Binding of 125I-labeled reovirus to cell surface receptors

Quantitative studies of 125I-labeled reovirus binding at equilibrium to several cell types was studied, including (1) murine L cell fibroblasts; (2) murine splenic T lymphocytes; (3) YAC cells, a murine lymphoma cell line; and (4) R1.1 cells, a murine thymoma cell line. Competition and saturation studies demonstrated (1) specific, saturable, high-affinity binding of reovirus types 1 and 3 to nonidentical receptors on L cell fibroblasts; (2) high-affinity binding of type 3 reovirus to murine splenic lymphocytes and R1.1 cells; (3) low-affinity binding of reovirus type 1 to lymphocytes and R1.1 cells; and (4) no significant binding of either serotype to YAC cells. Differences in the binding characteristics of the two reovirus serotypes to L cell fibroblasts were found to be a property of the viral hemagglutinin, as demonstrated using a recombinant viral clone. The equilibrium dissociation constant (Kd) for viral binding was of extremely high affinity (Kd in the range of 0.5 nM), and was slowly reversible. Experiments demonstrated temperature and pH dependence of reovirus binding and receptor modification studies using pronase, neuraminidase, and various sugars confirmed previous studies that reovirus receptors are predominantly protein in structure. The reovirus receptor site density was in the range of 2-8 X 10(4) sites/cell. These studies demonstrate that the pseudo-first-order kinetic model for ligand-receptor interactions provides a useful model for studying interactions of viral particles with membrane viral receptors. They also suggest that one cell may have distinct receptor sites for two serotypes of the same virus, and that one viral serotype may bind with different kinetics depending on the cell type.