Zc. Chroneos et al., PURIFICATION OF A CELL-SURFACE RECEPTOR FOR SURFACTANT PROTEIN-A, The Journal of biological chemistry, 271(27), 1996, pp. 16375-16383
In the present report we have characterized the binding of surfactant
protein A (SP-A) to bone marrow-derived macrophages, U937 cells, alveo
lar macrophages, and type II epithelial cells. The binding of SP-A to
all cell types is Ca2+-dependent and trypsin-sensitive, but type II ce
lls express distinct Ca2+-independent binding sites. The binding of SP
A to macrophages is independent of known cell surface carbohydrate-sp
ecific receptors and of glycoconjugate binding sites on the surface of
the cells and is distinct from binding to Clq receptors. Based on lig
and blot analysis, both type II cells and macrophages express a 210-kD
a SP-A-binding protein. The 210-kDa protein was purified to apparent h
omogeneity from U937 macrophage membranes using affinity chromatograph
y with noncovalently immobilized surfactant protein A, and was purifie
d from rat lung by differential detergent and salt extraction of isola
ted rat lung membranes. Polyclonal antibodies against the rat lung SP-
A-binding protein inhibit binding of SP-A to both type II cells and ma
crophages, indicating that the 210-kDa protein is expressed on the cel
l surface. The polyclonal antibodies also block the SP-A-mediated inhi
bition of phospholipid secretion by type II cells, indicating that the
210-kDa protein is a functional cell-surface receptor on type II cell
s. In a separate report we have determined that antibodies to the SP-A
receptor block the SP-A-mediated uptake of Mycobacterium bovis, indic
ating that the macrophage SP-A receptor is involved in SP-A-mediated c
learance of pathogens.