Surfactant protein-D regulates soluble CD14 through matrix metalloproteinase-12

Flotillins affect LPS-induced TLR4 signaling by modulating the trafficking and abundance of CD14

Lipopolysaccharide (LPS) induces a strong pro-inflammatory reaction of macrophages upon activation of Toll-like receptor 4 (TLR4) with the assistance of CD14 protein. Considering a key role of plasma membrane rafts in CD14 and TLR4 activity and the significant impact exerted on that activity by endocytosis and intracellular trafficking of the both LPS acceptors, it seemed likely that the pro-inflammatory reaction could be modulated by flotillins. Flotillin-1 and -2 are scaffolding proteins associated with the plasma membrane and also with endo-membranes, affecting both the plasma membrane dynamics and intracellular protein trafficking. To verify the above hypothesis, a set of shRNA was used to down-regulate flotillin-2 in Raw264 cells, which were found to also become deficient in flotillin-1. The flotillin deficiency inhibited strongly the TRIF-dependent endosomal signaling of LPS-activated TLR4, and to a lower extent also the MyD88-dependent one, without affecting the cellular level of TLR4. The flotillin depletion also inhibited the pro-inflammatory activity of TLR2/TLR1 and TLR2/TLR6 but not TLR3. In agreement with those effects, the depletion of flotillins down-regulated the CD14 mRNA level and the cellular content of CD14 protein, and also inhibited constitutive CD14 endocytosis thereby facilitating its shedding. Ultimately, the cell-surface level of CD14 was markedly diminished. Concomitantly, CD14 recycling was enhanced via EEA1-positive early endosomes and golgin-97-positive trans-Golgi network, likely to compensate for the depletion of the cell-surface CD14. We propose that the paucity of surface CD14 is the reason for the down-regulated signaling of TLR4 and the other TLRs depending on CD14 for ligand binding.

Atheroma-Relevant 7-Oxysterols Differentially Upregulate Cd14 Expression

The expression of CD14 in monocytic cells is elevated in atherosclerotic lesions where 7-oxyterols are abundant. However, it remains unknown whether atheroma-relevant 7-oxysterols are involved in receptor expression. Therefore, we investigated the effects of 7α-hydroxycholesterol (7αOHChol), 7β-hydroxycholesterol (7βOHChol), and 7-ketocholesterol (7K) on CD14 levels in THP-1 cells. The three 7-oxysterols increased CD14 transcript levels at a distinct time point, elevated cellular CD14 protein levels, and promoted the release of soluble CD (sCD14) from THP-1 cells. Our data revealed that CD14 expression was most strongly induced after treatment with 7αOHChol. Moreover, 7αOHChol alone upregulated membrane-bound CD14 levels and enhanced responses to lipopolysaccharides, as determined by CCL2 production and monocytic cell migration. The 7-oxysterols also increased the gelatinolytic activity of MMP-9, and a cell-permeable, reversible MMP-9 inhibitor, MMP-9 inhibitor I, significantly impaired sCD14 release. These results indicate that 7-oxysterols differentially induce CD14 expression in vascular cells and contribute to the monocytic cell expression of CD14 via overlapping, but distinct, mechanisms.

Intravenous surfactant protein D inhibits lipopolysaccharide-induced systemic inflammation

BACKGROUND

Surfactant protein D (SP-D) is an innate host defense protein that clears infectious pathogens from the lung and regulates pulmonary host defense cells. SP-D is also detected in lower concentrations in plasma and many other non-pulmonary tissues. Plasma levels of SP-D increase during infection and other proinflammatory states; however, the source and functions of SP-D in the systemic circulation are largely unknown. We hypothesized that systemic SP-D may clear infectious pathogens and regulate host defense cells in extrapulmonary systems.

METHODS

To determine if SP-D inhibited inflammation induced by systemic lipopolysaccharide (LPS), E.coli LPS was administered to mice via tail vein injection with and without SP-D and the inflammatory response was measured.

RESULTS

Systemic SP-D has a circulating half-life of 6 h. Systemic IL-6 levels in mice lacking the SP-D gene were similar to wild type mice at baseline but were significantly higher than wild type mice following LPS treatment (38,000 vs 29,900 ng/ml for 20 mg/kg LPS and 100,700 vs 73,700 ng/ml for 40 mg/kg LPS). In addition, treating wild type mice with purified intravenous SP-D inhibited LPS induced secretion of IL-6 and TNFα in a concentration dependent manner. Inhibition of LPS induced inflammation by SP-D correlated with SP-D LPS binding suggesting SP-D mediated inhibition of systemic LPS requires direct SP-D LPS interactions.

CONCLUSIONS

Taken together, the above results suggest that circulating SP-D decreases systemic inflammation and raise the possibility that a physiological purpose of increasing systemic SP-D levels during infection is to scavenge systemic infectious pathogens and limit inflammation-induced tissue injury.

CD14 recycling modulates LPS-induced inflammatory responses of murine macrophages

TLR4 is activated by the bacterial endotoxin lipopolysaccharide (LPS) and triggers two pro-inflammatory signaling cascades: a MyD88-dependent one in the plasma membrane, and the following TRIF-dependent one in endosomes. An inadequate inflammatory reaction can be detrimental for the organism by leading to sepsis. Therefore, novel approaches to therapeutic modulation of TLR4 signaling are being sought after. The TLR4 activity is tightly connected with the presence of CD14, a GPI-anchored protein that transfers LPS monomers to the receptor and controls its endocytosis. In this study we focused on CD14 trafficking as a still poorly understood factor affecting TLR4 activity. Two independent assays were used to show that after endocytosis CD14 can recycle back to the plasma membrane in both unstimulated and stimulated cells. This route of CD14 trafficking can be controlled by sorting nexins (SNX) 1, 2, and 6, and is important for maintaining the surface level and the total level of CD14, but can also affect the amount of TLR4. Silencing of these SNXs attenuated especially the CD14-dependent endosomal signaling of TLR4, making them a new target for therapeutic regulation of the inflammatory response of macrophages to LPS.

Advanced glycation end-products reduce lipopolysaccharide uptake by macrophages

Hyperglycaemia provides a suitable environment for infections and the mechanisms of glucose toxicity include the formation of advanced glycation end-products (AGEs), which comprise non-enzymatically glycosylated proteins, lipids, and nucleic acid amino groups. Among AGE-associated phenotypes, glycolaldehyde-derived toxic AGE (AGE-3) is involved in the pathogenesis of diabetic complications. Internalisation of endotoxin by various cell types contributes to innate immune responses against bacterial infection. An endotoxin derived from Gram-negative bacteria, lipopolysaccharide (LPS), was reported to enhance its own uptake by RAW264.7 mouse macrophage-like cells, and an LPS binding protein, CD14, was involved in the LPS uptake. The LPS uptake induced the activation of RAW264.7 leading to the production of chemokine CXC motif ligand (CXCL) 10, which promotes T helper cell type 1 responses. Previously, we reported that AGE-3 was internalised into RAW264.7 cells through scavenger receptor-1 Class A. We hypothesized that AGEs uptake interrupt LPS uptake and impair innate immune response to LPS in RAW264.7 cells. In the present study, we found that AGE-3 attenuated CD14 expression, LPS uptake, and CXCL10 production, which was concentration-dependent, whereas LPS did not affect AGE uptake. AGEs were reported to stimulate the receptor for AGEs and Toll-like receptor 4, which cause inflammatory reactions. We found that inhibitors for RAGE, but not Toll-like receptor 4, restored the AGE-induced suppression of CD14 expression, LPS uptake, and CXCL10 production. These results indicate that the receptor for the AGE-initiated pathway partially impairs the immune response in diabetes patients.

Reblastatins Inhibit Phenotypic Changes of Monocytes/Macrophages in a Milieu Rich in 27-Hydroxycholesterol

We investigated effects of reblastatins on phenotypic changes in monocytes/macrophages induced by 27-hydroxycholesterol (27OHChol). Treatment of THP-1 monocytic cells with reblastatin derivatives, such as 17-demethoxy-reblastatin (17-DR), 18-dehydroxyl-17-demethoxyreblastatin (WK88-1), 18-hydroxyl-17-demethoxyreblastatin (WK88-2), and 18-hydroxyl-17-demethoxy-4,5-dehydroreblastatin (WK88-3), resulted in blockage of CCL2, CCL3, and CCL4 expression at the transcription and protein levels, which, in turn, impaired migration of monocytes/macrophages and Jurkat T cells expressing CCR5, and almost complete inhibition of transcription of M1 marker cytokines, like CXCL10, CXCL11, and TNF-α. Reblastatins also downregulated surface CD14 as well as soluble CD14 along with inhibition of LPS response and matrix metalloprotease-9 expression. Surface levels of mature dendritic cell (mDC)-specific markers, including CD80, CD83, CD88, CD197, and MHC class I and II molecules, were remarkably down-regulated, and 27OHChol-induced decrease of endocytic activity was recovered following treatment with 17-DR, WK88-1, WK88-2, and WK88-3. However, 15-hydroxyl-17-demethoxyreblastatin (DHQ3) did not affect the molecular or functional changes in monocytic cells induced by 27OHChol. Furthermore, surface levels of CD105, CD137, and CD166 were also down-regulated by 17-DR, WK88-1, WK88-2, and WK88-3, but not by DHQ3. Collectively, results of the current study indicate that, except DHQ3, reblastatins regulate the conversion and differentiation of monocytic cells to an immunostimulatory phenotype and mDCs, respectively, which suggests possible applications of reblastatins for immunomodulation in a milieu rich in oxygenated cholesterol molecules.

Prednisolone suppresses the immunostimulatory effects of 27-hydroxycholesterol

In cholesterol-fed rabbits, site-specific targeting of prednisolone nanoparticles results in significantly reduced neo-intimal inflammation with a decreased infiltration of monocytes/macrophages. To understand the molecular mechanisms underlying this, the current study investigated whether prednisolone affects the immune attributes of 27-hydroxycholesterol (27OHChol), the major oxidized cholesterol molecule in circulation and tissue, in human (THP-1) monocyte/macrophage cells. THP-1 cells were exposed to 27OHChol in the presence of prednisolone followed by evaluation of inflammatory molecules at mRNA and protein levels by quantitative PCR, western blotting, ELISA and flow cytometry. The results revealed that prednisolone suppressed the 27OHChol-mediated expression of various macrophage (M)1 markers, including chemokine ligand 2, C-X-C chemokine motif 10, tumor necrosis factor-α and CD80. Treatment also impaired the 27OHCHol-enhanced migration of monocytic cells, downregulated the 27OHChol-induced cell surface expression of CD14 and inhibited the release of soluble CD14 comparable with a weakened lipopolysaccharide response. Furthermore, prednisolone suppressed the 27OHChol-induced expression of matrix metalloproteinase 9 at the transcriptional and protein level, as well as the phosphorylation of the p65 subunit. Prednisolone increased the transcription of CD163 and CD206 genes, and augmented the 27OHChol-induced transcription of CD163 without upregulating the 27OHChol-induced surface protein level of the gene. The results indicated that prednisolone inhibited the polarization of monocytes/macrophages towards the M1 phenotype, which that the immunostimulatory effects of 27OHCHol were being regulated and the immune responses in conditions that were rich in oxygenated cholesterol molecules were being modulated.

Effect of soluble cleavage products of important receptors/ligands on efferocytosis: Their role in inflammatory, autoimmune and cardiovascular disease

Efferocytosis, the clearance of apoptotic cells (ACs), is a physiologic, multifaceted and dynamic process and a fundamental mechanism for the preservation of tissue homeostasis by avoiding unwanted inflammation and autoimmune responses through special phagocytic receptors. Defective efferocytosis is associated with several disease states, including cardiovascular disease and impaired immune surveillance, as occurs in cancer and autoimmune disease. A major cause of defective efferocytosis is non-functionality of surface receptors on either the phagocytic cells or the ACs, such as TAM family tyrosine kinase, which turns to a soluble form by cleavage/shedding or alternative splicing. Recently, soluble forms have featured prominently as potential biomarkers, indicative of prognosis and enabling targeted therapy using several commonly employed drugs and inhibitors, such as bleomycin, dexamethasone, statins and some matrix metalloproteinase inhibitors such as TAPI-1 and BB3103. Importantly, to design drug carriers with enhanced circulatory durability, the adaptation of soluble forms of physiological receptors/ligands has been purported. Research has shown that soluble forms are more effective than antibody forms in enabling targeted treatment of certain conditions, such as autoimmune diseases. In this review, we sought to summarize the current knowledge of these soluble products, how they are generated, their interactions, roles, and their potential use as biomarkers in prognosis and treatment related to inflammatory, cardiovascular, and autoimmune diseases.

Genetic variation of matrix metalloproteinase enzyme in HIV-associated neurocognitive disorder

Matrix metalloproteinases (MMPs) play a key role in several diseases such as rheumatoid arthritis, HIV-associated neurological diseases (HAND), multiple sclerosis, osteoporosis, stroke, Alzheimer's disease, certain viral infections of the central nervous system, cancer, and hepatitis C virus. MMPs have been explained with regards to extracellular matrix remodeling, which occurs throughout life and ranges from tissue morphogenesis to wound healing in various processes. MMP are inhibited by endogenous tissue inhibitors of metalloproteinases (TIMPs). Matrix metalloproteases act as an interface between host's attack by Tat protein of HIV-1 virus and extracellular matrix, which causes breaches in the endothelial barriers by degrading ECM. This process initiates the dissemination of virus in tissues which can lead to an increase HIV-1 infection. MMPs are diverse and are highly polymorphic in nature, hence associated with many diseases. The main objective of this review is to study the gene expression of MMPs in HIV-related diseases and whether TIMPs and MMPs could be related with disease progression, HIV vulnerability and HAND. In this review, a brief description on the classification, regulation of MMP and TIMP, the effect of different MMPs and TIMPs gene polymorphisms and its expression on HIV-associated diseases have been provided. Previous studies have shown that MMPs polymorphism (MMP-1, MMP-2 MMP3, and MMP9) plays an important role in HIV vulnerability, disease progression and HAND. Further research is required to explore their role in pathogenesis and therapeutic perspective.

Magnesium sulfate inhibits binding of lipopolysaccharide to THP-1 cells by reducing expression of cluster of differentiation 14

We investigated effects of magnesium sulfate (MgSO₄) on modulating lipopolysaccharide (LPS)-macrophage binding and cluster of differentiation 14 (CD14) expression. Flow cytometry data revealed that the mean levels of LPS-macrophage binding and membrane-bound CD14 expression (mCD14) in differentiated THP-1 cells (a human monocytic cell line) treated with LPS plus MgSO₄ (the LPS + M group) decreased by 28.2% and 25.3% compared with those THP-1 cells treated with LPS only (the LPS group) (P < 0.001 and P = 0.037), indicating that MgSO₄ significantly inhibits LPS-macrophage binding and mCD14 expression. Notably, these effects of MgSO₄ were counteracted by L-type calcium channel activation. Moreover, the mean level of soluble CD14 (sCD14; proteolytic cleavage product of CD14) in the LPS + M group was 25.6% higher than in the LPS group (P < 0.001), indicating that MgSO₄ significantly enhances CD14 proteolytic cleavage. Of note, serine protease inhibition mitigated effects of MgSO₄ on both decreasing mCD14 and increasing sCD14. In conclusion, MgSO₄ inhibits LPS-macrophage binding through reducing CD14 expression. The mechanisms may involve antagonizing L-type calcium channels and activating serine proteases.

Matrix metalloproteinase-12 as an endogenous resolution promoting factor following myocardial infarction

Following myocardial infarction (MI), timely resolution of inflammation promotes wound healing and scar formation while limiting excessive tissue damage. Resolution promoting factors (RPFs) are agents that blunt leukocyte trafficking and inflammation, promote necrotic and apoptotic cell clearance, and stimulate scar formation. Previously identified RPFs include mediators derived from lipids (resolvins, lipoxins, protectins, and maresins), proteins (glucocorticoids, annexin A1, galectin 1, and melanocortins), or gases (CO, H₂S, and NO). Matrix metalloproteinase-12 (MMP-12; macrophage elastase) has shown promising RPF qualities in a variety of disease states. We review here the evidence that MMP-12 may serve as a novel RPF with potential therapeutic efficacy in the setting of MI.

Dexamethasone inhibits activation of monocytes/macrophages in a milieu rich in 27-oxygenated cholesterol

Molecular mechanisms underlying the decreased number of macrophages and T cells in the arteries of cholesterol-fed-rabbits following dexamethasone administration are unknown. We investigated the possibility that dexamethasone could affect activation of monocytic cells induced by oxygenated derivatives of cholesterol (oxysterols) using THP-1 monocyte/macrophage cells. 27-Hydroxycholesterol (27OHChol), an oxysterol elevated with hypercholesterolemia, enhanced production of CCL2, known as MCP1, chemokine from monocytes/macrophages and migration of the monocytic cells, but the CCL2 production and the cell migration were reduced by treatment with dexamethasone. Dexamethasone inhibited superproduction of CCL2 induced by 27OHChol plus LPS and attenuated transcription of matrix metalloproteinase 9 as well as secretion of its active gene product induced by 27OHChol. The drug downregulated cellular and surface levels of CD14 and blocked release of soluble CD14 without altering transcription of the gene. Dexamethasone also inhibited expression and phosphorylation of the NF-κB p65 subunit enhanced by 27OHChol. Collectively, these results indicate that dexamethasone inhibits activation of monocytes/macrophages in response to 27OHChol, thereby leading to decreased migration of inflammatory cells in milieu rich in oxygenated derivatives of cholesterol.

Structure, genetics and function of the pulmonary associated surfactant proteins A and D: The extra-pulmonary role of these C type lectins

The collectins family encompasses several collagenous Ca²⁺-dependent defense lectins that are described as pathogen recognition molecules. They play an important role in both adaptive and innate immunity. Surfactant proteins A and D are two of these proteins which were initially discovered in association with surfactant in the pulmonary system. The structure, immune and inflammatory functions, and genetic variations have been well described in relation to their roles, function and pathophysiology in the pulmonary system. Subsequently, these proteins have been discovered in a wide range of other organs and organ systems. The role of these proteins outside the pulmonary system is currently an active area of research. This review intends to provide a current overview of the genetics, structure and extra-pulmonary functions of the surfactant collectin proteins.

A responsive human triple-culture model of the air-blood barrier: incorporation of different macrophage phenotypes

Current pulmonary research underlines the relevance of the alveolar macrophage (AM) integrated in multicellular co-culture-systems of the respiratory tract to unravel, for example, the mechanisms of tissue regeneration. AMs demonstrate a specific functionality, as they inhabit a unique microenvironment with high oxygen levels and exposure to external hazards. Healthy AMs display an anti-inflammatory phenotype, prevent hypersensitivity to normally innocuous contaminants and maintain tissue homeostasis in the alveolus. To mirror the actual physiological function of the AM, we developed three different polarized [classically activated (M1) and alternatively activated (M2_wh , wound-healing; M2_reg , regulatory)] macrophage models using a mixture of differentiation mediators, as described in the current literature. To test their immunological impact, these distinct macrophage phenotypes were seeded on to the epithelial layer of an established in vitro air-blood barrier co-culture, consisting of alveolar epithelial cells A549 or H441 and microvascular endothelial cells ISO-HAS-1 on the opposite side of a Transwell filter-membrane. IL-8 and sICAM release were measured as functionality parameters after LPS challenge. The M1 model itself already provoked a severe inflammatory-like response of the air-blood barrier co-culture, thus demonstrating its potential as a useful in vitro model for inflammatory lung diseases. The two M2 models represent a 'non-inflammatory' phenotype but still showed the ability to trigger inflammation following LPS challenge. Hence, the latter could be used to establish a quiescent, physiological in vitro air-blood model. Thus, the more complex differentiation protocol developed in the present study provides a responsive in vitro triple-culture model of the air-blood-barrier that mimics AM features as they occur in vivo. © 2015 The Authors Journal of Tissue Engineering and Regenerative Medicine Published by John Wiley & Sons, Ltd.

Macrophage immunoregulatory pathways in tuberculosis

Macrophages, the major host cells harboring Mycobacterium tuberculosis (M.tb), are a heterogeneous cell type depending on their tissue of origin and host they are derived from. Significant discord in macrophage responses to M.tb exists due to differences in M.tb strains and the various types of macrophages used to study tuberculosis (TB). This review will summarize current concepts regarding macrophage responses to M.tb infection, while pointing out relevant differences in experimental outcomes due to the use of divergent model systems. A brief description of the lung environment is included since there is increasing evidence that the alveolar macrophage (AM) has immunoregulatory properties that can delay optimal protective host immune responses. In this context, this review focuses on selected macrophage immunoregulatory pattern recognition receptors (PRRs), cytokines, negative regulators of inflammation, lipid mediators and microRNAs (miRNAs).

Linking surfactant protein SP-D and IL-13: implications in asthma and allergy

Surfactant protein D (SP-D) is an innate immune molecule that plays a protective role against lung infection, allergy, asthma and inflammation. In vivo experiments with murine models have shown that SP-D can protect against allergic challenge via a range of mechanisms including inhibition of allergen-IgE interaction, histamine release by sensitised mast cells, downregulation of specific IgE production, suppression of pulmonary and peripheral eosinophilia, inhibition of mechanisms that cause airway remodelling, and induction of apoptosis in sensitised eosinophils. SP-D can also shift helper T cell polarisation following in vivo allergenic challenge, from pathogenic Th2 to a protective Th1 cytokine response. Interestingly, SP-D gene deficient (-/-) mice show an IL-13 over-expressing phenotype. IL-13 has been shown to be involved in the development of asthma. Transgenic mice over-expressing IL-13 in the lung develop several characteristics of asthma such as pulmonary eosinophilia, airway epithelial hyperplasia, mucus cell metaplasia, sub-epithelial fibrosis, charcot-Leyden-Like crystals, airways obstruction, and non-specific airways hyper-responsiveness to cholinergic stimulation. Although both IL-4 and IL-13 are capable of inducing asthma like phenotype, the effector activity of IL-13 appears to be greater than that of IL-4. SP-D -/- mice seem to express considerably higher levels of IL-13, which is consistent with increased sensitivity and exaggerated immune response of the mice to allergenic challenge. Allergenic exposure also induces elevation in SP-D protein levels in an IL-4/IL-13-dependent manner, which prevents further activation of sensitised T cells. This negative feedback loop seems essential in protecting the airways from inflammatory damage after allergen inhalation. Here, we examine this link between IL-13 and SP-D, and its implications in the progression/regulation of asthma and allergy.

Trypsin inhibits lipopolysaccharide signaling in macrophages via toll-like receptor 4 accessory molecules

AIMS

To examine the role of trypsin in the immune response of macrophages and to determine whether protease-activated receptors (PARs) are involved in the effects of trypsin.

MAIN METHODS

We used RAW264.7 cells and peritoneal macrophages isolated from C57BL/6 wild-type mice, PAR2 knockout mice, and ddY mice. Macrophages were stimulated with lipopolysaccharide (LPS) in the presence or absence of trypsin, thrombin, and PAR subtype-specific agonists (PARs-AP). Activation of macrophages was quantified by nitric oxide production and expression of inflammatory mediators, such as inducible nitric oxide synthase, interleukin-1β, and interleukin-6. To clarify the effect of trypsin on LPS receptors, we also investigated the expression of toll-like receptor 4 (TLR4), soluble MD-2 (sMD-2), membrane-bound MD-2 (mMD-2), soluble CD14 (sCD14), and membrane-bound CD14 (mCD14). To directly investigate the effect of trypsin on CD14 protein, we expressed recombinant CD14 protein.

KEY FINDINGS

Trypsin inhibited LPS-induced nitric oxide production and expression of inducible nitric oxide synthase, interleukin-1β, and interleukin-6. The same inhibitory effects of trypsin were observed in wild-type macrophages and in PAR2 knockout macrophages. Furthermore, the other PAR agonists, thrombin, PAR1-AP, PAR2-AP, and PAR4-AP, did not mimic the effect of trypsin. Although trypsin did not affect TLR4 or mMD-2 expression, sCD14, mCD14, and sMD-2 expressions were decreased by trypsin. Furthermore, trypsin also degraded recombinant CD14 protein.

SIGNIFICANCE

Trypsin inhibited LPS signaling PAR-independently via degradation of TLR4 accessory molecules. This observation provides a better understanding of the complicated immune response in acute pancreatitis.

Proteomic analysis of bronchoalveolar lavage fluid proteins from mice infected with Francisella tularensis ssp. novicida

Francisella tularensis causes the zoonosis tularemia in humans and is one of the most virulent bacterial pathogens. We utilized a global proteomic approach to characterize protein changes in bronchoalveolar lavage fluid from mice exposed to one of three organisms, F. tularensis ssp. novicida, an avirulent mutant of F. tularensis ssp. novicida (F.t. novicida-ΔmglA), and Pseudomonas aeruginosa. The composition of bronchoalveolar lavage fluid (BALF) proteins was altered following infection, including proteins involved in neutrophil activation, oxidative stress, and inflammatory responses. Components of the innate immune response were induced including the acute phase response and the complement system; however, the timing of their induction varied. F. tularensis ssp. novicida infected mice do not appear to have an effective innate immune response in the first hours of infection; however, within 24 h, they show an upregulation of innate immune response proteins. This delayed response is in contrast to P. aeruginosa infected animals which show an early innate immune response. Likewise, F.t. novicida-ΔmglA infection initiates an early innate immune response; however, this response is diminished by 24 h. Finally, this study identifies several candidate biomarkers, including Chitinase 3-like-1 (CHI3L1 or YKL-40) and peroxiredoxin 1, that are associated with F. tularensis ssp. novicida but not P. aeruginosa infection.

Polymorphisms in surfactant protein-D are associated with chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is characterized by alveolar destruction and abnormal inflammatory responses to noxious stimuli. Surfactant protein-D (SFTPD) is immunomodulatory and essential to host defense. We hypothesized that polymorphisms in SFTPD could influence the susceptibility to COPD. We genotyped six single-nucleotide polymorphisms (SNPs) in surfactant protein D in 389 patients with COPD in the National Emphysema Treatment Trial (NETT) and 472 smoking control subjects from the Normative Aging Study (NAS). Case-control association analysis was performed using Cochran-Armitage trend tests and multivariate logistic regression. The replication of significant associations was attempted in the Boston Early-Onset COPD Study, the Evaluation of COPD Longitudinally to Identify Predictive Surrogate Endpoints (ECLIPSE) Study, and the Bergen Cohort. We also correlated SFTPD genotypes with serum concentrations of surfactant protein-D (SP-D) in the ECLIPSE Study. In the NETT-NAS case-control analysis, four SFTPD SNPs were associated with susceptibility to COPD: rs2245121 (P = 0.01), rs911887 (P = 0.006), rs6413520 (P = 0.004), and rs721917 (P = 0.006). In the family-based analysis of the Boston Early-Onset COPD Study, rs911887 was associated with prebronchodilator and postbronchodilator FEV(1) (P = 0.003 and P = 0.02, respectively). An intronic SNP in SFTPD, rs7078012, was associated with COPD in the ECLIPSE Study and the Bergen Cohort. Multiple SFTPD SNPs were associated with serum SP-D concentrations in the ECLIPSE Study. We demonstrated an association of polymorphisms in SFTPD with COPD in multiple populations. We demonstrated a correlation between SFTPD SNPs and SP-D protein concentrations. The SNPs associated with COPD and SP-D concentrations differed, suggesting distinct genetic influences on susceptibility to COPD and SP-D concentrations.

Role of CD14 in lung inflammation and infection

This article is one of ten reviews selected from the Yearbook of Intensive Care and Emergency Medicine 2010 (Springer Verlag) and co-published as a series in Critical Care. Other articles in the series can be found online at http://ccforum.com/series/yearbook. Further information about the Yearbook of Intensive Care and Emergency Medicine is available from http://www.springer.com/series/2855.

Role of CD14 in Lung Inflammation and Infection

Toll-like receptors (TLR) on the surface of cells of the respiratory tract play an essential role in sensing the presence of microorganisms in the airways and lungs. These receptors trigger inflammatory responses, activate innate immune responses, and prime adaptive immune responses to eradicate invading microbes [1]. TLR are members of a family of pattern-recognition receptors, which recognize molecular structures of bacteria, viruses, fungi and protozoa (pathogen-associated molecular patterns or PAMPs), as well as endogenous structures and proteins released during inflammation (damage/danger-associated molecular patterns or DAMPs). To date, ten different TLR have been identified in humans and twelve in mice. TLR are expressed on all cells of the immune system, but also on parenchymal cells of many organs and tissues. The binding of a PAMP to a TLR results in cellular activation and initiates a variety of effector functions, including cytokine secretion, proliferation’ co-stimulation or phagocyte maturation. To facilitate microbial recognition and to amplify cellular responses, certain TLR require additional proteins, such as lipopolysaccharide (LPS) binding protein (LBP), CD14, CD36 and high mobility group box-l protein (HMGB-l). In this chapter, the role of CD14 as an accessory receptor for TLR in lung inflammation and infection is discussed. The central role of CD14 in the recognition of various PAMPs and amplification of immune and inflammatory responses in the lung is depicted in Fig. 1.

Fig. 1.

Role of CD14 in Lung Inflammation and Infection

Toll-like receptors (TLR) on the surface of cells of the respiratory tract play an essential role in sensing the presence of microorganisms in the airways and lungs. These receptors trigger inflammatory responses, activate innate immune responses, and prime adaptive immune responses to eradicate invading microbes [1]. TLR are members of a family of pattern-recognition receptors, which recognize molecular structures of bacteria, viruses, fungi and protozoa (pathogen-associated molecular patterns or PAMPs), as well as endogenous structures and proteins released during inflammation (damage/danger-associated molecular patterns or DAMPs). To date, ten different TLR have been identified in humans and twelve in mice. TLR are expressed on all cells of the immune system, but also on parenchymal cells of many organs and tissues. The binding of a PAMP to a TLR results in cellular activation and initiates a variety of effector functions, including cytokine secretion, proliferation, co-stimulation or phagocyte maturation. To facilitate microbial recognition and to amplify cellular responses, certain TLR require additional proteins, such as lipopolysaccharide (LPS) binding protein (LBP), CD14, CD36 and high mobility group box-1 protein (HMGB-1). In this chapter, the role of CD14 as an accessory receptor for TLR in lung inflammation and infection is discussed. The central role of CD14 in the recognition of various PAMPs and amplification of immune and inflammatory responses in the lung is depicted in Figure 1. Fig. 1.

The presence of CD14 overcomes evasion of innate immune responses by virulent Francisella tularensis in human dendritic cells in vitro and pulmonary cells in vivo

Francisella tularensis is a Gram-negative bacterium that causes acute, lethal disease following inhalation. We have previously shown that viable F. tularensis fails to stimulate secretion of proinflammatory cytokines following infection of human dendritic cells (hDC) in vitro and pulmonary cells in vivo. Here we demonstrate that the presence of the CD14 receptor is critical for detection of virulent F. tularensis strain SchuS4 by dendritic cells, monocytes, and pulmonary cells. Addition of soluble CD14 (sCD14) to hDC restored cytokine production following infection with strain SchuS4. In contrast, addition of anti-CD14 to monocyte cultures inhibited the ability of these cells to respond to strain SchuS4. Addition of CD14 or blocking CD14 following SchuS4 infection in dendritic cells and monocytes, respectively, was not due to alterations in phagocytosis or replication of the bacterium in these cells. Administration of sCD14 in vivo also restored cytokine production following infection with strain SchuS4, as assessed by increased concentrations of tumor necrosis factor alpha (TNF-alpha), interleukin-1beta (IL-1beta), IL-12p70, and IL-6 in the lungs of mice receiving sCD14 compared to mock-treated controls. In contrast to homogenous cultures of monocytes or dendritic cells infected in vitro, mice treated with sCD14 in vivo also exhibited controlled bacterial replication and dissemination compared to mock-treated controls. Interestingly, animals that lacked CD14 were not more susceptible or resistant to pulmonary infection with SchuS4. Together, these data support the hypothesis that the absence or low abundance of CD14 on hDC and in the lung contributes to evasion of innate immunity by virulent F. tularensis. However, CD14 is not required for development of inflammation during the last 24 to 48 h of SchuS4 infection. Thus, the presence of this receptor may aid in control of virulent F. tularensis infections at early, but not late, stages of infection.

Matrix metalloproteinases as drug targets in infections caused by gram-negative bacteria and in septic shock

The mammalian immune system is optimized to cope effectively with the constant threat of pathogens. However, when the immune system overreacts, sepsis, severe sepsis, or septic shock can develop. Despite extensive research, these conditions remain the leading cause of death in intensive care units. The matrix metalloproteinases (MMPs) constitute a family of proteases that are expressed in developmental, physiological, and pathological processes and also in response to infections. Studies using MMP inhibitors and MMP knockout mice indicate that MMPs play essential roles in infection and in the host defense against infection. This review provides a brief introduction to some basic concepts of infections caused by gram-negative bacteria and reviews reports describing MMP expression and inhibition, as well as studies with MMP-deficient mice in models of infection caused by gram-negative bacteria and of septic shock. We discuss whether MMPs should be considered novel drug targets in infection and septic shock.

Estimation of sCD14 levels in saliva obtained from patients with various periodontal conditions

AIM

To assess the concentration of soluble CD14 receptor in saliva of people with periodontal disease and healthy patients and its relationship with periodontal status.

SUBJECTS AND METHODS

Unstimulated whole saliva samples from patients with chronic periodontitis (n = 34), aggressive periodontitis (n = 19) and healthy controls (n = 17) were obtained for the study. The periodontal status of each subject was assessed by criteria based on probing depth, clinical attachment loss and the extent of periodontal breakdown. The levels of sCD14 were measured in saliva samples with an enzyme-linked immunosorbent assay (ELISA).

RESULTS

Although no significant difference (P > 0.05) was found for salivary sCD14 levels between periodontitis groups, they were significantly greater (P < 0.05) than those detected for healthy controls. Furthermore, Spearman's correlation analysis showed statistically significant correlations (P < 0.01) between data from salivary sCD14 levels and clinical measurements.

CONCLUSION

The findings of the present study reemphasize the importance of whole saliva as sampling method in terms of immunological purposes in periodontal disease and suggest that the elevated sCD14 concentration may be one of the host-response components associated with the clinical manifestations of periodontal disease.

Review: Surfactant protein D: A lung specific biomarker in COPD?

A major impediment in the development of novel drugs for chronic obstructive pulmonary disease (COPD) has been the scarcity of a well-validated, robust, and easily obtainable intermediate end point such as serum biomarkers. To date the best serum biomarkers in COPD have been non-speci“c pro-in”ammatory molecules synthesized largely by extra-pulmonary organs. In COPD, an ideal biomarker would be one that (1) was produced mostly in the lungs (and was reliably measurable in the peripheral circulation using commercially available kits), (2) changed with the clinical status of patients or with relevant exposures; and (3) had inherent functional attributes that suggested a possible causal role in the pathogenesis of the disease. In this paper, we review one promising systemic biomarker that ful“lls some of these criteria, surfactant protein D (SPD).

Surfactant protein D alters allergic lung responses in mice and human subjects

BACKGROUND

Surfactant protein (SP) D has been proposed to be protective in allergic airway responses.

OBJECTIVE

We aimed to determine the effect of SP-D deficiency on murine and human airway allergy.

METHODS

Immunologic responses of SP-D gene-deficient mice (Sftpd-/-) at baseline and after 4 intranasal Aspergillus fumigatus exposures were assessed. In addition, the significance of a single nucleotide polymorphism (Met(11)Thr) in the human SP-D gene (known to decrease SP-D function) was investigated.

RESULTS

Macrophage and neutrophil bronchoalveolar lavage fluid levels and large airway mucus production were increased in naive Sftpd-/- mice in association with increased lung CCL17 levels and CD4+ T cell numbers. T(H)2-associated antibody levels (IgG1 and IgE) were significantly lower in 4- to 5-week-old Sftpd-/- mice (P < .05). Accordingly, naive Sftpd-/- splenocytes released significantly less IL-4 and IL-13 on anti-CD3/CD28 stimulation (P < .01). After intranasal allergen exposures, a modest decrease in bronchoalveolar lavage fluid eosinophilia and IL-13 levels was observed in Sftpd-/- mice compared with values seen in wild-type mice in association with decreased airway resistance (P < .01). A single nucleotide polymorphism in the SFTPD gene, affecting SP-D levels and pathogen binding, was associated with decreased atopy in black subjects and potentially lower asthma susceptibility in white subjects.

CONCLUSION

Sftpd-/- mice have an impaired systemic T(H)2 response at baseline and reduced inflammation and airway responses after allergen exposure. Translational studies revealed that a polymorphism in the SFTPD gene was associated with lower atopy and possibly asthma susceptibility. Taken together, these results support the hypothesis that SP-D-dependent innate immunity influences atopy and asthma.

Role of CD14 promoter polymorphisms in Helicobacter pylori infection--related gastric carcinoma

PURPOSE

Genetic variation in CD14 may affect CD14 expression and susceptibility to Helicobacter pylori infection-related cancers. This study examined functional single nucleotide polymorphisms (SNP) in the CD14 promoter and their associations with risk of developing gastric carcinoma in relation to H. pylori infection.

EXPERIMENTAL DESIGN

Thirty individual DNAs were sequenced to identify variants, and the function of the variants was examined by reporter gene assays. Genotypes and haplotypes were analyzed in 470 patients and 470 controls, and odds ratios (OR) and 95% confidence intervals (95% CI) were estimated by logistic regression. Serologic H. pylori antibody and soluble CD14 (sCD14) levels were measured by ELISA.

RESULTS

Two SNPs (-651C>T and -260C>T) were identified, of which the -260CT and -260TT genotypes were associated with elevated risk of gastric carcinoma (OR, 1.77; 95% CI, 1.09-2.85 and OR, 1.95; 95% CI, 1.20-3.16, respectively). Haplotype analysis suggested a synergistic effect of the two SNPs (OR for the T(-651)-T(-260) haplotype, 3.39 versus OR for the C(-651)-T(-260) haplotype, 1.45; P = 0.02), which is consistent with reporter gene assays. A multiplicative joint effect between H. pylori infection and -260C>T polymorphism was observed (OR for the presence of both -260TT genotype and H. pylori infection, 4.03; 95% CI, 1.80-9.04). Patients had significantly higher sCD14 than controls (1,866 +/- 2,535 ng/mL versus 1,343 +/- 2,119 ng/mL; P < 0.001), and this difference was associated with the CD14 -260 polymorphism and H. pylori infection.

CONCLUSIONS

Functional polymorphism in CD14 is associated with greater risk of H. pylori-related gastric carcinoma, which might be mediated by elevated sCD14.

Soluble hemojuvelin is released by proprotein convertase-mediated cleavage at a conserved polybasic RNRR site

As the principal iron-regulatory hormone, hepcidin plays an important role in systemic iron homeostasis. The regulation of hepcidin expression by iron loading appears to be unexpectedly complex and has attracted much interest. The GPI-linked membrane protein hemojuvelin (GPI-hemojuvelin) is an essential upstream regulator of hepcidin expression. A soluble form of hemojuvelin (s-hemojuvelin) exists in blood and acts as antagonist of GPI-hemojuvelin to downregulate hepcidin expression. The release of s-hemojuvelin is negatively regulated by both transferrin-bound iron (holo-Tf) and non-transferrin-bound iron (FAC), indicating s-hemojuvelin could be one of the mediators of hepcidin regulation by iron. In this report, we investigate the proteinase involved in the release of s-hemojuvelin and show that s-hemojuvelin is released by a proprotein convertase through the cleavage at a conserved polybasic RNRR site.

The biochemical, biological, and pathological kaleidoscope of cell surface substrates processed by matrix metalloproteinases

Matrix metalloproteinases (MMPs) constitute a family of more than 20 endopeptidases. Identification of specific matrix and non-matrix components as MMP substrates showed that, aside from their initial role as extracellular matrix modifiers, MMPs play significant roles in highly complex processes such as the regulation of cell behavior, cell-cell communication, and tumor progression. Thanks to the comprehensive examination of the expanded MMP action radius, the initial view of proteases acting in the soluble phase has evolved into a kaleidoscope of proteolytic reactions connected to the cell surface. Important classes of cell surface molecules include adhesion molecules, mediators of apoptosis, receptors, chemokines, cytokines, growth factors, proteases, intercellular junction proteins, and structural molecules. Proteolysis of cell surface proteins by MMPs may have extremely diverse biological implications, ranging from maturation and activation, to inactivation or degradation of substrates. In this way, modification of membrane-associated proteins by MMPs is crucial for communication between cells and the extracellular milieu, and determines cell fate and the integrity of tissues. Hence, insights into the processing of cell surface proteins by MMPs and the concomitant effects on physiological processes as well as on disease onset and evolution, leads the way to innovative therapeutic approaches for cancer, as well as degenerative and inflammatory diseases.

Matrix metalloproteinase inhibitors as therapy for inflammatory and vascular diseases

Matrix metalloproteinases (MMPs) have outgrown the field of extracellular-matrix biology and have progressed towards being important regulatory molecules in cancer and inflammation. This rise in status was accompanied by the development of various classes of inhibitors. Although clinical trials with synthetic inhibitors for the treatment of cancer were disappointing, recent data indicate that the use of selective inhibitors might lead to new therapies for acute and chronic inflammatory and vascular diseases. In this Review, we compare the major classes of MMP inhibitors and advocate that future drug discovery should be based on crucial insights into the differential roles of specific MMPs in pathophysiology obtained with animal models, including knockout studies.

Surfactant protein D regulates chemotaxis and degranulation of human eosinophils

The collectin surfactant protein D (SP-D) is an important component of the pulmonary innate host defence. Up to now, little is known about the regulation of eosinophil function by SP-D. Various murine models of pulmonary hypersensitivity suggest that SP-D may be a potent anti-allergic protein. We investigated the modulation of eosinophil chemotaxis and degranulation by human SP-D. SP-D markedly inhibited the chemotaxis of eosinophils triggered by eotaxin, a major tissue-derived CC-chemokine, as shown in a modified Boyden chamber assay. In addition, degranulation of ECP in response to Ca2+ ionophore, immobilized IgG and serum from allergic patients was inhibited by SP-D. In a fixed-cell enzyme linked immunosorbent assay and in flow cytometry, SP-D bound to eosinophils. This binding was saturable and was inhibited by the addition of maltose and ethylenediaminetetraacetic acid, suggesting the involvement of the carbohydrate recognition domain of SP-D. In addition, flow cytometry showed significant interaction of SP-D with CD32 (FcgammaII receptor) on eosinophils, which might explain the inhibitory effect of SP-D on the IgG and serum-triggered eosinophil cationic protein degranulation of eosinophils. Our data further support the concept of an anti-inflammatory function of SP-D in the lung of patients with allergic diseases.

Matrix metalloproteinases and the regulation of tissue remodelling

Matrix metalloproteinases (MMPs) were discovered because of their role in amphibian metamorphosis, yet they have attracted more attention because of their roles in disease. Despite intensive scrutiny in vitro, in cell culture and in animal models, the normal physiological roles of these extracellular proteases have been elusive. Recent studies in mice and flies point to essential roles of MMPs as mediators of change and physical adaptation in tissues, whether developmentally regulated, environmentally induced or disease associated.

Matrix metalloproteinases in lung: multiple, multifarious, and multifaceted

The matrix metalloproteinases (MMPs), a family of 25 secreted and cell surface-bound neutral proteinases, process a large array of extracellular and cell surface proteins under normal and pathological conditions. MMPs play critical roles in lung organogenesis, but their expression, for the most part, is downregulated after generation of the alveoli. Our knowledge about the resurgence of the MMPs that occurs in most inflammatory diseases of the lung is rapidly expanding. Although not all members of the MMP family are found within the lung tissue, many are upregulated during the acute and chronic phases of these diseases. Furthermore, potential MMP targets in the lung include all structural proteins in the extracellular matrix (ECM), cell adhesion molecules, growth factors, cytokines, and chemokines. However, what is less known is the role of MMP proteolysis in modulating the function of these substrates in vivo. Because of their multiplicity and substantial substrate overlap, MMPs are thought to have redundant functions. However, as we explore in this review, such redundancy most likely evolved as a necessary compensatory mechanism given the critical regulatory importance of MMPs. While inhibition of MMPs has been proposed as a therapeutic option in a variety of inflammatory lung conditions, a complete understanding of the biology of these complex enzymes is needed before we can reasonably consider them as therapeutic targets.

Surfactant protein D regulates the cell surface expression of alveolar macrophage β2-integrins

The β2-integrin receptors (CD11a/CD18, CD11b/CD18, and CD11c/CD18) are expressed on the surface of alveolar macrophages and are important for the phagocytic clearance of pathogens. In the present study, we demonstrate that surfactant protein D (SP-D) modulates surface expression of CD11b and CD11c, but not CD11a or CD18, on alveolar macrophages. While cell surface receptors were reduced, CD11b and CD11c mRNAs were increased by SP-D deficiency. CCSP-rtTA+/(tetO)7-rSPD+/SP-D−/−mice, which conditionally express SP-D in the lung, were used to study the kinetics and reversibility of β2-integrin receptors in response to changes in alveolar SP-D. Surface CD11b and CD11c were reduced on the alveolar macrophages within 3 days of SP-D deficiency and were restored with 3 days for CD11b and 7 days for CD11c of repletion of SP-D. SP-D deficiency caused a loss of cellular CD11b and CD11c content, indicating that the decrease in total cell content of the receptors was related to degradation rather than to redistribution of the receptor within the macrophage. CD11b and CD11c staining colocalized with Lamp-1 during SP-D deficiency, supporting the concept that reduced macrophage receptor levels resulted from increased lysosomal trafficking. Hydroxychloroquine, a lysomotropic agent, prevented the reduction of cellular and surface CD11b and CD11c. SP-D regulates surface CD11b and CD11c levels on the alveolar macrophage by modulating receptor trafficking, providing a mechanism by which SP-D mediates phagocytic activity in the alveolar macrophage.

Matrix metalloproteinases, their production by monocytes and macrophages and their potential role in HIV-related diseases

Matrix metalloproteinases (MMPs) are zinc-dependent endopeptidases that are a subfamily of metzincins. Matrix metalloproteinases are responsible for much of the turnover of extra-cellular matrix components and are key to a wide range of processes including tissue remodeling and release of biological factors. Imbalance between the MMPs and endogenous tissue inhibitors of metalloproteinases (TIMPs) can result in dysregulation of many biologic processes and lead to the development of malignancy, cardiovascular disease, and autoimmune and inflammatory disorders. MMP production by monocyte/macrophages is dependent on the cell type, state of differentiation, and/or level of activation and whether they are infected, e.g., by HIV-1. MMP expression by HIV-1 infected monocytes and macrophages may alter cellular trafficking and contribute to HIV-associated pathology such as HIV-associated dementia (HAD). This review will provide a classification of the MMP super-family with particular reference to those produced by monocyte/macrophages, describe their regulation and function within the immune system, and indicate their possible roles in the pathogenesis of disease, including HIV-associated dementia.

Surfactant protein D in human lung diseases

The lung is continuously exposed to inhaled pollutants, microbes and allergens. Therefore, the pulmonary immune system has to defend against harmful pathogens, while an inappropriate inflammatory response to harmless particles must be avoided. In the bronchoalveolar space this critical balance is maintained by innate immune proteins, termed surfactant proteins. Among these, surfactant protein D (SP-D) plays a central role in the pulmonary host defence and the modulation of allergic responses. Several human lung diseases are characterized by decreased levels of bronchoalveolar SP-D. Thus, recombinant SP-D has been proposed as a therapeutical option for cystic fibrosis, neonatal lung disease and smoking-induced emphysema. Furthermore, SP-D serum levels can be used as disease activity markers for interstitial lung diseases. This review illustrates the emerging role of SP-D translated from in vitro studies to human lung diseases.

Structure and influence on stability and activity of the N-terminal propeptide part of lung surfactant protein C

Mature lung surfactant protein C (SP-C) corresponds to residues 24-58 of the 21 kDa proSP-C. A late processing intermediate, SP-Ci, corresponding to residues 12-58 of proSP-C, lacks the surface activity of SP-C, and the SP-Ci alpha-helical structure does not unfold in contrast to the metastable nature of the SP-C helix. The NMR structure of an analogue of SP-Ci, SP-Ci(1-31), with two palmitoylCys replaced by Phe and four Val replaced by Leu, in dodecylphosphocholine micelles and in ethanol shows that its alpha-helix vs. that of SP-C is extended N-terminally. The Arg-Phe part in SP-Ci that is cleaved to generate SP-C is localized in a turn structure, which is followed by a short segment in extended conformation. Circular dichroism spectroscopy of SP-Ci(1-31) in microsomal or surfactant lipids shows a mixture of helical and extended conformation at pH 6, and a shift to more unordered structure at pH 5. Replacement of the N-terminal hexapeptide segment SPPDYS (known to constitute a signal in intracellular targeting) of SP-Ci with AAAAAA results in a peptide that is mainly unstructured, independent of pH, in microsomal and surfactant lipids. Addition of a synthetic dodecapeptide, corresponding to the propeptide part of SP-Ci, to mature SP-C results in slower aggregation kinetics and altered amyloid fibril formation, and reduces the surface activity of phospholipid-bound SP-C. These data suggest that the propeptide part of SP-Ci prevents unfolding by locking the N-terminal part of the helix, and that acidic pH results in structural disordering of the region that is proteolytically cleaved to generate SP-C.

Innate immunity in the lungs

Innate immunity is a primordial system that has a primary role in lung antimicrobial defenses. Recent advances in understanding the recognition systems by which cells of the innate immune system recognize and respond to microbial products have revolutionized the understanding of host defenses in the lungs and other tissues. The innate immune system includes lung leukocytes and also epithelial cells lining the alveolar surface and the conducting airways. The innate immune system drives adaptive immunity in the lungs and has important interactions with other systems, including apoptosis pathways and signaling pathways induced by mechanical stretch. Human diversity in innate immune responses could explain some of the variability seen in the responses of patients to bacterial, fungal, and viral infections in the lungs. New strategies to modify innate immune responses could be useful in limiting the adverse consequences of some inflammatory reactions in the lungs.

Alveolar macrophages and emphysema in surfactant protein-D-deficient mice

Surfactant protein-D (SP-D) is a member of the collectin family of collagenous proteins with lectin activity. SP-D is expressed in numerous tissues, primarily in type II alveolar cells in the periphery of the lung. SP-D plays an important role in host defense of the lung. To evaluate the importance of SP-D in vivo, transgenic mice lacking SP-D (SP-D-/- mice) have been generated. Lipid accumulation and airspace enlargement were observed in the lungs of SP-D-/- mice within 3 weeks after birth, and progressed with advancing age. Airspace enlargement and abnormalities in elastin fibers supported the concept that SP-D was required to inhibit destruction of the alveoli. Alveolar macrophages from SP-D-/- mice produced more H2O2 and matrix metalloproteinases (MMP)-2, -9, and -12 compared with wild-type mice. In vitro studies demonstrated that oxidants derived in part from NADPH oxidase enhanced NF-kappaB activation and MMP production in alveolar macrophages from SP-D-/- mice. A specific inhibitor of NF-kappaB reduced MMP production by alveolar macrophages from SP-D-/- mice. Taken together, these data demonstrated oxidant-dependent activation of NF-kappaB and enhanced MMP expression by alveolar macrophages from SP-D-/- mice, a process likely to mediate airspace remodeling caused by SP-D deficiency. SP-D plays a critical role in regulating alveolar macrophage activation, oxidant production, and MMP activity that may influence the pathogenesis of various pulmonary disorders.

Differential protease, innate immunity, and NF-kappaB induction profiles during lung inflammation induced by subchronic cigarette smoke exposure in mice

Cigarette smoke exposure is a major determinant of adverse lung health, but the molecular processes underlying its effects on inflammation and immunity remain poorly understood. Therefore, we sought to understand whether inflammatory and host defense determinants are affected during subchronic cigarette smoke exposure. Dose-response and time course studies of lungs from Balb/c mice exposed to smoke generated from 3, 6, and 9 cigarettes/day for 4 days showed macrophage- and S100A8-positive neutrophil-rich inflammation in lung tissue and bronchoalveolar lavage (BAL) fluid, matrix metalloproteinase (MMP) and serine protease induction, sustained NF-kappaB translocation and binding, and mucus cell induction but very small numbers of CD3+CD4+ and CD3+CD8+ lymphocytes. Cigarette smoke had no effect on phospho-Akt but caused a small upregulation of phospho-Erk1/2. Activator protein-1 and phospho-p38 MAPK could not be detected. Quantitative real-time PCR showed upregulation of chemokines (macrophage inflammatory protein-2, monocyte chemoattractant protein-1), inflammatory mediators (TNF-alpha, IL-1beta), leukocyte growth and survival factors [granulocyte-macrophage colony-stimulating factor, colony-stimulating factor (CSF)-1, CSF-1 receptor], transforming growth factor-beta, matrix-degrading MMP-9 and MMP-12, and Toll-like receptor (TLR)2, broadly mirroring NF-kappaB activation. No upregulation was observed for MMP-2, urokinase-type plasminogen activator, tissue-type plasminogen activator, and TLRs 3, 4, and 9. In mouse strain comparisons the rank order of susceptibility was Balb/c > C3H/HeJ > 129SvJ > C57BL6. Partition of responses into BAL macrophages vs. lavaged lung strongly implicated macrophages in the inflammatory responses. Strikingly, except for IL-10 and MMP-12, macrophage and lung gene profiles in Balb/c and C57BL/6 mice were very similar. The response pattern we observed suggests that subchronic cigarette smoke exposure may be useful to understand pathogenic mechanisms triggered by cigarette smoke in the lungs including inflammation and alteration of host defense.

Beta-catenin regulates differentiation of respiratory epithelial cells in vivo

An activated form of beta-catenin [Catnb(Delta(ex3))] was expressed in respiratory epithelial cells of the developing lung. Although morphogenesis was not altered at birth, air space enlargement and epithelial cell dysplasia were observed in the early postnatal period and persisted into adulthood. The Catnb(Delta(ex3)) protein caused squamous, cuboidal, and goblet cell dysplasia in intrapulmonary conducting airways. Atypical epithelial cells that stained for surfactant pro protein C (pro-SP-C) and had morphological characteristics of alveolar type II cells were observed in bronchioles of the transgenic mice. Catnb(Delta(ex3)) inhibited expression of Foxa2 and caused goblet cell hyperplasia associated with increased staining for mucins and the MUC5A/C protein. In vitro, both wild type and activated beta-catenin negatively regulated the expression of the Foxa2 promoter. Catnb(Delta(ex3)) also caused pulmonary tumors in adult mice. Activation of beta-catenin caused ectopic differentiation of alveolar type II-like cells in conducting airways, goblet cell hyperplasia, and air space enlargement, demonstrating a critical role for the Wnt/beta-catenin signal transduction pathway in the differentiation of the respiratory epithelium in the postnatal lung.