Hemagglutinin stem reactive antibody response in individuals immunized with a seasonal influenza trivalent vaccine
The Author(s) 2015. This article is published with open access at Springerlink.com and journal.hep.com.cn
Hemagglutinin stem reactive antibody response in individuals immunized with a seasonal influenza trivalent vaccine
Dear Editor
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Influenza is a contagious, acute respiratory disease caused
by influenza viruses. Type A influenza virus has a broad host
range and has caused substantial human morbidity and
mortality. There are sixteen subtypes of influenza A virus so
far, which are divided into two distinct groups: group 1 (H1,
H2, H5, H6, H8, H9, H11, H12, H13 and H16) and group 2
(H3, H4, H7, H10, H14 and H15) (Corti et al., 2011). Seasonal
H1 and H3 subtype influenza viruses are circulating in the
human population. Vaccination is widely used for the
prophylaxis and the antibodies (Abs) induced by the vaccine
were conventionally thought to be mainly directed against the
variable head region in HA. Those Abs could block viral
binding to the sialic acid receptors on cell surface (Skehel and
Wiley, 2000). They are typically effective against antigenically
close-related strains and thus need to be updated annually.
Recently, a number of broadly neutralizing monoclonal
antibodies (BnAbs) directed against the HA stem have been
identified, including CR6261, F10, FI6v3, FE43 and FE17
and so on (Corti et al., 2010; Corti et al., 2011; Sui et al.,
2009; Throsby et al., 2008). The stem-reactive Abs also
performed neutralizing activity by either blocking viral fusion
or preventing the cleavage by host protease (Ekiert et al.,
2009). Furthermore, the development of those BnAbs is not
only correlated with antigen immunogenicity but also with the
host genetic background (Ellebedy et al., 2014; Li et al.,
2012; Pappas et al., 2014). However, whether human serum
has such kind of Abs and the frequency or magnitude of the
Abs in peripheral blood are not fully answered. BnAbs
against Group 1 HA have been discovered from 4 out of 24
donors vaccinated by seasonal-flu vaccine (Corti et al.,
2010). Here, we focused on the Chinese adults vaccinated
by a seasonal trivalent vaccine in 2009 containing
A/Brisbane/59/2007 (Br59, H1N1), A/Brisbane/10/2007 (H3N2),
and B/Florida/4/2006. The serum Ab profile on Day 0 and
Day 21 from 49 volunteers was determined.
Initially, the Ab response to homologous Br59-HA was
measured by enzyme-linked immunosorbent assay (ELISA).
Most donors had detectable Br59-HA binding antibody titer
before vaccination and the geometric mean titer (GMT) was
105.93 1.17. As expected, the strain-specific Ab titer
increased dramatically after vaccination (P < 0.0001) and the
GMT was up to 772.68 1.18 (Fig. 1A). In consistent with the
Hemagglutination-inhibition (HI) titers reported in the previous
study (Wu et al., 2011), a more than 2.5-fold increase of
Br59HA binding Ab titer was detected in 87.8% of the cohort after
immunization (Fig. 1B), suggesting that the vaccine was
efficient to induce homologous H1 subtype Ab response.
To determine the cross-reactive Abs after vaccination, we
then screened the 49 paired sera using recombinant HA
derived from A/California/04/2009 (CA04, H1N1). As shown
in the Fig. 1C, a low level of CA04-HA binding Abs, around
97.27 1.18 was observed, the Ab response was boosted
after vaccination and the GMT was 200.45 1.14. Among
them, 17 donors had a more than 2.5-fold increase of
CA04HA binding Ab titer after immunization (Fig. 1D). We further
measured if there were any heterosubtypic Abs against
H5HA in the 17 paired sera. Among them, only 6 had a
detectable H5-HA binding Abs and the GMT was 37.24 1.69
on Day 0, other 11 had a very low, even undetectable titer.
While after vaccination, a 2.5-fold increase of H5-HA binding
Ab titer was found in 11 donors and the GMT was 160.32
1.56 (P < 0.05, Fig. 1E).
Since Br59-HA has great antigenic variability with
CA04HA in the head region, with the amino acid identity in the
stem domain being high as 89.5%, we speculated the
cross-reactivity of the Abs might target HA stem, a highly
conserved domain in HA (Table S1). As stem-reactive Abs
were present at an extremely lower level and any biological
interference caused by agents from sera disturbing the
cross-binding Abs remained uncertain, we enriched the
immunoglobulins (Igs) in the 17 paired sera by Protein A
and measured their neutralizing activity with pseudovirus
particles (pps) bearing a chimeric HA (cH5/1 SZ) as
described in the Materials and Methods. The neutralizing Ab
titer was defined as the reciprocal of the serum dilution
causing a 90% reduction of relative luciferase unite (RLU)
compared to the control. Seven of them showed
neutralizing activity, four had a titer of more than 8 after
immunization, and one with a titer of 2 and two had a titer of 2
preand post-immunization (Fig. 2A). The correlation analysis
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Ab binding to Br59-HA (H1)
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