Correlation between serum amyloid A and antibody response to West Nile Virus vaccine antigen in healthy horses

Abstract The purpose of this study was to establish if peak serum amyloid A (SAA) concentrations can be used to determine an appropriate immune response to a vaccine containing West Nile Virus (WNV) antigen. A pilot study with 20 clinically healthy horses was performed to identify peak SAA concentration post-vaccination with a commercial multivalent WNV vaccine. Blood was collected for SAA at 0, 24, 48, 72, 96, 168 hours post-vaccination. Serum for WNV serum neutralization antibody testing was obtained immediately prior to and 30 days post-vaccination. An additional 40 horses underwent the study protocol, but with SAA measurements acquired at 0-hours and 72-hours post-vaccination. Ninety percent of the population had an increase in SAA in response to WNV vaccination, though no significant correlation was identified between SAA peak and antibody titer fold changes. WNV antibody titer fold changes between pre- and post-vaccination revealed 57% of horses had increased fold changes, 30% had no fold changes and 13% had negative fold changes. There was a negative correlation between age and SAA response (P=0.0008). The main conclusions were SAA response post-vaccination against WNV does not appear to mirror antibody response. Age appears to significantly affect SAA response. Further, vaccination with WNV antigen may not consistently induce a positive increase in WNV antibodies.