interleukin-8 and Acinetobacter-Infections

Topics: Acinetobacter baumannii; Acinetobacter Infections; Adhesins, Bacterial; Animals; Apoptosis; Bacterial Adhesion; Cells, Cultured; Epithelial Cells; Human Umbilical Vein Endothelial Cells; Humans; Interleukin-6; Interleukin-8; Larva; Moths; Mutation; Phylogeny; Type V Secretion Systems; Umbilical Cord; Virulence; Virulence Factors

Mast cells serve important roles as sentinels against bacterial infection by secreting mediators stored in granules. Much of their effectiveness depends upon recruiting and/or modulating other immune cells. The location of mast cells implies that they recognize pathogens invading tissues or mucosal tissues. Acinetobacter baumannii is a gram-negative bacterium that is considered an emerging nosocomial pathogen and causes a wide range of infections associated with high morbidity and mortality. To date, the interaction of A. baumannii with mast cells remains unclear. In this study, we demonstrated an interaction between human LAD2 mast cells and A. baumannii in vitro. When LAD2 cells were co-cultured with live A. baumannii or Pseudomonas aeruginosa PAO1 in vitro for 4h, TNF-α and IL-8 were produced in the culture supernatant. These inflammatory cytokines were not detected in the supernatant after the cells were treated with live bacteria without serum. Gene expression analysis showed that TNF-α and IL-8 mRNA expression increased in A. baumannii- and P. aeruginosa-infected LAD2 cells. Scanning electron microscopy showed that A. baumannii was tightly attached to the surface of LAD2 cells and suggested that A. baumannii may bind to FcγRII (CD32) on LAD2 cells. TNF-α in the culture supernatant from A. baumannii-infected LAD2 cells, showed that PMN activation and migration increased in Boyden chamber assays. These results suggest that mast cells recognize and initiate immune responses toward A. baumannii by releasing the preformed mediator TNF-α to activate effector neutrophils.

Topics: Acinetobacter baumannii; Acinetobacter Infections; Bacterial Adhesion; Cell Line; Humans; Immunity; Inflammation; Interleukin-8; Mast Cells; Neutrophils; Receptors, IgG; Tumor Necrosis Factor-alpha

Hospital-acquired infections as a result of Acinetobacter baumannii have become problematic because of high rates of drug resistance. Although neutrophils play a critical role in early protection against bacterial infection, their interactions with A. baumannii remain largely unknown. To elucidate the interactions between A. baumannii and human neutrophils, we cocultured these cells and analyzed them by microscopy and flow cytometry. We found that A. baumannii adhered to neutrophils. We next examined neutrophil and A. baumannii infiltration into Matrigel basement membranes by an in vitro transmigration assay. Neutrophils were activated by A. baumannii, and invasion was enhanced. More interestingly, A. baumannii was transported together by infiltrating neutrophils. Furthermore, we observed by live cell imaging that A. baumannii and neutrophils moved together. In addition, A. baumannii-activated neutrophils showed increased IL-8 production. The transport of A. baumannii was suppressed by inhibiting neutrophil infiltration by blocking the effect of IL-8. A. baumannii appears to use neutrophils for transport by activating these cells via IL-8. In this study, we revealed a novel bacterial transport mechanism that A. baumannii exploits human neutrophils by adhering to and inducing IL-8 release for bacterial portage. This mechanism might be a new treatment target.

Topics: Acinetobacter; Acinetobacter baumannii; Acinetobacter Infections; Animals; Bacterial Adhesion; Bacterial Translocation; Cells, Cultured; Collagen Type I; Escherichia coli; Female; Gels; Humans; Interleukin-8; Membranes, Artificial; Mice; Mice, Inbred C3H; Neutrophils; Phagocytosis; Pseudomonas aeruginosa; Respiratory Burst; Species Specificity; Time-Lapse Imaging; Virulence

Infected airway epithelial cells up-regulate the expression of chemokines, chiefly IL-8, and antimicrobial molecules including beta-defensins (BD). Acinetobacter baumannii is a cause of hospital-acquired pneumonia. We examined whether A. baumannii induced the expressions of IL-8 and BD2 by airway epithelial cells and the receptors implicated in bacterial detection. A549 and human primary airway cells released IL-8 upon infection. A. baumannii-infected cells also increased the expression of BD2 which killed A. baummannii strains. IL-8 induction was via NF-kappaB and mitogen-activated kinases p38 and p44/42-dependent pathways. A. baumannii engaged Toll-like receptor (TLR) 2 and TLR4 pathways and A549 cells could use soluble CD14 as TLRs co-receptor. A. baumannii lipopolysaccharide stimulated IL-8 release by A549 cells and sCD14 facilitated the recognition of the lipopolysaccharide. Mass spectrometry analysis revealed that A. baumannii lipid A structure matches those with endotoxic potential. These results demonstrate that airway epithelial cells produce mediators important for A. baumannii clearance.

Topics: Acinetobacter baumannii; Acinetobacter Infections; beta-Defensins; Cell Line; Epithelial Cells; Host-Pathogen Interactions; Humans; Inflammation; Inflammation Mediators; Interleukin-8; Pneumonia; Respiratory System; Signal Transduction; Up-Regulation