INVOLVEMENT OF THE MEMBRANE FORM OF TUMOR-NECROSIS-FACTOR-ALPHA 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 tumour necrosis factor-alpha (TNF-alpha) response s (desensitization/endotoxin tolerance) were accompanied by increased (priming) nitric oxide (NO) responses. Priming was also inducible with recombinant interferon-beta (IFN-beta). The requirement of TNF-alpha biosynthesis in the LPS-induced priming was also suggested by the obse rvation that both anti-TNF-alpha serum and pentoxifylline inhibited th is effect. However, addition of mouse recombinant TNF-alpha (mrTNF-alp ha) did not enhance the priming induced by LPS or IFN-beta, and preinc ubation with mrTNF-alpha alone, or in association with other cytokines produced by macrophages (interleukin-1 beta, interleukin-6, or leukae mia inhibitory factor), did not induce a priming effect. We found howe ver, that pentoxifylline, which blocked the priming, also decreased th e level of membrane-bound TNF-alpha. Furthermore, exposure to compound BB-3103 (a metalloproteinase inhibitor that blocks the processing of membrane-bound TNF-alpha yielding to the secreted cytokine) enhanced t he priming effect, the expression of membrane TNF-alpha and the specif ic binding of LPS. These observations suggest that the membrane form o f TNF-alpha is involved in the interaction of LPS with a receptor requ ired for LPS-induced priming.