Psychological distress, depressive symptoms, and cellular immunity among healthy individuals: a 1-year prospective study.

Cross-sectional and case-control studies have reported that psychological distress and depression are associated with reduced cellular immune competence but the directionality of the relationship remains uncertain. This study investigated whether levels of psychological distress and depressive symptoms are related to subsequent changes in counts of lymphocyte subsets (natural killer (NK), B, and T cell) and/or whether changes of immune markers predict psychological distress/depressive symptoms in a 1-year prospective study design. A total of 105 healthy employees (67 men and 38 women), aged 23-59 (mean 40) years with an average of 15years of education, underwent a blood draw for the measurement of circulating immune cells and completed the Japanese version of the 28-item General Health Questionnaire (GHQ-28) and the Center for Epidemiologic Studies Depression Scale (CES-D) in April 2002 (time 1) and 2003 (time 2). Hierarchical multiple linear regression analyses revealed that GHQ-28 and CES-D scores at time 1 were significantly (p<.05) and inversely associated with NK cells at time 2 controlling for potential confounders including time 1 NK cells (β=-.221 and -.177, respectively). In contrast, NK cells and NK cell cytotoxicity at time 1 did not predict GHQ-28 or CES-D score at time 2 controlling for GHQ-28/CES-D score at time 1. GHQ-28 and CES-D scores were not related to T or B cells at times 1 and 2. The present findings indicate that psychological distress and depressive symptoms may precede and predict suppression of NK cell immunity while NK cells did not lead to subsequent psychological distress and depressive symptoms, suggesting an absence of the bi-directional relationships.