Immunogenic Correlation between Cross-Reacting Material (CRM197) Produced by a Mutant of Corynebacterium diphtheriae and Diphtheria Toxoid

Abstract
The in vivo immunizing potency of diphtheria toxoid and formalin-treated cross-reacting material (CRM197, a nontoxic mutant protein) was compared in guinea pigs. Major antigenic differences between the 2 untreated proteins were also tested in rats. Diphtheria toxoid and CRM197 were equally effective immunogens, but only if the latter was treated with formalin in the same concentration (0.7% vol/vol) as that of the toxoid. Formalin treatment rendered the antigens more resistant to enzymatic proteolysis by trypsin in vitro.

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