CD4 and autoimmune disease: Although the mechanism by which NK cells exert their regulatory role in autoimmune diseases needs to be identified, studies indicate that activated CD56bright NK cells kill autologous CD4+ T cells via cell-to-cell interaction and releasing granzyme B. In abnormal conditions, CD56bright NK cells can not kill autologous CD4+ T cells because of the increased expression of HLA-E on CD4+ T cells.