DOI: 10.5061/dryad.66t1g1jxw
title: Noninvasive measurement of mucosal immunity in a free‐ranging baboon population

description: Ecoimmunological patterns and processes remain understudied in wild
 primates, in part because of the lack of noninvasive methods to measure
 immunity. Secretory immunoglobulin A (sIgA) is the most abundant antibody
 present at mammalian mucosal surfaces and provides an important first line
 of defense against pathogens. Recent studies show that sIgA can be
 measured noninvasively in feces and is a good marker of mucosal immunity.
 Here we validated a commercial ELISA kit to measure fecal IgA in baboons,
 tested the robustness of its results to variation in collection and
 storage conditions, and developed a cost‐effective in‐house ELISA for
 baboon fecal IgA. Using data from the custom ELISA, we assessed the
 relationship between fecal IgA concentrations and gastrointestinal
 parasite burden, and tested how sex, age, and reproductive effort predict
 fecal IgA in wild baboons. We find that IgA concentrations can be measured
 in baboon feces using an in‐house ELISA and are highly correlated to the
 values obtained with a commercial kit. Fecal IgA concentrations are stable
 when extracts are stored for up to 22 months at −20°C. Fecal IgA
 concentrations were negatively correlated with parasite egg counts
 (Trichuris trichiura), but not parasite richness. Fecal IgA did not vary
 between the sexes, but for males, concentrations were higher in adults
 versus adolescents. Lactating females had significantly lower fecal IgA
 than pregnant females, but neither pregnant nor lactating female
 concentrations differed significantly from cycling females. Males who
 engaged in more mate‐guarding exhibited similar IgA concentrations to
 those who engaged in little mate‐guarding. These patterns may reflect the
 low energetic costs of mucosal immunity, or the complex dependence of IgA
 excretion on individual condition. Adding a noninvasive measure of mucosal
 immunity will promote a better understanding of how ecology modulates
 possible tradeoffs between the immune system and other energetically
 costly processes in the wild.
description: To validate the commercial
 kit, develop and validate the in‐house assay, and to measure natural
 variation in IgA, we collected fecal samples from wild baboons
 opportunistically, immediately after defecation, from known individuals in
 Amboseli. Samples were homogenized, and an aliquot of each sample was
 placed in an empty tube, stored in a cooler with ice packs, brought to our
 camp site (within 8 hr), and stored in camp at −20°C. Samples were then
 sent to University of Nairobi where they were freeze dried and stored at
 −20°C until shipment to the United States. In this study, we analyzed
 fecal IgA concentrations of 310 fecal samples from 168 baboons collected
 in May–June 2013, May–Jul 2014, and May–June 2015. The samples collected
 in years 2013 and 2014 (206 samples) were analyzed using the commercial
 kit, and all samples from year 2013 to 2015 (310 samples) were analyzed
 using the in‐house ELISA. For a small subset of these samples (31
 samples), we also collected an aliquot in a tube containing 10% of
 buffered formalin for parasite determination. To explore whether field storage
 conditions affected measured IgA concentrations and to test inter‐assay
 variation of the commercial kit), we collected one fecal sample from each
 of four captive baboons held at the Division of Laboratory Animal
 Resources, Duke University Medical Center. Samples were collected
 immediately following defecation, after which each sample was homogenized
 and divided into six aliquots: one was collected in 95% ethanol and five
 were collected in empty tubes; all six aliquots were frozen at −20°C. The
 aliquots were then shipped on dry ice to Princeton University and stored
 at −20°C until processed as indicated in Goal 2 below to simulate
 processing of field samples in Kenya. Processed samples were freeze dried
 and sifted to a fecal powder (Gesquiere et al., 2008; Khan, Altmann,
 Isani, & Yu, 2002), before being extracted and assayed.