Salivary cytokines in stress research: Reactivity kinetics in response to placebo-controlled acute psychosocial stress and associations with plasma cytokines and endocrine stress markers

Background/objectives

In stress research, the measurement of cytokines from saliva may provide a non-invasive alternative to blood sampling. However, current research is limited by methodological shortcomings, including lack of placebo-stress control groups, comparison with plasma cytokine stress reactivity, infrequent sampling, and insufficient control for salivary flow rate. The aim of this study was to investigate repeatedly measured salivary cytokine responses to the Trier-Social-Stress-Test (TSST) compared to a placebo-TSST (PlacTSST), and to explore associations with plasma cytokines and endocrine stress markers.

Methods

In this placebo-controlled, single-blind, between-subject study, healthy young men were randomized to a stress condition (TSST;n = 30) or a placebo-stress condition (PlacTSST;n = 20). Salivary interleukin-(IL)-6, IL-1β, tumor-necrosis-factor-(TNF)-α were measured at baseline and repeatedly up to 30 min post-stress, with correction for salivary flow rate. Plasma cytokines were assessed up to 90 min post-stress. Salivary cortisol, epinephrine, and norepinephrine were assessed to explore potential endocrine mechanisms.

Results

The TSST induced significantly greater increases in salivary IL-6 (p = 0.024, η_p² = 0.07) and IL-1β (p = 0.031, η_p² = 0.07) compared to the PlacTSST, with peak responses at + 1 min post-stress and return to baseline by + 30 min. TNF-α was not stress-reactive, neither in saliva (p = 0.35) nor in plasma (p = 0.16). Higher total salivary IL-6 reactivity predicted higher plasma IL-6 reactivity (β = 0.48, p < 0.001, ΔR² = 0.31), with salivary responses preceding those in plasma. Higher norepinephrine increases related to higher salivary IL-1β responses (β = 0.45, p = 0.018, ΔR² = 0.15), pointing to a potential noradrenergic modulation.

Conclusions

Our findings demonstrate that acute psychosocial stress induces rapid and transient independent increases in salivary IL-6 and IL-1β but not TNF-α that relate to plasma cytokine and endocrine changes. These results support the utility of salivary cytokine assessment as a sensitive and non-invasive and less cost-intensive alternative to plasma sampling. Further research is warranted to elucidate underlying regulatory mechanisms and extend findings to different populations.