Interaction of human Waldenström's IgM proteins with guinea pig and human complement

The activity of purified human Waldenström's IgM protein to fix complement of human and guinea pig origins was compared at different temperatures using the polystyrene latex particle-adsorption method. It was shown that the interaction of the IgM proteins with complement differed depending on the source of complement and that a pronounced heterogeneity in complement-fixing activity was observed among the IgM proteins when tested with guinea pig complement. Thus, by the use of guinea pig complement, six human IgM proteins examined were classified roughly into two groups, one having a high and the other a low activity at 3 C as well as at 37 degrees C. With human complement, five proteins showed a rather uniform activity at 37 degrees C. However, there was one protein with no detectable activity, suggesting the presence of non-complement-fixing protein in the IgM class. All the six proteins showed no significant activity with human complement at 3 C. No antigenic difference has been found as yet in the Fc or Cmu2 region among these IgM proteins examined.