Effect of formalin toxoiding on Pseudomonas aeruginosa toxin A: Biological, chemical, and immunochemical studies

We investigated the effect of Formalin toxoiding on the biological, chemical, and immunological activities of Pseudomonas aeruginosa toxin A. Formalin treatment alone resulted in a 1,000-fold decrease in toxin-induced cell cytotoxicity and altered the antigenicity of the toxin A molecule without adversely affecting enzymatic activity. Competitive blocking experiments indicated that Formalin-mediated detoxification proceeded via alterations in a region of the toxin molecule other than the active site of the enzyme. The addition of lysine to Formalin-toxin mixtures not only increased the rate and extent of detoxification and antigenic alteration, but also completely destroyed enzymatic activity. The immunogenicities of different toxoids varied substantially. Upon dialysis and storage, Formalin-derived toxoids underwent partial toxic reversion, whereas a Formalin-lysine-derived toxoid did not. The sodium dodecyl sulfate-polyacrylamide gel patterns of Formalin- and Formalin-lysine-treated toxins indicated that these treatments caused the formation of a heterogenous group of high-molecular-weight species and produced substantial changes in the electrophoretic mobility of toxin A.