Release of wild-type, C28a, C28, and P111S HN from receptor. RBC were bound to cells expressing wild-type (wt), C28a, C28, or P111S HN at 4°C. The cells were then transferred to 37°C, and RBC release was quantified as described in Materials and Methods at the indicated times (minutes) (abscissa). The amount of released RBC is given as a percentage of total bound RBC (ordinate).