Involvement of the membrane form of tumour necrosis factor-α in lipopolysaccharide-induced priming of mouse peritoneal macrophages for enhanced nitric oxide response to lipopolysaccharide

We studied the pathways of macrophage response to lipopolysaccharide (LPS). When mouse macrophages pre-exposed to LPS were restimulated with this agent, reduced turmour necrosis factor-α (TNF-α) responses (desensitization/endotoxin tolerance) were accompanied by increased (priming) nitric oxide (NO) responses. Priming was also inducible with recombinant interferon-β (IFN-β). The requirement of TNF-α biosynthesis in the LPS-induced priming was also suggested by the observation that both anti-TNF-α serum and pentoxifylline inhibited this effect. However, addition of mouse recombinant TNF-α (mrTNF-α) did not enhance the priming induced by LPS or IFN-β, and preincubation with mrTNF-α alone, or in association with other cytokines produced by macrophages (interleukin-1β, interleukin-6, or leukaemia inhibitory factor), did not induce a priming effect. We found however, that pentoxifylline, which blocked the priming, also decreased the level of membrane-bound TNF-α. Furthermore, exposure to compound BB-3103 (a metalloproteinase inhibitor that blocks the processing of membrane-bound TNF-α yielding to the secreted cytokine) enhanced the priming effect, the expression of membrane TNF-α and the specific binding of LPS. These observations suggest that the membrane form of TNF-α is involved in the interaction of LPS with a receptor required for LPS-induced priming.