Nonspecific Agglutination of Tanned Sheep Erythrocytes by Heat-Inactivated Mouse Serum Collected from Diluted Blood

Summary Mouse plasma collected from diluted blood, when heated at 56°C for ½ hr, produces agglutination of tanned sheep erythrocytes to high titers. The nonspecific agglutination can be removed by absorption of the sera with tanned cells but not with washed erythrocytes. Five minutes at 56°C is sufficient to activate the substance responsible for nonspecific agglutination, but heating at 35°C for ½ hr did not produce a significant increase of nonspecific titers. Exclusion of complement did not increase nonspecific agglutination. When mouse blood was allowed to clot, the nonspecific agglutination by serum did not take place either before or after heating the serum, indicating that substance involved in the clotting mechanism was responsible for the nonspecific agglutination. This substance might be mainly fibrinogen. Human fibrinogen solutions, when heated at 56°C for ½ hr, produced agglutination of tanned sheep erythrocytes. This agglutinating capacity could be removed by absorption with tanned but not with washed erythrocytes. Similar nonspecific agglutination of tanned sheep erythrocytes was also observed in human and rabbit plasma but not in guinea pig plasma.