The stability of plasma IP-10 enhances its utility for the diagnosis of Mycobacterium bovis infection in African buffaloes (Syncerus caffer)

The measurement of interferon gamma-induced protein 10 (IP-10) in antigen-stimulated whole blood is a sensitive biomarker of Mycobacterium bovis infection in African buffaloes (Syncerus caffer). However, this species often occurs in remote locations and diagnostic samples must be transported to centralised laboratories for processing. In humans, plasma IP-10 is highly stable and this feature contributes to its diagnostic utility; for this reason we aimed to characterize the stability of this molecule in buffaloes. Blood from M. bovis-infected and -uninfected animals was incubated with pathogen-specific peptides, saline and phytohaemagglutinin, respectively. Plasma fractions were harvested and aliquots of selected samples were: (i) stored at different temperatures for various times; (ii) heat treated before storage at RT, and (iii) stored on Protein Saver Cards (PSCs) at RT for either 2 or 8 weeks before measurement of IP-10. Incubation of plasma at 65 °C for 20 min caused no loss of IP-10 and this protein could be quantified in plasma stored on PSCs for 2 and 8 weeks. Moreover, for all storage conditions, IP-10 retained its excellent diagnostic characteristics. These features of IP-10 might allow for the heat inactivation of potentially infectious plasma which would facilitate the safe and simple transport of samples.