According to the researchers, the new cell is created when the cell that originally controlled the excessive immune reactions mutates, the Japan times reported.
The study on mice found that it later powerfully promotes the activities of osteoclast, a cell that destroys bones.
The team, which included University of Tokyo visiting researcher Noriko Komatsu and professor Hiroshi Takayanagi, revealed that the same mutation is believed to happen in human arthritis patients.
Bones and cartilage in joints are usually shielded by synovial membrane and fluid secreted from it. In arthritis patients, abnormal growth of cells in the membrane causes inflammation.
The team also found that interleukin-6 released by cells, in the membrane that causes inflammation, triggers the mutation.
The study is published in journal Nature Medicine.