Purified gp90 protein was used to immunize BALB/c mice. After cell fusion and screening, several hybridoma cell lines were generated, which produced gp90-reactive mAbs. One monoclonal antibody produced by the line designated as A9E8 was selected for strong reactivity with recombinant gp90 protein in Western blot ( Figure 1A ) and in an indirect ELISA (data not shown). It also showed strong reactivity with purified whole virus in Western blot ( Figure 1B) and could be used to detect REV-A antigen by an indirect immunofluorescence assay (IFA; Figure 1C ). The mAb A9E8 was compose of an IgG2b heavy chain paired with a k-type light chain, as determined using the SBA Clonotyping TM System/ HRP Kit. The titers of antibody in hybridoma cell culture supernatants and in ascites were measured by indirect ELISA and determined to be 1:3,200 and 1:128,000, respectively.