The serological reactivity in indirect ELISA of five different bluetongue virus (BTV) serotypes (4, 10,
15, 16 & 20) was compared using polyclonal antisera raised against virus particles and an outer
structural protein, VP2. Rabbit and sheep antisera against BTV-10 produced higher ELISA values with
their homologous antigens than with heterologous serotypes. A hyperimmune rabbit serum specific for
virus particles was able to distinguish heterologous serotypes from each other, but a sheep serum from
an infected animal was not. An antiserum directed against VP2, the protein responsible for serotype
specificity in neutralization tests, was not serotype-specific in ELISA and cross-reacted with other
serotypes. The discriminatory ability of a BTV-4 antiserum was improved by cross-absorption with
heterologous antigens. This greatly reduced the ELISA signals with heterologous serotypes and produced
an antiserum that was effectively serotype-specific.
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