Abstract
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.
Highlights
Ato infected cellsover control cellswas observed. opsonin in the phagocytosis of herpes simplex virus type l\
Influence of Carbohydrates on the Binding of surfactant protein A (SP-A)-To study whether the ability of SP-A to bind to carbohydrates, in particular mannose, isinvolved in the binding of SP-A to SP-A infected cells, the following studies were designed
Binding of SP-A toinfected cells was performed in thepresence of yeast mannan, a mannose homopolysaccharide
Summary
Ato infected cellsover control cellswas observed. opsonin in the phagocytosis of herpes simplex virus type l\. Heparin could dissociate cell-bound is involved in the recognition of virus, binding studies using Fluorometric Phagocytosis Assay-The phagocytosis of FITC-labeled HSV-1 by rat alveolar macrophages was recorded using the fluorometric phagocytosis assay as described previously (19).
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