V . Capping , Cell Movement , and Microtubular Function in Normal and Lectin - Treated Lymphocytes

Interaction of ligands with the antigen receptor on B lymphocytes leads to a rapid and dramatic series of surface and cytoplasmic events that have been mostly studied using as a probe anti-immunoglobulin (Ig) antibodies (anti-Ig) in murine lymphocytes. Four separate but overlapping events can be identified as occurring during capping: (a) an initial formation of aggregates of variable sizes on the cell surface, which is temperature but not energy dependent (1, 2); (b) a rapid distribution of the complexes into a single aggregate or cap (3, 4); (c) the stimulation of translational motility of the cell ¢5); and (d) the internalization of the aggregates by pinocytosis with subsequent partial degradation of the complexes (3, 6). These latter three events are both temperature and energy dependent. There is general agreement that capping results from the interaction of a critical amount of cross-linking, bivalent anti-Ig with surface Ig and that it involves an energy-dependent step not directly associated with the translation of the cell. We have recently discussed the possibility that movement of complexes on the cell surface may be brought about by some form of cell surface "activity," perhaps in the form of "waves" or "membrane flow" (5). This activity directed towards one zone of the cell surface moves the aggregates of complexes initially distributed at random into one lattice forming the cap. This putative "surface activity" can be separated from the actual process of movement of the cell on a solid surface, since by several experimental maneuvers capping can be induced in the absence of actual translation (5). However, it should be clearly pointed out that an association also exists between the surface activity involved in translation and capping. It was shown both in the neutrophil polymorphonuclear leukocyte (PMN) ~ (7) and in the lymphocytes that movement serves to direct the