Morphological characterization of a cell population responsible for natural killer activity.

Large granular lymphocytes (LGL) were observed in the peripheral blood, spleen, lung and, to a lesser extent, bone marrow and lymph nodes, but not in the thymus of C3H/HeN mice 8 weeks old. The organ distribution of natural-killer (NK) cytotoxicity closely followed that of LGL. Nude mice had higher LGL percentages and NK activity than normal mice. In addition, the age distribution of LGL from the peripheral blood followed that of NK activity. Employing discontinuous Percoll density gradients the percentage of LGL and the NK cytotoxicity of the low density fractions could be enriched in comparison with the original populations of lymphocytes from peripheral blood and spleen, but not from thymus. These results suggest that, as recently shown for humans and rats, in mice too LGL are associated with NK activity.