β 2 -Adrenergic receptor signaling mediates the preferential mobilization of differentiated subsets of CD8+ T-cells, NK-cells and non-classical monocytes in response to acute exercise in humans.
Level 2 - randomized trial
Randomized, double-blind crossover trial in humans
PubMed 30172948 · doi:10.1016/j.bbi.2018.08.017
What was done
In a randomized, double-blind, complete crossover trial, 14 healthy cyclists completed three 30-minute cycling sessions at +10% of blood lactate threshold separated by at least 7 days. Before exercise, participants ingested either a placebo, a selective beta-1-adrenergic receptor antagonist (10 mg bisoprolol), or a non-selective beta-1 + beta-2 antagonist (80 mg nadolol). Bisoprolol served as a hemodynamic control to match heart rate and blood pressure reductions induced by nadolol without blocking beta-2-adrenergic receptors. Circulating lymphocyte and monocyte subsets were measured to distinguish beta-2 receptor signaling from hemodynamic mechanisms.
What was found
Nadolol significantly blunted or completely abrogated the exercise-induced mobilization of total NK-cells, CD57+ terminally differentiated NK-cells, non-classical monocytes, gamma-delta T-cells, and specific CD8+ T-cell subsets (central memory, effector memory, and CD45RA+ effector memory) compared to both bisoprolol and placebo. In contrast, nadolol did not inhibit the mobilization of classical monocytes, naive CD8+ T-cells, or CD4+ T-cells and their subsets. Specific numerical cell counts, percentages, and effect sizes were not reported in the abstract.
Why it matters
This study demonstrates that the selective redeployment of cytotoxic and differentiated immune cells into the bloodstream during acute exercise is directly driven by beta-2-adrenergic receptor catecholamine signaling rather than secondary hemodynamic forces alone.
Limits
The sample size was small (n = 14) and limited to healthy cyclists, restricting generalizability to sedentary, older, or clinical populations. The abstract omits exact cell counts, variance, and effect sizes. Only a single acute exercise intensity and duration was tested.
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