Phagocytic capacity of normal and malignant rat glial cells in culture.

The phagocytic capacity of 4 continuous rat glioma cell lines (BT2C, BT4Cn, BT5c, and 9L) and normal BD IX fetal rat glial cells in culture has been studied. This was done by flow cytometric measurements of single cells from monolayer cultures having ingested fluorescent bacteria, zymosan particles, red blood cells, or fragments of normal glial cells. In addition, phagocytosis was studied in a three-dimensional culture system. The BT4Cn, BT5C, and 9L cell lines were tumorigenic and invasive both in vivo and in organ culture in vitro. In contrast, BT2C has shown variable tumorigenicity and does not seem to be invasive. The phagocytic capacity of the cell lines was compared to their destructive properties during invasion. Depending on the particle type, 30-40% of the normal glial cells were phagocytic. The fractions of phagocytic glioma cells were dependent on the particle type and the prey load. Of the invasive cell lines, BT5C showed high phagocytic activity both in monolayer and three-dimensional cultures. Two of the invasive cell lines (BT5C and 9L) had about the same fraction of phagocytic cells as normal glial cells. These 2 cell lines showed highly destructive growth during invasion. In contrast, the third invasive cell line (BT4Cn) had almost no phagocytic cells. The BT4Cn cells showed single-cell invasion with little destruction of target tissue. The noninvasive cell line (BT2C) showed low phagocytic activity, and almost no destruction was observed in the border zone between tumor cells and normal tissue. Phagocytosis seems to be an inherent property of both normal and malignant glial cells, although the fraction of phagocytic cells varies from one cell line to another. In organ culture high phagocytic capacity of invasive glioma cells seems to be related to destructive activity on the normal brain tissue during invasion.