CD8A and juvenile idiopathic arthritis: Furthermore, the compromised killing activity of NK cells may contribute to extensive activation and expansion of cytotoxic CD8 T lymphocytes, production of IFNγ and other macrophage activating factors, which in turn stimulate macrophages for prolonged periods, resulting in excessive activation and expansion of macrophages that induce the onset and progression of JIA through heightened inflammatory immune activation (28).