Measurement of anti-influenza neuraminidase antibody induced by H7N9 influenza vaccine

Objective To develop an enzyme-linked lectin assay (ELLA) for measuring neuraminidase inhibition (NI) antibody titers in subjects vaccinated with H7N9 influenza vaccine. Methods Neuraminidase substrate, the dilution and incubation time of enzyme-labeled antibody, the concentration of influenza antigen for coating and pH value of the dilution buffer were optimized. Based on that, ELLA was established and used to detect anti-influenza neuraminidase antibody titers in serum samples of 34 subjects before and after vaccination with H7N9 influenza vaccine. Results The optimal neuraminidase substrate was fetuin at a coating concentration of 7.5 μg/ml. The optimal dilution of enzyme-labeled antibody was 1∶500. The virus strain of influenza H7N9 vaccine was used as antigen at a concentrations of 4.5lgCCID50/ml in solution with a pH of 6.5. Influenza-specific NI titers detected after immunization with vaccine were significantly higher than those before vaccination (P<0.001). In the 34 subjects receiving H7N9 vaccine, the seroconversion rate of NI antibody was 47% (≥40 in NI titer ), which was lower than that of HI antibody (P<0.05). Conclusions An ELLA with natural substrate for measurement of anti-influenza NI antibody was developed. It is simple and practical and might be used in the establishment of immune evaluation system for influenza vaccines and NI antibody. Key words: H7N9 influenza vaccine; Neuraminidase inhibition antibody; ELLA