Studies on the Treponema pallidum immobilizing activity in normal human serum. 2. Serum factors participating in the normal immobilization reaction.

The T. pallidum immobilization reaction to be achieved by unheated normal serum was found to be complement dependent and the results presented suggested that complement was activated via the classical pathway. Besides complement, an immobilizing antibody of the IgM class was necessary for the immobilization reaction to occur. Lysozyme exerted an enhancing effect on the normal serum immobilization reaction.