Detection of antigenic variants of the influenza B virus by melting curve analysis with LCGreen.

Automated, high-throughput detection methods for single-nucleotide polymorphisms have been applied to the routine genotyping of genetic polymorphisms influencing drug metabolism. Melting curve analysis with LCGreen was introduced recently as one such technique which can be performed rapidly and easily. This technique was used to detect antigenic variants of the influenza B virus. The antigenic variants and vaccine-type strains of the influenza B virus are isolated from clinical specimens of one epidemic season, and they usually differ in one nucleotide in the HA1 gene, corresponding to one amino-acid substitution. By means of melting curve analysis with LCGreen, an antigenic variant clone and a vaccine-type clone were clearly distinguished. In addition, the proportions of the antigenic variants in the mixture-type isolates were estimated. The clinical isolates were detected as the vaccine-type strains, antigenic variants, or a mixture of both. It became clear that humans were infected with a mixture of the vaccine-type strains and the antigenic variants for a certain period after which the viral antigenicities vary. This technique will contribute to the analysis of antigenic shifts in influenza B virus.