Cellular visualization of tissue prokallikrein in human neutrophils and myelocytes

The vasoactive peptides bradykinin and kallidin (lysyl-bradykinin) have bee n implicated in diapedesis, a cellular process by which neutrophils migrate through endothelial cell gap junctions. The kinin peptides are released fr om their precursor moiety, kininogen, by the specific action of endoprotein ases, the kallikreins. Kininogens have been demonstrated on the surface of neutrophils. and the presence of a competent processing enzyme such as tiss ue prokallikrein in neutrophils has been postulated, but firm evidence for this is still lacking, We have raised antibodies to a synthetic peptide tha t is a sequence copy of the activation segment of human TK and demonstrated that the anti-peptide antibodies specifically recognized the zymogen but n ot the active form of kallikrein. Using these anti-peptide antibodies, we s howed by Western blotting, immunocytochemistry and electron microscopy that the tissue prokallikrein antigen was localized in neutrophils and their pr ecursor cells, the myelocytes. We further demonstrated by in sills hybridiz ation the presence of tissue kallikrein mRNA in the mature neutrophils and myelocytes. Our findings lend credence to the hypothesis that upon release and activation, neutrophil-borne TK acts on cell-associated kininogens to t rigger the release of kinins, which may open endothelial gates for neutroph il diapedesis.