ABSTRACT
The plasma membrane of eukaryotic cells is asymmetric with regard to only structure but also function. Its capacity to maintain ion concentration gradients, to receive chemical signals from neighboring cellular and surface-derived molecules, and to participate in the release of intracellular molecules requires that the functions of the external side and cytoplasmic side of the membrane differ. The plasma membrane is a dynamic organelle whose components are in a state of continuous motion. Membrane constituents are synthesized and inserted into the bilayer from within the cell such that membranes grow by expansion of an already formed closed vessel. Immunoregulatory molecules, including immunoglobulin, Fc and C3 molecules are shed from the surface of lymphocytes in association with vesicles in vitro and in vivo Owing to the technical complexity of analyzing cell-cell transfers over short distances, in vivo studies aimed at determining the physiological relevance of membrane-associated hematopoietic regulators have been difficult to perform.
