Demonstration of human erythrocyte C3b receptors (CR1) by haemadsorption and indirect haemagglutination techniques.

A closed chamber haemadsorption (HA) technique with tissue sections and an indirect haemagglutination (IHA) technique with monoclonal anti-C3b receptor (CR1) antibody were used to measure CR1 on human erythrocytes (E) (ECR1). In the HA technique the indicator cells were sheep E coated with rabbit IgM antibodies (A) and various amounts of human C3b (EAC). The ECR1 activity was classified according to the degree of haemadsorption of EAC. High ECR1 activity was found in 24% of healthy blood donors, intermediate activity in 62%, low activity in 12% and no activity in 2% of the blood donors. The results obtained using the IHA technique showed a good correlation with the results obtained using the HA technique. Both techniques are sensitive and the results are highly reproducible. The techniques are easy to perform and do not require expensive reagents or equipment. The HA and IHA techniques therefore offer an alternative to other techniques for measuring ECR1 activity.