Eficient mice contained 63.8 or 37.8 ring-infected RBCs, respectively. These results suggested that almost all ring-infected RBCs in LMP7-deficient were captured by macrophages, presumably resulting 
in the partial resistance to lethal infection with PyL in these mutant mice.DiscussionIn this study, we analyzed the importance of LMP7 in protection against infection with malaria parasites by order 56-59-7 infecting LMP7-deficient mice with PyNL or PyL. In contrast to our expectation that the failure to activate protective CD8+ T cells due to the absence of LMP7 would lead to impaired protection, LMP7-deficient mice were partially resistant to malaria. Indeed, immune responses, especially CD8+ T cell responses, were less activated compared with WT mice. However, lack of LMP7 conferred resistance to malaria, overcoming the partially impaired activation of CD8+ T cells. Our results demonstrate that resistance observed in LMP7-deficient mice was attributed to the higher susceptibility of pRBCs for phagocytosis by macrophages. These results do not deny the importance of CD8+ T cells in protective immunity against malaria, because CD8+ T cells specific for LMP7-independent epitopes could be activated [37]. Indeed, substantial numbers of CD8+ T cells expressed CD69 and IFN-c in response to malaria infection in LMP7-deficient mice (Fig. 2A, C). Furthermore, our previous studies clarified that the protective effects of CD8+ T cells are due to phagocytosis by macrophages activated by an IFN-c dependent mechanism. In the presence of strong protection during the early phase of infection due to Tubastatin A supplier enhanced phagocytosis, the additional effects of CD8+ T cells might be difficult to observe. Phagocytosis of pRBCs occurring in reticuloendothelial systems has been reported to be critical for the elimination of malariaparasites in various situations [38]. Attachment of pRBCs infected with P. falciparum, a causative agent of malignant malaria, to endothelial cells may be an escape mechanism to prevent trafficking to the spleen where phagocytosis occurs [39]. Considering these facts, 
it is possible that the enhanced phagocytosis is responsible for resistance of LMP7-deficient mice. As the phagocytic ability of LMP7-deficient macrophages was comparable to that of WT macrophages, the alterations of RBCs observed during infection might be important for the enhanced phagocytosis. Under physiological conditions, macrophages in the reticuloendothelial system destroy senescent RBCs to maintain homeostasis by recognizing physical alterations in RBCs, such as lack of flexibility and deformity. Macrophages also recognize chemical and antigenic alterations. For instance, they capture “eryptotic” RBCs exposing phosphatidylserine (PS) flipped from the internal leaflet of the RBC membrane [40]. Externalization of PS is a hallmark of apoptosis in nucleated cells, which provides phagocytes with “eat-me” signals. RBCs exposing PS are also observed in iron-deficiency anemia and drug treatment enhanced phagocytosis of pRBCs during malaria, resulting in a partial protection against malaria [41,42]. Thus, we examined the exposure of PS in RBCs from LMP7-deficient mice infected with PyL. However, infection with PyL did not cause externalization of PS to the surface of RBCs in either WT or LMP7-deficient mice (data not shown). Instead, we found that RBCs have deformations during malaria in LMP7-deficient mice. As patients with abnormal RBCs disorders such as hereditary spherocytosis suffer fr.Eficient mice contained 63.8 or 37.8 ring-infected RBCs, respectively. These results suggested that almost all ring-infected RBCs in LMP7-deficient were captured by macrophages, presumably resulting in the partial resistance to lethal infection with PyL in these mutant mice.DiscussionIn this study, we analyzed the importance of LMP7 in protection against infection with malaria parasites by infecting LMP7-deficient mice with PyNL or PyL. In contrast to our expectation that the failure to activate protective CD8+ T cells due to the absence of LMP7 would lead to impaired protection, LMP7-deficient mice were partially resistant to malaria. Indeed, immune responses, especially CD8+ T cell responses, were less activated compared with WT mice. However, lack of LMP7 conferred resistance to malaria, overcoming the partially impaired activation of CD8+ T cells. Our results demonstrate that resistance observed in LMP7-deficient mice was attributed to the higher susceptibility of pRBCs for phagocytosis by macrophages. These results do not deny the importance of CD8+ T cells in protective immunity against malaria, because CD8+ T cells specific for LMP7-independent epitopes could be activated [37]. Indeed, substantial numbers of CD8+ T cells expressed CD69 and IFN-c in response to malaria infection in LMP7-deficient mice (Fig. 2A, C). Furthermore, our previous studies clarified that the protective effects of CD8+ T cells are due to phagocytosis by macrophages activated by an IFN-c dependent mechanism. In the presence of strong protection during the early phase of infection due to enhanced phagocytosis, the additional effects of CD8+ T cells might be difficult to observe. Phagocytosis of pRBCs occurring in reticuloendothelial systems has been reported to be critical for the elimination of malariaparasites in various situations [38]. Attachment of pRBCs infected with P. falciparum, a causative agent of malignant malaria, to endothelial cells may be an escape mechanism to prevent trafficking to the spleen where phagocytosis occurs [39]. Considering these facts, it is possible that the enhanced phagocytosis is responsible for resistance of LMP7-deficient mice. As the phagocytic ability of LMP7-deficient macrophages was comparable to that of WT macrophages, the alterations of RBCs observed during infection might be important for the enhanced phagocytosis. Under physiological conditions, macrophages in the reticuloendothelial system destroy senescent RBCs to maintain homeostasis by recognizing physical alterations in RBCs, such as lack of flexibility and deformity. Macrophages also recognize chemical and antigenic alterations. For instance, they capture “eryptotic” RBCs exposing phosphatidylserine (PS) flipped from the internal leaflet of the RBC membrane [40]. Externalization of PS is a hallmark of apoptosis in nucleated cells, which provides phagocytes with “eat-me” signals. RBCs exposing PS are also observed in iron-deficiency anemia and drug treatment enhanced phagocytosis of pRBCs during malaria, resulting in a partial protection against malaria [41,42]. Thus, we examined the exposure of PS in RBCs from LMP7-deficient mice infected with PyL. However, infection with PyL did not cause externalization of PS to the surface of RBCs in either WT or LMP7-deficient mice (data not shown). Instead, we found that RBCs have deformations during malaria in LMP7-deficient mice. As patients with abnormal RBCs disorders such as hereditary spherocytosis suffer fr.
