Complement receptor 3 sends a signal to dampen the immune system

Rheumatology researchers have discovered that a well-known cell receptor sends a signal to dampen the immune system.

While not having an immediate application to treating disease, the finding raises the possibility that by targeting that receptor, physicians could stimulate a "nondanger" signal to rein in overzealous human immune responses. Controlling those responses could potentially protect transplant patients from rejection episodes or could relieve symptoms of autoimmune diseases such as rheumatoid arthritis and lupus.

The study, which was performed in mice, appeared in the May 15 issue of the Journal of Immunology.

Researchers from The Children's Hospital of Philadelphia and The University of Pennsylvania reported that complement receptor 3 (CR3), a protein found on cell surfaces, inhibits dendritic cells, the sentinels of the immune system, from setting off an alarm signal that brings on a full immune response.

"Normally, dendritic cells patrol different tissues and organs and look for danger signals sent by tissues undergoing stress or responding to invading microorganisms," said Stefania Gallucci, M.D., leader of the study team at The Children's Hospital of Philadelphia. "We found that when we stimulate CR3 on dendritic cells, CR3 sends a ,nondanger, signal that suppresses the ability of dendritic cells to set off an immune response," added Dr. Gallucci, who is also an assistant professor at the University of Pennsylvania.

In their study, the researchers used a monoclonal antibody, engineered to bind to CR3, to trigger a cascade of responses that had a net result of decreasing the activation of T cells that would normally be produced. T cells are immune cells that fight infection while contributing to the inflammation seen in an immune response.

"What is exciting about our research is that we have a new agent for modifying dendritic cell function," said pediatric rheumatologist Edward M. Behrens, M.D., the first author of the study. "The monoclonal antibody we used is already in a form that can be used for further studies. It has anti-inflammatory effects, so it may be a potential weapon against inflammatory diseases."

One such disease is lupus erythematosus, an autoimmune disease in children and adults that may damage many organs. A next step, said Dr. Gallucci, is to test the antibody in mice that have a disease similar to lupus in humans. The study team also expects to test the antibody in animal models of rheumatoid arthritis. In addition, the researchers may investigate a possible role for the antibody as an immunosuppressant, in preventing a patient's immune system from rejecting cell and organ transplants.