A non-competitive chemiluminescence enzyme immunoassay for the equine acute phase protein serum amyloid A (SAA) — a clinically useful inflammatory marker in the horse.

The research article discusses the development of a chemiluminescence enzyme immunoassay for measuring the equine acute phase protein serum amyloid A (SAA), a protein triggered by inflammation in the horse, and tests its clinical validity in monitoring inflammatory responses to different conditions.

Research Methodology

• The researchers developed a non-competitive chemiluminescence enzyme immunoassay to measure the SAA in equine serum. This assay was made specific to equine SAA by using a polyclonal anti-equine-amyloid A antiserum.
• A purified form of equine SAA was used to standardize the assay. An ‘acute phase’ horse serum was also calibrated against the purified SAA, and served as a control standard.
• The developed assay was able to measure serum SAA concentrations in the range of 3-1210 mg/l.

Clinical Validation of the Assay

• The researchers applied the assay to various clinical scenarios to observe and evaluate the SAA response.
• A consistent SAA response was observed after the horses underwent a surgical procedure (castration), with peak SAA concentrations on the 2nd day and a return to normal levels within eight days.
• Aseptic arthritis, an experimentally induced condition, resulted in an SAA response pattern that mirrored the response post-surgery, demonstrating peak SAA levels 36-48 hours after induction.
• Some horses demonstrated a biphasic pattern with a second spike in SAA levels on days 4 and 5, but eventually all animals returned to normal SAA levels (<7 mg/l) by day 15.

Comparison of SAA Response to Different Inflammatory Conditions

• All horses with viral and bacterial infections exhibited SAA concentrations above 7 mg/l, indicating an inflammatory response.
• However, the range of SAA concentrations following different types of inflammation overlapped, confirming that the SAA response, while sensitive, is nonspecific to the inflammation’s cause.

Conclusion and Application

• The study showed that Serum Amyloid A is a sensitive but nonspecific inflammatory marker in horses.
• The assay, via its ability to detect SAA levels, could be helpful in monitoring inflammation in horses after surgery, and also with infections and experimentally induced conditions.
• The research sheds light on the dynamics of the SAA response after a known and quantified tissue damage, providing a valuable tool in equine veterinary medicine.