Phagocytosis of candida albicans by lymphatic tumour cells in vitro

Experiments were carried out to investigate whether different lymphatic tumour cell lines have similar kinetic characteristics of phagocytosis of microorganisms. Six tumour cell lines were used. These were a human T-cell line (CEM), a mouse T-cell line (YAC-1), a human B-cell line (LAZ), and a human erythroleukemic tumour cells (K562), whereas 2 cell lines of professional phagocytosis were used as controls, a human macrophage cell line (THP1) and a mouse macrophage cell line (P388D1). Tumour cells were mixed with candida albicans at a ratio of 10:1 of candida to tumour cells and the percentage of tumour cells that had attached/phagocytosed candida was determined. After 4 h coculture with candida, tumour cells not of T-cell origin (LAZ and K562) showed moderate level of phagocytosis (28%), whereas tumour cells of T-cell origin (CEM and YAC-1) demonstrated low levels of phagocytosis (15%) as compared to macrophage cell lines (THP1 and P388D1) that showed maximum phagocytosis (64-78%). Acid phosphatase (AcPase) activity was increased by 33% during coculture of YAC-1 cells and yeast cells. In conclusion, the results suggest that lymphatic tumour cells of nonphagocytic origin acquire phagocytic properties during the course of malignancy, and digestion of phagocytosed yeast cells maybe related with AcPase activity, as well as that of other lysosomal enzymes. This phenomenon may represent one mechanism by which tumour cells downregulate immune surveillance.