Balance of proinflammatory and antiinflammatory cytokines in mice immunized with Escherichia coli and correlation with mortality after lethal challenge

Abstract

The balance of proinflammatory and antiinflammatory cytokines, their correlation with endotoxin levels and mortality rate after lethal challenge of Escherichia coli was investigated in mice immunized weekly for 8 weeks with formalin-killed E. coli either untreated or treated with 0.5×minimal inhibitory concentration of aztreonam. Control mice treated in parallel with saline, died within 24 h after challenge with 100× lethal dose (LD₅₀) of viable E. coli O6:K–. Mice immunized with antibiotic-treated bacteria showed a significantly higher survival than mice immunized with untreated E. coli. Cytokines were not detected in the sera of control mice during the entire period of immunization. At 90 min after immunization, mice immunized with antibiotic-treated E. coli showed tumor necrosis factor-α (TNF-α) levels significantly lower and interleukin (IL)-6 levels significantly higher (P<0.05) than mice immunized with untreated E. coli, while comparable levels of interferon-γ (IFN-γ) were measured in both groups. TNF-α and IL-10 levels measured 90 min after lethal challenge correlated with the mortality rate observed in each group (r=0.96 for TNF-α and 0.94 for IL-10). IL-6 levels correlated with survival (r = 0.95), while IFN-γ serum levels did not differ in the two immunized groups, but were significantly higher than those measured in the control mice. IL-4 was detected only after challenge of mice immunized with antibiotic-treated bacteria. Comparable levels of circulating endotoxin were measured after lethal challenge in both control and immunized mice. These data showed that in the presence of a protective immune response the survival of immunized mice was correlated with an early alteration of cytokine expression pattern including enhanced secretion of IL-4, IL-6 and IFN-γ, and reduced secretion of TNF-α and IL-10.