Protective Roles of Mast Cells and Mast Cell-Derived TNF in Murine Malaria Takahisa Furuta, 1 * Takane Kikuchi, 2 * Yoichiro Iwakura, † and Naohiro Watanabe ‡ TNF plays important roles in the protection and onset of malaria. Although mast cells are known as a source of TNF, little is known about the relationship between mast cells and pathogenesis of malaria. In this study, mast cell-deficient WBB6F 1 -W/W v (W/W v ) and the control littermate WBB6F 1 / (/) mice were infected with 1  10 5 of Plasmodium berghei ANKA. / mice had lower parasitemia with higher TNF levels, as compared with W/W v mice. Diminished resistance in W/W v mice was considered to be due to mast cells and TNF. This fact was confirmed by experiments in W/W v mice reconstituted with bone marrow-derived mast cells (BMMCs) of / mice or of TNF / mice. W/W v mice with BMMCs of / mice exhibit lower parasitemia and mortality accompanying significantly higher TNF levels than those of W/W v mice. Parasitemia in W/W v mice with BMMCs of TNF / mice was higher than that in / mice. Activation of mast cells by anti-IgE or compound 48/80 resulted in release of TNF and decrease of parasitemia. In addition, splenic hypertrophy and increased number of mast cells in the spleen were observed after infection in / mice and W/W v mice reconstituted with BMMCs of / mice as compared with W/W v mice. These findings propose a novel mechanism that mast cells and mast cell-derived TNF play protective roles in malaria. The Journal of Immu- nology, 2006, 177: 3294 –3302. M alaria is the most serious parasitic disease of humans in the world. Approximately 2.7 million people die from the disease every year, and most of them are children under 5 years old (1). Malaria infections can cause fever, severe anemia, coma, and renal failure in children and adults (2, 3), and poor birth outcomes in pregnant women (4). The pathogenesis of malaria is complex, and the immune system may mediate both protection from malaria and development of disease. Many studies (3, 5–11) indicate that elevations in immune mediators such as IL-1, IL-6, IL-8, IL-10, TNF, and NO have been associated with disease severity. Especially, high concentrations of TNF have been associated with disease severity in human Plasmodium falciparum infections and several animal malarias (8). Mast cells can be a major source of TNF (12, 13), suggesting that they may play im- portant roles in protection and disease in malaria. Despite these observations, little is known about the relationship between mast cells and malaria pathogenesis. Mast cells are a pivotal effector cell in allergic disease by their capacity to respond rapidly to stimuli and release a wide range of preformed and newly generated proinflammatory mediators (14). They are best known for IgE-mediated immediate-type hypersen- sitivity reactions. Mast cells are abundant in tissues exposed to the external environment including the skin, intestinal tract, and tra- chea, and also normally present in heart, lymph nodes, spleen, and CNS (15). Because these sites are also common portals of infec- tion, mast cells are likely to be one of the first inflammatory cells to make contact with invading pathogens. Mast cells can be acti- vated by a multitude of stimuli such as Abs, cytokines, chemo- kines, and neuropeptides, and also exert their biological effects by releasing preformed and de novo-synthesized mediators such as histamine, proteases, leukotrienes, PGs, and various cytokines, in- cluding TNF (16 –20). Although blood monocytes, tissue macro- phages, and Kupffer cells of liver are the best known sources of TNF, mast cells are the only cell type capable of storing presyn- thesized TNF (18, 2). Because of this unique capability, mast cells provide the only readily available source of TNF within peripheral tissues during the early course of infection. In deed, mast cells secrete TNF within minutes of bacterial challenge and then clear invading bacteria (12, 13, 21, 22). Recently, mast cells have been reported to bind various bacteria via TLRs 2 and 4 (23) and then secrete TNF. The mast cell therefore represents not only a sustain- able source but also a potential “early” source of TNF, which may be especially important when rapid mobilization of local responses is critical, as in innate immune responses to bacteria and in ac- quired immune responses to pathogens. Despite the findings that mast cells are vital in mediating clearance of pathogens at sites of infection through the release of TNF and recruitment of immune inflammatory cells (24), little is known about the relationship be- tween mast cells and malaria. In this study, we demonstrated for the first time the importance of mast cells for host immunity in malaria infection. Materials and Methods Mice and infection of Plasmodium berghei ANKA Genetically mast cell-deficient WBB6F 1 -W/W v (W/W v ) and the control WBB6F 1 +/+ (+/+) mice, and C57BL/6 were obtained from Japan SLC. TNF -/- mice were bred and maintained under specific pathogen-free con- ditions in an environmentally controlled clean room at the Center for Ex- perimental Medicine, Institute of Medical Science (University of Tokyo, Tokyo, Japan) (25). Five- to 6-wk-old W/W v , +/+, and C57BL/6 mice were inoculated i.v. with 1  10 5 P. berghei-infected erythrocytes to ex- amine the parasite growth. Male Wistar rats aged 8 wk old were also obtained from Japan SLC. The animal experiments were approved by the *Department of Microbiology and Immunology, Division of Infectious Genetics, and † Division of Cell Biology, Center for Experimental Medicine, Institute of Medical Science, University of Tokyo, Tokyo, Japan; and ‡ Department of Tropical Medicine, Jikei University School of Medicine, Tokyo, Japan Received for publication June 22, 2005. Accepted for publication June 15, 2006. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. 1 Address correspondence and reprint requests to Dr. Takahisa Furuta, University of Tokyo, Division of Infections Genetics, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108- 8639, Japan. E-mail address: furuta@ims.u-tokyo.ac.jp 2 Current address: Department of Veterinary Biosciences, College of Veterinary Med- icine, Ohio State University, 1925 Coffey Road, Columbus, OH 43210-1093. The Journal of Immunology Copyright © 2006 by The American Association of Immunologists, Inc. 0022-1767/06/$02.00