Effects of proteases and neuraminidase on RBC surface charge and agglutination. A kinetic study.

Electrophoretic mobility, membrane sialic acid content and agglutinability by "incomplete" antisera against Rh-o, hr' and k antigens were determined for red blood cells in the course of treatment with trypsin, ficin and neuraminidase. Neuraminidase gradually produces a slight to moderate agglutinability as it reduced surface charge density in proportion to the amount of sialic acid removed. Proteases acted in two distinct steps. The first stage is characterized by the cells rapidly becoming highly agglutinable and by the unmasking of new negative charge as the first half of the sialic acid is removed. In the second stage the cells show a slight gain in agglutinability as surface charge is removed in proportion to sialic acid removal as in the case of neuraminidase. Neuraminidase-treated cells are considerably less agglutinable than cells reduced to the same zeta-potential by protease treatment. The greater efficacy of proteases compared to neuraminidase in making cells agglutinable could be because they not only reduce surface charge density but also increase antigen-antibody bond strength, render antigens more mobile in the membrane to allow clustering in regions of cell to cell antibody bridging and remove glycopeptide chains which may be causing steric hindrance to antigen-antibody binding or to cell-cell contact.