TRANSCELLULAR BIOSYNTHESIS OF LIPOXIN A(4) DURING ADHESION OF PLATELETS AND NEUTROPHILS IN EXPERIMENTAL IMMUNE-COMPLEX GLOMERULONEPHRITIS

Polymorphonuclear neutrophils are important effecters of injury in hos t defense and inflammation. Many inflammatory diseases are self-limiti ng, raising the possibility that compounds are generated in vivo durin g the course of inflammation that inhibit neutrophil recruitment and t issue destruction. Lipoxins, a more recent addition to the families of bioactive eicosanoids, are potential candidates in this regard. Lipox ins are generated via pathways that initially involve the dual lipoxyg enation of arachidonic acid and are potent inhibitors of several neutr ophil trafficking events in vitro. Here, we present evidence that lipo xin A(4) is generated in rat kidneys during experimental immune comple x-mediated glomerulonephritis in vivo. Renal lipoxin A(4) levels were markedly reduced by prior depletion of animals of either neutrophils o r platelets, suggesting that most lipoxin A(4) generated in vivo was d erived from transcellular biosynthetic pathways during platelet-neutro phil interactions. Electron microscopic examination of glomerulonephri tic kidneys revealed areas of intimate contact between neutrophils and platelets within the lumen of glomerular capillaries. P-selectin on p latelets is an important mediator of platelet-neutrophil adhesion in v itro and in vivo. Prior treatment of animals with a blocking monoclona l antibody (mAb) against P-selectin (mAb CY1747), but not an isotype-m atched non-blocking control mAb (mAb PNB1.6), caused striking inhibiti on of lipoxin A(4) generation without attenuating neutrophil recruitme nt. Anti-P-selectin mAb also blunted transcellular lipoxin A(4) genera tion during coincubations of activated neutrophils and platelets in vi tro. Together, these data suggested that adhesion of activated platele ts and neutrophils through P-selectin within glomerular capillaries en hances transcellular lipoxin A(4) formation by priming lipoxygenase pa thways of adherent cells and/or by facilitating the transfer of arachi donate intermediates between adherent platelets and neutrophils. Lipox in A(4) inhibits neutrophil chemotaxis, adhesion to endothelial cells and diapedesis in some in vitro systems, and exposure of neutrophils t o lipoxin A(4) ex vivo in the present study resulted in striking atten uation of their recruitment to inflamed glomeruli. These observations provide evidence that neutrophil adhesion, in addition to facilitating neutrophil recruitment during the initial stages of inflammation, als o promotes transcellular generation of lipid-derived signals that regu late neutrophil trafficking and may contribute to the suppression of n eutrophil-mediated tissue injury.