Lymphocyte response in depressed patients and subjects anticipating bereavement.

Lymphocyte response to stimulation with phytohaemagglutinin (PHA) was assessed in 11 patients with major depression and 8 subjects anticipating bereavement, in order to examine whether altered immune response (PHA stimulation index) was more closely related to depressed mood than to sleep and weight changes. No significant relationship was found between sleep or weight changes and immune response. Depression, measured using the HRSD (with and without sleep scores) and the BDI, was related differently in the two groups. For the depressed patients, increasing depression was associated with reduction in immune response; among those anticipating bereavement (with low depression scores), increasing depression was associated with enhanced immune response. A regression curve using data from both samples demonstrated an inverted 'U'-shaped curve relating immune response to mild and severe depressed states. The results of this study suggest a hypothesis that may explain previous discrepant results and which requires testing on more subjects.