Antigenicity of Formaldehyde-Inactivated Staphylococcal Enterotoxin B

Abstract

Abstract The reactivity toward or ability to stimulate production of antibodies specific for native staphylococcal enterotoxin B (nSEB) demonstrated by formaldehyde-inactivated toxin (fSEB) is directly related to the extent to which SEB is polymerized by aqueous formaldehyde. Combined use of polyacrylamide gel electrophoresis in sodium dodecyl sulfate and agarose gel chromatography revealed that: 1) 30-days incubation of SEB in 1% formaldehyde solution buffered to pH 5.0 or 7.5 resulted in a series of small to very large SEB polymers, while SEB incubated at pH 9.5 formed heterogeneous monomers and a small amount of dimer; 2) SEB was polymerized to maximal extent in pH 7.5 formaldehyde. Polymeric fSEB obtained with neutral or acid formaldehyde retained the capacity to precipitate quantitatively nSEB antibodies from rabbit antiserum and to induce the formation of nSEB hemagglutinins in rhesus monkeys. In contrast, the nonpolymerized fSEB failed to react with, or stimulate production of nSEB antibodies. Furthermore, the relative in vitro antibody-combining activities of the two polymeric fSEB products were inversely related to in vivo antibody production. Thus, although quantitative precipitation experiments revealed that 50% of the native antigenic determinants were retained after polymerization in acid aqueous formaldehyde (5.0-fSEB), while only 15% were preserved upon polymerization in neutral formaldehyde solution (7.5-fSEB), hemagglutinin responses of rhesus monkeys were generally several fold greater after parenteral injection of 7.5-fSEB than of 5.0-fSEB. The greater antibody response to 7.5-fSEB may be explained by its more extensive polymerization; the greater average molecular size of the 7.5-fSEB antigenic complex may permit more efficient processing by macrophages or provide a more effective presentation of reactive sites for attachment with, or activation of, immunocompetent cells.