Protective antibody response of Balb/c mice to Bali rabies virus isolate propagated in BHK-21 cells

The protective antibody response of Balb/c mice to Bali rabies virus (RABV) in BHK-21 cells was studied. The virus was isolated from a rabid dog and was adapted to replicate in BHK-21 cell culture for seven passages. The BHK-21-adapted Bali RABV (BHK-Bali RABV) was inactivated with binary ethylenimine and 24 mice were immunized twice at 21-days intervals with the inactivated virus and Rabisin® vaccine. Virus replication was detected using indirect immunofluorescence, immunocytochemistry, and western blotting assays. Enzyme-linked immunosorbent assay examination 2 weeks after the first immunization revealed RABV antibody titers that were mostly below the minimum protective level (<0.5 equivalent unit, EU). Antibody titers increased sharply after the second immunization. Antibody titers in serum of mice induced by inactivated BHK-Bali RABV one week after the second immunization were slightly lower (0.8-3.8 EU) than those induced by Rabisin vaccine (0.9-6.3 EU). RABV antibody titers were stable for at least 6 weeks after the second immunization. Both Rabisin vaccine and inactivated BHK-Bali RABV induced neutralizing antibodies with neutralization titers (50% protective dose per ml) of 29.84 for 0.1 ml Rabisin, 211.41 for 0.2 ml Rabisin, 27.41 for 0.1 ml BHK-Bali RABV, and 28.25 for 0.2 ml BHK-Bali RABV. Thus, inactivated BHK-Bali RABV induces a protective immune response in Balb/c mice, but at lower levels compared to induction by Rabisin vaccine.