Mouse Natural Killer Cells: Induction Specificity, and Function

Abstract Attention has recently focused on the possible significance of natural killer (NK)2 lymphocytes in the surveillance of tumors by the immune system (1). This is because NK cells from several species preferentially lyse transformed target cells in vitro (2–5). NK lymphocytes from mouse and man have both been studied in detail, but the manipulability of the mouse model has allowed for the better resolution of NK cell properties. In this review I will restrict most of my comments to the mouse NK cell system. The properties of human NK cells have recently been reviewed elsewhere (6). Characterization and tissue distribution. It is agreed that mouse NK cells are x-ray-resistant (7) lymphocytes lacking cell surface immunoglobulin (8, 9). They are thought to be derived from bone marrow since their activity is removed by depletion of bone marrow cells with anti-bone marrow antibody or with 89Strontium (7, 10). Most reports indicate that NK cells have neither Fc receptors nor θ antigen on their plasma membranes (3, 4), but low concentrations of both surface markers on NK cells have recently been reported by Herberman’s laboratory (11, 12) and confirmed by us (unpublished). Although it is clear that NK cells are neither macrophages, polymorphonuclear leukocytes (PMN), B cells, nor T cells, it is possible that they may be precursors of such cells. The reported presence of low concentrations of θ antigen has led Herberman and others to suggest that they may be prethymic T cells (12). In comparison, the human NK cells have been distinguished from the four major groups of leukocytes by lymphocyte morphology and lack of B cell (surface immunoglobulin) and high concentration T cell (E-rosette formation)markers (reviewed in 6). However, human NK cells can be recovered in E-rosette fractions under optimal rosetting conditions, suggesting that low concentrations of T cell antigens may exist on human NK cells, in analogy to the mouse system (13). Fc receptors are easily detected on human NK cells (6, 13).