Mesenchymal stem cells (MSCs) have been found to aid in the treatment of autoimmune-related lung fibrosis. Interstitial pneumonia is the inflammation of alveoli, and affects patients with pulmonary fibrosis and other connective tissue diseases. Increased fibrosis is due to an overactive immune response--mainly cytotoxic T cells. Past therapies have tried to suppress all immune cells to lower pro-fibrotic molecules. Mesenchymal stem cells are able to selectively change the composition of T cells from cytotoxic to regulatory. Bone marrow derived stem cells interfered with overactive autoimmune processes, and promoted the repair of alveoli tissue.