Neopterin as a Tool for Primate Ecoimmunology: Current Knowledge, Practical Application, and New Directions From...

Neopterin is a well-established biomarker of interferon-gamma-mediated macrophage activation that indicates cell-mediated immune system responses in humans. Because it is readily quantifiable in urine, it is increasingly used in nonhuman primates to study cell-mediated immune functioning in relation to infectious diseases, but also environmental and individual factors, in both captive and wild primates. This review synthesizes our current knowledge on these topics with a focus on nonhuman primates. We cover the influence of various methodological factors during sampling and analysis on the reliability of neopterin measurements and give practical advice on how these factors can be mitigated. Furthermore, we address the advantages and disadvantages of different biological matrices in which neopterin can be measured and propose best practice guidelines for handling and storage of samples that consider challenges encountered during fieldwork. We conclude this review with an outlook on topics within primatology where neopterin, as a marker of cell-mediated immune functioning, could become a valuable tool to answer applied questions and test evolutionary hypotheses about immune functioning in primates.