Characterization of a murine ovarian reticulum cell sarcoma of histiocytic origin

We have studied the M5076 tumor, a transplantable murine reticulum cell sarcoma that arose spontaneously in the ovary of a C57BL/6 mouse. This tumor displays functional and ultrastructural characteristics indicating that it is of macrophage origin. Cells from the M5076 tumor are phagocytic, form rosettes with sheep red blood cells, mediate antibody-depend-ent cellular cytotoxicity against ⁵¹Cr-labeled red blood cells, and display macrophage-like cytotoxicity against syngeneic tumor target cells but do not exhibit any natural killer cell activity. The tumor cells possess lysozyme, nonspecific esterase, and phosphatase activities comparable to that seen in rodent macrophages. Ultrastructural examination revealed phagocytic vacuoles and a lack of tight junctions typical of macrophage morphology. Karyotype analysis showed that M5076 tumor cells are hypodiploid with a high percentage (>80%) of metacentric chromosomes that serve as an excellent marker for identification of these tumor cells.