Six-week-old female BALB/c mice were subcutaneously immunized with 100 mg of the purified recombinant gp90 protein emulsified with an equal volume of Freund's complete adjuvant (Sigma, St. Louis, MO, USA). Two boosters of the Freund's incomplete adjuvant (Sigma, St. Louis, MO, USA) emulsified antigen were given at two week interval. Two weeks after the third immunization, the mice were intraperitoneally boosted with 100 mg antigen alone. Three days later, the spleen cells from immunized mice were fused with myeloma cells SP2/0 (SP2/0-Agl4; ATCC CRL 1581) [17] , using 50% (wt/vol) polyethylene glycol and 10% dimethyl sulfoxide (DMSO) (vol/vol) (Sigma, St Louis, MO, USA). Hybridomas were screened by indirect enzyme-linked immunosorbent assay (ELISA) and indirect immunofluorescence assay (IFA). The hybridomas producing mAbs were cloned three times by limiting dilution of the cells. Antibody subtype identification was performed using SBA Clonotyping TM System/HRP Kit (Southern Biotech, Birmingham, AL, USA).