| Influenza is a contagious, acute respiratory disease caused by influenza viruses. Type A virus has a broad host range and has caused substantial human morbidity and mortality. Vaccination is widely used in the prophylaxis of influenza virus infection. Anti-HA antibody response induced by vaccination is mainly directed against the globular head region, which mediates attachment of the virus to the target cell. However, antibodies targeting the HA head are typically effective against antigenically close-related strain, the vaccines need to be updated almost annually. Till now, a number of broadly neutralizing antibodies (BnAbs) directed against the HA stem have been identified. The stem-reactive antibodies do not prevent the viral HA from binding to the sialic acid receptor of target cell; nevertheless, they tend to mediate neutralization activity by either blocking viral fusion or being cleaved by the host protease. The question of whether human serum has such kind of Abs, the frequency or magnitude of the Ab in peripheral blood is not answered. Here, the anti-HA stem antibody (Ab) response in 49 healthy adult volunteers after administered with a trivalent vaccine in fall 2009 and 51 2009 pdmHlN1 vaccinees was evaluated. The cross-reactivity of the serum Ab was initially tested by its binding to HA protein of A/Brisbane/59/2007(HlN1, Br59), A/California/04/2009(H1N1, CA04) and A/Anhui/01/2005(H5N1, AH1) using ELISA. 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 selected sera by Protein A for further investigation. Moreover, the neutralizing(NT) activity was measured by pseudovirus particles (pps) that harbored a chimeric HA composed of the head region from a H5N1 virus(A/Shenzhen/1/2011) and the stem domain from the A/Puerto Rico/8/1934(H1N1, PR8), namely cH5/1(SZ) pps. To identify the epitopes recognizing by the serum Abs, the HI against a H5N1 reassortant containing a chimeric HA with the head of Goose/Qinghai/1/05 (H5N1) and the stem domain from PR8, Br59 and A/California/07/2009 and the competition ELISA against biotin-CR6261 were tested.ResultsI Cross-reactive antibody response in individuals immunized with a seasonal influenza trivalent vaccine.1. Comparing the Ab titer from the paired sera on Day 0 and Day 21 of the 49 donors, 17(34.79%,17/49) individuals had a more than 2.5-fold increase of CA04-HA binding Ab titer after immunization. Among them, the binding to AH1-HA was detected in sera on Day 21 from 11 donors (64.71%,11/17).2. Seven of the 17 individuals after vaccination had NT Ab against cH5/1(SZ) pps. The CR6261-like Abs, were present in 3 donors prevaccination and the 7 vaccinees. The titers of CR6261-like Abs in serum on Day 21 were around 0.0017%-0.017% in total IgG 10mg/mL).3.The cross-reactive Abs did present in serum although the traditional HI assay suggested a low or non response induced. Thus,our data strongly suggested that cross-reactive Abs measurement should not be ignored during influenza vaccination efficacy evaluation. II Cross-reactivc atibody response in individuals immunized with 2009 pandemic HlNl monovalent vaccine.1.Thirty individuals from 51 donors 8.82%,30/5 had a more than 2.5-fold increase of binding AHl-HA Ab titer after immunization.2. Two donors before vaccination and 16 of the 30 individuals after vaccination had Nt Ab against H5(sz) pps. The CR626 tike Abs, were present in donors prevaccination and 16 individuals postvaccination. The titers of CR6261-like Abs in serum on Day 21 were around 0.002%-0.037% in total IgG(lOmg/mL).Conclusions:Both seasonal influenza and 2009 pdmH1N1 vaccine could induce the HA stem-reactive antibody response in Chinese cohort. The levels of CR6261-like Abs on Day 21 postvaccination in both groups, around 0.007%-0.017% and 0.002%-0.037% in total IgG, showed no difference. |
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