Background: Acinetobacter baumannii is a nosocomial pathogen of increasing importance, but the pathogenic mechanism of this microorganism has not been fully explored. This study investigated the potential of A. baumannii to invade epithelial cells and determined the role of A. baumannii outer membrane protein A (AbOmpA) in interactions with epithelial cells.

SummaryAcinetobacter baumannii is an emerging opportunistic pathogen responsible for healthcare-associated infections. The outer membrane protein A of A. baumannii (AbOmpA) is the most abundant surface protein that has been associated with the apoptosis of epithelial cells through mitochondrial targeting. The nuclear translocation of AbOmpA and the subsequent pathology on host cells were further investigated. AbOmpA directly binds to eukaryotic cells. AbOmpA translocates to the nucleus by a novel monopartite nuclear localization signal (NLS). The introduction of rAbOmpA into the cells or a transient expression of AbOmpA-EGFP causes the nuclear localization of these proteins, while the fusion proteins of AbOmpADNLS-EGFP and AbOmpA with substitutions in residues lysine to alanine in the NLS sequences represent an exclusively cytoplasmic distribution. The nuclear translocation of AbOmpA induces cell death in vitro. Furthermore, the microinjection of rAbOmpA into the nucleus of Xenopus laevis embryos fails to develop normal embryogenesis, thus leading to embryonic death. We propose a novel pathogenic mechanism of A. baumannii regarding the nuclear targeting of the bacterial structural protein AbOmpA.

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Suppression of an excessive systemic inflammatory response is a promising and potent strategy for treating endotoxic sepsis. Indoleamine 2,3-dioxygenase (IDO), which is the rate-limiting enzyme for tryptophan catabolism, may play a critical role in various inflammatory disorders. In this study, we report a critical role for IDO in the dysregulated immune response associated with endotoxin shock. We found that IDO knockout (IDO ؊/؊ ) mice and 1-methyl-D-tryptophan-treated, endotoxin-shocked mice had decreased levels of the cytokines, TNF-␣, IL-6, and IL-12, and enhanced levels of IL-10. Blockade of IDO is thought to promote host survival in LPS-induced endotoxin shock, yet little is known about the molecular mechanisms that regulate IDO expression during endotoxin shock. In vitro and in vivo, IDO expression was increased by exogenous IL-12, but decreased by exogenous IL-10 in dendritic cells and splenic dendritic cells. Interestingly, whereas LPS-induced IL-12 levels in serum were higher than those of IL-10, the balance between serum IL-12 and IL-10 following challenge became reversed in IDO Sepsis is a systemic inflammatory response syndrome induced by microbial infection that is characterized by hemodynamic shock and multiple organ failure (1, 2). The pathogenesis of sepsis involves a progressive and dynamic expansion of a systemic inflammatory response to bacterial infection (3). Endotoxin, or LPS, is a major component of the outer membrane of Gram-negative bacteria; as such, it is an effective trigger of the inflammatory response during infection with Gram-negative bacteria. Uncontrolled activation of LPS-induced mechanisms results in sepsis. However, growing evidence supports the idea that LPS does not directly cause septic shock and tissue injury. Rather, it stimulates the production of proinflammatory cytokines, such as TNF-␣ and IL-1␤, which, in the context of massive infections associated with sepsis, can precipitate tissue injury and lethal shock (1, 4). It is a major cause of morbidity and mortality in hospitalized patients, yet effective treatment modalities remain elusive. Sepsis is associated with acute and systemic host immune responses; in the case of cell-mediated immune responses, the release of cytokines, such as TNF-␣, IL-1␤, IL-6, IL-12p70, and IFN-␥, is mechanistically involved in sepsis development (5). Immune and inflammatory systems are controlled by multiple proand anti-inflammatory cytokines, many of which are absent under normal, homeostatic conditions. However, massive bacterial infections cause the host to produce excessive amounts of proinflammatory cytokines that threaten the host's survival (6). Thus, the balance between proinflammatory and anti-inflammatory influences is likely a critical element in the mechanism of sepsis.Dendritic cells (DCs) 3 are potent APCs and provide costimulatory signals for innate and adaptive immune responses. For example, LPS promotes DC maturation and IL-12 secretion, which primes naive CD4 T cell toward a Th1 phenotype (7). In contrast, IL-10 produc...

Indoleamine 2,3-dioxygenase (IDO) catalyzes the initial and rate-limiting step in the degradation of tryptophan and is strongly induced in interferon-␥ (IFN␥)-stimulated dendritic cells (DCs). IDO has recently been established as a key enzyme inT-cell suppression-mediated immune tolerance to tumors. STAT1 phosphorylation appears to play an important role in the control of IDO expression by IFN␥, but the precise regulatory mechanism remains obscure. Here we present a novel mechanism of IFN␥-induced IDO expression in bone marrow-derived dendritic cells. In addition, we demonstrate that curcumin, an active component of turmeric, significantly inhibited the induction of IDO expression and activity by IFN␥. We found that curcumin suppressed STAT1 activation by directly inhibiting Janus-activated kinase 1/2 and protein kinase C␦ phosphorylation in bone marrow-derived DCs, suppressing the subsequent translocation and binding of STAT1 to the GAS element of the IRF-1 promoter. Coincident with these inhibitory effects on IFN␥-induced IDO expression, curcumin reversed IDO-mediated suppression of T-cell responses. Our results, thus, suggest that down-regulation of IDO in DCs is an important immunomodulatory property of curcumin that may be exploited therapeutically in the control of cancers.Dendritic cells (DCs) 3 are professional antigen-presenting cells that function as immune sentinels for the initiation of T-cell responses against microbial pathogens and tumors (1, 2). It is now well known that DCs not only induce immunity but are also important for the induction of T-cell tolerance. In particular, murine CD11c ϩ DCs that coexpress the markers CD8␣, B220, DX5, and DEC205 promote tolerance rather than immunity to specific antigens (3, 4). One of the mechanisms that might contribute to this tolerance in antigen-presenting cells involves the expression of the immunoregulatory enzyme indoleamine 2,3-dioxygenase (IDO).IDO catalyzes the initial and rate-limiting step in the catabolism of tryptophan along the kynurenine pathway. IDO has also recently been established as a key enzyme in T-cell suppression and the induction of immune tolerance (5-7). The expression of IDO by various cell types has broad immunological significance. In particular, in many tumors and tolerant antigen-presenting cells, IDO degrades tryptophan to kynurenine, leading to the depletion of tryptophan and resulting in the suppression of T-cell proliferation (8 -10). Recent in vivo studies suggest that IDO-expressing DCs isolated from tumordraining lymph nodes contribute to the progression of tumors by creating local immunosuppression (11-13).The control of IDO transcription is complex and cell typespecific (6). A number of pathways, including the mitogen-activated protein kinase and noncanonical NF-B signaling pathways as well as the Janus-activated kinase-signal transducer and activator of transcription (JAK-STAT) pathway, can modulate IDO expression in response to a variety of stimuli (14,15). In macrophages and DCs, transcription of the IDO gene is s...