Determination of serum neutralization antibodies against seasonal influenza A strain H3N2 and the emerging strains 2009 H1N1 and avian H5N1

Background: Humoral virus neutralizing activity is crucial in preventing influenza virus infection. However, the influenza neutralizing activity in the general population remains unclear. Methods: In this study we performed a serological survey of 200 blood donors from Guangzhou, China. Using a microneutralization (MN) assay, neutralizing activities against influenza A 2009 H1N1, H3N2 and H5N1 were measured. Anti-haemagglutinin antibody was assayed by haemagglutination inhibition (HI) test. Also, antibodies against M1 and M2 matrix proteins were measured using an enzyme-linked immunosorbent assay (ELISA). Results: By MN assay, 86% of the individuals showed neutralizing activity against H3N2, 11% against 2009 H1N1, and none against H5N1. The positive rate for H3N2 increased as the age of individuals increased. Interestingly, males displayed a 4 times higher positive rate against 2009 H1N1 than females. The results of ELISA revealed that 97.5% of the individuals had positive M1 titres and 21% had positive M2 titres. Furthermore, anti-haemagglutinin antibody had a much higher correlation with the neutralization activity than anti-M1 and anti-M2 antibodies. Conclusions: Neutralizing activities against H5N1 and 2009 H1N1 were low in the general population. Therefore, public health agencies should design strategies for preventing potential H5N1 and 2009 H1N1 pandemics.