Immune System May Trigger a
Form of Heart Disease

NEW YORK (Reuters Health) - The chronic heart muscle disorder known as dilated cardiomyopathy is thought to be brought on by a variety of factors--from heredity to chronic, heavy drinking. Now, new research in mice suggests that in some cases, the body's own immune system may be behind the life-threatening condition.

Dilated cardiomyopathy is marked by diseased heart muscle fibers that result in abnormal enlargement of one or more of the heart's chambers. This weakens the heart's ability to pump efficiently and can trigger heart failure. Although in some cases clear genetic or environmental causes can be determined, in other cases the cause may remain unknown.

But one explanation may rest in the body's immune system, according to study findings published in the January 12th issue of Science. Japanese researchers report that in some cases, a misguided immune system assault may inflict the damage seen in dilated cardiomyopathy.

Dr. Tasuku Honjo of Kyoto University in Japan led the study. Honjo told Reuters Health that researchers have speculated the disease may involve an abnormal immune response because some patients have been shown to have antibodies to their own muscle protein and to certain chemical receptors.

However, Honjo noted, it has been unclear whether these so-called ``autoantibodies'' are the cause or a result of dilated cardiomyopathy.

In the current study, the investigators found that a strain of mice lacking an immune system regulator known as PD-1 developed a form of dilated cardiomyopathy. All of the affected mice showed autoantibodies to a protein on the surface of heart muscle cells.

Honjo's team also found that a second strain of mice without PD-1 did not develop the heart disease. This, they report, suggests that other genetic factors are also involved.

If these findings are confirmed in humans, it may be possible to treat some cases of dilated cardiomyopathy with drugs that suppress the immune system or possibly with gene therapy, Honjo said.