Microglial Cell Death Following Phagocytosis of Zymosan-A Under a Video-Enhanced Contrast — Differential Interference Contrast Microscope: Does This Include Apoptosis?

Abstract

Employing a novel video-enhanced contrast-differential interference contrast (VEC-DIC) microscope with a mercury light source, the process of microglial cell death after phagocytosis of zymosan-A was examined for its morphological changes, especially of the nucleus. The materials used were microglia (exp. n = 15) isolated from the newborn rat brain. Zymosan-A was introduced into the chamber on the stage of the microscope where the microglia were being observed. Aggregates of zymosan-A became partially or totally engulfed by the microglia. At ca. 10–30min of phagocytosis, the microglia began to swell, with ballooning of the cell membrane, and then burst. The cell body changes in terms of the circumferential length were: 84.38µm in the control and 141.71µm at the time of bursting (p < 0.05). Those in the area of the cell body were: 36.43µm2 in the control and 47.92µm2 at the time of bursting (p < 0.05). The average dimensional changes of the nucleus (n = 5, where the nuclear changes could be followed) in the control, at the time before bursting, after bursting, and at 10 min after bursting were 7.45, 7.32, 7.25, respectively, and 7.01µm for the long axis, and 6.53, 6.13, 6.81, respectively, and 6.55µm for the short axis. The minimal change in nuclear size together with swelling/dissolution of the plasma membrane suggests that the self-inflicted cell death triggered by zymosan-A, and possibly facilitated by the UV light, might result from necrosis due to self-inflicted effects of autogenous toxic substances. However, the findings were not conclusive since chromatin condensation with cell shrinkage was observed in some cases, suggestive of apoptosis.