Differential effects of Escherichia coli subtilase cytotoxin and Shiga toxin 2 on chemokine and proinflammatory cytokine expression in human macrophage, colonic epithelial, and brain microvascular endothelial cell lines.

Subtilase cytotoxin (SubAB) is the prototype of a recently emerged family of AB5 cytotoxins produced by Shiga-toxigenic Escherichia coli (STEC). Its mechanism of action involves highly specific A-subunit-mediated proteolytic cleavage of the essential endoplasmic reticulum (ER) chaperone BiP. Our previous in vivo studies showed that intraperitoneal injection of purified SubAB causes a major redistribution of leukocytes and elevated leukocyte apoptosis in mice, as well as profound splenic atrophy. In the current study, we investigated selected chemokine and proinflammatory cytokine responses to treatment with SubAB, a nontoxic derivative (SubAA272B), or Shiga toxin 2 (Stx2) in human macrophage (U937), brain microvascular endothelial (HBMEC), and colonic epithelial (HCT-8) cell lines, at the levels of secreted protein, cell-associated protein, and gene expression. Stx2 treatment upregulated expression of chemokines and cytokines at both the protein and mRNA levels. In contrast, SubAB induced significant decreases in secreted interleukin-8 (IL-8) and monocyte chemoattractant protein 1 (MCP-1) in all three tested cell lines and a significant decrease in secreted IL-6 in HBMECs. The downregulation of secreted chemokines or cytokines was not observed in SubAA272B-treated cells, indicating a requirement for BiP cleavage. The downregulation of secreted chemokines and cytokines by SubAB was not reflected at the mRNA and cell-associated protein levels, suggesting a SubAB-induced export defect.

The B subunit of an AB5 toxin produced by Salmonella enterica serovar Typhi up-regulates chemokines, cytokines, and adhesion molecules in human macrophage, colonic epithelial, and brain microvascular endothelial cell lines.

The principal function of bacterial AB5 toxin B subunits is to interact with glycan receptors on the surfaces of target cells and mediate the internalization of holotoxin. However, B subunit-receptor interactions also have the potential to impact cell signaling pathways and, in so doing, contribute to pathogenesis independently of the catalytic (toxic) A subunits. Various Salmonella enterica serovars, including Salmonella enterica serovar Typhi, encode an AB5 toxin (ArtAB), the A subunit of which is an ADP-ribosyltransferase related to the S1 subunit of pertussis toxin. However, although the A subunit is able to catalyze ADP-ribosylation of host G proteins, a cytotoxic phenotype has yet to be identified for the holotoxin. We therefore examined the capacity of the purified B subunit (ArtB) from S. Typhi to elicit cytokine, chemokine, and adhesion molecule responses in human macrophage (U937), colonic epithelial (HCT-8) cell, and brain microvascular endothelial cell (HBMEC) lines. Secretion of the chemokines monocyte chemotactic protein 1 (MCP-1) and interleukin 8 (IL-8) was increased in all three tested cell lines, with macrophage inflammatory protein 1α (MIP-1α), MIP-1ß, and granulocyte colony-stimulating factor (G-CSF) also significantly increased in U937 cells. ArtB also upregulated the cytokines tumor necrosis factor alpha (TNF-α) and IL-6 in HBMECs and HCT-8 cells, but not in U937 cells, while intercellular adhesion molecule 1 (ICAM-1) was upregulated in HCT-8 and U937 cells and vascular cell adhesion molecule 1 (VCAM-1) was upregulated in HBMECs. Thus, ArtB may contribute to pathogenesis independently of the A subunit by promoting and maintaining a strong inflammatory response at the site of infection.

Role of lipid rafts and flagellin in invasion of colonic epithelial cells by Shiga-toxigenic Escherichia coli O113:H21.

Shiga-toxigenic Escherichia coli (STEC) O113:H21 strains that lack the locus of enterocyte effacement (LEE) efficiently invade eukaryotic cells in vitro, unlike LEE-positive O157:H7 strains. We used a fliC deletion mutant of the O113:H21 STEC strain 98NK2 (98NK2ΔfliC) to show that invasion of colonic epithelial (HCT-8) cells is heavily dependent on production of flagellin, even though adherence to the cells was actually enhanced in the mutant. Flagellin binds and signals through Toll-like receptor 5 (TLR5), but there was no evidence that either TLR5, the adaptor protein myeloid differentiation primary response gene 88 (MyD88), or the serine kinase interleukin-1 receptor-associated kinase (IRAK) were required for invasion of HCT-8 cells by strain 98NK2, as judged by transfection, RNA knockdown, or inhibitor studies. However, pretreatment of cells with anti-asialo-GM1 significantly decreased 98NK2 invasion (by 40.8%), while neuraminidase treatment (which cleaves terminal sialic acid residues, thus converting GM1 into asialo-GM1) significantly increased invasion (by 70.7%). Pretreatment of HCT-8 cells with either the cholesterol-depleting agent methyl-ß-cyclodextrin (MßCD) or the tyrosine kinase inhibitor genistein significantly decreased invasion by 98NK2, indicating a potential role for lipid rafts in the invasion mechanism. Confocal microscopy also showed invading 98NK2 colocalized with lipid raft markers caveolin-1 and GM1. Interestingly, anti-asialo-GM1, neuraminidase, MßCD, and genistein have similar effects on the vestigial level of STEC invasion seen for STEC strain 98NK2ΔfliC, indicating that lipid rafts mediate a common step in flagellin-dependent and flagellin-independent cellular invasion.

Immunomodulatory effect of cytosine-phosphate-guanosine (CpG)-oligonucleotides in nonasthmatic chronic rhinosinusitis: an explant model.

BACKGROUND: The use of cytosine-phosphate-guanosine-oligodeoxynucleotides (CpG-ODNs) or immunostimulatory sequences (ISSs) in the treatment of airway diseases is gaining interest. Binding of the CpG-ODN ligand to Toll-like receptor 9 (TLR9) triggers a shift from a Th2- to a Th1-type response in the target tissue. In this study, we explored the potential use of CpG-ODN to dampen the predominantly Th2-driven chronic inflammatory state in our cohort of patients. METHODS: An in vitro explant model comprising of sinonasal tissue from patients with asthma (n = 12) and without asthma (n = 11) were stimulated with CpG-ODN or Staphylococcus aureus enterotoxin B (SEB) or CpG-ODN in combination with SEB for 48 hours. Ten of the 12 asthma patients had nasal polyps. RNA was extracted for multiplex real-time reverse transcription polymerase chain reaction analysis and the 2(-delta deltaC(T)) method used to determine interleukin (IL)-5, p35 IL-12, interferon (IFN) gamma, and TLR9 expression levels. RESULTS: CpG-ODN significantly reduced IL-5 mRNA expression in patients without asthma (p = 0.0379) but not in the asthma-associated group. SEB alone caused an increase in IL-5 levels that could be dampened when CpG-ODN was added in combination with SEB. Significant differences in mean IL-5 expression levels between the asthmatic and nonasthmatic categories were detected (Welch t-test; **p = 0.0041). Asthmatic and nonasthmatic patients present as two distinct categories as reflected by significant differences in their IL-5 response to CpG-ODN (F = 11.93; ***p = 0.0008), SEB (F = 41.34; *p = 0.0476) and CpG-ODN with SEB (F = 13.2; *p = 0.0114). In contrast, no significant differences were observed in the expression levels of IL-12, IFN-gamma, and TLR9. CONCLUSION: Localized application of CpG-ODN on its own or in combination with SEB may potentially reduce the expression of the proinflammatory cytokine IL-5 in nonasthmatic patients and may be further developed as an immunotherapeutic agent.

Enhanced CXC chemokine responses of human colonic epithelial cells to locus of enterocyte effacement-negative shiga-toxigenic Escherichia coli.

There is increasing evidence that by facilitating translocation of Shiga toxin (Stx) across the intestinal epithelium and by transporting bound toxin to remote sites such as the renal endothelium, polymorphonuclear leukocytes (PMNs) play a key role in the pathogenesis of Shiga-toxigenic Escherichia coli (STEC) disease. Plasma levels of PMN-attracting CXC chemokines such as interleukin-8 (IL-8) also appear to correlate in humans with the severity of disease. Thus, the capacity of STEC strains to elicit CXC chemokine responses in intestinal epithelial cells may be a crucial step in pathogenesis. Accordingly, we attempted to determine which STEC factors are responsible for CXC chemokine induction in human colonic epithelial cells. Infection of Hct-8 cells with locus for enterocyte effacement (LEE)-negative STEC strains isolated from patients with severe STEC disease resulted in up-regulation of IL-8, macrophage inflammatory protein 2alpha (MIP-2alpha), MIP-2beta, and ENA-78 mRNA significantly higher and earlier than that elicited by several LEE-positive STEC strains, including the O157:H7 strain EDL933. Similarly, levels of IL-8 protein in LEE-negative STEC-infected Hct-8 culture supernatants were significantly higher than in LEE-positive STEC-infected culture supernatants. The difference in responses could not be attributed to the expression or nonexpression of LEE genes, the presence or absence of an STEC megaplasmid, or differences in O serogroups or in the type or amount of Stx produced. Interestingly, however, several of the LEE-negative STEC strains eliciting the strongest chemokine responses belonged to flagellar serotype H21. Incubation of Hct-8 cells with isolated H21 flagellin elicited IL-8 and MIP-2alpha responses similar to those seen in the presence of the most potent LEE-negative STEC strains. Deletion of the fliC gene, but not the stx(2) gene, largely abolished the capacity of O113:H21 LEE-negative STEC strain 98NK2 to elicit IL-8 and MIP-2alpha responses in Hct-8 cells. Taken together, these data suggest that although Stx is capable of inducing CXC chemokine responses, the elevated responses seen in cells infected with certain STEC strains are largely attributable to the production of flagellin.