Discordant Correlation between Serological Assays Observed When Measuring Heterosubtypic Responses against Avian Influenza H5 and H7 Viruses in Unexposed Individuals

Purpose: The human population is constantly exposed to multiple

influenza A subtypes due to zoonotic spillover and rapid viral evolution

driven by intrinsic error-prone replication and immunological pressure.

In this context, antibody responses directed against the HA protein are

of importance since they have been shown to correlate with protective

immunity. Serological techniques, detecting these responses, play

a critical role for influenza surveillance, vaccine development, and

assessment. As the recent human pandemics and avian influenza

outbreaks have demonstrated, there is an urgent need to be better prepared

to assess the contribution of the antibody response to protection

against newly emerged viruses and to evaluate the extent of preexisting

heterosubtypic immunity in populations.

Methods & Materials: SRH, HI, MN and pp-NT were used in a comparative

serology approach to deliniate the humoral response against

avian viruses in human sera.

Results: In this study, 68 serum samples collected from the Italian

population between 1992 and 2007 were found to be positive for antibodies

against H5N1 as determined by single radial hemolysis (SRH),

but most were negative when evaluated using haemagglutination inhibition

(HI) and microneutralisation (MN) assays.

Conclusion: As a result of these discordant serological findings, the

increased sensitivity of lentiviral pseudotypes was exploited in pseudotype-

based neutralisation (pp-NT) assays and the results obtained

provide further insight into the complex nature of humoral immunity

against influenza A viruses.