Transcellular biosynthesis of lipoxin A4 during adhesion of platelets and neutrophils in experimental immune complex glomerulonephritis

Abstract

Polymorphonuclear neutrophils are important effectors of injury in host defense and inflammation. Many inflammatory diseases are self-limiting, raising the possibility that compounds are generated in vivo during the course of inflammation that inhibit neutrophil recruitment and tissue destruction. Lipoxins, a more recent addition to the families of bioactive eicosanoids, are potential candidates in this regard. Lipoxins are generated via pathways that initially involve the dual lipoxygenation of arachidonic acid and are potent inhibitors of several neutrophil trafficking events in vitro. Here, we present evidence that lipoxin A4 is generated in rat kidneys during experimental immune complex-mediated glomerulonephritis in vivo. Renal lipoxin A4 levels were markedly reduced by prior depletion of animals of either neutrophils or platelets, suggesting that most lipoxin A4 generated in vivo was derived from transcellular biosynthetic pathways during platelet-neutrophil interactions. Electron microscopic examination of glomerulonephritic kidneys revealed areas of intimate contact between neutrophils and platelets within the lumen of glomerular capillaries. P-selectin on platelets is an important mediator of platelet-neutrophil adhesion in vitro and in vivo. Prior treatment of animals with a blocking monoclonal antibody (mAb) against P-selectin (mAb CY1747), but not an isotype-matched non-blocking control mAb (mAb PNB1.6), caused striking inhibition of lipoxin A4 generation without attenuating neutrophil recruitment. Anti-P-selectin mAb also blunted transcellular lipoxin A4 generation during coincubations of activated neutrophils and platelets in vitro. Together, these data suggested that adhesion of activated platelets and neutrophils through P-selectin within glomerular capillaries enhances transcellular lipoxin A4 formation by priming lipoxygenase pathways of adherent cells and/or by facilitating the transfer of arachidonate intermediates between adherent platelets and neutrophils. Lipoxin A4 inhibits neutrophil chemotaxis, adhesion to endothelial cells and diapedesis in some in vitro systems, and exposure of neutrophils to lipoxin A4 ex vivo in the present study resulted in striking attenuation 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, also promotes transcellular generation of lipid-derived signals that regulate neutrophil trafficking and may contribute to the suppression of neutrophil-mediated tissue injury.