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Over 1.3 million Americans suffer from rheumatoid arthritis, an autoimmune condition that hampers and halts physical movement by gradually destroys bones, muscles, joints, cartilage and other connective tissue. While the cause of rheumatoid arthritis is not yet known, scientists have recently found that fat cells can trigger the chronic inflammatory disorder.

A new study on mice published in the Journal of Immunology, reveals that fat cells in the knee secrete a protein linked to arthritis. Researchers said the latest finding might pave the way for new gene therapies that could offer relief and mobility to millions worldwide.

"We found that fat in the knee joints secretes a protein called pro-factor D which gives rise to another protein known as factor D that is linked to arthritis," senior author Nirmal Banda, Ph.D., associate professor of medicine in the Division of Rheumatology at the University of Colorado School of Medicine said in a news release. "Without factor D, mice cannot get rheumatoid arthritis."

Researchers explain that factor D is part of the complement system, a complex array of over 40 proteins that help the body fight off bacteria and other pathogens.  Banda previously found that the complement pathway involving factor D made mice susceptible to inflammatory arthritis.

In the new study, Banda and his team found that removing factor D, rather than the entire complement system, achieves the same result without compromising other parts of the immune system.  Researchers explain that while it is theoretically possible to destroy the entire complement system in humans to prevent arthritis, the condition can eventually return along with a renewed risk of contracting the disease. Another thing is that patients with no complement system will be at a higher risk of getting infections and other complications because they lack this critical part of the immune system.

"The complement system is both friend and foe," Banda explained. "We believe we can shut down one part of the complement system that triggers disease without shutting down the rest. If so, we will be making a major stride toward treating and perhaps even curing rheumatoid arthritis."

While the latest finding was based on fat cells in the knees, researchers said that fat cells do the same thing in all the joints in the body, meaning that new treatments resulting from the recent study could treat inflammatory arthritis throughout the body.

"We know that fat is normally present around all organs of the body," Banda concluded. "But what we didn't know until now was that the fat is secreting this protein which actually triggers arthritis in the joints."