[Study on characteristic of current measles wild-type strains after continuous passage from Vero cells]

To investigate the change on infection capacity of measles epidemic strain after continuous passage from Vero cell line, and to analyze the possible reasons in genetic level that caused change on cell-recognition site.

Measles virus epidemic strain Ningbo 05-2 was continuous passaged from Vero cells and Cytopathic Effect (CPE) was observed and recorded. After confirmation by real-time Reverse Transcription-Polymerase Chain Reaction (RT-PCR), hemagglutinating activity of Ningbo 05-2/P18 was detected using hemagglutination (HA) test and the completed sequences within Hemagglutinin (H) and Necleoprotein (N) gene were amplified by RT-PCR.

Measles epidemic strain Ningbo 05-2 has been continuous cultured for 17 times (P18) on Vero cells, but CPE began to be observed from the 13th passage. Although the passaged strains were confirmed as measles virus by real-time RT-PCR, the hemagglutinating activity of Ningbo 05-2/P18 was still negative. Compared with the Ningbo 05-2, there were three amino acid mutations within H protein of Ningbo 05-2/P18 (312aa, 314aa, 546aa), which changed the beta-sheet on the 311aa and the beta-turn during 312aa to 316aa to the alpha-helix. Phylogenetic tree based on H gene indicated the Ningbo 05-2/P18 still belonged to sub-genotype H(1b), locating at the same branch with the original strain. However, sequences of the original and passaged strains were identical within N protein.

Only a few amino acid mutations within H protein could results in cell-recognition site alternative of measles epidemic strain after continuous culture in Vero cell line, and consequently affecting the infection of measles virus.