Cell differentiation increases astrocyte phagocytic activity. A quantitative analysis of both GFAP labeling and PAS-stained yeast cells.

Since efficiency of phagocytic potential in activated astrocytes is still a subject of controversy, an attempt was made to quantify simultaneously phagocytic activity and astrocyte differentiation. Resorting to Junin virus, known to induce astrocyte activation, infected vs control samples of cultured rat astroglial cells were serially harvested up to day 12 post-inoculation (pi), and subjected to a triple staining procedure consisting in immunoperoxidase labeling of GFAP, periodic acid-Schiff (PAS) reaction in added baker's yeast cells and hematoxylin for nuclear staining of the whole cell monolayer. Adopting GFAP labeling as a specific marker of astrocyte differentiation, the immunoprecipitate development over time was measured. Direct calculation of the initial reaction rate was feasible given its linear behavior during the first 10 min, so that GFAP amount was regarded proportional to peroxidase activity. As determined by digital image analysis, mean optical density (MOD) values of GFAP in infected samples increased from 0.618 +/- 0.082 at day 1 pi to 0.825 +/- 0.125 at day 3, leveling off at 1.010 +/- 0.101 as from day 9, while control uninfected samples remained unchanged at roughly 0.6 during the entire observation period. In turn, phagocytosis was quantified by PAS staining densitometry, whose intensity varied according to wall degradation of yeast cells. MOD levels of PAS-stained phagocytized yeast cells were significantly lower (p < 0.05) in infected vs control cultures at 48 and 72 h following their addition to the astroglial monolayer. According to simultaneous quantification of two components of astrocyte response to viral infection, it is concluded that phagocytic activity increases with astrocyte differentiation.