Tumor necrosis factor alpha (TNF-α) production in mice immunized with Escherichia coli: Correlation with mortality after lethal challenge and production of a native inhibitor of TNF-α activity

Abstract

The kinetics of tumor necrosis factor alpha (TNF-α) production, the correlation between cytokine levels and mortality rates after lethal challenge, and the production of a native inhibitor of TNF-α activity was investigated in mice immunized with formalin-killed Escherichia coli. Groups of mice were injected for 8 weeks with either untreated bacteria or bacteria treated with 0.5 MIC of aztreonam and subsequently challenged with 100 50% lethal doses of viable E. coli. Mice receiving saline only (controls) died within 24 h. The mortality of mice immunized with aztreonam-treated E. coli was significantly lower than that of mice immunized with untreated E. coli. There were no measurable levels of TNF-α in sera obtained from control mice during the entire period of immunization. TNF-α levels ranging from 90 to 306 U/ml were measured 90 min after each vaccination in sera obtained from mice immunized with untreated E. coli. Sera from mice immunized with antibiotic-treated E. coli showed lower TNF-α levels, ranging from 40 to 128 U/ml. TNF-α levels measured 90 min after lethal challenge correlated with the mortality rate observed in each group (r = 0.95). The cytotoxic activity of recombinant murine TNF-α was inhibited by the sera from immunized mice but not by the sera from controls. The inhibition was drastically reduced by preincubation of the sera with staphylococcal protein A. In immunoblot experiments, class G immunoglobulins reacting with recombinant murine TNF-α were observed in the sera of immunized mice. These data confirm the correlation existing between TNF-α levels and mortality and suggest that native inhibitors may play a role in the regulation of the biological function of the cytokine.