Examination of variables affecting syncytium formation by, and serum neutralization of, feline immunodeficiency virus on CrFK cells.

The feline immunodeficiency virus (FIV) induces syncytia in Crandell feline kidney (CrFK) cells grown in low fetal bovine serum-containing medium. This finding has allowed the development of sensitive FIV titration and neutralization assays using syncytium formation as an indicator of infection. In this report we examine several variables that can influence number and size of syncytia. In addition, by performing assays under rigidly controlled culture conditions, we confirm that serum neutralization assays based on FIV-induced syncytium formation in CrFK cells detect broadly reactive neutralizing antibodies.