Cytokine production after intravenous or peritoneal gram-negative bacterial challenge in mice: Comparative protective efficacy of antibodies to tumor necrosis factor-α and to lipopolysaccharide

The production of TNF-α, IL-1, and IL-6 was measured in mice after bolus i.v. Escherichia coli O111 LPS injections and during bacteremia induced either by bolus i.v. or by i.p. challenges of live E. coli O111. High but transient TNF-α peaks were observed after bolus i.v. LPS or bacterial challenges. In contrast, the levels during lethal peritonitis increased progressively to values 50- to 100-fold lower than the peak values observed after i.v. injections, and remained sustained until death. Whereas after i.v. challenge with 1000 LD₅₀ of LPS, anti-TNF-α antibody fully protected mice from death and reduced serum IL-1 and IL-6 levels, anti-TNF-α antibody did not improve the survival of mice nor reduced serum IL-1 and IL-6 levels after i.p. bacterial challenge. In contrast to anti-TNF-α antibodies, anti-LPS antibodies were protective in the peritonitis model. Protection was accompanied by a striking reduction of bacterial numbers and of TNF-α, IL-1, and IL-6 levels in the serum, but the levels of these cytokines were only marginally affected in the peritoneal lavage fluid. This latter observation demonstrates that the local peritoneal cytokines did not diffuse readily into the circulation, thus suggesting that at least part of the circulating cytokines are produced systemically. In conclusion, the striking differences between cytokine profiles as well as the divergent efficacy of anti-TNF-α antibody after i.v. bolus and after i.p. challenges suggest that TNF-α may not be as important in the pathogenesis of lethal peritonitis than after lethal acute bacteremia.