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Faulty dendritic cell mechanism triggers autoimmune diseases

by Ruth SoRelle, M.P.H.

	Front row, from left : Min Chen, Zainuer Shabier, Lily Huang. Back row, from left: Alan Guerrero, Hector Sandoval, Jin Wang

Autoimmune disease occurs when a person's immune system turns against him or her, resulting in diseases such as systemic lupus erythematosus or type 1 diabetes.

Cells in the immune system not only attack foreign invaders, they attack the organ tissues of the person's own body with a debilitating and too often deadly result. The mechanism designed to protect against that is called apoptosis or programmed cell death.

Simply put, when immune system cells have achieved their purpose, signals tell them to die. Dendritic cells are critical immune system components that actually "present" foreign proteins (antigens) to the lymphocytes that go on to attack the invaders.

Mechanism fails

The failure of apoptosis or the programming that sparks the death of dendritic cells can initiate autoimmune disease, said Jin Wang, Ph.D., assistant professor of immunology at Baylor College of Medicine. In fact, in studies carried out in his laboratory, mice bred to have a defect in apoptosis of their dendritic cells went on to develop autoimmune disease, he said.

"This suggests that defective apoptosis of dendritic cells can be a critical component of autoimmune diseases," said Wang.

"We knew that autoimmunity in general can be caused when dendritic cells are unchecked, either by programmed cell death or overactivation," said Wang.

Initiators of immunity

"Dendritic cells are the initiators of immunity," said Wang.

They do this by showing or presenting foreign antigens from invading bacteria or viruses to the immune system, which then activates lymphocytes to attack.

Previously, many people thought autoimmunity occurred through apoptosis because of accumulating lymphocytes or white blood cells–key elements of the immune system.

"If they didn't die, we thought they would start to accumulate and do damage to the body's own tissues," he said. However, at least eight studies that suppressed programmed cell death in lymphocytes did not induce autoimmune disease in animals.

In the future, Wang said, he and his colleagues plan to fill in the gaps between what happens when apoptosis is hindered in the dendritic cells and the occurrence of autoimmune disease.

Others who participated in this research include: Drs. Min Chen, Li Huang and Hector Sandoval of BCM, and Drs. Yui-Hsi Wang, Yihong Wang, and Yong-Jun Liu of The University of Texas M.D. Anderson Cancer Center.

Funding for this project came from the Cancer Research Institute, American Society of Hematology, the National Institutes of Health and a Ruth L. Kirschstein National Research Service Award.

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