Dynamics of actin filaments in microglia during Fc receptor-mediated phagocytosis.

The phagocytic ability of mouse microglia during their differentiation in culture and after stimulation with bacterial wall lipopolysaccharide (LPS) has been investigated using Fc receptor-mediated phagocytosis of immunoglobulin (IgG)-coated sheep erythrocytes (SRBCs). We observed that in 10-14 day-confluent neopallial cell cultures some immature microglia are not phagocytic but, on further culturing, they do become phagocytic. LPS-stimulated microglia are able to phagocytose larger numbers of IgG-coated SRBCs and at a faster rate than non-stimulated microglia. Within 5-10 min of phagocytosis the actin filaments of the LPS-stimulated microglia become depolymerized, leaving only bundles of actin filaments around the phagocytosed SRBCs (phagosome cups). At 30 min after the start of phagocytosis the actin filaments of the LPS-stimulated microglia begin to polymerize, and within 2 h the original pre-phagocytosis pattern of the actin filament network is re-established. The non-LPS-stimulated microglia exhibit actin filament depolymerization in only a few lamellipodia and polymerization of actin filaments around engulfed particles, but much later during phagocytosis.