The inhibitory effect of IgM RF on the release of lysosomal substances.

Isolated IgM RF inhibited the IgG-induced release of lysosomal substances, measured as 'large molecular size vitamin B12-binding protein' (LBP) and beta-glucronidase, from separated human granulocytes. The effect was most marked when cytochalasin B was added to the experimental system. The results indicate that the RFs interact with the granulocyte binding region of IgG.