Specific and nonspecific channels leading to proteolysis in antibody preparations.

Current ways of fractionating immune sera give rise in the guinea-pig species to an active plasmin that contaminates antibody preparations. The enzyme appears as a free molecule separable from the immunoglobulin. In contrast, when a purified antibody has been obtained through the immunoabsorption process, plasmin activated during the contact between antibody and polymer binds firmly to the immunoglobulin. This phenomenon occurs separately and indistinctly with IgG1 and IgG2. Moreover, the alternate pathway of complement activation could be a tributary to the plasmin system.