Fc receptor-directed phagocytic stimuli induce transient actin assembly at an early stage of phagocytosis in neutrophil leukocytes.

The phagocytic pathway for the uptake of multivalent Fc complexes by neutrophil leukocytes can be partially dissected by using a pulse-chase protocol at different chase temperatures. Utilising a deoxyribonuclease I inhibition assay, we show that an early response to recognition of phagocytic substrate by neutrophils is a rapid (less than 10 sec) polymerization of actin. Net actin assembly is transient and is reversed at higher chase temperatures which appears to allow for further progress of the pulse of phagocytic substrate along the pathway. Assembly of actin monitored in whole cells is paralleled by an increase in total actin retained in the cortical filamentous network of detergent-insoluble ghosts prepared from phagocytosing neutrophils. These data provide direct evidence for the reversible reorganisation of actin filaments in the cortical cytoplasm of phagocytic cells during phagocytosis. Furthermore, this experimental system provides an opportunity to study the characteristics of ligand-induced actin assembly, and subsequent disassembly in situ.