Interference with Immune Hemolysis by Glycoprotein Antigens*, by E. R. Arquilla,

Hemagglutination and hemolytic titrations of antisera using red cells to which antigens have been conjugated with bis(diazo)benzidine have been used as a measure of antibody activities (1--4) in this laboratory. Hemagglutination and immune hemolysis fitrations have comparable sensitivities. Immune hemolysis, however, can be modified to give a high degree of precision (5). Both methods have been used to advantage with a number of protein antigens; i.e., insulin, egg albumin, bovine serum albumin, human gamma globulin, ferrifin, and others (2). This investigation is concerned with the diminished immune hemolysis and relatively elevated hemagglutination titers noted with three different immunological systems involving sialic acid-containing antigens. These glycoprotein immune systems were capable of complement fixation. Consequently, the dirnlnished immune hemolysis could not be attributed to the lack of complement fixation. Large amounts of these three glycoproteins in solution did not interfere with immune hemolysis observed with insulin and homologous antibody. When red cell preparations were sensitized with a mixture of sialic acid-containing glycoprotein and insulin, immune hemolysis by insulin antisera was diminished. Red cells treated with neuraminidase to remove sialic acid, and then incubated with complement, hemolyzed in the absence of any known immune reaction. Furthermore, such hemolysis of neuraminidase-treated ceils by complement could be interfered with by conjugating sialic acid-containing glycoproteins to the cell surface. These observations are consistent with the postulate that during immune hemolysis a sialic acid-containing substrate is enzymatically cleaved from the cell surface prior to lysis of the red cell.