Positive Correlation between IP-10 and IFN-γ Levels in Rhesus Monkeys (Macaca mulatta) with Either Naturally Acquired or Experimental Infection of Mycobacterium tuberculosis

Numerous studies identify that IP-10 and IFN-γ are involved in leucocyte migration and activation and regarded as promising surrogate biomarkers in human and bovine tuberculosis infection, but there is lack of evidence for IP-10 in nonhuman primates. In this study, we directly determined IP-10 and IFN-γ levels in plasma from 30 healthy monkeys, 30 monkeys with naturally acquired tuberculosis, 4 monkeys experimentally infected with tuberculosis, and PPD stimulated whole blood of 14 monkeys with naturally acquired tuberculosis by ELISA. Higher plasma levels of IP-10 and IFN-γ were observed in natural tuberculosis monkeys than in healthy controls. The dynamic changes of plasma IP-10 and IFN-γ in experimental infections showed consistent representation of a transient increase during the infection period. After PPD stimulation, release of IP-10 and IFN-γ is significantly induced in natural tuberculosis monkeys, but the stimulation index of IP-10 was significantly lower than IFN-γ. Further analysis showed that positive correlation between IP-10 and IFN-γ existed in healthy and tuberculosis monkeys. Our findings support plasma IP-10 and IFN-γ as biomarkers for monitoring ongoing inflammation of nonhuman primate tuberculosis, and IFN-γ is a more valuable diagnostic biomarker.