Inhibition of interleukin-8 production in human endothelial cells by Staphylococcus aureus supernatant

Recent reports have shown that Staphylococcus aureus infection increases the expression of cytokines and cell adhesion molecules in endothelial cells and enhances leucocyte migration, thereby resulting in bacterial elimination. In this study, we analysed the production of the chemokine interleukin (IL)-8 in human umbilical vein endothelial cells (HUVEC) infected with several S. aureus strains by using reverse transcription-polymerase chain reaction and enzyme-linked immunosorbent assay. We found that the avirulent strains (00-51 and 00-62) increased IL-8 production but the virulent strains (A17 and A151) decreased it at both the mRNA and protein levels. We considered that the inhibition of IL-8 production depended on certain inhibitory factor(s) secreted by bacteria. This was because S. aureus also abolished IL-8 expression in HUVEC treated with cytochalasin D, and the addition of culture supernatants of strains A17 and A151 decreased IL-8 production in HUVEC. This factor(s) in the bacterial culture supernatant inhibited both basal and tumour necrosis factor (TNF)-alpha-induced IL-8 production. In contrast, no inhibitory effect was observed on monocyte chemotactic protein-1 (MCP-1) production. These results indicate that S. aureus can down-regulate IL-8 release in endothelial cells through the secretion of inhibitory factor(s), and this may result in decreased neutrophil recruitment, thus interfering with the host immune response to bacterial infection.