Characterization of the Mobility of FcγRIIa in Primary Human Macrophages

Fcγ receptor-mediated phagocytosis is an active process requiring receptor clustering as a signal initiation event. The mechanisms controlling Fcγ receptor clustering are unknown, as are the parameters governing the receptor lateral mobility in the plasma membrane. This work investigated the lateral mobility of Fcγ receptor IIa in resting primary human macrophages using single-molecule tracking methodology. In the absence of ligands, the receptor was found to exist mostly as a monomeric species. Detailed receptor dynamics revealed the existence of two receptor populations: one that was mobile, the other confined. The actin cytoskeleton was shown to be important for receptor confinement but did not affect receptor diffusion. Such findings are important in understanding the mechanisms for receptor clustering and signal initiation in phagocytosis.MAS

Actin Cytoskeleton Reorganization by Syk Regulates Fcγ Receptor Responsiveness by Increasing Its Lateral Mobility and Clustering

Clustering of immunoreceptors upon association with multivalent ligands triggers important responses including phagocytosis, secretion of cytokines, and production of immunoglobulins. We applied single-molecule detection and tracking methods to study the factors that control the mobility and clustering of phagocytic Fcγ receptors (FcγR). While the receptors exist as monomers in resting macrophages, two distinct populations were discernible based on their mobility: some diffuse by apparent free motion, while others are confined within submicron boundaries that reduce the frequency of spontaneous collisions. Src-family and Syk kinases determine the structure of the actin cytoskeleton, which is fenestrated, accounting for the heterogeneous diffusion of the FcγR. Stimulation of these kinases during phagocytosis induces reorganization of the cytoskeleton both locally and distally in a manner that alters receptor mobility and clustering, generating a feedback loop that facilitates engagement of FcγR at the tip of pseudopods, directing the progression of phagocytosis

Actin Cytoskeleton Reorganization by Syk Regulates Fcγ Receptor Responsiveness by Increasing Its Lateral Mobility and Clustering

Clustering of immunoreceptors upon association with multivalent ligands triggers important responses including phagocytosis, secretion of cytokines, and production of immunoglobulins. We applied single-molecule detection and tracking methods to study the factors that control the mobility and clustering of phagocytic Fcγ receptors (FcγR). While the receptors exist as monomers in resting macrophages, two distinct populations were discernible based on their mobility: some diffuse by apparent free motion, while others are confined within submicron boundaries that reduce the frequency of spontaneous collisions. Src-family and Syk kinases determine the structure of the actin cytoskeleton, which is fenestrated, accounting for the heterogeneous diffusion of the FcγR. Stimulation of these kinases during phagocytosis induces reorganization of the cytoskeleton both locally and distally in a manner that alters receptor mobility and clustering, generating a feedback loop that facilitates engagement of FcγR at the tip of pseudopods, directing the progression of phagocytosis