Osteoarthritis may be caused by an abnormal or impaired immune system. Scientists at Stanford University School of Medicine have definitively linked mast cells to the development of osteoarthritis. A mast cell, also know as a mastocyte, are located in connective tissue including in bone marrow, the skin, the gastrointestinal tract and other sites. They are part of the immune system and play a critical role in helping defend tissue from disease. https://elifesciences.org/articles/39905 Note: Despite all advances in stem cells research and the application of these therapies in many countries all over the world, stem cells therapies are not legally approved yet in San Diego, Los Angeles, Chicago, Dallas, New York, Jacksonville, Seattle, Houston, San Francisco, Salt Lake City, Miami, Beverly Hills and other US cities. However, stem cell treatments are legal in Costa Rica.