Results based on immune assays currently popular in human evolutionary biology (e.g., secretory IgA from saliva, neopterin and beta-2 microglobulin from urine, c-reactive protein and Epstein-Barr virus antibodies from blood spots, etc.) are difficult to interpret because they represent non-specific markers of general inflammation that can also be elevated for a variety of other reasons, including stress and subclinical infection. Because of the need, we have developed a new noninvasive functional measure of immunity using saliva. In brief, the assay involves mixing diluted saliva with a standard number of live E. coli, incubating the samples overnight on agar, quantifying the remaining microbes, and comparing to reference plates (bacteria without sample). The assumption is that more antimicrobial activity is advantageous for the host. Because it measures the ability to eliminate an actual pathogen, this assay provides a functionally relevant measure of immunity that involves the actions of complement, lysozyme, antibodies and phagocytic cells. We have also developed and validated a fecal cortisol assay for use with orangutans and a urinary oxytocin assay for use in humans.
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