Complement and cold agglutinins. I. Complement coating of normal human erythrocytes by cold agglutinins.

Abstract

The antiglobulin test has been used to study the interaction of cold agglutinins and human complement with human erythrocytes. In confirmation of others, it was found that the 11S component, C'1 and C'4 must react in sequence with the EA complex for the antiglobulin test to become positive. 11S and C'1 reacted maximally at 1°C and were unreactive at 37°C. In contrast, C'4 failed to react at 1°C, a feature believed to be uniquely associated with reactions of cold agglutinins. C'4 reacted maximally at 20°C, but failed to react, or reacted very weakly, at 37°C. Calcium ions were required for the reaction of C'1 while neither calcium nor magnesium was required for 11S or C'4. Although the presence of C'1 in the EAC'1 complex gave an increased degree of `stability' to the involved cold agglutinin at 20°C, the cold agglutinin could be removed totally from the EAC'1 complex by repeated washing or from the EAC'1,4 complex by raising the temperature to 37°C. The fact that the cold agglutinin is a poor haemolysin, except under unusual circumstances, and yet is easily manipulated, offers an advantage in the study of the mechanisms of action of complement in immune systems.