Discordant Correlation between Serological Assays Observed When Measuring Heterosubtypic Responses against Avian Influenza H5 and H7 Viruses in Unexposed Individuals
Figure 2
(a) Comparison of SRH assay versus pp-NT assay for antibody responses against the A/Vietnam/1194/04 antigen. SRH titres expressed as diameter of haemolysis (in mm2) are plotted on the -axis. SRH titres > 25 mm2 are considered to be sero-protective and this cutoff is represented on the plot by a vertical dotted line. IC50 pseudotype neutralization titres expressed as the reciprocal of the serum dilution that results in a 50% inhibition of pseudotype virus entry are plotted on the -axis; (b) comparison of HI assay versus pp-NT assay for antibody responses against the A/Vietnam/1194/04 antigen. HI titres expressed as the reciprocal of the highest dilution causing complete inhibition of haemagglutination are plotted on the -axis. IC50 pseudotype neutralization titres expressed as the reciprocal of the serum dilution that results in a 50% inhibition of pseudotype virus entry are plotted on the -axis; (c) comparison of MN assay versus pseudotype-based neutralization assay for antibody responses against the A/Vietnam/1194/04 antigen. The vertical dashed lines indicate the value of MN log 10 titre = 1.9 (corresponding to a titre of 1 : 80) and the proposed threshold of protective antibodies; horizontal dashed line indicates the corresponding value of pp-NT log 10 titre = 2.55 (corresponding to a titre of 1 : 357).
