We provide the first evidence for a link between polyamines and biofilm levels in Yersinia pestis, the causative agent of plague. Polyamine-deficient mutants of Y. pestis were generated with a single deletion in speA or speC and a double deletion mutant. The genes speA and speC code for the biosynthetic enzymes arginine decarboxylase and ornithine decarboxylase, respectively. The level of the polyamine putrescine compared to the parental speA ؉ speC ؉ strain (KIM6؉) was depleted progressively, with the highest levels found in the Y. pestis ⌬speC mutant (55% reduction), followed by the ⌬speA mutant (95% reduction) and the ⌬speA ⌬speC mutant (>99% reduction). Spermidine, on the other hand, remained constant in the single mutants but was undetected in the double mutant. The growth rates of mutants with single deletions were not altered, while the ⌬speA ⌬speC mutant grew at 65% of the exponential growth rate of the speA ؉ speC ؉ strain. Biofilm levels were assayed by three independent measures: Congo red binding, crystal violet staining, and confocal laser scanning microscopy. The level of biofilm correlated to the level of putrescine as measured by high-performance liquid chromatography-mass spectrometry and as observed in a chemical complementation curve. Complementation of the ⌬speA ⌬speC mutant with speA showed nearly full recovery of biofilm to levels observed in the speA ؉ speC ؉ strain. Chemical complementation of the double mutant and recovery of the biofilm defect were only observed with the polyamine putrescine.

Extensive data in a wide range of organisms point to the importance of polyamine homeostasis for growth. The two most common polyamines found in bacteria are putrescine and spermidine. The investigation of polyamine function in bacteria has revealed that they are involved in a number of functions other than growth, which include incorporation into the cell wall and biosynthesis of siderophores. They are also important in acid resistance and can act as a free radical ion scavenger. More recently it has been suggested that polyamines play a potential role in signaling cellular differentiation in Proteus mirabilis. Polyamines have also been shown to be essential in biofilm formation in Yersinia pestis. The pleiotropic nature of polyamines has made their investigation difficult, particularly in discerning any specific effect from more global growth effects. Here we describe key developments in the investigation of the function of polyamines in bacteria that have revealed new roles for polyamines distinct from growth. We describe the bacterial genes necessary for biosynthesis and transport, with a focus on Y. pestis. Finally we review a novel role for polyamines in the regulation of biofilm development in Y. pestis and provide evidence that the investigation of polyamines in Y. pestis may provide a model for understanding the mechanism through which polyamines regulate biofilm formation.

Chronic obstructive pulmonary disease (COPD) is a debilitating, progressive lung disease punctuated by exacerbations of symptoms. COPD exacerbations are most often associated with viral infections, and exposure to cigarette smoke (CS) followed by viral infection has been shown experimentally to enhance lung inflammation, tissue destruction, and airway fibrosis. Despite this, however, the cellular mechanisms responsible for this effect are unknown. In this study, we examined NK cell function in a mouse model of COPD given the vital role of NK cells following viral infection. Ex vivo stimulation of lung leukocytes with poly(I:C), ssRNA40, or ODN1826 enhanced production of NK cell-derived IFN-γ in CS-exposed mice. NK cells from CS-exposed mice exhibited a novel form of priming; highly purified NK cells from CS-exposed mice, relative to NK cells from filtered air-exposed mice, produced more IFN-γ following stimulation with IL-12, IL-18, or both. Further, NK cell priming was lost following smoking cessation. NKG2D stimulation through overexpression of Raet1 on the lung epithelium primed NK cell responsiveness to poly(I:C), ssRNA40, or ODN1826 stimulation, but not cytokine stimulation. In addition, NK cells from CS-exposed mice expressed more cell surface CD107a upon stimulation, demonstrating that the NK cell degranulation response was also primed. Together, these results reveal a novel mechanism of activation of the innate immune system and highlight NK cells as important cellular targets in controlling COPD exacerbations.

Chronic obstructive pulmonary disease (COPD) is characterized by peribronchial and perivascular inflammation and largely irreversible airflow obstruction. Acute disease exacerbations, due frequently to viral infections, lead to enhanced disease symptoms and contribute to long-term progression of COPD pathology. Previously, we demonstrated that NK cells from cigarette smoke (CS)-exposed mice exhibit enhanced effector functions in response to stimulating cytokines or toll-like receptor ligands. Here, we show that the activating receptor NKG2D is a key mediator for CS stimulated NK cell hyperresponsiveness as CS-exposed NKG2D-deficient mice (Klrk1-/-) did not exhibit enhanced effector functions as assessed by cytokine responsiveness. NK cell cytotoxicity against MHC class I-deficient targets was not affected in a COPD model. However, NK cells from CS-exposed mice exhibit greater cytotoxic activity towards cells that express the NKG2D ligand RAET1ε. We also demonstrate that NKG2D-deficent mice exhibit diminished airway damage and reduced inflammation in a model of viral COPD exacerbation without affecting viral clearance. Furthermore, adoptive transfer of NKG2D+ NK cells into CS-exposed, influenza-infected NKG2D-deficient mice recapitulated the phenotypes observed in CS-exposed, influenza-infected WT mice. Our findings indicate that NKG2D stimulation during long term CS-exposure is a central pathway in the development of NK cell hyperresponsiveness and influenza-mediated exacerbations of COPD.

Summary We previously showed that mutations in the genes encoding the two main biosynthetic enzymes responsible for polyamine production, arginine decarboxylase (SpeA) and ornithine decarboxylase (SpeC), cause a loss of biofilm formation in Yersinia pestis. In Y. pestis the development of a biofilm is dependent on 6 Hms (hemin storage) proteins (HmsH, F, R, S, T, and P) grouped into 3 operons; hmsHFRS, hmsT, and hmsP. In this article we show that polyamines are necessary to maintain the levels of key Hms proteins. In the absence of polyamines there is an ~93%, ~43%, and ~90% reduction in protein levels of HmsR, HmsS, and HmsT respectively. Over-expression of hmsR and hmsT from plasmids alone can restore biofilm formation to a SpeA− SpeC− mutant. Addition of exogenous putrescine also restores normal levels of HmsR, HmsS, HmsT, and biofilm production. Analyses using transcriptional reporters and quantitative RT-PCR indicate that the initiation of transcription and mRNA stability are not reduced by polyamine deficiency. Instead, translational reporters indicate that polyamines function at least in part by modulating the translation of HmsR and HmsT. Although construction of a consensus Shine-dalgarno sequence upstream of hmsT modestly reduced the stimulation of translation by putrescine, additional mechanisms likely contribute to the polyamine-dependent expression of HmsT. Finally, we have shown that polyamines play a role in bubonic plague.

Cigarette smoke (CS) exposure is the primary risk factor for the development of chronic obstructive pulmonary disease (COPD). COPD is characterized by chronic peribronchial, perivascular and alveolar inflammation. The inflammatory cells consist primarily of macrophage, neutrophils and lymphocytes. Although myeloid cells are well studied, the role of lymphocyte populations in pathogenesis of COPD remains unclear. Using a mouse model of CS-induced emphysema our laboratory has previously demonstrated that CS exposure causes changes in the T cell receptor repertoire suggestive of an antigen specific response and triggers a pathogenic T cell response sufficient to cause alveolar destruction and inflammation. We extend these findings to demonstrate that T cells from CS-exposed mice of Balb/cJ or C57B6 strain are sufficient to transfer pulmonary pathology to CS-naïve, immunosufficient mice. CS exposure causes a proinflammatory phenotype among pulmonary T cells consistent with from COPD patients. We provide evidence that donor T cells from CS-exposed mice depend on antigen recognition to transfer alveolar destruction using MHC class I deficient recipient mice. Neither CD4+ nor CD8+ T cells from donor mice exposed to CS are alone sufficient to cause inflammation or pathology in recipient mice. We found no evidence of impaired suppression of T cell proliferation among regulatory T cells from CS-exposed mice. These results suggest that CS exposure initiates an antigen specific response that leads to pulmonary destruction and inflammation that involves both CD8+ and CD4+ T cells. These results are direct evidence for an autoimmune response initiated by CS exposure.

Chronic Obstructive Pulmonary Disease (COPD) is a devastating disease with no effective therapies. We investigated the role of the C-type lectin receptor, CLEC5A, in macrophage activation and pulmonary pathogenesis in a mouse model of COPD. We demonstrate that CLEC5A is expressed on alveolar macrophages in mice exposed long-term to cigarette smoke (CS) and in human smokers. We also show that CLEC5A-mediated activation of macrophages enhanced cytokine elaboration alone, and in combination with LPS or GM-CSF in CS-exposed mice. Furthermore, using Clec5a-deficient mice, we demonstrate that CS-induced macrophage responsiveness is mediated by CLEC5A and CLEC5A is required for the development of inflammation, proinflammatory cytokine expression and airspace enlargement. These findings suggest a novel mechanism that promotes airway inflammation and pathologies in response to CS exposure and identifies CLEC5A as a novel target for the therapeutic control of COPD pathogenesis.

CCR7 is a chemokine receptor expressed on the surfaces of T cells, B cells, and mature dendritic cells that controls cell migration in response to the cognate ligands CCL19 and CCL21. CCR7 is critical for the generation of an adaptive T cell response. However, the roles of CCR7 in the host defense against pulmonary infection and innate immunity are not well understood. We investigated the role of CCR7 in the host defense against acute pulmonary infection with Pseudomonas aeruginosa. We intranasally infected C57BL/6 mice with P. aeruginosa and characterized the expression of CCR7 ligands and the surface expression of CCR7 on pulmonary leukocytes. In response to infection, expression of CCL19 and expression of CCL21 were oppositely regulated, and myeloid dendritic cells upregulated CCR7 expression. We further examined the effects of CCR7 deficiency on the inflammatory response to P. aeruginosa infection. We infected Ccr7 ؊/؊ and wild-type mice with P. aeruginosa and characterized the accumulation of pulmonary leukocytes, production of proinflammatory mediators, neutrophil activation, and bacterial clearance. CCR7 deficiency led to an accumulation of myeloid dendritic cells and T cells in the lung in response to infection. CCR7 deficiency resulted in higher expression of CD80 and CD86 on dendritic cells; increased production of interleukin-12/23p40 (IL-12/23p40), gamma interferon (IFN-␥), and IL-1␣; increased neutrophil respiratory burst; and, ultimately, increased clearance of acute P. aeruginosa infection. In conclusion, our results suggest that CCR7 deficiency results in a heightened proinflammatory environment in response to acute pulmonary P. aeruginosa infection and contributes to more efficient clearance.