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Journal of Clinical Microbiology, August 2002, p. 3068-3070, Vol. 40, No. 8
0095-1137/02/$04.00+0 DOI: 10.1128/JCM.40.8.3068-3070.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
Emergence of an Influenza B Virus with Antigenic Change
Naoko Nakagawa,1* Souichi Nukuzuma,1 Shigekazu Haratome,1 Shosan Go,1 Toshimasa Nakagawa,2 and Kozaburo Hayashi1
Department of Parasitic Agents, Kobe Institute of Health, 4-6, Minatojima-nakamachi, Kobe 650-0046,1
Department of Clinical Pathology, Osaka Medical College, Takatsuki 569-8686, Japan2
Received 3 January 2002/
Returned for modification 10 February 2002/
Accepted 18 May 2002

ABSTRACT
Influenza B virus Yamagata group strains, isolated in the 2000
to 2001 influenza epidemic season, reacted poorly to the polyclonal
ferret sera prepared against strains isolated earlier. The results
of genetic analysis clarified that a point mutation of the nucleotide
at position 126 in the HA1 region and the corresponding one-amino-acid
substitution altered viral antigenicity.

TEXT
There are influenza epidemics every year. In recent years, diagnosis
is rapidly confirmed in a clinic when the virus is detected
by diagnosing kits, such as enzyme immunosorbent assays or direct
immunofluorescence. In contrast, in a reference laboratory participating
in influenza surveillance, the detailed antigenic characterization
of isolates is required. In Japan, virus is isolated mainly
in Madin-Darby canine kidney (MDCK) cells. Subsequently, it
is subtyped by the hemagglutination inhibition (HI) test using
the polyclonal ferret sera against influenza virus A or B. To
subtype influenza A virus, the antibody has to be prepared continually,
because the antigenic drift of hemagglutinin (HA) protein hampers
its identification (
2,
3,
6). On the other hand, the evolution
of influenza B virus is characterized by a lower rate of antigenic
change (
7,
8). Recent isolates of influenza B virus are classified
into two major phylogenetic trees: the influenza virus B/Victoria/2/87
subclass or the influenza virus B/Yamagata/16/88 subclass (
4,
7,
8,
13,
15,
17). Group-specific antigens have been conserved
among influenza virus B/Yamagata strains. In Japan, the standard
ferret sera were prepared using influenza virus B/Mie/1/93 strain
for the epidemic seasons in 1994 to 1995 through 1998 to 1999.
It reacted well with all the 1998 to 1999 influenza virus B/Yamagata
isolates in Osaka Prefecture by HI tests. However, their reactivities
against monoclonal antibody (MAb) 5H4 were heterogeneous. MAb
5H4 had potent HI and neutralization activities against the
influenza virus B/Yamagata strains isolated earlier. Approximately
6% of the isolates did not react against MAb 5H4, and a single
amino acid substitution of Arg to Lys at position 149 in the
HA1 region caused the phenomenon (
12).
We studied the variation in antigenicity and nucleotide sequence of the 2000 to 2001 isolates of Kobe City, Japan.
MAbs were obtained by immunizing mice with influenza B virus strains as described previously (9-12). Ascitic fluid samples from mice injected with hybridoma cells were used as the sources of MAbs. The standard ferret sera were provided by the National Institute of Health, Tokyo, Japan: the sera against influenza virus B/Yamanashi/166/98 for influenza virus B/Yamagata and the sera against influenza virus B/Shangdong/7/97 for influenza virus B/Victoria. The methods for virus inoculation and visualization of infected cells by peroxidase-antiperoxidase (PAP) staining were described previously (9, 14, 16). Briefly, infected cells were treated successively with MAbs, rabbit anti-mouse immunoglobulin antibody, goat anti-rabbit immunoglobulin antibody, and PAP complex. The visualized cells were then observed under a light microscope. The results of HI tests are expressed as the reciprocal of antibody dilution (14). Direct sequencing of viral nucleotide was performed as described previously (10-12). Briefly, reverse transcriptase PCR products were sequenced with the DYEnamic ET terminator cycle sequencing kit (Amersham Pharmacia, Piscataway, N.J.) and analyzed by the ABI Prism 310 automatic sequencer (Perkin-Elmer, Foster City, Calif.).
The reactivities of the 2000 to 2001 isolates against anti-influenza virus B/Yamagata sera in HI tests were as low as 20 to 40, while the reactivities of the earlier influenza virus B/Yamagata isolates ranged from 160 to 320 (Table 1). The isolates were PAP stained and identified as influenza virus B/Yamagata group strains with MAbs, NP-specific 9F3 and HA-specific 7H11. An influenza virus B/Victoria group HA-specific MAb, MAb10B8, did not react with these isolates. Nucleotide sequences and deduced amino acid sequences of the HA gene indicated that strains with two different origins were isolated in the 2000 to 2001 influenza season (Fig. 1), as observed in the previous two seasons (12). Four strains had 99% similarity to influenza virus B/Kadoma/409/2000, which was derived from influenza virus B/Shiga/T30/98, while influenza virus B/Kobe/87/2001 had 98% similarity to influenza virus B/Osaka/1201/2000, which was derived from influenza virus B/Tokyo/942/96. In both groups, there was an Asn-to-Asp substitution at position 126.
Influenza virus B/Kobe/69/2001 had high similarity to influenza
virus B/Kadoma/409/2000; however, two nucleotide residues were
not determined in direct sequencing, suggesting that the virus
was a mixture of more than one strain. Therefore, the virus
was cloned, and 21 clones were obtained. When the ferret sera
were used in HI tests, 8 clones had HI titers as low as 20,
while the remaining 13 clones had titers of 160. HA1 regions
of four representative strains were sequenced (Table
2). Among
1,060 nucleic acids in the HA1 region, only two points were
different, which correspond to two amino acid substitutions.
The strains with low reactivities had Phe at position 58 and
Asp at position 126, while those with high reactivities had
Leu and Asn at these two sites, respectively. Therefore, amino
acid substitutions at position 126 strongly influenced the virus
reactivity to the ferret sera. Amino acids in HA1 polypeptides
of the influenza B virus strains were numbered according to
the numbering used for the influenza virus A/Aichi sequence
for the structural reference of the H3 HA protein of influenza
A virus (
1,
5). The amino acid at position 126 corresponds to
the amino acid at position 129 of AH3 virus by this method.
Position 126 is located near the receptor region.
The amino acid residues Asn at position 126 and Arg at position
149 had been conserved in influenza virus B/Yamagata group strains
for 10 years (
7). Influenza virus B/Taiwan/2027/99 was the first
strain found with Lys at position 149, while influenza virus
B/Taiwan/1265/2000 was the first strain found with Asp at 126,
according to the DDBJ Data Base. In Japan, substitution at position
149 was initially observed only with strains of the B/Tokyo/942/96
lineage. In the following seasons, it was also detected in those
of influenza virus B/Shiga/T30/98 lineage (
12) (Table
1). They
became the major strains in the 2000 to 2001 influenza season,
because the Kobe isolates in this period did not react to MAb
5H4 in HI tests or PAP staining (Table
1). The substitution
at position 126 was observed with strains of both lineages in
the 2000 to 2001 influenza season. Influenza virus B/Shiga/T30/98
and influenza virus B/Tokyo/942/96 are classified in different
phylogenic trees, which diverged from their origins around 1993
(
7). It is significant that the same amino acid substitutions
at these positions created new strains with lower reactivity
to the antibodies. This finding is compatible with the idea
that the new antigenic variants are generated to escape from
the existing human immunity and displace the old variants (
6,
7,
11).
Henceforth, influenza virus B/Yamagata group viruses might emerge from the antigenic variants of the influenza virus B/Victoria group (11) and new group strains may appear from the variants of influenza virus B/Yamagata strains. This information will benefit the management of public health (foretelling the scale of future epidemics and selecting suitable strains for vaccines).
Nucleotide sequence accession numbers.
The nucleotide sequences of influenza B viruses from the 2000 to 2001 influenza season were deposited in DDBJ database under accession numbers as follows: influenza B/Kobe/64/2001, AB071515; B/Kobe/65/2001, AB071516; B/Kobe/79/2001, AB071518; B/Kobe/83/2001, AB071519; B/Kobe/87/2001, AB071520; and B/Kobe/69/2001 clones 1 (AB071521), 2 (AB071522), 3 (AB071523), and 4 (AB071524).

ACKNOWLEDGMENTS
We thank T. Iwamoto for valuable advice on nucleotide sequencing.

FOOTNOTES
* Corresponding author. Mailing address: Department of Parasitic Agents, Kobe Institute of Health, 4-6, Minatojima-nakamachi, Chuo-ku, Kobe 650-0046, Japan. Phone: 81-78-302-4321, ext. 4033. Fax: 81-78-302-0894. E-mail:
kih-info-1{at}mse.biglobe.ne.jp.


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Journal of Clinical Microbiology, August 2002, p. 3068-3070, Vol. 40, No. 8
0095-1137/02/$04.00+0 DOI: 10.1128/JCM.40.8.3068-3070.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
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