Macrophage movements

Abstract

At the last conference, a simple hypothesis incorporating known macrophage cytoplasmic structural proteins was proposed to explain amoeboid movements of macrophages. In this hypothesis, cell movement was believed to result from regional alterations in the cytoplasmic calcium concentration. Increases in calcium in a domain of the cell would activate gelsolin, a calcium binding protein which fragments actin filaments and binds to their fast growing ends, thereby diminishing the mechanical rigidity of cytoplasm in that area, and promote myosin-mediated movements of actin filaments. While this hypothesis remains useful for explaining certain movements of cytoplasm, in particular retractions of plasma membrane, profilin, a protein that binds actin monomers and acumentin, a protein that binds to the slow-growing ends of actin filaments, must be integrated into the mechanism and suggest a different explanation for propulsive macrophage movements. Profilin can function with gelsolin and calcium to regulate the reversible assembly of cytoplasmic actin filaments. Here we review the 1984 status of knowledge on proteins we believe are involved in macrophage motility (Table I) and attempt to use this knowledge to explain the movements of phagocytosis.