Binding of surfactant protein A (SP-A) to herpes simplex virus type 1-infected cells is mediated by the carbohydrate moiety of SP-A.
Pulmonary surfactant protein A (SP-A) has been shown to act as an opsonin in the phagocytosis of viruses by alveolar macrophages. To determine whether SP-A binds to viral proteins and which part of the SP-A molecule is involved in this interaction, binding studies were undertaken. SP-A was labeled with fluorescein isothiocyanate, and its binding to herpes simplex virus type 1-infected HEp-2 cells, as a model for virus-infected cells in general, was studied using flow cytometry. The binding of SP-A to virus-infected cells was saturable, reversible, and both time- and concentration-dependent, reaching a maximal level after 30 min at an SP-A concentration of 10 micrograms/ml. An approximately 4-fold increase in binding of SP-A to infected cells over control cells was observed. Yeast mannan, a mannose homopolysaccharide, did not influence the binding. However, heparin inhibited binding of SP-A in a concentration-dependent manner. In addition, heparin could also dissociate cell-bound SP-A, indicating that polyanionic oligosaccharides are involved in the binding of SP-A to virus-infected cells. Deglycosylated SP-A, obtained by digestion with N-glycosidase F, did not bind to infected cells. Heparin or deglycosylation of SP-A had no effect on the stimulation of alveolar macrophages by SP-A. It is concluded that the carbohydrate moiety of SP-A is involved in the recognition of viruses by SP-A and may play a role in the antiviral defenses of the lung.
van Iwaarden
J F
JF
Laboratory of Veterinary Biochemistry, University of Utrecht, The Netherlands.
van Strijp
J A
JA
Visser
H
H
Haagsman
H P
HP
Verhoef
J
J
van Golde
L M
LM
D000818:Animals; D001665:Binding Sites; D001992:Bronchoalveolar Lavage Fluid / Q000378:metabolism; D002478:Cells, Cultured; D016650:Fluorescein-5-isothiocyanate; D005609:Free Radicals; D006023:Glycoproteins / Q000302:isolation & purification / Q000378:metabolism*; D006493:Heparin / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D016676:Macrophages, Alveolar / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008351:Mannans / Q000494:pharmacology; D011510:Proteolipids / Q000302:isolation & purification / Q000378:metabolism* / Q000494:pharmacology; D011649:Pulmonary Alveolar Proteinosis / Q000378:metabolism; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants / Q000302:isolation & purification / Q000378:metabolism* / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D018139:Simplexvirus / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D005609:Free Radicals; D006023:Glycoproteins; D008351:Mannans; D011510:Proteolipids; D037662:Pulmonary Surfactant-Associated Protein A; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants; D006493:Heparin; D016650:Fluorescein-5-isothiocyanate; D013755:Tetradecanoylphorbol Acetate