Immune responses to experimental stress: Effects of mental effort and uncontrollability

Objective: Two important determinants of physiological stress responses hav e been identified, uncontrollability of the stressor and amount of effort i nvolved in coping with the stressor. In the present experiment, we tried to identify the specific contributions of effort and uncontrollability to imm une system responses to stress. Methods: In a 2 x 2 design, effort and unco ntrollability were manipulated independently of each other. Subjects partic ipated in one of four experimental conditions, and their endocrine, immune, and sympathetic nervous system responses to the task were assessed. Result s: Effort had a stimulating effect on enumerative immunological parameters (CD8(+) and CD16(+) cells) and on natural killer cell activity. The effect occurred immediately after the stressor and was transient. Regression model s indicated that this effort effect may have been mediated by activation of the sympathetic nervous system. Uncontrollability influenced in vitro prod uction of the cytokine interleukin-6, leading to decreased production 15 an d 30 minutes after the stressor. Uncontrollability also led to an increased level of cortisol, but no evidence was found that the decrease in cytokine production was mediated by cortisol release. Conclusion: The results sugge st that two major stressor characteristics, effort and uncontrollability, m ay have differential effects on the immune system.