A198V HA mutation may contribute to escape from
neutralizing-antibodies
As the Figure 2A shown, amino acid position 198 is located in the sialic
acid binding domain as one of the receptor binding sites, suggesting
that A198V substitution might play a key role in the evolution of H9N2
viruses. In order to study the role of the mutation A198V in escaping
from neutralizing antibodies, microneutralization (MN) assay was
performed, which is more sensitive than HI assay
(Segovia,Franca,Bahnson,Latorre-Margalef, & Stallknecht, 2019). In
comparison to the parental F/98 strain, the rF/HAA198Vvirus exhibited 8-fold reduction in MN titers to anti-F/98 serum (Figure
2B), and 8-fold reduction to homologous anti-rF/HAA198Vserum (Figure 2C), which suggested that the A198V mutation promoted the
rF/HAA198V virus escape from anti-F/98 or
anti-rF/HAA198V serum. Further, we comprehensively
compared the serological cross-reactivity induced by the H9N2 viruses
A/Chicken/Guangdong/SS/1994 (GD/SS/94, original HA A198),
A/Chicken/Jiangsu/YZ618/2012 (JS/YZ618/12, original HA T198) (R. Zhu et
al., 2018), and rF/HAA198V in chickens. Results showed
that the rF/HAA198V virus displayed 4-fold reduction of
MN titers to anti-GD/SS/94 serum
compared to the GD/SS/94 virus (Figure 2D); the
rF/HAA198V virus displayed 8-fold reduction of MN titers
to anti-JS/YZ618/12 serum (Figure
2E) compared to the JS/YZ618/12 virus. However, compared to the viruses
GD/SS/94 and JS/YZ618/12, the
rF/HAA198V virus displayed 4- and 8-fold reductions of
HI titers to homologous
anti-rF/HAA198V serum,
respectively (Figure 2F). These
results showed that HA A198V mutation could decrease the readout of MN
titers to anti-H9N2 sera significantly, even to anti-
rF/HAA198V serum, indicating that this substitution
could promote viral escape from neutralizing-antibodies.