The effect of concanavalin A (Con A) on the capping of mouse lymphocyte surface immunoglobulin (surface lg), cross-linked by rabbit anti-mouse Ig antibody, and on the capping of mouse thymocyte 0 antigen, cross-linked by anti-0 alloantibody

The effect of concanavalin A (Con A) on the capping of mouse lymphocyte surface immunoglobulin (surface lg), cross-linked by rabbit anti-mouse Ig antibody, and on the capping of mouse thymocyte 0 antigen, cross-linked by anti-0 alloantibody and rabbit anti-mouse lg antibody, has been studied by immunofluorescence, using fluorescein conjugated Con A and rhodamine-conjugated anti-mouse lg antibody, and by electron microscopy, using native or fluorescein-conjugated Con A and ferritin-conjugated anti-mouse lg antibody. Prior incubation of the cells with Con A inhibited only partially capping of surface Ig, whereas it blocked almost completely capping of 0 antigens. Both on cells with rings and on cells with caps the staining for surface Ig or 0 antigen was superimposed to the staining for Con A. When Con A receptors on spleen cells were capped by Con A at concentrations of 10 ug/ml or higher, and the distribution of surface lg was examined under noncapping conditions, all detectable surface lg were found in the caps. As shown by electron microscopy, surface lg remained dispersed in a layer of Con A. The ability of Con A to cap surface ig was not alterecl by the presence of colchicine or vinblastine. These results suggest that surface lg are cross-linked by Con A to other Con A receptors. In these conditions surface lg behave essentially as Con A receptors, as for example, in their sensitivity to cytochalasin B during inhibition or reversal of capping induced by this drug. The behavior of surface lg parallels that of Con A receptors also in the presence of vinblastine. It is concluded that in the presence of Con A, antimitotic drugs do not modify directly the interaction between Con A receptors and surface lg, but probably influence the capping ability of the Con A receptors or, more in general, affect the ability to elicit movements over the cell surface. The role in capping of cytochalasin-sensitive and vinblastine-sensitive structures is discussed. Both types of structures appear to play an active role in the formation of a cap, although the former probably corresponds to the main mechanical system responsible for the active displacement of cytoplasmic and surface material. THE JOURNAL OF CELL BIOLOG~t VOLUME 65. 1975 • pages 123-146 123 on M ay 8, 2017 D ow nladed fom Published April 1, 1975