A simplified method for the preparation of EAC14.

Sheep erythrocytes (E), sensitized with unheated rabbit antiserum containing IgG antibodies (EA), bound human C4 when heat-inactivated serum was used as the source of complement (EAC). The EA were not agglutinated by antiserum to rabbit C3 and were not lysed in the presence of C4-deficient guinea pig serum. The EAC were agglutinated by antiserum to human C4, lysed by the addition of C4-deficient serum and were reactive in immune adherence. They were not agglutinated by antiserum to human C3. Accordingly, the cells could be designated as EAC14. They were stable and could be stored at 4 degrees C for at least 1 week without haemolysis occurring, and with no loss of reactivity in immune adherence test. E sensitized in the presence of EDTA or with heat-inactivated rabbit serum did not bind C4.