Roles of tumor necrosis factor and macrophages in lipopolysaccharide-induced accumulation of neutrophils in cutaneous air pouches

The role of tumor necrosis factor (TNF) in macrophage-dependent neutrophil accumulation induced by lipopolysaccharide (LPS) was examined through the use of cutaneous air pouches formed on the backs of mice. To investigate the possibility that TNF functions in LPS-induced neutrophil accumulation, we injected LPS into newly formed air pouches (containing relatively few endogenous macrophages), 48-h-old air pouches (containing large numbers of endogenous macrophages), or newly formed air pouches instilled with 10(6) alveolar macrophages (AM). Six hours after LPS injection, air pouches possessing either AM or endogenous macrophages contained large numbers of neutrophils. Infusion of anti-TNF immunoglobulin G into the air pouches inhibited LPS-induced neutrophil accumulation by 84% in air pouches containing AM and 71% in air pouches containing large numbers of endogenous macrophages. TNF was also capable of including neutrophil accumulation when injected into air pouches containing relatively large numbers of either endogenous or exogenous macrophages but not when injected into air pouches containing small numbers of macrophages. In addition, incubation of AM in vitro with TNF induced the AM to cause neutrophil accumulation upon injection into newly formed air pouches. These results indicate that TNF functions in LPS-induced neutrophil accumulation. Furthermore, the results indicate that TNF functions by enhancing the ability of macrophages to cause neutrophil emigration. This is consistent with the possibility that LPS induces TNF production and that TNF, in turn, induces macrophages to produce cytokines with inflammatory activities.