Quantitative Haemagglutination

Summary. The polycations Polybrene®, protamine and polylysine aggregate red cell suspensions. Mild neuraminidase treatment abolishes aggregation by Polybrene® and protamine, but not by polylysine. Blood samples, separated into old and young populations on the basis of density, aggregate to the same degree despite the decreased total NANA of older cells. Aggregation appears to be mainly dependent upon the degree to which the polycation disturbs the vicinal water of the erythrocyte. Desialated red cells are probably less hydrated and do not compete as vigorously with Polybrene® and protamine for the available water. Polylysine may act by cross‐linking red cells, but more Polybrene® and protamine is required to cause aggregation than would completely saturate surface NANA. Protamine may bind to some NANA molecules preferentially since it prevents total desialation by neuraminidase, but neither Polybrene® nor polylysine significantly affects neuraminidase action.