The binding of hepatitis A virus to cell surfaces shows evidence of positive co-operativity.

Radio-iodinated hepatitis A virus binds to cultured mammalian cells in a saturable manner, with about 1.4 x 10(3) sites/cell and a S0.5 of about 1.4 x 10(-11) M for FRhK-4 cells. This binding to FRhK-4 cells shows evidence of positive co-operativity, with a Hill coefficient of 2.1 (+/- 0.1). This implies that the cellular receptor for the virus may have multiple binding sites and that the affinity of HAV for its receptor is increased if one of the binding sites is occupied by virus. Binding is completely blocked by two neutralising monoclonal antibodies, which also inhibit viral haemagglutination. A non-neutralising monoclonal antibody partially inhibits binding to FRhK-4 cells, but has no effect on haemagglutination.