Shoichiro Mineo

Roles of IFN-γ and γδ T Cells in Protective Immunity Against Blood-Stage Malaria

Malaria is caused by infection with Plasmodium parasites. Various studies with knockout mice have indicated that IFN-γ plays essential roles in protective immunity against blood-stage Plasmodium infection. However, after Plasmodium infection, increased IFN-γ production by various types of cells is involved not only in protective immunity, but also in immunopathology. Recent reports have shown that IFN-γ acts as a pro-inflammatory cytokine to induce not only the activation of macrophages, but also the generation of uncommon myelolymphoid progenitor cells after Plasmodium infection. However, the effects of IFN-γ on hematopoietic stem cells and progenitor cells are unclear. Therefore, the regulation of hematopoiesis by IFN-γ during Plasmodium infection remains to be clarified. Although there are conflicting reports concerning the significance of γδ T cells in protective immunity against Plasmodium infection, γδ T cells may respond to infection and produce IFN-γ as innate immune cells in the early phase of blood-stage malaria. Our recent studies have shown that γδ T cells express CD40 ligand and produce IFN-γ after Plasmodium infection, resulting in the enhancement of dendritic cell activation as part of the immune response to eliminate Plasmodium parasites. These data suggest that the function of γδ T cells is similar to that of NK cells. Although several reports suggest that γδ T cells have the potential to act as memory cells for various infections, it remains to be determined whether memory γδ T cells are generated by Plasmodium infection and whether memory γδ T cells can contribute to the host defense against re-infection with Plasmodium. Here, we summarize and discuss the effects of IFN-γ and the various functions of γδ T cells in blood-stage Plasmodium infection.

Enhancement of dendritic cell activation via CD40 ligand-expressing γδ T cells is responsible for protective immunity to Plasmodium parasites

Previous reports have shown that γδ T cells are important for the elimination of malaria parasites in humans and mice. However, how γδ T cells are involved in protective immunity against blood-stage malaria remains unknown. We infected γδ T-cell–deficient (TCRδ-KO) mice and control wild-type mice with Plasmodium berghei XAT, which is a nonlethal strain. Although infected red blood cells were eliminated within 30 d after infection, TCRδ-KO mice could not clear the infected red blood cells, showed high parasitemia, and eventually died. Therefore, γδ T cells are essential for clearance of the parasites. Here, we found that γδ T cells play a key role in dendritic cell activation after Plasmodium infection. On day 5 postinfection, γδ T cells produced IFN-γ and expressed CD40 ligand during dendritic cell activation. These results suggest that γδ T cells enhance dendritic cell activation via IFN-γ and CD40 ligand–CD40 signaling. This hypothesis is supported strongly by the fact that in vivo induction of CD40 signaling prevented the death of TCRδ-KO mice after infection with P. berghei XAT. This study improves our understanding of protective immunity against malaria and provides insights into γδ T-cell–mediated protective immunity against various infectious diseases.

Epithelioid trophoblastic tumor of the lung

Epithelioid trophoblastic tumor (ETT) is a rare type of gestational trophoblastic disease and only 25 cases have been reported so far. It was first proposed by Mazur and Kurman in 1994 as an unusual type of trophoblastic tumor that is distinct from placental site trophoblastic tumor and choriocarcinoma and has features resembling carcinoma. A case of ETT of the lung in a 38‐year‐old Japanese woman is reported. The patient had suffered from a hydatidiform mole at the age of 27 years, and had four normal deliveries at the ages of 24, 31, 35 and 37 years. Because no tumor lesions were detected in the uterus, the patient was suspected of having metastatic choriocarcinoma with multiple lesions in the lung accompanied by an elevated level of human chorionic gonadotropin (hCG). In order to make an exact diagnosis, a partial resection of metastatic foci in the lung was performed. Microscopically, the tumor showed hemorrhagic necrotic foci and was composed of mainly mononuclear tumor cells and some giant tumor cells resembling trophoblastic cells. Immunohistochemical examination showed that a few large cells were stained positively for hCG, and that other cells were positive for human placental lactogen, pregnancy‐specific β1‐glycoprotein, cytokeratin 7 and inhibin‐α. In the ultrastructure, the tumor cells contained large nuclei and rich organella with desmosomes and well‐formed filaments. The diagnosis of ETT was confirmed from the findings as described above.

P57kip2 immunohistochemical expression and ultrastructural findings of gestational trophoblastic disease and related disorders

Gestational trophoblastic disease (GTD) is a unique spectrum of diseases ranging from complete hydatidiform mole (CHM), partial hydatidiform mole (PHM), and invasive mole (IM) to choriocarcinoma (CC). Placental site trophoblastic tumor (PSTT) and epithelioid trophoblastic tumor (ETT) have been classified as related disorders. Mesenchymal dysplasia (MD) may be misdiagnosed as PHM; however, it is said to have a quite different histogenesis from PHM. P57kip2 is the protein product of a paternally imprinted or maternal gene that inhibits cyclin-dependent kinases (CDK), thus serving to inhibit cell proliferation and to suppress tumor growth. Its lack of expression in trophoblastic disease plays a role in its abnormal proliferation and differentiation. In this study, P57kip2 immunostaining was absent in the trophoblastic layers of CHM and was positive in the trophoblast layer of nonmolar villi and MD. Ultrastructure of complete molar cystic villi showed tree-like branching of microvillous processes and intracytoplasmic lacunae without capillaries in the stroma, whereas MD contained many newly formed blood vessels and collagen. Also, large lacunae with microvilli and polymorphic nuclei of syncytiotrophoblast cells with well-developed organelles were observed in IM. Lung ETT following CHM and normal deliveries showed two types of large mononuclear cells and binuclear cells with abundant organelles and bundles of intermediate-type filaments in the stroma.

The protective effect of CD40 ligand-CD40 signalling is limited during the early phase of Plasmodium infection

γδ T cells are essential for eliminating Plasmodium berghei XAT. Because administration of the agonistic anti‐CD40 antibody can induce elimination of P. berghei XAT parasites in γδ T cell‐deficient mice, we considered that γδ T cells might activate dendritic cells via CD40 signalling during infection. Here we report that administration of the anti‐CD40 antibody to γδ T cell‐deficient mice 3–10 days post‐P. berghei XAT infection could eliminate the parasites. Our data suggest that dendritic cell activation via γδ T cells expressing CD40 ligand is critical during the early phase of infection.

Review: Exploration of placentation from human beings to ocean-living species

This review covers four topics. 1) Placental pathology in Himalayan mountain people. To determine morphological changes of the placenta at high altitude, pathological examination was made of 1000 Himalayan placentas obtained in Nepal and Tibet and the results compared with Japanese placentas delivered at sea level. Characteristic findings in the placental villi of the Himalayan group included high incidences of villous chorangiosis and chorangioma. These processes were clarified by ultrastructural observation. 2) Placentation in Sirenians. The giant Takikawa sea cow, which lived 5 million years ago, was discovered on Hokkaido, Japan. It was an ancestor of the dugong as well as the manatees. Sirenia, the sea cow group, shares a common ancestor with Proboscidea, the elephants, even though they now inhabit quite different environments. A comparison was made of their zonary endothelial type of placentation. 3) Placentation in sharks and rays. The remarkable placentation of hammerhead sharks and manta rays is described. 4) Placentation in the Antarctic minke whale. Placental tissue samples of this whale were obtained from the Japan Institute of Cetacean Research. In an ultrastructural study of the utero-placental junction, microfilamental processes of the allantochorionic zone and crypt formation were visualized.

Development of Severe Pathology in Immunized Pregnant Mice Challenged with Lethal Malaria Parasites

ABSTRACT Pregnant women are highly susceptible to malaria infection because of their low immunity and are at increased risk of maternal illness or death, in addition to spontaneous abortion, stillbirth, premature delivery, and low birth weight. However, the detailed pathogenesis of maternal malaria remains unclear. In this study, we evaluated a mouse model that shows similar severe pathological features of pregnant women during Plasmodium falciparum infection and investigated the pathogenesis of maternal malaria. Pregnant mice immunized by infection with an attenuated parasite, Plasmodium berghei XAT, were more susceptible to virulent P. berghei NK65 challenge/infection than were nonpregnant mice and showed high levels of parasitemia and a poor pregnancy outcome associated with placental pathology, such as accumulation of parasitized red blood cells, in the late phase of pregnancy. Notably, the pregnant immune mice challenged/infected with P. berghei NK65 developed liver injury associated with microvesicular fatty infiltration in late pregnancy. The pathological features were similar to acute fatty liver of pregnancy. Higher levels of gamma interferon and nitric oxide (NO) were found in plasma from pregnant immune mice infected with P. berghei NK65 than in plasma from nonpregnant mice. These findings suggest that development of liver injury and placental pathology in pregnant immune mice challenged/infected with P. berghei NK65 is accompanied by enhanced production of proinflammatory cytokines.

IFNGR1 signaling is associated with adverse pregnancy outcomes during infection with malaria parasites

Complicated/severe cases of placental pathology due to Plasmodium falciparum and P. vivax, especially adverse pregnancy outcomes during P. vivax infection, have been increasing in recent years. However, the pathogenesis of placental pathology during severe malaria is poorly understood, while responses against IFN-γ are thought to be associated with adverse pregnancy outcomes. In the present study, we explored the role of IFN-γ receptor 1 (IFNGR1) signaling in placental pathology during severe malaria using luciferase-expressing rodent malaria parasites, P. berghei NK65 (PbNK65L). We detected luciferase activities in the lung, spleen, adipose tissue, and placenta in pregnant mice, suggesting that infected erythrocytes could accumulate in various organs during infection. Importantly, we found that fetal mortality in IFNGR1-deficient mice infected with PbNK65L parasites was much less than in infected wild type (WT) mice. Placental pathology was also improved in IFNGR1-deficient mice. In contrast, bioluminescence imaging showed that parasite accumulation in the placentas of IFNGR1-deficient pregnant mice was comparable to that in WT mice infected with PbNK65L. These findings suggest that IFNGR1 signaling plays a pivotal role in placental pathology and subsequent adverse pregnancy outcomes during severe malaria. Our findings may increase our understanding of how disease aggravation occurs during malaria during pregnancy.