Acute respiratory distress syndrome (ARDS) is characterized by an excessive pulmonary inflammatory response. Removal of excess cholesterol from the plasma membrane of inflammatory cells helps reduce their activation. The secreted apolipoprotein A-I binding protein (AIBP) has been shown to augment cholesterol efflux from endothelial cells to the plasma lipoprotein HDL. Here, we find that AIBP was expressed in inflammatory cells in the human lung and was secreted into the bronchoalveolar space in mice subjected to inhalation of LPS. AIBP bound surfactant protein B and increased cholesterol efflux from alveolar macrophages to calfactant, a therapeutic surfactant formulation. In vitro, AIBP in the presence of surfactant reduced LPS-induced p65, ERK1/2 and p38 phosphorylation, and IL-6 secretion by alveolar macrophages. In vivo, inhalation of AIBP significantly reduced LPS-induced airspace neutrophilia, alveolar capillary leak, and secretion of IL-6. These results suggest that, similar to HDL in plasma, surfactant serves as a cholesterol acceptor in the lung. Furthermore, lung injury increases pulmonary AIBP expression, which likely serves to promote cholesterol efflux to surfactant and reduce inflammation.

This study examined the impact of an interleukin-6 (IL-6) knockout on fracture healing in terms of histological and biomechanical responses. Following IACUC approval, tibial fractures were produced in 4-to 6-week-old IL-6 knockouts (n ¼ 35) and wild-type mice (n ¼ 36) and harvested along with contralateral limbs at 2 and 6 weeks postsurgery. Histology quantified stage of healing, lymphocyte infiltration, TRAPþ cells, and osteocalcin deposition. Bend testing established maximum load and stiffness. Based on normality assessments, Mann-Whitney U or independent t-tests were used for data analysis using a p-value threshold of 0.05. Stage of healing, lymphocyte infiltration, and osteocalcin deposition were similar for all time points (p ! 0.243). TRAPþ cell counts were reduced approximately 10-fold in the knockout at 2 weeks (p ¼ 0.015) but were similar at 6 weeks (p ¼ 0.689). Force-to-failure in knockouts was approximately 40% that of wild-type mice at 2 weeks (p ¼ 0.040) but similar at 6 weeks (p ¼ 0.735). Knockout bone was about 25% less stiff at 2 weeks but approximately 60% stiffer at 6 weeks (p ! 0.110). The absence of IL-6 during early fracture healing significantly reduced osteoclastogenesis and impaired callus strength. By 6 weeks, most histological and biomechanical parameters were similar to fractures in wild-type bone. Keywords: cytokines; interleukin-6; fracture healing Inflammation is a key component to both wound and bony healing responses. Leukocytosis is a part of this phenomenom and is integral to fracture healing.1-3 In particular, neutrophil infiltration is apparently allied with establishing chondrogenesis, a sentinel component of endochondral ossification. 4Cytokines are also involved in regulating the healing response. IL-1 plays a prominent role in the early response to injury, 5-7 exerting both proliferative [7][8][9][10] and catabolic effects. 11 It also stimulates the expression of IL-6 by osteoblasts. [12][13][14] There is a substantial body of research that suggest that IL-6 exerts effects on bone homeostasis and repair. IL-6 stimulates production of RANK ligand by osteoblasts which, in turn, catalyzes the formation of osteoclasts from peripheral blood monocytes.15 It was shown to induce differentiation of pre-osteoblasts, [16][17][18] inhibit nodule formation in bone culture, 19 and induce cathepsin B production by osteoblasts.20 During distraction osteogenesis, IL-6 is produced by osteoblasts, hemopoietic cells, and cells associated with the lengthening callus. 21 Murine models of fracture healing have shown elevations in IL-6 during intramembranous callus remodeling 22 as well as secondary bone remodeling associated with endochondral ossification. 23 Recently, Yang et al. 24 provided insight into the effects of IL-6 on fracture healing, noting an impairment of osteoclastogenesis. Similarly, Axmann et al. 25 showed that abrogating IL-6 receptor function also reduced osteoclast counts in a model of inflammatory (RA) bone erosion.Given the importance of the inflammatory response ...

The myeloid C-type lectin receptor Dectin-2 directs the generation of Th2 and Th17 immune responses to the house dust mite Dermatophagoides farinae (Df) through the generation of cysteinyl leukotrienes (cys-LTs) and pro-inflammatory cytokines, respectively, but a role for Dectin-2 in effector phase responses has not been described. Here, we demonstrate that administration of the Dectin-2 mAb solely at the time of Df challenge abrogated eosinophilic and neutrophilic inflammation in the bronchoalveolar lavage (BAL) fluid and Th1, Th2, and Th17 inflammation in the lung of previously sensitized mice. Furthermore, Dectin-2 null mice (Clec4n−/−) sensitized with the adoptive transfer of Df-pulsed wild-type (WT) bone marrow-derived DCs (BMDCs) also had less Df-elicited pulmonary inflammation, supporting an effector function for Dectin-2. The protection from pulmonary inflammation seen with the Dectin-2 mAb or in Clec4n−/− mice was associated with little or no reduction in lung-draining lymph node cells or their cytokine production, and with no reduction in serum IgE. WT and Clec4n−/− mice recipients, sensitized with Df-pulsed WT BMDCs, had comparable levels of Df-elicited IL-6, IL-23, TNF-α, and cys-LTs in the lung. By contrast, Df-elicited CCL4 and CCL8 production from pulmonary CD11c+CD11b+Ly6C+ and CD11c+CD11b+Ly6C−CD64+ monocyte-derived DCs was reduced in Clec4n−/− recipients. Addition of CCL8 at the time of Df challenge abrogated the protection from eosinophilic, neutrophilic, and Th2 pulmonary inflammation seen in Clec4n−/− recipients. Taken together, these results reveal that Dectin-2 regulates monocyte-derived DC function in the pulmonary microenvironment at Df challenge to promote the local inflammatory response.

We have shown that obesity-associated attenuation of murine acute lung injury is driven, in part, by blunted neutrophil chemotaxis, yet differences were noted between the two models of obesity studied. We hypothesized that obesity-associated impairment of multiple neutrophil functions contributes to increased risk for respiratory infection but that such impairments may vary between murine models of obesity. We examined the most commonly used murine obesity models (diet-induced obesity, db/db, CPE fat/fat , and ob/ob) using a Klebsiella pneumoniae pneumonia model and LPS-induced pneumonitis. Marrow-derived neutrophils from uninjured lean and obese mice were examined for in vitro functional responses. All obesity models showed impaired clearance of K. pneumoniae, but in differing temporal patterns. Failure to contain infection in obese mice was seen in the db/db model at both 24 and 48 hours, yet this defect was only evident at 24 hours in CPE fat/fat and ob/ob models, and at 48 hours in diet-induced obesity. LPS-induced airspace neutrophilia was decreased in all models, and associated with blood neutropenia in the ob/ob model but with leukocytosis in the others. Obese mouse neutrophils from all models demonstrated impaired chemotaxis, whereas neutrophil granulocyte colony-stimulating factor-mediated survival, LPS-induced cytokine transcription, and mitogen-activated protein kinase and signal transducer and activator of transcription 3 activation in response to LPS and granulocyte colony-stimulating factor, respectively, were variably impaired across the four models. Obesity-associated impairment of host response to lung infection is characterized by defects in neutrophil recruitment and survival. However, critical differences exist between commonly used mouse models of obesity and may reflect variable penetrance of elements of the metabolic syndrome, as well as other factors.

The interactions between and the host environment at the site of infection are largely unknown. Pulmonary surfactant serves as an initial point of contact for inhaled bacteria entering the lung and is thought to contain molecular cues that aid colonization and pathogenesis. To gain insight into this ecological transition, we characterized the transcriptional response of MGH 78578 to purified pulmonary surfactant. This work revealed changes within the transcriptome that likely contribute to host colonization, adaptation, and virulence Notable transcripts expressed under these conditions include genes involved in capsule synthesis, lipopolysaccharide modification, antibiotic resistance, biofilm formation, and metabolism. In addition, we tested the contributions of other surfactant-induced transcripts to survival using engineered isogenic KPPR1 deletion strains in a murine model of acute pneumonia. In these infection studies, we identified the MdtJI polyamine efflux pump and the ProU glycine betaine ABC transporter to be significant mediators of survival within the lung and confirmed previous evidence for the importance of leucine synthesis to bacterial survival during infection. Finally, we determined that pulmonary surfactant promoted type 3 fimbria-mediated biofilm formation in and identified two surfactant constituents, phosphatidylcholine and cholesterol, that drive this response. This study provides novel insight into the interactions occurring between and the host at an important infection site and demonstrates the utility of purified lung surfactant preparations for dissecting host-lung pathogen interactions.