2.3. Stress reactivity
Despite their relatively benign nature, even brief psychological stressors are effective elicitors of an immune response (Herbert and Cohen, 1993). In older adults, as in young adults, cellular immune responses to a brief mental arithmetic task (6–12 min) include increased numbers of suppressor/cytotoxic CD8 cells, increased natural killer cell (NKC) numbers and lytic activity, and decreased leukocyte proliferation in response to the mitogen, concanavalin A (Con A)
(Cacioppo et al., 1998). Typically, the magnitude of the physiological response to an acute stressor is related to the objective intensity of the stressor. Physiological stress responses (i.e., stress reactivity; see Fig. 1, column 2) show wide individual differences, however, and these differences may contribute to differential health consequences. Stress intensity also has a substantial subjective component, and differences in perceived stress (another aspect of stress reactivity; see Fig. 1, column 2) can contribute to differential physiological responses. Differences in psychological stress reactivity may take a long-term toll on immune functioning. This possibility was demonstrated in an animal study in which behaviorally ‘‘slow’’ mice, those which showed greater anxiety in stressful situations, exhibited faster age-related immune declines than did ‘‘fast’’ mice (Guayerbas et al.,2002). Although comparable studies have not been conducted in humans, these findings support the hypothesis that stress accelerates the aging of the immune system.