The specificity of neutralizing antibodies to feline leukaemia viruses

Feline leukaemia viruses (FeLV) of subgroups A (FeLV-A), B(FeLV-B) and C(FeLV-C) were examined by neutralization. The FeLV-A isolates were monotypic. By contrast, there was antigenic variation within subgroups B and C. There was also considerable cross-reactivity between subgroups. Thus, FeLV-A viruses showed weak cross-reactivity to the standard FeLV-C isolate; four of the subgroup B viruses were identical and cross-reactied with the standard FeLV-C, but not with FeLV-A or the fifth FeLV-B, and this latter virus weakly cros-reacted with FeLV-A but not with the FeLV-C; within subgroup C, one virus was indistinguishable from the standard FeLV-C strain but the other two were very similar to FeLV-A. Therefore, subgroup classification based on interference did not altogether correspond with neutralizing behaviour for subgroups B and C.