Conversely, rH1 binding to human B lymphocytes was blocked when PBMCs were stained following a pre-incubation step with either C. perfringens NA, which cleaves α-2,3- α-2,6- and α-2,8-linked sialic-acids, or with H3N2 human influenza mono-bulk antigens, which are known for preferential binding to α-2,6-sialic-acids. Here, XK is linked to influenza.