|Budget Amount *help
¥2,200,000 (Direct Cost : ¥2,200,000)
Fiscal Year 1991 : ¥800,000 (Direct Cost : ¥800,000)
Fiscal Year 1990 : ¥1,400,000 (Direct Cost : ¥1,400,000)
1. To study the influence of the host cell type on the selection of antigenie variants of influenza C virus, six strains were isolated and passaged in the amniotic sac of embryonated hen's eggs or in the HMV-II line of human malignant melanoma cells and were tested for the reactivity with a panel of monoclonal antibodies (MAbs) to the hemagglutininesterase (HE) glycoprotein. It was observed with two strains (Yamagata/4/88, Yamagata/7/88) that the HE protein of the virus serially passaged in HMV-II cells was antigenically distinguishable from that of the virus cultivated in eggs. It was also found that all virus clones obtained after repeated passages of these two strains in HMV-II cells possessed a markedly increased ability to replicate in the cell culture compared to the clones derived from egg-grown virus preparations, although no difference was seen in the ability to grow in eggs between HMV-II cell-and egg-grown virus clones. These observations suggest that isolation and passage o
f influenza C virus in HMV-II cells sometimes result in the selection of antigenie variants which have the growth advantage in this host cell type.
2. To obtain informations about the molecular mechanisms for the selection of antigenic variants in HMV-II cells, the HE gene sequences were determined for the C/Yamagata/4/88 and C/ Yamagata/7/88 strains serially passaged in the cell culture and then compared with the sequences of the viruses passaged exclusively in eggs. The results showed that the C/Yamagata/4/88 and C/Yamagata/7/88 viruses adapted to HMV-II cells had amino acid changes at positions 283(Asp -> Asn)and 212(Glu -> Lys), compared with the viruses cultivated in eggs. Recently, we revealed that the MAb-selected antigenic variants which had the same amino acid changes as those found in HMV-II cell-adapted viruses exhibited the increased affinity to chicken erythrocyte receptors. It appears likely, therefore, that the emergence of antigenic variants which occurred during the passages of the C/Yamagata /4/88 and C/Yamagata/7/88 strains in HMV-II cells is the result of the selection of variants having the increased binding capacity to host cell receptors.