| Research Abstract |
Polymorphonuclear leukocytes (PMN) play crucial roles in protecting hosts against invading microbes and in the pathogenesis of inflammatory tissue injury. Although PMN migrate into mucosal layers of digestive and respiratory tracts, only limited information is available of their fate and function in situ. We previously reported that, unlike circulating PMN (CPMN), PMN in the oral cavity spontaneously generate superoxide radical and nitric oxide (NO) in the absence of any stimuli. To understand the mechanism of spontaneous generation of reactive oxygen species, possible involvement of protein kinases was examined. When incubated at 37℃ in the absence of any ligands, phosphorylation of tyrosyl residues of various proteins in OPMN, such as 115, 85, 75, 63, and 55-kDa proteins, occurred within 20 s and reached a maximum at 3-5 min. This phosphorylation occurred with concomitant activation of lyn and syk kinase. Tyrosine kinase inhibitors, such as genistein and herbimycin A, inhibited the generation of reactive oxygen species by OPMN without affecting their secretion of myeloperoxidase. Inhibitors of protein kinase C (PKC) , such as 1-(5-isoquinolinesulfonyl)-3-methylpiperazine (H-7) and calphostine C, had no appreciable effect on the generation of reactive oxygen species. These results suggested that tyrosine kinase might underlie the mechanism for the spontaneous generation of reactive oxygen species by OPMN.
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