Potential psychosocial mechanisms linking depression to immune function in elderly subjects.

Although depression and immune changes in elderly subjects constitute a considerable health risk, mechanisms underlying the association between depression and immune function are unclear. The question of whether personality and social support can explain the variation in immune function during depression was addressed in 21 elderly depressive and 23 control subjects. The following variables were studied: neuroticism, extraversion, received social support, depression-related immune parameters [i.e. numbers of lymphocytes, lymphocyte subsets CD3+, CD8+, natural killer-like T cells (NKT), CD4/CD8 ratio, and interleukin-6 (Il-6)]. We found that neuroticism reduced the association between depression and Il-6 (from 62 to 22.4%) and between depression and CD3+ (from 27.6 to 21.6%), and was also directly related to Il-6 (i.e. adjusted for age and depression). Social support reduced the association between depression and NKT cells from 25 to 18%, while it was also directly related to NKT cells. Extraversion, adjusted for age and depression, was negatively related to CD4/CD8 ratio. Subjects with high extraversion and high social support had more NKT cells. We concluded that changes in immune function during depression can partly be explained by neuroticism and received social support, whereas immune function is also directly related to these psychosocial variables. Neuroticism may exert its contribution to the risk for depression partly via Il-6 production.