Depression and immunity: age, severity, and clinical course.

To begin exploring the relationships between immunity and clinical characteristics of depressive disorders and to further investigate the association of Major Depressive Disorder with age- and severity-related alterations in T lymphocyte numbers and in response to mitogens, we investigated 53 untreated adult outpatients with DSM III-R Major Depressive Episode (MDE) and 53 healthy matched controls. The only group difference between MDE patients and matched controls was a trend (p < .06) for a decreased number of NK cells in depressed subject. In the MDE subjects, increasing age was observed to have a significant independent correlation with decreased numbers of total lymphocyte (p < .01), B cells (p < .05), and DR+ cells (p < .05) and reduced phytohemagglutinin (PHA) (p < .01) and concanavalin A (Con A) (p < .05) mitogen responses. In addition, in the depressed subjects there was: (1) an age-independent negative correlation between increased duration of the last Major Depressive Syndrome and PHA (p < .005), Con A (p < .05), and Pokeweed mitogen (p < .01) responses and (2) an age-independent correlation between increased time from the last antidepressant medication and total number of lymphocytes (p < .05), T cells (p < .05), and NK cells (p = .001). All the above were independent of current life habits such as current tobacco, alcohol, and benzodiazepine use. The present study suggests that both age at the time of study and clinical characteristics of the depressive disorder may be important independent factors in understanding psychoimmunological relationships in Major Depression.