Hemolysis of Sheep Erythrocytes by Complement Without Participation of Antibody

Sheep erythrocytes, to which aggregated human IgG (EagG) was coupled by CrCl3, were lysed by diluted guinea pig serum. The kinetics of the lytic process, the mode of inhibition of the hemolysis by ethylenediaminetetraacetic acid (EDTA) and the formation of the intermediate products of the complement reaction, i.e., EagG C′1a, EagG C′1a4 and EagG C′4, all confirmed the participation of complement in the process. IgM-coupled erythrocytes were also lysed by complement; in contrast IgA- or IgD-coupled erythrocytes were not lysed even at much higher concentrations of complement. These observations are consistent with the facts that IgM, as well as IgG, fix complement while IgA does not. From the hemolytic behavior of IgD-coupled erythrocytes and estimation of the complement-fixing capacity of IgD, it was concluded that IgD does not fix complement. Direct coupling of partially purified human C′1a to sheep erythrocytes by CrCl3 was also achieved.