The relationship between salivary secretory immunoglobulin A and cortisol: neuroendocrine response to awakening and the diurnal cycle

Abstract

The level of secretory immunoglobulin A (sIgA) measured in saliva is downregulated during periods of chronic stress. In contrast, the response to an acute stress challenge is a transient increase. The process of awakening is associated with stress neuroendocrine activation characterised by increases in salivary cortisol. We therefore examined if this period of hypothalamic–pituitary–adrenal (HPA) activation was associated with changes in salivary sIgA. Associations of sIgA with the diurnal cortisol cycle were also investigated in a separate study. The awakening cortisol response was measured in 30 healthy day-active young adults. There was a marked elevation from the first awakening level over the succeeding 30 min. SIgA showed the opposite response with a marked fall from the highest first awakening concentration in the same samples over the same period. The cortisol rise was significantly correlated with the sIgA fall ( r=0.42). Salivary sIgA showed a similar diurnal cycle to cortisol in a study on eight healthy young adults. An early morning acrophase was followed by a decline to a stable base some 6 h after awakening. The physiological significance of these relationships and possible implications for vulnerability to infection are discussed.