Depression and immunity: clinical factors and therapeutic course.

While many reports describe associations between depressive disorders and altered immunity, findings have not been fully consistent. Diagnostic subtype, demographic factors such as age and gender, medical characteristics, and the immune measures selected for assessment may have contributed to the heterogeneous findings. In a study of 21 medically healthy young adults with major depression, we found, consistent with previous reports, evidence of increased lymphocyte activation to mitogen challenge and decreased natural killer (NK) cell numbers and function during acute depression. Fifteen subjects were followed longitudinally. T, CD4+, CD29+, and CD45RA+ lymphocytes and T-cell mitogen responses decreased significantly (P<0.05) during 6 weeks of pharmacotherapy and concurrent clinical improvement. There was no change in NK activity or CD56+ cells. The longitudinal effects appeared unrelated to tricyclic antidepressant levels. Changes in the immune system with short-term clinical improvement in depressed patients are not uniform providing further evidence that several mechanisms are involved in the altered immunity associated with clinical depression.