Phagocytosis by trabecular meshwork cells: sequence of events in cats and monkeys

Trabecular meshwork cells have well-established phagocytic properties. However, the sequential stages of this process have not been studied in detail. Zymosan particles, yeast cell walls 3 micron in diameter, were either injected or perfused into the anterior chambers (AC) of cats and monkeys. Glutaraldehyde (3%) was then infused into the AC at 1-, 6-, 17-, 30- and 60 min and the fate of the particles observed by transmission electron microscopy. After contact with zymosan particles, trabecular meshwork cells demonstrated short cytoplasmic extensions at contact sites and an increased number of cytoplasmic organelles. Internalization of the particles occurred by 6 min in the cat and by 17 min in the monkey. In both species similar events occurred following internalization of zymosan: trabecular cells, laden with particles, rounded up, detached from their underlying collagenous beams and migrated towards Schlemm's canal or the aqueous plexus. By 1 hr the individual trabecular cells completed the entire sequence of phagocytic events although some cells were always observed in earlier stages of the process. These data document for the first time the timing of the cellular events that take place during zymosan particle phagocytosis by trabecular meshwork cells.