Regulatory NK-cell functions in inflammation and autoimmunity

Natural killer (NK) cells were viewed traditionally as cytotoxic effector cells whose rapid killing of infected and transformed cells without preactivation provides a first line of defense prior to the initiation of an adaptive immune response against infection and tumor development. However, it has become clear that NK cells interact with various components of the immune system, and therefore have the potential to function as regulatory cells. While NK cells can assist in dendritic cell (DC) maturation and T-cell polarization, increasing evidence indicates that NK cells can also prevent and limit adaptive (auto) immune responses via killing of autologous myeloid and lymphoid cells. Investigating immunoregulatory NK-cell functions might generate exciting insights into the reciprocal regulation between NK-cell-mediated innate immunity and adaptive immune responses, improve our capacity to monitor these cells as surrogate markers for disease activity and treatment responses in autoimmune diseases, and, perhaps, provide new prospects for NK cell-directed therapies.