Organ distribution of natural cytotoxicity in the rat

The natural (spontaneous) cytotoxicity (NC) of cell populations from different lymphoid organs of the rat were examined using a human myeloid cell line (K562) and a rat fibrosarcoma cell line (Mc40) as target cells. Rat blood and spleen lymphoid cell populations gave high cytotoxicity against K562, while lymph node cells and bone-marrow cells gave low levels of cytotoxicity and thymus cells virtually no activity. Addition of thymus or lymph node cells to spleen effector cells did not suppress the high cytotoxicity of spleen cells. A similar organ distribution of reactivity was observed against Mc40 cells, but the levels of cytotoxicity were much lower than for K562. A strain difference was monitored in the levels of natural cytotoxicity and cell populations from inbred Wistar rats consistently gave higher activity on a cell-to-cell basis than the corresponding population from PVG/c rats. Natural cytotoxicity was not removed when spleen cell populations were depleted of cells adhering to nylon-fibre columns or plastic surfaces, or depleted of cells ingesting carbonyl iron. In agreement with other studies using human and animal lymphoid cells, the natural killer cell in this system was found to be non-adherent and non-phagocytic and its distribution did not correspond to the established organ distribution of T or B lymphocytes.