Severe depression depresses immunity.

There appears to be something related to severe, incapacitating depression -- and not to milder depression, other psychiatric disorders or being in a hospital -- that weakens the body's immune system and increases susceptibility to physical illness, according to researchers at Mount Sinai School of Medicine in New York City. In their studies, sharply reduced immune responses occur only among depressed patients who are hospitalized due to the seriousness of the disorder; less-depressed individuals who are treated in an outpatient clinic have normal immune function.

Last year the same investigators reported that lymphocytes, the cells most involved in immunity, proliferate far less in severely depressed, hospitalized patients than they normally would when stimulated to reproduce (SN: 6/2/84, p. 341). In the February ARCHIVES OF GENERAL PSYCHIATRY, that prior result is compared with similar data on hospitalized schizophrenics, hospitalized surgical patients and depressed outpatients.

"The preliminary findings suggest that decreased lymphocyte function is associated with the severity of depression and is not related to hospital effects or to other psychiatric disorders," says study director Steven J. Schleifer.

Schleifer and colleagues measured responses to lymphocyte stimulation and the total number of lymphocytes for each subject. Breakdowns were obtained for T cells and B cells, important types of lymphocytes. The project included 15 depressed outpatients studied with 15 healthy controls; 16 hospitalized schizophrenics studied with 16 healthy controls; and 10 men hospitalized for surgical repair of hernias studied with 10 healthy controls. Depressed patients had not used antidepressant drugs for at least three months, and schizophrenics underwent a drug "washout" period of several weeks.

There were no statistically significant differences between these three groups of subjects and their healthy controls in the total numbers of lymphocytes and in the numbers and percentages of T and B cells. This indicates, says Schleifer, that psychiatric or surgical hospitalization does not change immune function. Several recent studies, however, report varying lymphocyte levels in schizophrenics, he adds.

What stands out from the data, say the researchers, is that severe depression, but not milder forms of the disorder, is associated with a steep drop in immune activity. This connection may be fostered by the weight loss and sleep disturbance that are characteristic of severe depression, notes Schleifer. Biological processes are probably also involved, but investigators first need to see if altered immunity persists among severe depressives, who typically enter periods of remission. The group plans to study a larger sample of patients with severe and mild depression using additional tests of immune function.

"Does the state of depression lead to changes in immunity, or is altered immunity a trait among some depressives?" asks Schleifer. "We need to explore this question."