Testosterone, Immune Function, and Life History Transitions in Filipino Males (Homo sapiens)

Testosterone contributes to male life history trade-offs through effects on behavior and energy usage. Testosterone's role as a trade-off mediator is often discussed as manifesting partly through a negative impact on investment in survival, via immune suppression. Studies across species also show that testosterone in males commonly fluctuates with social changes, providing natural experiments to evaluate any potential immune impacts of intraindividual changes in testosterone. Using longitudinal data from Metropolitan Cebu City, the Philippines, we recently showed that men transitioning to fatherhood experienced substantial declines in testosterone over a 4.5-yr period. Drawing on a subsample of the same men here (N = 330), we evaluate whether these socially mediated changes in testosterone are paralleled by changes in immune function as reflected in salivary secretory immunoglobulin A (SIgA), a localized marker of mucosal immunity. Men reporting more cold/flu symptoms had lower testosterone and a trend toward lower SIgA in cross-section. Intraindividual changes in testosterone between baseline and follow-up 4.5 yr later were strong, positive predictors of changes in SIgA. Men becoming new fathers did not differ in Delta SIgA compared to other men. The positive relationship between Delta SIgA and Delta T in this sample runs counter to the expectation of a mating-maintenance trade-off, and may reflect direct effects of androgens on SIgA production. Our results add to the dialogue on the complex relationships between the reproductive and immune axes, providing additional evidence that in humans testosterone is not uniformly immunosuppressive.