The cooperative effects of TNF-alpha and IFN-gamma are determining factors in the ability of IL-10 to protect mice from lethal endotoxemia.

Recent studies have demonstrated that interleukin-10 (IL-10) has the capacity to protect mice from the lethal effects of endotoxin. In this investigation, we have examined the ability of IL-10 to protect both normal mice and Corynebacterium parvum-primed mice against endotoxin lethality. In the overwhelming majority of experiments, recombinant murine IL-10 (rMuIL-10) and recombinant human IL-10 (rHuIL-10) did not protect normal BALB/cJ mice from lipopolysaccharide (LPS)-induced lethality at doses up to 10 micrograms/mouse. Despite their inability to protect, both IL-10 preparations were highly effective in preventing the increase in serum tumor necrosis factor alpha (TNF-alpha) that occurred in response to the lethal dose of LPS. Moreover, a neutralizing antibody against TNF-alpha gave only partial protection when administered alone to BALB/cJ mice. Treatment with a combination of neutralizing antibodies against TNF-alpha and interferon-gamma (IFN-gamma) resulted in complete protection. In contrast to BALB/cJ mice, normal BDF1 mice were protected from lethal endotoxemia by treatment with both rMuIL-10 and rHuIL-10. However, IL-10 did not protect C. parvum-primed BDF1 against LPS lethality even though it caused a reduction in the LPS-induced serum TNF-alpha response in C. parvum-primed mice as well as in normal BDF1 mice. Neutralizing antibodies against TNF-alpha and IFN-gamma were protective when administered alone to normal BDF1 mice, as previously demonstrated in C. parvum-primed mice. These findings suggest that lethal endotoxemia is a result of the cooperative activities of TNF-alpha and IFN-gamma in normal mice of the BALB/cJ and BDF1 strains as well as in C. parvum-primed BDF1 mice. IL-10 appears to be less effective in protecting mice from lethal endotoxemia when cooperation between IFN-gamma and TNF-alpha is facilitated by high-level production of the cytokines as in C. parvum-primed mice or when there is evidence of strong synergy between them as in normal BALB/cJ mice.