Factors inducing a loss of net negative surface charge on spleen cells of mice grafted with a slow-growing tumour

The mean electrophoretic mobility (EPM) of splenic cells was determined in 4 different host-tumour systems. In splenic cells harvested from mice bearing slow-growing tumours, a significant EPM decrease was observed (12%) and in increase in the proportion of cells with slow mobility. Moreover, after 1 h incubation in RPMI medium at 37 degrees C and 2 washings, spleen cells showed a marked increase in their EPM (average 30%). Finally, the supernatant from incubation medium after contact with normal spleen cells (1 h at 37 degrees C) produced a significant decrease in their EPM (approximately 12%). On the other hand, no significant EPM variations were found between control spleen cells and cells from fast-growing tumours, before or after 1h incubation. The existence of factors which induce a loss of negative surface charge on spleen cells of some tumour-grafted mice is discussed.