Internalization of Staphylococcus aureus by endothelial cells induces cytokine gene expression

Abstract

The ability of the vascular endothelium to elaborate cytokines in response to gram-positive sepsis has received limited attention. This study examined cytokine expression by human umbilical vein endothelial cells (EC) following infection with a gram-positive bacterial pathogen, Staphylococcus aureus. S. aureus infection of EC resulted in the production of interleukin-6 (IL-6) and IL-1␤. For IL-6, message was detected at 3 h after infection, protein was present at 24 h, and both message and protein persisted for 72 h. IL-1␤ message was detected at 12 h, IL-1␤ protein was detected at 24 h, and both persisted for 72 h. Message for colonystimulating factor 1 remained unaltered. UV-killed S. aureus also elicited IL-1␤ and IL-6 message and protein expression at 24 and 48 h. Twenty-one clinical isolates of S. aureus were tested, and all induced IL-6 release by 48 h. However, the laboratory strain 8325-4 did not induce cytokine expression at any time point and was internalized by EC 1,000-fold less than other strains were. Internalization of latex beads by EC did not induce IL-6 gene expression. Furthermore, cytochalasin D treatment of the EC prevented IL-1 and IL-6 induction by S. aureus but not by tumor necrosis factor alpha or lipopolysaccharide. These results indicate that S. aureus is a potent inducer of IL-1 and IL-6 in EC and that internalization of S. aureus by EC is necessary for their cytokine expression. Thus, our data suggest that the vascular endothelium may play an important role in the pathogenesis of septicemia caused by gram-positive organisms.

Variations among clinical isolates of Staphylococcus aureus to induce expression of E-selectin and ICAM-1 in human endothelial cells

“…These results are in accordance with reports showing internalization of Eselectin after stimulation of ECs with TNF-K [25]. HU-VEC have been reported to express IL-1L, IL-6, IL-8, granulocyte-colony stimulating factor and MCP-1 following infection with S. aureus [7,8,10,26]. IL-1L may activate HUVEC in an auto-or paracrine manner to express cell adhesion molecules.…”

“…Beekhuizen et al [11] used a single S. aureus strain, whereas we analyzed 18 di¡erent clinical isolates, some of which did not induce HUVEC-surface expression of E-selectin. Internalization of S. aureus into HUVEC is required for induction of cell adhesion molecules and cytokines, mere adhesion of bacteria to the cell surface is not su¤cient [7,11]. Viable and UV-killed, but not heat-killed bacteria are internalized [11].…”

Induction of monocyte chemoattractant protein-1 by Porphyromonas gingivalis in human endothelial cells

“…For that purpose, HUVEC were treated with cytochalasin D, an inhibitor of endocytosis. Cytochalasin D, acting as an inhibitor of actin polymerization, prevents uptake of bacteria without interfering with the binding of bacteria [16,25]. Cytochalasin D (1 Wg ml 31 ) treatment of HUVEC did not a¡ect E. coli LPS (0.1 Wg ml 31 )-or rFimA (5 Wg ml 31 )-induced MCP-1 mRNA expression ( Fig.…”

“…Bacteria play an active role in internalization, making certain species and strains more invasive than others. Cytochalasin D treatment of HUVEC prevented IL-1 and IL-6 induction by Staphylococcus aureus and a poorly internalized S. aureus strain did not induce cytokine gene expression in HUVEC [25]. Internalization of microorganisms was also critical for cytokine or adhesion molecule induction in response to Listeria monocytogenes and Candida albicans in endothelial cells [26,32].…”

“…P. gingivalis can adhere to and invade endothelial cells [16,22]. Endothelial cells function as non-professional phagocytes, and a variety of live or killed microorganisms, or even inert particles have been shown to be internalized by endothelial cells [25,26,31,32]. Bacteria play an active role in internalization, making certain species and strains more invasive than others.…”