ABSTRACT. We have developed a new quantitative method for rabies virus (RV) detection using enzyme-linked immunosorbent assay (ELISA). The method named N-ELISA was based on the quantitation of nucleoprotein (N) in RV virions captured by RV-specific polyclonal antibodies on an ELISA plate. Both infective and defective interfering (DI) particles of RV could be detected by this method. When viruses were propagated in a medium of pH 7.4 adjusted with 7% NaHCO 3 , N-ELISA could detect them with titers of more than 10 6 pfu/ml, though the result did not correlate highly with that of the infectivity assay. The reason for this was considered to be that RVs included spikeless and damaged particles which were produced under conditions of low or high pH. However, in the time course of virus yield, titers of N-ELISA correlated well with those of the infectivity assay.-KEY WORDS: ELISA, G protein, N protein, rabies virus.J. Vet. Med. Sci. 61(4): 411-416, 1999 HmLu-1 cells were cultured in Eagle's minimum essential medium (Eagle's MEM) supplemented with 5% fetal calf serum (FCS).Virus propagation: RV was inoculated on HmLu-1 cells at a m.o.i. (multiplicity of infection) of 0.01 pfu/cell. After adsorption for 1 hr at 37°C, the cells were added Eagle's MEM of pH 7.4 supplemented with 1% FCS. The pH of the medium was adjusted with 7% NaHCO 3 . The cells were cultured at 34°C without CO 2 .In the test of virus-growth, the pH of the medium was controlled by addition of 20 mM HEPES buffer (pH 6.5, 7.0 or 7.5) into Eagle's MEM supplemented with 1% FCS and 1.4 mM NaHCO 3 . After adsorption of the virus, the cells were added to each medium and incubated at 34°C in air. Ten ml aliquots of culture fluids were sampled every day for 6 days, and their pH was measured. The samples were concentrated to 10 µl by ultracentrifugation (100,000 × g, 1 hr, 4°C).
Purification of RV:Purified RV was prepared according to the method of Kawai et al. [10]. The fractions with infective RV were collected as purified virion and then dialyzed against PBS.Antibodies: To prepare an anti-N serum, N protein derived from purified RV was resolved by SDS-polyacrylamide gel electrophoresis (SDS-PAGE). The band of N protein in the gel was cut, and then homogenized in PBS. The homogenate was emulsified with oil-adjuvant ISA70 (Seppic, France) at a ratio of 3:7. Three guinea pigs were injected intramuscularly three times with the emulsion at three week-intervals. One week after final injection, the animals were bled to collect sera. Antibody titers of the sera measured by the indirect fluorescent antibody method were 1,280 to 2,560.To prepare RV-specific antiserum, two rabbits were immunized with an emulsion of purified RV and oiladjuvant ISA70 three times at three week-intervals. The serum obtained showed a neutralizing antibody titer of [5,13,18,20,23,25]. ELISA in particular is an easy to use and highly sensitive method.Several investigators have developed ELISA methods for the quantitation of RV glycoprotein (G) [13,25]. These methods have been used to test in...