Trypan blue inhibition of complement receptor function on various cells

Trypan blue has previously been shown to inhibit complement-mediated phagocytosis by interaction with the C3 receptor but not with the Fc receptor. In studies reported here, trypan blue inhibited EAC3 rosette formation with human polymorphonuclear leucocytes (PMN) and mononuclear cells, rabbit alveolar macrophages (AM) and peritoneal PMN, and guinea-pig spleen cells. Trypan blue also inhibited C3-mediated bacterial adherence to the same receptor-bearing cells and to human glomerular cells. EAC3bi rosette formation was also inhibited, but EAC3d rosettes were not detected in our assay system. Although the precise molecular nature of C3b fragments deposited on antibody-sensitized erythrocytes has not been fully determined, trypan blue probably inhibits all C3 receptors from different species and may prove useful in vivo and in vitro for the definition of C3-receptor function in various aspects of the immune response.