High heart rate reactors display greater decreases in tear SIgA concentration following a novel acute stressor

•A novel, field-based acute stressor reduced tear SIgA concentration.•High heart rate reactivity predicted greater decreases in tear SIgA post-stress.•High reactors may experience an “open window” of impaired host defence post-stress.•Tears have potential as a medium to monitor immune responses to acute stress. Tear secretory immunoglobulin-A (SIgA) is a putative biomarker of common-cold risk with potential utility in non-invasive diagnostics. As SIgA secretion at the ocular surface is under strong autonomic control, we investigated the relationship between HR reactivity and tear SIgA responses to novel experiential stress. Thirty-two healthy participants undertook a 60 s zip-line ride to evoke acute stress and a seated-rest control trial in a randomised-crossover design. We recorded heart rate (HR) continuously and collected unstimulated tear samples 5 min pre-, 2 min post- and 20 min post-stress/control. Stress increased HR and state anxiety whereas tear SIgA concentration decreased 44% post-stress vs. control. Higher peak HR values during stress uniquely explained 21% of the variance in tear SIgA reactivity to stress (p