Phagocytosis requires repeated triggering of macrophage phagocytic receptors during particle ingestion

Abstract

The phagocytic functions of polymorphonuclear leukocytes and mononuclear phagocytes are crucial elements in host defence against a variety of invading microorganisms. Phagocytosis is a highly selective process, requiring specific interactions between the surface of the particle to be ingested and the plasma membrane of the phagocytic cell. The phagocyte can therefore discriminate between 'ingestible' and 'non-ingestible' particles even when the different particles are located in close proximity on the plasma membrane of the phagocytic cell. Previous work has demonstrated that these specific interactions between particle and phagocyte are required not only for the initiation of phagocytosis--that is, attachment of the particle to the phagocytic cells and generation of a signal to trigger phagocyte pseudopod extension--but also for the subsequent progression of pseudopods over the entire surface of the particle. We present evidence here that the continued interactions between phagocyte plasma membrane receptors and particle-bound ligands do not function merely to direct otherwise random phagocyte pseudopod movement, but instead are required for the repeated generation of intracellular phagocytic signals during the entire ingestion process.