Cytotoxicity of human lymphocytes induced by rabbit antibodies to chicken erythrocytes. Inhibition by normal IgG and by human myeloma proteins of different IgG subclasses.

Normal IgG preparations of human, rabbit or guinea-pig origin (IgG2) were tested for their capacity to inhibit the cytotoxicity of purified human lymphocytes, as induced by rabbit IgG antibodies to chicken erythrocytes. All IgGs were found to be about equally efficient inhibitors. Human F(ab′) used for control, gave no inhibition. Human myeloma proteins of subclasses IgG1, IgG2 and IgG3, were about equally efficient inhibitors. In contrast, the inhibitory action of myeloma proteins belonging to subclass IgG4 was weak and more irregular. In this assay system, a large excess (∼ 10 ×) of normal IgG over antibodies had to be added in order to achieve ≥50 per cent inhibition. Heating of the inhibitors to 63° for 30 minutes did not significantly enhance their inhibitory capacity. For comparison, the same human IgG preparations and myeloma proteins were also tested for their capacity to inhibit phagocytosis by human blood monocytes of chicken erythrocytes sensitized with rabbit IgG antibody. As was to be expected in this system, only HGG, IgG1 and IgG3 caused inhibition whereas F(ab′), IgG2 and IgG4 were completely negative.