Serological responses of infected and vaccinated pigs to recombinant influenza a proteins.

Abstract

Influenza A virus is constantly evolving in swine herds and it is important to evaluate the performance of serological diagnostic tools in the screening of pigs. Hemagglutination inhibition (HI) and ELISA are frequently used in the subtype specific detection of swine influenza virus (SIV) infections, but there is poor correlation reported between these assays. Conserved proteins of the virus, such as nucleoprotein (NP) and matrix 1 (M1), are potential antigen candidates to detect antibody response across different SIV subtypes. Although good candidates for use in diagnostic assays, the antibody profile against these proteins in infected and vaccinated animals is not fully understood. In an attempt to improve the agreement between ELISA and HI assays, and to better understand the antibody profile against M1 and NP proteins in infected and vaccinated pigs, 433 sera were screened using an indirect H3 ELISA, 384 samples were screened using a commercial NP ELISA, 433 were screened using recombinantly expressed M1 in indirect ELISA, and 304 were screened using HI. Sera were obtained from pigs vaccinated and challenged with a diverse SIV subtypes in an attempt to mimic the diversity of strains circulating in the field. Agreement between ELISA assays and HI was low, and induction of anti NP and M1 antibodies in vaccinated pigs was delayed in comparison to antibodies directed against hemagglutinin. Contrary to anti NP antibodies, anti M1 antibody levels did not increase after challenge. Although high specificity was obtained, antigenic mismatches between strains used in the vaccination and challenge of pigs seemed to interfere with the sensitivity of H3 ELISA. Anti-NP and -M1 antibodies were detected regardless of the infecting influenza subtype or the strain used for vaccination, but poor performance of M1 ELISA excluded the possibility of using this antigen in a diagnostic tool to screen swine herds for anti-influenza A virus antibodies.