Figure 3: Role of NK cells in MS. Two schools of thought were developed. The first indicates that NK cells help Th1 cells to differentiate into Th1 through the release of IFN-. Th1 cells must also receive a signal from APCs that present encephaloantigens which include PLP, MOG, or MBP. These APCs also activate NK cells to release IFN-γ by secreting IL-12 and IL-18. Autoreactive Th1 cells damage the myelin sheath by the release of IFN-γ and TNF-α, among other toxic molecules. The second school indicates that NK cells ameliorate the disease via either directly lysing autoreactive Th1 cells or by lysing APCs, and hence, impeding antigen presentation to these T cells.