The nonadherent splenic cells from normal and tumour-bearing (mouse fibrosarcoma-MFS) Swiss mice were divided into 6 subpopulations on Percoll step density gradient and characterised. For the determination of their cytotoxicity towards syngeneic MFS cells and their electrophoretic mobility (EPM), the splenic cell populations were pooled to form 2 broad groups: a lower-density group (density of saline to just less than 1.069 g/ml) and a higher-density group (1.069 to just less than 1.087 gm/ml). In general, the splenic cells from mice bearing 10- to 11-day-old MFS tumours differed in certain characteristics from those of normal mice in that they showed an increase in the following: proliferation, heterogeneity, with appearance of large cells (greater than 70 mu2); cells with a lower density (less than 1.069 g/ml); cells with a lower (less than 0.85 micron/sec/Volt/cm) anodi cEPM. The cytotoxicity studies revealed that: a) the lower-density splenic cells of both normal and tumour-bearing mice were more cytotoxic than the higher-density splenic cells; b) the lower- and higher-density splenic cells of tumour-bearing mice were more cytotoxic than the corresponding cells of normal mice. These findings indicate that the splenic cells of mice with a lower EPM and a lower density are the main contributors of cell-mediated cytolysis of a subpopulation of MFS cells.

We have studied and discussed the significance of the use of ascorbic acid in 51Cr labelling of cells. The following two advantages seem credible if cells (mouse fibrosarcoma) in culture are incubated for about 2 h in a medium containing Na2 51CrO4 and then ascorbic acid is added to the medium and incubation continued for ten more minutes: (a) the natural intracellular conversion of Cr6+ to Cr3+ appears to be aided, (b) the incorporation of chromium by cells is higher.

When nonadherent splenic cells from normal and tumor-bearing (mouse fibrosarcoma, MFS) Swiss mice were added to wells made in agarose layers in plastic petri dishes, subpopulations of cells from tumor-bearing mice were seen to migrate out of the wells, whereas those from normal mice did not. The proportion of migratory cells among the lower density (< 1.057 to < 1.069 g/ml) cells was larger than that of higher density (<1.069 to < 1.087 g/ml) cells. When the plastic surface underneath the agarose layer was covered with a monolayer of MFS cells, the splenic cells from normal mice also migrated out of the wells. About 20 % dead MFS cells were observed in the zone of migration when the migratory cells were from normal mice, and about 30 % when the migratory cells were from tumor bearing mice. Apart from revealing the differences between the migratory behavior of splenic cells, the present work also suggests a novel application of agarose methodology in the study of interaction of cytotoxic cells with malignant cells.