Enhancement of antibody activity to bovine leukemia virus by complement

Cocultivation of fetal lamb kidney cells infected with bovine leukemia virus (BLV) and the cat cells containing murine sarcoma virus genome resulted in the rapid production of syncytia. This syncytia formation was inhibited by serum containing antibodies to glycoprotein antigen of BLV. When rabbit complement was added to the antiserum for early syncytia inhibition (ESI) test, a significant enhancement of ESI activity of the antiserum was observed. This enhancement was associated with IgG fraction but not with IgM fraction of the antiserum. The results of the comparative serological tests showed that the ESI test with complement was much more sensitive than either immunodiffusion or complement fixation tests in the detection of BLV antibodies.