Depressed smokers ride immune downer.

Depression and cigarette smoking may make for a particularly dangerous combination. Men suffering from major depression who smoke around a pack of cigarettes a day experience immune-cell changes that research has linked to cancer development, a new study finds.

These disruptions of immune function do not occur in depressed nonsmokers, report Waymond Jung and Michael Irwin, both psychiatrists at the San Diego Veterans Affairs Medical Center. People in good mental health don't exhibit the immune-system change either, whether or not they smoke up to a pack a day.

A prior independent study found that mentally healthy individuals who smoke two packs of cigarettes or more each day display immune changes comparable to those now observed in moderate smokers with depression.

Long-term data indicate that cigarette smokers who endure bouts of clinical depression exhibit elevated cancer rates, even for cancers not associated with cigarette use. This raises health concerns, since rates of cigarette use are high for people with major depression.

"Our findings are compatible with epidemiological data showing that a combination of depressed mood and [cigarette] smoking increases the risk of cancer development," Jung and Irwin contend. Their results appear in the May/June PSYCHOSOMATIC MEDICINE.

Jung and Irwin explored an immune pathway by which depression and smoking together might promote cancer. They collected blood samples from 127 nonsmokers who did not have any psychiatric disorders, 11 moderate smokers in good mental health, 46 nonsmokers diagnosed with major depression, and 61 moderate smokers also suffering from major depression.

Compared with the other three groups, depressed men who smoked cigarettes had substantially greater numbers of white blood cells--a general sign of compromised immunity--and their natural killer cells responded only weakly to foreign cells introduced in laboratory tests.

Natural killer cells play a surveillance role in the healthy immune system by destroying any cells that show early signs of cancerous growth.

Jung and Irwin's finding of low activity in depressed smokers' natural kill cells is "provocative and potentially important," remark psychologist Janice K. Kiecolt-Glaser and immunologist Ronald Glaser in an accompanying editorial.

Combined with moderate cigarette use, physiological effects of depression may boost susceptibility to tumor progression, suggest Kiecolt-Glaser and Glaser, both of the Ohio State University College of Medicine in Columbus.

They add that the results have broad implications for the burgeoning field of immunotoxicology, which examines how various substances undermine the immune system. Certain chemicals may disrupt immune functions only in the presence of psychological conditions such as depression or sustained mental stress, the Ohio scientists maintain.

Further studies should examine whether a mix of depression and cigarette smoking accompanies impaired immune function in women, note Jung and Irwin. Moreover, nobody knows yet whether immune function declines sharply in cigarette smokers who suffer from other psychiatric disorders, such as schizophrenia, they say.