CD28 and Autoimmunity: However, CD28 may also function as a pro-inflammatory or anti-inflammatory role depending on the type of cell and the context in which it is expressed.[42] CD28 is required for both thymic development and peripheral homeostasis of Treg cells.[43] It has been demonstrated that CD28 prevents spontaneous autoimmunity by promoting the anti-inflammatory function of the Treg cells.[44] CD28 plays such an important role in the anti-inflammatory effects of Treg cells that it is reasonable to assume that CD28 expression on Treg cells is inversely associated with the risk of Crohn disease.