Quantitative evaluation of opsonin-independent phagocytosis by alveolar macrophages in monolayer using polystyrene microspheres.

Macrophages can bind and engulf a variety of particles in the absence of specific opsonins. Polystyrene-type microspheres are often employed to quantitate opsonin-independent phagocytic activities of macrophages in vitro. Reliable measurement of this cell function, however, requires the ability of the investigator to distinguish between particles that are merely attached to the cell surface and those that are actually internalized. We have developed a simple, rapid, and reproducible method for quantitating phagocytosis using polystyrene microspheres and adherent alveolar macrophages. Basically, particles associated with macrophages after a given incubation time are microscopically quantitated on a cell-by-cell basis before and after toluene dissolution of external particles. Particle/macrophage values obtained after toluene treatment exclusively index phagocytosis.