Psychosocial stress moderates the relationship of cancer history with natural killer cell activity.

Data suggest that both cancer history and psychosocial stress may be associated with reductions in natural killer cell activity (NKA). Therefore, we tested whether individual differences in cancer history, chronic/perceived stress, and their interactions would be associated with decreased levels of NKA. We tested these hypotheses in 80 spouse caregivers of victims of Alzheimer's Disease (AD) (persons known to report high levels of psychosocial stress) and in 85 age- and sex-matched spouses of non-demented controls. Participants were assessed at study entry (Time 1) and 15-18 months later (Time 2). Individuals with cancer histories (N = 43) had not been treated with immune altering medications within the last year. At both Times 1 and 2, cross-sectional main effects were weak or absent for cancer history, perceived stress (e.g. high hassles, low uplifts), and caregiver status; however, interactions occurred between cancer history and perceived stress, such that persons with cancer histories and high hassles/low uplifts had the lowest NKA values (p < .05). These results occurred even after controlling for age, gender, beta-blocker use, hormone replacement therapy, alcohol, and exercise. At Time 1, an interaction also occurred between caregiver status and cancer history--caregivers with cancer histories had lower NKA than did controls with cancer histories and caregivers/controls without cancer histories (p < .05). At Time 2, this interaction only showed a trend (p < .08), primarily because caregivers with cancer histories experienced increases in NKA (p < .05) from Time 1 to Time 2, whereas in the other three groups NKA did not change. Importantly, in caregivers with cancer histories, high perceived stress at Time 1 predicted low NKA at Time 2 (p < .05). This research suggests that the combinations of biological vulnerabilities and chronic/perceived stress may have interactive effects resulting in reduced NKA.