Isolation of single-chain antibody fragments against Venezuelan equine encephalomyelitis virus from two different immune sources.

Venezuelan equine encephalomyelitis (VEE) virus is an important human and veterinary pathogen of Central and South America. The virus can cause widespread epidemics, affecting hundreds of thousands of horses, and thousands of humans. Detection of the virus early in infection and in mosquito populations may allow epidemics to be predicted such that suitable prophylaxis, such as vaccination, can be used to reduce disease severity and transmission. The sensitivity and specificity of current immunoassays, based on conventional monoclonal and polyclonal antibodies, needs to be improved for the diagnosis of infection. We have examined phage display libraries expressing single-chain antibodies (scFv) produced from two different immune sources, a hybridoma cell line and an immunized mouse spleen. The libraries were panned against VEE virus to select for specific scFvs. scFvs isolated from both libraries were specific for the same epitope on the VEE virus and sequence analysis showed that the scFvs were almost identical apart from the CDR3 region of the heavy chain. The data presented in this article suggest that although scFvs may be useful tools for the detection of viruses, there are serious limitations with the use of phage display as a tool for the isolation of specific antibodies.