Jay Y. Westcott

Macrophages that have ingested apoptotic cells in vitro inhibit proinflammatory cytokine production through autocrine/paracrine mechanisms involving TGF-beta, PGE2, and PAF.

Apoptosis in vivo is followed almost inevitably by rapid uptake into adjacent phagocytic cells, a critical process in tissue remodeling, regulation of the immune response, or resolution of inflammation. Phagocytosis of apoptotic cells by macrophages has been suggested to be a quiet process that does not lead to production of inflammatory mediators. Here we show that phagocytosis of apoptotic neutrophils (in contrast to immunoglobulin G-opsonized apoptotic cells) actively inhibited the production of interleukin (IL)-1beta, IL-8, IL-10, granulocyte macrophage colony-stimulating factor, and tumor necrosis factor-alpha, as well as leukotriene C4 and thromboxane B2, by human monocyte-derived macrophages. In contrast, production of transforming growth factor (TGF)-beta1, prostaglandin E2, and platelet-activating factor (PAF) was increased. The latter appeared to be involved in the inhibition of proinflammatory cytokine production because addition of exogenous TGF-beta1, prostaglandin E2, or PAF resulted in inhibition of lipopolysaccharide-stimulated cytokine production. Furthermore, anti-TGF-beta antibody, indomethacin, or PAF receptor antagonists restored cytokine production in lipopolysaccharide-stimulated macrophages that had phagocytosed apoptotic cells. These results suggest that binding and/or phagocytosis of apoptotic cells induces active antiinflammatory or suppressive properties in human macrophages. Therefore, it is likely that resolution of inflammation depends not only on the removal of apoptotic cells but on active suppression of inflammatory mediator production. Disorders in either could result in chronic inflammatory diseases.

Pulmonary prostacyclin synthase overexpression in transgenic mice protects against development of hypoxic pulmonary hypertension

Prostacyclin synthase (PGIS) is the final committed enzyme in the metabolic pathway leading to prostacyclin (PGI2) production. Patients with severe pulmonary hypertension have a PGIS deficiency of their precapillary vessels, but the importance of this deficiency for lung vascular remodeling remains unclear. We hypothesized that selective pulmonary overexpression of PGIS may prevent the development of pulmonary hypertension. To study this hypothesis, transgenic mice were created with selective pulmonary PGIS overexpression using a construct of the 3.7-kb human surfactant protein-C (SP-C) promoter and the rat PGIS cDNA. Transgenic mice (Tg+) and nontransgenic littermates (Tg-) were subjected to a simulated altitude of 17,000 ft for 5 weeks, and right ventricular systolic pressure (RVSP) was measured. Histology was performed on the lungs. The Tg+ mice produced 2-fold more pulmonary 6-keto prostaglandin F1alpha (PGF1alpha) levels than did Tg- mice. After exposure to chronic hypobaric hypoxia, Tg+ mice have lower RVSP than do Tg- mice. Histologic examination of the lungs revealed nearly normal arteriolar vessels in the Tg+ mice in comparison with vessel wall hypertrophy in the Tg- mice. These studies demonstrate that Tg+ mice were protected from the development of pulmonary hypertension after exposure to chronic hypobaric hypoxia. We conclude that PGIS plays a major role in modifying the pulmonary vascular response to chronic hypoxia. This has important implications for the pathogenesis and treatment of severe pulmonary hypertension.

Bronchoalveolar lavage fluid mediator levels 5 minutes after allergen challenge in atopic subjects with asthma: Relationship to the development of late asthmatic responses

Inflammatory mediators have been implicated in the pathogenesis of human asthma and have been demonstrated to increase in bronchoalveolar lavage fluid during the time of the immediate asthmatic response (IAR) after allergen instillation in the lungs. However, the relationship of these mediators, measured early to the late asthmatic response (LAR), airway reactivity, and clinical asthma, is unknown. In the present study, we evaluated mediator levels in bronchoalveolar lavage fluid before and 5 minutes after allergen challenge from three subject groups: atopic subjects without asthma (N = 7), atopic subjects with asthma and without LAR [-) LAR) (N = 6), and atopic subjects with asthma and with LAR [+) LAR) (N = 6). Subjects with asthma were differentiated into subjects with and without LARs based on at least a 15% decrease in FEV1 between 3 to 8 hours postallergen inhalation. The mediators, prostaglandin D2 thromboxane B2 leukotriene C4 (LTC4), and histamine, were measured both before and after allergen instillation. Baseline prechallenge levels were similar, except in the case of LTC4. LTC4 was detectable at baseline significantly more frequently in the atopic subjects with asthma with and without LAR when these subjects were compared to the atopic subjects without asthma (nine of 12 detectable versus one of seven detectable). In all groups, significant increases in mediator levels were observed in the groups with asthma postallergen challenge, compared to the atopic subjects without asthma. Atopic subjects with asthma and without LAR had significantly higher levels of all four mediators after challenge than atopic subjects with asthma and with LAR and atopic subjects without asthma.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression and activation of 15-lipoxygenase pathway in severe asthma: relationship to eosinophilic phenotype and collagen deposition.

Background Although 15(S)‐hydroxyeicosatetraenoic acid (15(S)‐HETE), a product of 15‐lipoxygenase (15‐LO), may be involved in mild to moderate asthma, little is known about its potential roles in severe asthma.

Transforming Growth Factor-β2 Induces Bronchial Epithelial Mucin Expression in Asthma

The transforming growth factor (TGF)-beta family is important for tissue repair in pathological conditions including asthma. However, little is known about the impact of either TGF-beta1 or TGF-beta2 on asthmatic airway epithelial mucin expression. We evaluated bronchial epithelial TGF-beta1 and TGF-beta2 expression and their effects on mucin expression, and the role of TGF-beta1 or TGF-beta2 in interleukin (IL)-13-induced mucin expression. Epithelial TGF-beta1, TGF-beta2, and mucin expression were evaluated in endobronchial biopsies from asthmatics and normal subjects. The effects of TGF-beta1 or TGF-beta2 on mucin MUC5AC protein and mRNA expression, and the impact of IL-13 on epithelial TGF-beta1, TGF-beta2, and MUC5AC were determined in cultured bronchial epithelial cells from endobronchial brushings of both subject groups. In biopsy tissue, epithelial TGF-beta2 expression levels were higher than TGF-beta1 in both asthmatics and normals. TGF-beta2, but not TGF-beta1, was increased in asthmatics compared with normals, and significantly correlated with mucin expression. TGF-beta2, but not TGF-beta1, increased mucin expression in cultured epithelial cells from both subject groups. IL-13 increased the release of TGF-beta2, but not TGF-beta1, from epithelial cells. A neutralizing TGF-beta2 antibody partially inhibited IL-13-induced mucin expression. These data suggest that TGF-beta2 production by asthmatic bronchial epithelial cells may increase airway mucin expression. IL-13-induced mucin expression may occur in part through TGF-beta2 up-regulation.

TGF-β and IL-13 Synergistically Increase Eotaxin-1 Production in Human Airway Fibroblasts

Chronic diseases may involve an “innate” response followed by an adaptive immune response, of a Th1 or Th2 variety. Little is known regarding the interactions of these responses. We hypothesized that TGF-β1 (innate response factor associated with wound repair) in combination with IL-13 (Th2 factor) might augment inflammatory processes associated with asthma. Airway fibroblasts were cultured from asthmatic subjects and normal controls. These fibroblasts were exposed to TGF-β1 and IL-13 alone or in combination, and eotaxin-1 expression and production were evaluated. At 48 h, eotaxin-1 production was markedly increased with the combination of TGF-β1 and IL-13 (p < 0.0001) compared with either stimulus alone. mRNA increased slightly at 1 h with IL-13 or TGF-β1 plus IL13, peaked, and became significantly increased over IL-13 alone at 24 h. Protein was measurable from 6 h with IL-13 and TGF-β1 plus IL-13, but greater levels were measured over time with the combination. Actinomycin ablated the increase in mRNA and protein seen with IL-13 alone and with TGF-β1 plus IL-13. Cycloheximide blocked the increase in mRNA at 6 h in both conditions, but also blocked the increase at 24 h with TGF-β1 plus IL-13. STAT-6 was rapidly activated with both IL-13 and the combination, without difference. Finally, eotaxin-1-positive fibroblasts were identified in severe asthma biopsies in greater numbers than in normals. These results support the concept that interactions of innate and adaptive immune systems may be important in promoting the tissue eosinophilia of asthma, particularly in those with more severe disease.

Inflammatory cells and eicosanoid mediators in subjects with late asthmatic responses and increases in airway responsiveness

To determine the relationship of inflammatory cells and eicosanoid mediators to the pathogenesis of the late asthmatic response (LAR) and increases in nonspecific airway responsiveness, we studied bronchoalveolar lavage (BAL) cells and fluid in 27 subjects 12 hours after inhaled antigen challenge. Methacholine challenge was performed before antigen challenge and 24 hours later (12 hours after BAL). Eight subjects had no LAR (-LAR, less than or equal to 10% fall in FEV1), nine subjects had an equivocal LAR (+/- LAR, 11% 25% fall in FEV1), and 10 subjects had a definite LAR (+LAR, greater than 25% fall in FEV1). Subjects developing +LAR had increased airway responsiveness at baseline compared with that of subjects developing an +/- LAR, but not with subjects having -LAR. If airway responsiveness was markedly increased at baseline, further increases after antigen challenge were often not observed. We found that both percent neutrophils and eosinophils increased in BAL as the severity of the LAR increased, but significant differences between the groups with -LAR and +LAR were only observed when both cell types were considered together. In addition, there was a significant correlation between the combined cell percentages and the severity of the LAR as determined by fall in FEV1. Likewise, increases in airway responsiveness were associated with significant increases in both neutrophil and eosinophil numbers, but only neutrophils correlated with the change in airway responsiveness after antigen challenge. However, despite the significant physiologic and cellular differences that we found between our groups, no significant differences could be found in BAL eicosanoid-mediator concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Eicosanoids in human ventricular cerebrospinal fluid following severe brain injury

Recent evidence has shown that a variety of prostaglandins and leukotrienes can be produced in brain tissue after injury in animals. It has also been speculated that increases in brain prostaglandins occur in humans following injury. Ventricular cerebrospinal fluid (CSF) samples have been obtained from children with static lesions (controls) as well as children with acute brain injury and eicosanoids measured by immunologic techniques. Metabolites of prostacyclin (6-keto-PGF1 a) and thromboxane A2 (thromboxane B2) were the major eicosanoids found in CSF, and levels of these compounds were increased 3-10 times in acutely injured patients. Prostaglandin E2 was also found in lower amounts, although in one case its level was very high. Prostaglandin D2 was also present, but in low amounts. No leukotrienes were found in CSF samples that were purified by HPLC prior to immunoassay. Elevated levels of hydroxyeicosatetraenoic acids (HETEs) were observed in those samples stored frozen, but these metabolites were most probably due to autooxidation of arachidonic acid in CSF. Arachidonic acid concentration in CSF was typically found to be in the range of 10-200 ng/ml, but was found to be 5-10 fold higher in one severely injured patient. Thus, elevated free arachidonic acid and various oxygenated metabolites were observed in CSF following brain injury.

Single oral dose of prednisone decreases leukotriene B4 production by alveolar macrophages from patients with nocturnal asthma but not control subjects: Relationship to changes in cellular influx and FEV1

BACKGROUND Nocturnal worsening of asthma is associated with an increase in numbers of airway inflammatory cells during the early morning. However, cell function during the night, with and without administration of steroids, has not been investigated. OBJECTIVE This study was designed to determine the effect of prednisone on pulmonary alveolar macrophage production of leukotriene B2 and thromboxane B2 at night and how it relates to changes in pulmonary function and cellular influx. METHODS Alveolar macrophages were obtained from patients with nocturnal asthma, patients with nonnocturnal asthma, and normal control subjects at 4:00 AM by bronchoalveolar lavage after administration of placebo and prednisone. Cells were placed in limited cell culture, and eicosanoids were measured from baseline and stimulated cells. RESULTS Patients with nocturnal asthma had both a significantly greater fall in forced expiratory volume in 1 second (FEV1) and a greater influx of neutrophils and eosinophils at 4:00 AM than normal subjects after placebo treatment, whereas patients with nonnocturnal asthma had intermediary responses. There was no difference in baseline or stimulated LTB4 production during placebo administration in the three groups. After prednisone treatment, there was an improvement in the nocturnal fall in FEV1 and a significant decrease in the neutrophil influx in patients with nocturnal asthma compared with the other groups. These changes were accompanied by a significant decrease in the stimulated LTB4 production in patients with nocturnal asthma compared with a small increase in both patients with nonnocturnal asthma and normal subjects. Thromboxane B2 production did not change. The decrease in LTB4 production was correlated with the fall in granulocytic cells and improvement in the nocturnal FEV1. However, the two variables with the greatest combined influence on the improvement in FEV1 were the decrease in stimulated LTB4 production and the fall in neutrophil influx. CONCLUSIONS We demonstrate for the first time that a single oral dose of prednisone decreases LTB4 production from alveolar macrophages, obtained at night from patients with nocturnal asthma, during a time of known inflammation. Further, this decrease in stimulated production is associated with decreases in cellular influx and improvement in pulmonary function.

Analysis of leukotriene B4 in human lung lavage by HPLC and mass spectrometry

Although leukotrienes are believed to mediate symptoms of human lung disease, there is little direct evidence of their existence in the lung. This is due to the difficulty in obtaining lung samples, the small amounts of leukotrienes typically present in such samples and the problems associated with purifying and analyzing leukotrienes in complex biological samples. In this study, lung lavagates were collected and analyzed for leukotrienes. The methods in this analysis included solid phase extraction using a C-18 reverse phase cartridge followed by HPLC using a new photodiode array detector which provides full UV spectra of eluting compounds. Lung lavage fluid from a patient with chronic pulmonary disease contained a compound with a UV spectra of LTB4 which was found to elute with synthetic [3H]-LTB4. This compound was confirmed as LTB4 using gas chromatography/mass spectrometry in the negative ion-chemical ionization mode. The inclusion of oxygen-18 LTB4 as an internal standard allowed approximate quantitation of the amount of LTB4 present in this 5 ml lung lavagate as 40-50 ng.