ISSN:
1059-910X
Keywords:
C1q
;
Calcium
;
Specific binding
;
SP-A
;
Life and Medical Sciences
;
Cell & Developmental Biology
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Natural Sciences in General
Notes:
We analyzed the binding mechanism of human recombinant lung surfactant protein A (SP-A) to rat alveolar macrophages using anti-SP-A antiserum and protein A coated onto gold particles. Results were compared with our recent data on binding and uptake of SP-A-coated colloidal gold particles. The rationale for the current approach was to avoid any possible steric effects on SP-A binding to the cell surface. Binding of unlabeled SP-A depends on the presence of calcium ions in the medium and involves a mannose-specific mechanism. Binding is partly inhibited by the collagenase-resistent fragment of SP-A, representing mainly the globular part of SP-A. Taken together, these facts indicate binding of SP-A via the carbohydrate binding site on the globular region of SP-A. On the other hand, a partial inhibition of SP-A binding by fragments of C1q (representing the collagenous region of C1q) indicates a second binding site for SP-A by the collagen-like portion to the C1q receptor of macrophages. We conclude that two different mechanisms are probably involved in SP-A binding to alveolar macrophages. Specificity of the binding was shown with fluorescein-labeled SP-A. Binding was inhibited by an excess of unlabeled SP-A. Binding and uptake of SP-A are seen only with alveolar macrophages and not with other macrophage populations isolated from rat, such as liver macrophages (Kupffer cells), resident peritoneal macrophages, and peritoneal macrophages activated by Corynebacterium parvum. Therefore, binding sites for SP-A occur exclusively on alveolar macrophages. In addition, the intracellular Ca2+ concentration of the lung macrophages was determined by using the fluorescent dye fura-2/AM. Intracellular [Ca2+] increased immediately after addition of SP-A. This indicates immediate activation of macrophages by SP-A. © 1993 Wiley-Liss, Inc.
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jemt.1070260505
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