Applicability of composite materials for space radiation shielding of spacecraft.

Energetic ion beam experiments with major space radiation elements, 1H, 4He, 16O, 28Si and 56Fe, have been conducted to investigate the radiation shielding properties of composite materials. These materials are expected to be used for parts and fixtures of space vehicles due to both their mechanical strength and their space radiation shielding capabilities. Low Z materials containing hydrogen are effective for shielding protons and heavy ions due to their high stopping power and large fragmentation cross section per unit mass. The stopping power of the composite materials used in this work is intermediate between that of aluminum and polyethylene, which are typical structural and shielding materials used in space. The total charge-changing cross sections per unit mass, σUM, of the composite materials are 1.3-1.8 times larger than that of aluminum. By replacing conventional aluminum used for spacecraft with commercially available composite (carbon fiber / polyether ether ketone), it is expected that the shielding effect is increased by ∼17%. The utilization of composite materials will help mitigate the space radiation hazard on future deep space missions.

Investigation of shielding material properties for effective space radiation protection.

Geant4 Monte Carlo simulations were carried out to investigate the possible shielding materials of aluminum, polyethylene, hydrides, complex hydrides and composite materials for radiation protection in spacecraft by considering two physical parameters, stopping power and fragmentation cross section. The dose reduction with shielding materials was investigated for Fe ions with energies of 500 MeV/n, 1 GeV/n and 2 GeV/n which are around the peak of the GCR energy spectrum. Fe ions easily stop in materials such as polyethylene and hydrides as opposed to materials such as aluminum and complex hydrides including high Z metals with contain little or no hydrogen. Attenuation of the primary particles in the shielding and fragmentation into more lightly charged and therefore more penetrating secondary particles are competing factors: attenuation acts to reduce the dose behind shielding while fragmentation increases it. Among hydrogenous materials, 6Li10BH4 was one of the more effective shielding materials as a function of mass providing a 20% greater dose reduction compared to polyethylene. Composite materials such as carbon fiber reinforced plastic and SiC composite plastic offer 1.9 times the dose reduction compared to aluminum as well as high mechanical strength. Composite materials have been found to be promising for spacecraft shielding, where both mass and volume are constrained.

Alkyne aza-Prins cyclization of N-(hexa-3,5-diynyl)tosylamides with aldehydes using triflic acid and a binuclear aluminum complex.

The alkyne aza-Prins cyclization of 3,5-diynyl amides and various aldehydes was developed using TfOH with/without (Me2AlO)2SO2. This method, which could be applied to homopropargyl amides, provides TfO-substituted pyrrolidines with E-selectivities and exclusive regioselectivities. This work represents a first example of the aza-Prins cyclization with the introduction of TfO groups.

Clearance of CD43-capped cells by macrophages: capping alone leads to phagocytosis.

Apoptotic cells must be recognized early for phagocytosis to ensure that their toxic contents do not damage neighboring cells. In some cases this is achieved via CD43-capped membrane glycoproteins, the sialylpolylactosaminyl chains of which serve as ligands for phagocytosis by macrophages. However, because many additional changes occur during apoptosis, determining exactly which events are responsible for signaling macrophages to initiate phagocytosis remains a challenge. Here, we examined one clearance mechanism in detail and determined that capping of CD43 alone is sufficient to initiate phagocytosis. We induced macrophage-mediated phagocytosis by using cytochalasin B to artificially cap CD43 on healthy (non-apoptotic) Jurkat cells. Additional experiments confirmed that sialylpolylactosaminyl chains formed through this capping method are a prerequisite for removal, and that nucleolin is the macrophage receptor responsible for their detection. These findings strongly suggest that capping of CD43 presents a sufficient signal for phagocytosis without any additional membrane changes.

Recent advancements in cytotoxic T lymphocyte generation methods using carbohydrate-coated liposomes.

Both tumor-specific CD4(+) and CD8(+) T cells have been identified, and the latter is known as a major effector of adaptive antitumor immune responses. Optimal antitumor immune responses are considered to require the concomitant activation of both CD8(+) and CD4(+) T cells and the additional selective activation of CD4(+) T cells with helper, but not regulatory function. As optimal antitumor immune responses are generated by the concomitant activation of both T cell types, it is necessary for vaccine methods involving cytotoxic T-lymphocytes (CTLs) generation to possess a mechanism whereby antigen presenting cells can present administrated exogenous antigens on not only Major histocompatibility complex (MHC) class II, but also MHC class I molecules.

Generation of IFN-gamma-producing cells that recognize the major piroplasm surface protein in Theileria orientalis-infected bovines.

Theileriosis is a tick-borne protozoan disease caused by Theileria species. The Theileria species are classified into two groups depending on the cell type in which they proliferate and the clinical symptoms. The first group consists of lymphoproliferative Theileria species (T. parva and T. annulata), which mainly proliferate in lymphocytes, causing uncontrolled lymphocyte proliferation. The other group consists of a nonlymphoproliferative Theileria species (T. orientalis, also known as T. sergenti) that proliferates in erythrocytes and causes hemolytic anemia. Based on reports of generation of antigen-specific CD4(+) and CD8(+) T cells in lymphoproliferative theileriosis, we investigated whether T cells specific to the T. orientalis antigen are present in the nonlymphoproliferative form of the disease. In this study, we developed a new assay based on an enzyme-linked immunospot (ELISpot) to detect interferon-gamma (IFN-gamma)- and interleukin-10 (IL-10)-secreting cells in a series of cryogenically preserved bovine peripheral blood mononuclear cells (PBMCs). We first determined that IFN-gamma- and IL-10-secreting T cells were present in PBMCs by stimulating them with phytohemagglutinin L (PHA-L=red kidney bean lectin L, known as T cell stimulator), and then determined whether T. orientalis-specific T cells are present in T. orientalis-infected bovines. Peptides derived from T. orientalis major piroplasm surface protein (MPSP) were used as a T. orientalis-specific stimulator in the ELISpot assay, and peptides from glycoprotein B (gB) of the bovine herpes virus-1 (BHV-1) were used as a BHV-1-specific stimulator as a control for monitoring the immune response. Compared with results obtained using the BHV-1 (gB peptides)-specific IFN-gamma ELISpot assay to assess BHV-1-immunized Holsteins, prominent T. orientalis MPSP peptide-specific IFN-gamma and IL-10 positive spots were detected in T. orientalis-infected Holsteins but weak positive responses were exhibited by T. orientalis-infected Angus and Japanese Black cattle. As far as we are aware, this is the first report to show direct evidence of the presence of T. orientalis-specific T cells in T. orientalis-infected bovines using an antigen-specific ELISpot assay system and that T. orientalis-specific, IFN-gamma- and IL-10-producing T cells are produced in T. orientalis-infected Holsteins.

Deletion polymorphism of SIGLEC14 and its functional implications.

Human Siglec-14, a member of the Siglec family of sialic acid-binding lectins, shows extensive sequence similarity to human Siglec-5. To analyze respective expression patterns of Siglec-14 and Siglec-5, we developed specific antibodies against each of them. We found that the former was expressed on granulocytes and monocytes, while the latter was on granulocytes and B-cells. Surprisingly, some individuals lacked the expression of Siglec-14, while they all expressed Siglec-5. We found that a fusion between SIGLEC14 and SIGLEC5 genes, resulting in the functional deletion of SIGLEC14, underlies this phenotype. The presence of the "SIGLEC14 null" allele in all human populations we tested implies an ancient origin, while its allelic frequency is higher in Asians compared with Africans and Europeans. The forced expression of Siglec-14 in a monocytic cell line-enhanced TNF-alpha secretion elicited by lipopolysaccharide. These results imply that Siglec-14 may play some role in bacterial infection.

Clearance of oxidatively damaged cells by macrophages: recognition of glycoprotein clusters by macrophage-surface nucleolin as early apoptotic cells.

The mechanism of macrophage recognition of oxidatively damaged cells was investigated. Jurkat T cells exposed to various concentrations of H(2)O(2) were bound and phagocytosed by macrophages. The cells exposed to 0.1 mM H(2)O(2) were best bound. The cell-surface ligands recognized by macrophages were suggested to be sialylpolylactosaminyl sugar chains of a major sialoglycoprotein CD43 because 1) the cell binding was inhibited by oligosaccharides containing sialylpolylactosaminyl chains, and their inhibitory activity was destroyed by a polylactosamine-cleaving enzyme endo-beta-galactosidase, and by neuraminidase; 2) the oxidized Jurkat cells pretreated with either glycosidase or with anti-CD43 antibody were not bound. The macrophage receptor involved in the binding was suggested to be cell-surface nucleolin because 1) anti-nucleolin antibody inhibited the binding; 2) nucleolin-transfected HEK293 cells bound the oxidized cells; and 3) this binding was inhibited by anti-nucleolin antibody and by anti-CD43 antibody. CD43 on oxidized Jurkat cells tended to form clusters in good accordance with their susceptibility to the macrophage binding. CD43 clustering and the oxidized-cell binding to macrophages were prevented by a caspase inhibitor Z-VAD-fmk, suggesting that the oxidized and bound cells were undergoing apoptosis. Indeed, caspase-3 activity of Jurkat cells increased by the oxidation. These results suggest that moderately oxidized cells undergo apoptosis and are recognized by macrophages as early apoptotic cells.

A multifunctional shuttling protein nucleolin is a macrophage receptor for apoptotic cells.

Early apoptotic Jurkat T cells undergo capping of CD43, and its polylactosaminyl saccharide chains serve as ligands for phagocytosis by macrophages. This suggests the presence of a polylactosaminoglycan-binding receptor on macrophages. Here we show that this receptor is nucleolin, a multifunctional shuttling protein present in nucleus, cytoplasm, and on the surface of some types of cells. Nucleolin was detected at the surface of macrophages, and anti-nucleolin antibody inhibited the binding of the early apoptotic cells to macrophages. Nucleolin-transfected HEK293 cells expressed nucleolin on the cell surface and bound the early apoptotic cells but not phosphatidylserine-exposing late apoptotic cells. This binding was inhibited by anti-nucleolin antibody, by polylactosamine-containing oligosaccharides, and by anti-CD43 antibody. Deletion of the antibody binding region of nucleolin resulted in loss of the apoptotic cell-binding ability. Moreover, truncated recombinant nucleolin in solution containing this region blocked the apoptotic cell binding to macrophages, and the blocking effect was cancelled by the oligosaccharides. These results indicate that nucleolin is a macrophage receptor for apoptotic cells.

Carbohydrate chains and phosphatidylserine successively work as signals for apoptotic cell removal.

At an early stage of apoptosis, Jurkat cells transiently become susceptible to binding and phagocytosis by macrophages through the polylactosamine-type carbohydrate chains of CD43 [J. Biol. Chem. 279 (2004) 5967]. Susceptibility of apoptotic Jurkat cells to macrophage recognition was studied over an extended time range of 0-24 h including a later stage. Jurkat cells incubated with appropriate concentrations of apoptosis-inducing agents etoposide or anti-Fas antibody became susceptible to macrophage-binding at 2 h, and the susceptibility fell to the control level at 4 or 6 h. However, it increased again at later hours (6-24 h). Flow cytometric analyses of CD43 and phosphatidylserine (PS) on the apoptotic cells indicated that CD43 began to degrade at around 4 h, and PS is externalized significantly at 4 or 6 h. The macrophage-binding at 2 h was prevented by glycosidase treatment of Jurkat cells, but not by annexin V. Conversely, the later binding at 12 or 18 h was not prevented by glycosidase treatment, but was done so by annexin V. These results suggest that Jurkat cells become susceptible to phagocytic removal at an early stage of apoptosis by the carbohydrate-mediated mechanism, and at a later stage by the PS-mediated mechanism.

Carbohydrate-mediated phagocytic recognition of early apoptotic cells undergoing transient capping of CD43 glycoprotein.

A novel mechanism of phagocytic recognition of apoptotic cells was found and characterized. Jurkat cells incubated with appropriate concentrations of etoposide or anti-Fas antibody transiently became susceptible to binding and phagocytosis by THP-1 cell-derived macrophages at 2 h. The bound Jurkat cells showed no chromatin condensation, but the binding was prevented by a caspase inhibitor, indicating that they were recognized at an early stage of apoptosis. The ligands recognized on the apoptotic cells were sialylpolylactosaminyl sugar chains because 1) the binding was inhibited by an oligosaccharide preparation of erythrocyte membrane, and its inhibitory activity was destroyed by polylactosaminoglycan-specific endo-beta-galactosidase or neuraminidase; 2) Jurkat cells pretreated with endo-beta-galactosidase or neuraminidase failed to be recognized; and 3) treatment of the apoptotic cells with polylactosaminoglycan-binding Datura stramonium agglutinin prevented recognition. The sialylpolylactosaminyl chains involved were most likely those of a major sialoglycoprotein CD43 because anti-CD43 antibody inhibited recognition. CD43 on apoptotic Jurkat cells was found to form a cap at 2 h, and the cap disappeared at 4 h. This transient capping of CD43 coincided with the transient increase in the susceptibility of the cells to macrophage recognition, suggesting that CD43 capping is responsible for generation of the carbohydrate ligands for recognition. Furthermore, microscopic observation suggested that the apoptotic cells were recognized at the CD43 cap. Taken together, we conclude that apoptotic Jurkat cells transiently undergo CD43 capping at an early stage of apoptosis and are recognized by macrophages through the cluster of sialylpolylactosaminyl chains of the capped CD43.