Antigenic modulation of lymphocytic surface immunoglobulin yielding resistance to complement-mediated lysis. II. Relationship to redistribution of the antigen.

Experiments were carried out on guinea-pig L2C leukaemic lymphocytes to investigate the mechanism of antigenic modulation of their surface immunoglobulin (Ig) defined as the conferring by anti-Ig of resistance to lysis by anti-Ig plus complement. The phenomenon reflects, and is probably a consequence of, redistribution of the Ig molecules by bivalent antibody. Fab fragments of the antibody were completely ineffective. Parallel studies by indirect immunofluorescence of the movement of th surface antigen-antibody complexes revealed that modulation for syngeneic complement was apparent when the complexes were minimally aggregated: capping and extensive endocytosis were not necessary. Modulation for xenogeneic (rabbit) complement required more extensive movement but was still appreciable while complexes persisted on the surface. Sodium azide at 10 mM, which inhibits antibody-induced redistribution of surface molecules, diminished modulation. In experiments omitting pre-incubation with antibody alone, the presence of azide during incubations with anti-Ig plus syngeneic complement increased lysis from a low and variable to a consistently high level; there was no effect on the already high level of lysis occurring with the non-modulating anti-Ia plus syngeneic complement. This effect of azide provides further evidence that antigenic modulation can be a major factor determining a cell's survival when it is confronted simultaneously by antibody and complement.