The dynamic state of the macrophage plasma membrane. Attachment and fate of immunoglobulin, antigen and lectins.

Abstract

AbstractThe dynamic state of the macrophage plasma membrane and its possible role in antigen presentation were studied by fluorescence microscopy. Our main observations are as follows: (a) macrophages from the peritoneal cavity of mice have easily detectable surface Ig which, in small/medium macrophages, remains associated with the membrane for four days in culture. On larger macrophages it is progressively lost by capping. Most of this surface Ig is rapidly redistributed in polar caps by divalent but not monovalent anti‐Ig reagents. Complete clearance of the membrane is, however, difficult to obtain. (b) Binding and redistribution of concanavalin, phytohemagglutinin and poly‐L‐lysine on macrophages are as described for lymphocytes. However, pokeweed mitogen, which binds in a detectable way only to thymocytes and not to peripheral B or T lymphocytes, binds also to macrophages and redistributes in polar caps by itself. (c) Antigen binds well to macrophages at 37 °C and weakly at 0 °C, but binding is not sensitive to NaN3. Macrophages do not show selectivity for antigen binding. Part of the bound antigen is redistributed in caps and endocytozed, but some antigen is still detected at the cell surface after 4 days of culture. Antigen binding is not antibody mediated. Antigen appears to stick to a ubiquitous macrophage membrane component and not to a receptor. Part of the endocytozed antigen is later reexposed at the plasma membrane surface.These findings extend the fluid mosaic model to the macrophage membrane and reconcile high endocytic activity and membrane fluidity with the antigen presentation role of macrophages.