1,720,977 research outputs found
Structural requirements for SP-D function in vitro and in vivo: therapeutic potential of recombinant SP-D
No full textSurfactant protein D has multiple functions in innate immunity in the lung. The generation of SP-D knock-out mice has revealed a central role for this protein in the control of lung inflammation. Accumulating evidence in mouse models of infection and inflammation indicates that truncated recombinant forms of surfactant protein D are biologically active in vivo. This review addresses the structural requirements for recognised activities of SP-D in vitro and in vivo, with emphasis on evidence arising from studies with transgenic mice and mouse models of inflammatory lung disease. The potential of truncated recombinant forms of surfactant protein D as novel therapy for infectious and inflammatory disease is discussed
The human lung surfactant proteins A (SP-A) and D (SP-D) interact with apoptotic target cells by different binding mechanisms
No full textThe role of the lung surfactant proteins SP-A and SP-D in immune defence is well established. They bind to foreign organisms that invade the lungs and target them for phagocytic clearance by resident alveolar macrophages. SP-A and SP-D also bind to various apoptotic cells and facilitate their phagocytic uptake. To date, the molecular mechanisms by which the lung surfactant proteins interact with apoptotic cells and phagocytes are poorly understood.The aims of this study were to investigate further the interactions between SP-A and SP-D and apoptotic cells using human neutrophils and Jurkat cells as model systems.Specifically the binding behaviour of SP-A and SP-D with viable, early apoptotic and late apoptotic cells was investigated and compared. SP-A and SP-D show very distinct binding to the various cell types. SP-A bound to viable and early apoptotic cells in a predominantly Ca2+-dependent manner but the interaction with late apoptotic cells was Ca2+-independent, suggesting involvement of other than the lectin- or Ca2+-binding sites. This was consistent for neutrophils and Jurkat cells.SP-D in contrast, did not interact with viable and early apoptotic Jurkat cells but strongly and in a Ca2+-independent manner with late apoptotic Jurkat cells. SP-D-binding to viable and early apoptotic neutrophils was inhibited by maltose and ethylene-diamin-tetra-acetate (EDTA), suggesting lectin-binding site involvement whereas the binding to late apoptotic neutrophils was predominantly Ca2+-independent.These results represent a detailed study of the binding behaviour of SP-A and SP-D with different cell types and stages of viability. The mechanisms of these interactions appear to involve preferential recognition of different ligands on the apoptotic cell surface, which may include nucleic acid, phospholipid, protein and glycan structure
Nucleic acid is a novel ligand for innate, immune pattern recognition collectins surfactant proteins A and D and mannose-binding lectin
No full textCollectins are a family of innate immune proteins that contain fibrillar collagen-like regions and globular carbohydrate recognition domains (CRDs). The CRDs of these proteins recognize various microbial surface-specific carbohydrate patterns, particularly hexoses. We hypothesized that collectins, such as pulmonary surfactant proteins (SPs) SP-A and SP-D and serum protein mannose-binding lectin, could recognize nucleic acids, pentose-based anionic phosphate polymers. Here we show that collectins bind DNA from a variety of origins, including bacteria, mice, and synthetic oligonucleotides. Pentoses, such as arabinose, ribose, and deoxyribose, inhibit the interaction between SP-D and mannan, one of the well-studied hexose ligands for SP-D, and biologically relevant D-forms of the pentoses are better competitors than the L-forms. In addition, DNA and RNA polymer-related compounds, such as nucleotide diphosphates and triphosphates, also inhibit the carbohydrate binding ability of SP-D, or 60 kDa trimeric recombinant fragments of SP-D that are composed of the -helical coiled-coil neck region and three CRDs (SP-D(n/CRD)) or SP-D(n/CRD) with eight GXY repeats (SPD(GXY)8(n/CRD)). Direct binding and competition studies suggest that collectins bind nucleic acid via their CRDs as well as by their collagen-like regions, and that SP-D binds DNA more effectively than do SP-A and mannose-binding lectin at physiological salt conditions. Furthermore, the SP-D(GXY)8(n/CRD) fragments co-localize with DNA, and the protein competes the interaction between propidium iodide, a DNA-binding dye, and apoptotic cells. In conclusion, we show that collectins are a new class of proteins that bind free DNA and the DNA present on apoptotic cells by both their globular CRDs and collagen-like regions. Collectins may therefore play an important role in decreasing the inflammation caused by DNA in lungs and other tissues
Surfactant protein D reduces alveolar macrophage apoptosis In vivo
No full textSurfactant protein D (SP-D) is a molecule of the innate immune system that recognizes the patterns of surface carbohydrate on pathogens and targets them for phagocytosis and killing. SP-D-deficient mice show an increased number of macrophages in the alveolar space, excess surfactant phospholipid, overproduction of reactive oxygen species, and the development of emphysema. We report here that SP-D-deficient mice have a 5- to 10-fold increase in the number of apoptotic and necrotic alveolar macrophages, as defined by annexin V and propidium iodine staining, respectively. Intrapulmonary administration of a truncated 60-kDa fragment of human recombinant SP-D reduces the number of apoptotic and necrotic alveolar macrophages and partially corrects the lipid accumulation in SP-D-deficient mice. The same SP-D fragment binds preferentially to apoptotic and necrotic alveolar macrophages in vitro, suggesting that SP-D contributes to immune homeostasis in the lung by recognizing and promoting removal of necrotic and apoptotic cells
Surfactant protein D binds genomic DNA and apoptotic cells, and enhances their clearance, in vivo
No full textCollectins, such as surfactant protein D (SP-D), bind apoptotic cells; however, the ligands that they recognize on these cells are unknown. We hypothesized that SP-D binds to the DNA present on these cells. We show that SP-D binds and aggregates mouse alveolar macrophage DNA effectively. Alveolar macrophages of SP-D((-/-)) mice contained more nicked DNA than those of SP-A((-/-)) and wild type mice. Our results also suggest that carbohydrate recognition domains of SP-D may recognize DNA present on the apoptotic cells. Therefore, cell-surface DNA could be a ligand for recognition of apoptotic cells by collectins
Susceptibility of mice genetically deficient in SP-A or SP-D gene to invasive pulmonary aspergillosis
No full textPulmonary surfactant proteins, SP-A and SP-D, are carbohydrate pattern recognition molecules of innate immunity, which significantly enhance phagocytosis and killing of Aspergillus fumigatus, a pathogenic fungus, by neutrophils and macrophages. The present study examined the susceptibility of immunosuppressed SP-A gene deficient (SP-A(-/-)) or SP-D gene deficient (SP-D(-/-)) mice to A. fumigatus conidia challenge compared to wild-type (WT) mice. A. fumigatus-challenged SP-A(-/-) (SP-A(-/-) IPA) mice showed less mortality (40%) than the WT-IPA mice (100%) and increased mortality (60%) following administration of SP-A with decreased TNF-alpha and IFN-gamma to IL-4 ratio than SP-A(-/-) IPA mice. The SP-D(-/-) IPA mice (57.14%) showed similar mortality as WT-IPA mice (60%). However, the SP-D (-/-) IPA mice (42.86% mortality on day 2) died earlier than the WT-IPA mice (20% mortality on day 2), showed a higher hyphal density and tissue injury in lungs. Treatment with SP-D or a recombinant fragment of human SP-D rhSP-D reduced the mortality to 50% and 33%, respectively, concomitant with higher IFN-gamma to IL-4 ratios in treated SP-D(-/-) mice, compared to untreated control group. The results showed that SP-D gene deficient mice are more susceptible to IPA while SP-A gene deficient mice acquire resistance to IPA.<br/
Surfactant protein A binds to HIV and inhibits direct infection of CD4(+) cells, but enhances dendritic cell-mediated viral transfer
No full textThe identification of surfactant protein A (SP-A) as an important innate immune factor of the lungs, amniotic fluid, and the vaginal tract suggests that it could play an important role during various stages of HIV disease progression and transmission. Therefore, we examined whether SP-A could bind to HIV and also had any effect on viral infectivity. Our data demonstrate that SP-A binds to HIV in a calcium-dependent manner that is inhibitable by mannose and EDTA. Affinity capture of the HIV viral lysate reveals that SP-A targets the envelope glycoprotein of HIV (gp120), which was confirmed by ELISA using recombinant gp120. Digestion of gp120 with endoglycosidase H abrogates the binding of SP-A, indicating that the high mannose structures on gp120 are the target of the collectin. Infectivity studies reveal that SP-A inhibits the infection of CD4(+) T cells by two strains of HIV (BaL, IIIB) by >80%. Competition assays with CD4 and mAbs F105 and b12 suggest that SP-A inhibits infectivity by occlusion of the CD4-binding site. Studies with dendritic cells (DCs) demonstrate that SP-A enhances the binding of gp120 to DCs, the uptake of viral particles, and the transfer of virus from DCs to CD4+ T cells by >5-fold at a pH representative of the vaginal tract. Collectively, these results suggest that SP-A acts as a dual modulator of HIV infection by protecting CD4+ T cells from direct infection but enhancing the transfer of infection to CD4+ T cells mediated by DCs
Surfactant proteins A and D protect mice against pulmonary hypersensitivity induced by Aspergillus fumigatus antigens and allergens
No full textAllergic bronchopulmonary aspergillosis (ABPA) is an allergic disorder caused by an opportunistic fungal pathogen, Aspergillus fumigatus (Afu). Lung surfactant proteins SP-A and SP-D can interact with the glycosylated antigens and allergens of Afu, inhibit specific IgE binding to these allergens, and block histamine release from sensitized basophils. We have now examined the therapeutic effect of exogenous administration of human SP-A, SP-D, and a recombinant fragment of SP-D (rSP-D), in a murine model of pulmonary hypersensitivity induced by Afu antigens and allergens, which resembles human ABPA immunologically. The ABPA mice exhibited high levels of Afu-specific IgG and IgE, blood eosinophilia, extensive infiltration of lymphocytes and eosinophils in the lung sections, and a Th2 cytokine response. Treatment with SP-A, SP-D, and rSP-D lowered blood eosinophilia, pulmonary infiltration, and specific Ab levels considerably, which persisted up to 4 days in the SP-A–treated ABPA mice, and up to 16 days in the SP-D– or rSP-D–treated ABPA mice. The levels of IL-2, IL-4, and IL-5 were decreased, while the level of IFN- was raised in the splenic supernatants of the treated mice, indicating a marked shift from Th2 to Th1 response. These results clearly implicate pulmonary SP-A and SP-D in the modulation of allergic reactions
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