Brief Definitive Report Spontaneous Redistribution of Surface Immunoglobulin in the Motile B Lymphocyte* Materials and Methods the Journal of Experimental Medicine @bullet Volume

Most macromolecules are assumed to be distributed randomly on the cell surface, diffusing freely within the plane of the plasma membrane. However, upon interaction with ligands, surface proteins undergo an orderly redistribution and segregation from other macromolecules the phenomenon of capping (1). Capping of various molecules shares certain requirements: a cross-linking ligand producing the stimulus, plus metabolic energy, membrane fluidity, and the participation, still ill defined, of cytoplasmic microfilaments and microtubules (for example, see references 1-5). In this paper we report an example of a surface protein selectively segregated from other surface macromolecules in the absence of any stimulation by ligands. B lymphocytes, during translatory motion, accumulate immunoglobulin (Ig) to one area of their surface. In contrast, two other surface macromolecules remain diffusely distributed. This capping of surface Ig demonstrates a spontaneous change in the distribution of a surface protein during a particular functional state of the cell and may reflect a reversible association between membrane proteins and cytoplasmic structures.