Studies on the mechanism of phagocytosis. I. Requirements for circumferential attachment of particle-bound ligands to specific receptors on the macrophage plasma membrane.

Abstract

Phagocytosis of a variety of inert and metabolically active particulates plays an essential role in metazoan nutrition, metabolic economy, and defense against viral, bacterial, and protozoan pathogens . With the development ofthe lysosome concept (1-3), the processes governing the intracellular digestion of ingested particles have been clarified. In contrast, the mechanisms which regulate the ingestion phase of phagocytosis remain poorly understood. The recognition of contractile proteins in the cytoplasm of a variety of nonmuscle cells (4-7), including macrophages (4, 5, 7), has resolved one mechanism whereby chemical energy released during phagocytosis may be coupled to mechanical processes requisite for membrane movement and particle interiorization. However, no information is available which suggests how a phagocyte directs this system of contractile elements in order to engulf specific particles which are attached to its plasma membrane . That the process is indeed specific and limited to the segments of plasma membrane to which the particles to be ingested are bound has been carefully documented (8,9).The fastidious appetite of phagocytes is also well known. These cells avidly ingest some particles with which they come into contact while they totally ignore others (8, 9) . The presence or absence of opsonins (complement and immunoglobulins) on the surface of a particle is widely recognized as the most important factor governing the fate ofthe particle . Particles coated with ligands such as IgG and/or complement are avidly ingested by phagocytes while the same particles lacking such ligands are neither bound to, nor ingested by, phagocytic cells.The experiments reported in this paper were performed to examine the mechanisms which govern the vectorial and discriminatory qualities of the phagocytic process and to define the factors responsible for the segmental nature

The presence of two Fc receptors on mouse macrophages: evidence from a variant cell line and differential trypsin sensitivity.

“…The presence of Fc receptors on macrophages, and the role of the Fc receptor in the recognition and ingestion of antibody-coated particles (33)(34)(35) have been well established. The results described in this paper demonstrate that the P388D1 macrophage cell line and normal mouse peritoneal macrophages have two Fc receptors which differ in the Ig's they bind and in their sensitivity to trypsinization.…”

Severity of E. coli mastitis is mainly determined by cow factors

“…The process of opsonisation, though not essential for phagocytosis, certainly promotes the uptake of E. coli by PMN, which is energy-dependent and requires the presence of a functional cytoskeleton [103]. The cytoskeleton machinery, sequentially activated following receptor stimulation, is thought to envelope the micro-organism in a "zipper mechanism" [86]. Thus, PMN are fully armed to confront invading E. coli.…”

Mechanisms of Attachment of Neutrophils to Candida albicans Pseudohyphae in the Absence of Serum, and of Subsequent Damage to Pseudohyphae by Microbicidal Processes of Neutrophils In Vitro

“…The process resembles incomplete phagocytosis, and probably occurs by a similar mechanism, involving sequential interactions of receptors on organism and neutrophil (40). Through the use of inhibitors, we defined some features that affect attachment of neutrophils to Candida.…”