Immune response to infection -: Interleukin-8 release from human neutrophils after phagocytosis of Listeria monocytogenes and Yersinia enterocolitica

The release of interleukin-8 (IL-8) from human neutrophils was investigated after their internalisation of the invasive bacteria Listeria monocytogenes and Yersinia enterocolitica. Three pairs of bacterial strains were used to study the influence of listeriolysin O, invasiveness and Yersinia virulence plasmid (pYV)-encoded proteins on neutrophil cytokine synthesis. The neutrophils secreted IL-8 into the culture supernate after exposure to all strains tested. With L. monocytogenes, the virulence factor listeriolysin O had no effect on IL-8 secretion, whereas a non-invasive mutant induced greater IL-8 release than the corresponding invasive strain. With Y. enterocolitica, expression of virulence plasmid-encoded proteins appeared to be responsible for diminished IL-8 release. Northern blot analysis showed that the induced IL-8 release was always accompanied by an enhanced level of cytoplasmic IL-8 mRNA. Cytokine priming of neutrophils with granulocyte macrophage colony-stimulating growth factor (GM-CSF), unlike granulocyte colony-stimulating factor (G-CSF), led to further enhancement of IL-8 secretion induced after internalisation of the bacteria. Again, the increased IL-8 release, from GM-CSF primed neutrophils, was accompanied by an increased level of cytoplasmic IL-8 mRNA. The results emphasise the role of IL-8 in neutrophil-mediated host defence mechanisms during the acute phase of L. monocytogenes and Y. enterocolitica infection.