To optimize and verify direct immunofluorescence assay (DFA) for rabies virus titer detection, so as to be better applied to the quality control in large-scale production.

Rabies virus was tested by DFA with different culture temperature (35 and 37 ℃), culture time (24 and 48 h), cells (Vero cells and BSR cells) and dilution ratios (3, 5, and 10 times), and the titer results were statistically analyzed. Repeatability and intermediate precision of the optimized method were validated. Samples from different batches were detected by intracranial titration in mice and DFA to analyze their correlation.

The optimal condition was to be cultured at 37 ℃ for 24 h, inoculated with BSR cells, and serially diluted by 5 times. The coefficient of variation of the repeatability and intermediate precision of DFA was both less than 2%. The titers of 16 samples by intracranial titration in mice and DFA were significantly correlated, with correlation coefficient by 0.952 and P value less than 0.000 1.

The optimized DFA has the advantage of fast and accurate, and has good consistency with intracranial titration in mice, which can replace the intracranial titration as a quality control method for large-scale production of rabies vaccine.

Direct immunofluorescence assay; Titers; Rabies virus