Experimental syphilis in the rabbit: passive transfer of immunity with immunoglobulin G from immune serum.

A preparation of immunoglobulin G isolated from a pool of immune sera derived from rabbits with long-term syphilis was shown to possess a high degree of purity as judged by immunodiffusion and protein electrophoresis. The antitreponemal power of the preparation of immunoglobulin G and that of the immune serum pool from which it was derived were found to be equivalent in both the skin protection and the systemic protection test. The observation that neither normal serum nor a pool of serum derived from animals "immunized" with Salmonella typhi, Escherichia coli, Streptococcus pyogenes, or zymosan was protective indicates that the protective power of the immune serum studied was due to specific antibodies residing principally, if not entirely, in the immunoglobulin G fraction of the serum.