Purification of a cell-surface receptor for surfactant protein A.

Division of Pulmonary Biology, Children's Hospital Medical Center, Cincinnati, Ohio 45229-3039, USA.
Journal of Biological Chemistry (Impact Factor: 4.6). 08/1996; 271(27):16375-83. DOI: 10.1074/jbc.271.27.16375
Source: PubMed

ABSTRACT In the present report we have characterized the binding of surfactant protein A (SP-A) to bone marrow-derived macrophages, U937 cells, alveolar macrophages, and type II epithelial cells. The binding of SP-A to all cell types is Ca2+-dependent and trypsin-sensitive, but type II cells express distinct Ca2+-independent binding sites. The binding of SP-A to macrophages is independent of known cell surface carbohydrate-specific receptors and of glycoconjugate binding sites on the surface of the cells and is distinct from binding to C1q receptors. Based on ligand blot analysis, both type II cells and macrophages express a 210-kDa SP-A-binding protein. The 210-kDa protein was purified to apparent homogeneity from U937 macrophage membranes using affinity chromatography with noncovalently immobilized surfactant protein A, and was purified from rat lung by differential detergent and salt extraction of isolated rat lung membranes. Polyclonal antibodies against the rat lung SP-A-binding protein inhibit binding of SP-A to both type II cells and macrophages, indicating that the 210-kDa protein is expressed on the cell surface. The polyclonal antibodies also block the SP-A-mediated inhibition of phospholipid secretion by type II cells, indicating that the 210-kDa protein is a functional cell-surface receptor on type II cells. In a separate report we have determined that antibodies to the SP-A receptor block the SP-A-mediated uptake of Mycobacterium bovis, indicating that the macrophage SP-A receptor is involved in SP-A-mediated clearance of pathogens.

  • [Show abstract] [Hide abstract]
    ABSTRACT: Purpose: Surfactant protein A (SP-A) up regulates cytokine expression in lung disease of prematurity. Here we present data that for the first time characterizes SP-A expression and localization in the mouse retina and its impact on neovascularization (NV) in the mouse. Methods: Retinal SP-A was localized in wild type (WT) mice with the cell markers Glutamine Synthase (Müller cells), Neurofilament-M (ganglion cells), Glial acid fibrillary acid protein (astrocytes) and Cluster of differentiation 31 (endothelial cells). Toll like receptor 2 and 4 (TLR-2 and TLR-4) ligands were used to up regulate SP-A protein expression in WT and Myeloid differentiation primary response 88 (MyD88-necessary for NFκB signaling) null mouse retinas and Müller cells, which was quantified using ELISA. Retinal SP-A was then measured in the oxygen induced retinopathy (OIR) mouse model. The effect of SP-A on retinal NV was then studied in SP-A null (SP-A-/-) mice. Results: SP-A is present at birth in the WT mouse retina and co-localizes with GS. TLR-2 and TLR-4 ligands increase SP-A both in the retina as well as in Müller cells. SP-A is increased at P17 in WT mouse pups with OIR compared to controls (p=0.02) and SP-A-/- mice have reduced NV as compared to WT (p=0.001) in the OIR model. Conclusions: Retinal and Müller cell SP-A is up regulated via the NFκB pathway and is up regulated during the hypoxia phase of OIR. Absence of SP-A attenuates NV in the OIR model. Thus SP-A may be a marker of retinal inflammation during NV. Copyright © 2014 by Association for Research in Vision and Ophthalmology.
    Investigative Ophthalmology &amp Visual Science 11/2014; 56(1). DOI:10.1167/iovs.13-13652 · 3.66 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The lung surfactant collectin proteins SP-A and SP-D have been shown to interact with phagocytic cells, such as macrophages and dendritic cells to facilitate uptake of pathogens and apoptotic cells. However, the mechanism by which the collectins interact with the phagocytes and which surface molecules on the phagocytic cells are involved is not yet clear. In the present study, we demonstrate the interaction of SP-A and SP-D with phagocytic cells including human monocyte-derived macrophages and immature dendritic cells. Results show that both proteins bind in a similar manner to both cell types. A prominent 20-22 kDa doublet band was observed on SDS-PAGE analysis as the major Ca 2+ -dependent ligand for SP-A and SP-D on both macrophages and dendritic cells. However, we were unable to identify the proteins involved.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Collections are a group of multimeric proteins mostly consisting of 9–18 polypeptides organised into either ‘bundle-of-tulips’ or ‘X-like’ overall structures. Each polypeptide contains a short N-terminal segment followed by a collagen-like sequence and then by a C-terminal lectin domain. A collectin molecule is assembled from identical or very similar polypeptides by disulphide bonds at the N-terminal segment, formation of triple helices in the collagen-like region and clusters of three lectin domains at the peripheral ends of triple helices. These proteins can bind to sugar residues on microorganisms via the peripheral lectin domains and subsequently interact, via the collagen-like triple-helices, with receptor(s) on phagocytes and/or the complement system to bring about the killing and clearance of the targets without the involvement of antibodies. The collectins can also bind to phagocyte receptor(s) to enhance phagocytosis mediated by other phagocytic receptors. Lack, or low levels, of collectin expression can lead to higher susceptibility to infections, especially during childhood when specific immunity has not fully developed. Therefore, the collectins play important roles in the enhancement of innate immunity.
    BioEssays 06/1997; 19(6). DOI:10.1002/bies.950190610 · 4.84 Impact Factor