Testosterone, cortisol, and secretory immunoglobulin-A within a single day and across two sequential days among...

Previous research on the association between testosterone (T) and immunity has produced conflicting results.

We address two potential reasons for these empirical inconsistencies in the present research. First, the association between T and immunity may depend on which branch of the immune system is considered. Here, we examine secretory IgA (sIgA), a measure of mucosal immunity functionally related to respiratory infection risk. Second, the association between T and immunity may depend on a third regulatory variable. Therefore, we examine the interaction between T and cortisol (CORT) as well as their independent and combined effects on mucosal immunity. To do this, we explore intra-individual associations between sIgA, CORT, and T within a single day (i.e., morning vs. evening) and across 2 sequential mornings. We target two samples of men: (1) cisgender (i.e., born and identifying as men), and (2) transgender (i.e., born female but identifying as men) undergoing T therapy for gender realignment.

One hundred and forty-eight adult men (transgender n = 29) provided saliva samples at three time points: (1) upon waking, (2) before sleep on the same day, and (3) upon waking the following day. Samples were assayed in duplicate for sIgA, T and CORT.

For cisgender men, sIgA, T, and CORT exhibited clear circadian rhythms and were significantly related within and between samples. For transgender men, evidence for circadian change was found for sIgA and CORT, but not T. Further, sIgA was associated with CORT, but not T.

This study provides the first evidence that salivary T and sIgA concentrations are associated within a single day and across sequential days for cisgender men. Differences between cis- and transgender men suggest that this may only be true for T levels driven by endogenous production; however, future studies should employ a larger sample size.