Quantification of antigens with haemolysing antibodies exemplified by the bovine J blood group system

1. The J blood group activity of red cells is measured in terms of 50% haemolysis ('direct test'), that of dissolved or suspended samples in terms of 50% haemolysis inhibition ('indirect test') in a standardized bovine J system. 2. The volume of J-containing sample required for a 50% haemolysis inhibition decreases with increasing J activity. 3. The volume of anti-J required for a 50% haemolysis of J-positive erythrocytes also decreases with increasing J activity. 4. The use of antigen units (UAg) was introduced to serve as a measure of J activity of dissolved or suspended samples. 5. Antigen units were also used to characterize J-containing red cells. This was made possible by measuring the relation of the direct test (on red cells). Thus, a relatively simple method of determination of red cell UAg is obtained. 6. It was confirmed by absorption experiments that erythrocytes containing high concentrations of antigen require relatively low amounts of antibody to bring about a 50% haemolysis, but are able to bind a relatively high excess of antibody.