Effects of neuraminidase and trypsin on surface charge and aggregation of red blood cells

Trypsin and neuraminidase decrease the surface charge of red blood cells (RBC) and should, therefore, increase red cell aggregation (RCA). To assess the reliability of the Myrenne aggregometer to detect extremely strong RCA, RBC from normal adults were treated with neuraminidase or trypsin in vitro. RBC surface charge was estimated by partitioning of RBC in a two phase system containing dextran and polyethyleneglycol. RBC aggregation was studied by means of a Myrenne aggregometer and by microscopic observation in a rheoscope. RBC partition coefficient (i.e. surface charge) was 89% for normal RBC, 34% for trypsin and 5% for neuraminidase treated RBC. RCA in the Myrenne aggregometer increased markedly with trypsin, but tended to decrease with neuraminidase treatment. Observation of RCA in the rheoscope showed that neuraminidase caused strong RBC aggregation and that dispersion of RBC aggregates was incomplete even at high shear. We conclude that studies of RCA should always include microscopic observation.