activation of ILC2 responsible for parasite expulsion in the early phase.

Critical role for the immunoproteasome subunit LMP7 in the resistance of mice to Toxoplasma gondii infection

Proteasome‐mediated proteolysis is responsible for the generation of immunogenic epitopes presented by MHC class I molecules, which activate antigen‐specific CD8+ T cells. Immunoproteasomes, defined by the presence of the three catalytic subunits LMP2, MECL‐1, and LMP7, have been hypothesized to optimize MHC class I antigen processing. In this study, we demonstrate that the infection of mice with a protozoan parasite, Toxoplasma gondii, induced the expression of LMP7 mRNA in APC and increased the capacity of APC to induce the production of IFN‐γ by antigen‐specific CD8+ T cells. In vitro infection of a DC cell line with T. gondii also induced the expression of LMP7 and resulted in enhanced proteasome proteolytic activity. Finally, mice lacking LMP7 were highly susceptible to infection with T. gondii and showed a reduced number of functional CD8+ T cells. These results demonstrate that proteasomes containing LMP7 play an indispensable role in the survival of mice infected with T. gondii, presumably due to the efficient generation of CTL epitopes required for the functional development of CD8+ T cells.

Development of experimental cerebral malaria is independent of IL-23 and IL-17.

Cerebral malaria (CM) is the most severe complication of Plasmodium infection. Although inappropriate immune responses to Plasmodium falciparum are reported as the major causes of CM, the precise mechanisms for development remain unclear. IL-23 and IL-17 have critical roles in the onset of autoimmunity and inflammatory diseases triggered by microbial infections. Thus, we investigated the influence of IL-23 and IL-17 on experimental CM (ECM) using Plasmodium berghei ANKA infection of C57BL/6 mice. Both IL-23 deficient mice and wild-type (WT) mice developed ECM. IL-17 deficient mice also developed ECM, while IL-17 producing cells other than CD4(+) T cells (Th17) were increased in WT mice that developed ECM. In conclusion, this study showed that IL-23 and IL-17 are not involved in ECM development.

A critical role for phagocytosis in resistance to malaria in iron‐deficient mice

Both iron‐deficient anemia (IDA) and malaria remain a threat to children in developing countries. Children with IDA are resistant to malaria, but the reasons for this are unknown. In this study, we addressed the mechanisms underlying the protection against malaria observed in IDA individuals using a rodent malaria parasite, Plasmodium yoelii (Py). We showed that the intra‐erythrocytic proliferation and amplification of Py parasites were not suppressed in IDA erythrocytes and immune responses specific for Py parasites were not enhanced in IDA mice. We also found that parasitized IDA cells were more susceptible to engulfment by phagocytes in vitro than control cells, resulting in rapid clearance of parasitized cells and that protection of IDA mice from malaria was abrogated by inhibiting phagocytosis. One possible reason for this rapid clearance might be increased exposure of phosphatidylserine at the outer leaflet of parasitized IDA erythrocytes. The results of this study suggest that parasitized IDA erythrocytes are eliminated by phagocytic cells, which sense alterations in the membrane structure of parasitized IDA erythrocytes.

IL‐23 protection against Plasmodium berghei infection in mice is partially dependent on IL‐17 from macrophages

Although IL‐12 is believed to contribute to protective immune responses, the role played by IL‐23 (a member of the IL‐12 family) in malaria is elusive. Here, we show that IL‐23 is produced during infection with Plasmodium berghei NK65. Mice deficient in IL‐23 (p19KO) had higher parasitemia and died earlier than wild‐type (WT) controls. Interestingly, p19KO mice had lower numbers of IL‐17‐producing splenic cells than their WT counterparts. Furthermore, mice deficient in IL‐17 (17KO) suffered higher parasitemia than the WT controls, indicating that IL‐23‐mediated protection is dependent on induction of IL‐17 during infection. We found that macrophages were responsible for IL‐17 production in response to IL‐23. We observed a striking reduction in splenic macrophages in the p19KO and 17KO mice, both of which became highly susceptible to infection. Thus, IL‐17 appears to be crucial for maintenance of splenic macrophages. Adoptive transfer of macrophages into macrophage‐depleted mice confirmed that macrophage‐derived IL‐17 is required for macrophage accumulation and parasite eradication in the recipient mice. We also found that IL‐17 induces CCL2/7, which recruit macrophages. Our findings reveal a novel protective mechanism whereby IL‐23, IL‐17, and macrophages reduce the severity of infection with blood‐stage malaria parasites.

Cytotoxic activities of CD8+ T cells collaborate with macrophages to protect against blood-stage murine malaria

The protective immunity afforded by CD8+ T cells against blood-stage malaria remains controversial because no MHC class I molecules are displayed on parasite-infected human erythrocytes. We recently reported that rodent malaria parasites infect erythroblasts that express major histocompatibility complex (MHC) class I antigens, which are recognized by CD8+ T cells. In this study, we demonstrate that the cytotoxic activity of CD8+ T cells contributes to the protection of mice against blood-stage malaria in a Fas ligand (FasL)-dependent manner. Erythroblasts infected with malarial parasites express the death receptor Fas. CD8+ T cells induce the externalization of phosphatidylserine (PS) on the infected erythroblasts in a cell-to-cell contact-dependent manner. PS enhances the engulfment of the infected erythroid cells by phagocytes. As a PS receptor, T-cell immunoglobulin-domain and mucin-domain-containing molecule 4 (Tim-4) contributes to the phagocytosis of malaria-parasite-infected cells. Our findings provide insight into the molecular mechanisms underlying the protective immunity exerted by CD8+ T cells in collaboration with phagocytes. DOI: http://dx.doi.org/10.7554/eLife.04232.001

CD8+ T cell activation by murine erythroblasts infected with malaria parasites

Recent studies show that some human malaria parasite species Plasmodium falciparum and P. vivax parasitize erythroblasts; however, the biological and clinical significance of this is unclear. To investigate further, we generated a rodent malaria parasite (P. yoelii 17XNL) expressing GFP-ovalbumin (OVA). Its infectivity to erythroblasts was confirmed, and parasitized erythroblasts were capable of initiating malaria infections. Experiments showed that MHC class I molecules were highly expressed on parasitized erythroblasts. As CD8+ T cells recognize MHC class I and peptide complexes on target cells, and are involved in protection or pathology against malaria, we examined whether erythroblasts are targeted by CD8+ T cells. Purified non-parasitized erythroblasts pulsed with OVA peptides were recognized by OVA-specific CD8+ T cells. Crucially, parasitized erythroblasts isolated from GFP-OVA-, but not GFP- infected-mice, activated OT-I CD8+ T cells, indicating that CD8+ T cells recognize parasitized erythroblasts in an antigen-specific manner.

Plasmodium berghei ANKA causes intestinal malaria associated with dysbiosis

Gastrointestinal symptoms, such as abdominal pain and diarrhea, are frequently observed in patients with Plasmodium falciparum malaria. However, the correlation between malaria intestinal pathology and intestinal microbiota has not been investigated. In the present study, infection of C57BL/6 mice with P. berghei ANKA (PbA) caused intestinal pathological changes, such as detachment of epithelia in the small intestines and increased intestinal permeability, which correlated with development with experimental cerebral malaria (ECM). Notably, an apparent dysbiosis occurred, characterized by a reduction of Firmicutes and an increase in Proteobacteria. Furthermore, some genera of microbiota correlated with parasite growth and/or ECM development. By contrast, BALB/c mice are resistant to ECM and exhibit milder intestinal pathology and dysbiosis. These results indicate that the severity of cerebral and intestinal pathology coincides with the degree of alteration in microbiota. This is the first report demonstrating that malaria affects intestinal microbiota and causes dysbiosis.