Acute inflammatory lung injury retards pulmonary particle clearance

Failure of respiratory defenses in the pathogenesis of bacterial pneumonia of cattle

The respiratory system is well defended against inhaled bacteria by a dynamic system of interacting layers, including mucociliary clearance, host defense factors including antimicrobial peptides in the epithelial lining fluid, proinflammatory responses of the respiratory epithelium, resident alveolar macrophages, and recruited neutrophils and monocytes. Nevertheless, these manifold defenses are susceptible to failure as a result of stress, glucocorticoids, viral infections, abrupt exposure to cold air, and poor air quality. When some of these defenses fail, the lung can be colonized by bacterial pathogens that are equipped to evade the remaining defenses, resulting in the development of pneumonia. This review considers the mechanisms by which these predisposing factors compromise the defenses of the lung, with a focus on the development of bacterial pneumonia in cattle and supplemented with advances based on mouse models and the study of human disease. Deepening our understanding of how the respiratory defenses fail is expected to lead to interventions that restore these dynamic immune responses and prevent disease.

Mucociliary clearance is enhanced in rat models of cigarette smoke and lipopolysaccharide-induced lung disease

In this study, the authors describe a new technique enabling the rapid assessment of mucociliary clearance (MCC) in rats and characterize this aspect of innate host defense in 2 animal models of bronchitis. Following instillation into the airways, fluorescent microspheres were rapidly cleared over 24 hours, with 60% to 80% of clearance occurring within 4 hours. On a background of airway neutrophilia and mucus hypersecretion, induced by either lipopolysaccharide or cigarette smoke, MCC was significantly enhanced. This reserve capacity in the MCC system will need to become overwhelmed in order to model the clinically observed impairment of lung mucus clearance in an animal system.

Effects of gadolinium on the retention and translocation of 239Pu-hydroxide

The effect of gadolinium on the lung retention, excretion, and translocation of plutonium was studied in rats instilled intratracheally with plutonium hydroxide with and without gadolinium. Three types of plutonium hydroxide were prepared: pure 239Pu-hydroxide colloid, that containing a high concentration of gadolinium, and that containing a low concentration of gadolinium. The lung retention of 239Pu was higher and the fecal excretion was lower in the rats administered 239Pu-hydroxide containing a high concentration of gadolinium than those administered pure 239Pu-hydroxide colloid. The translocation of 239Pu from lung to other organs including the liver, spleen, femur, and kidney was not affected by gadolinium. The cytological examination of bronchoalveolar lavage cells showed that the administration of 239Pu-hydroxide containing a high concentration of gadolinium induced the inflammatory reactions in the lung. The delayed alveolar clearance of plutonium in the rats administered 239Pu-hydroxide colloid containing a high concentration of gadolinium may be attributable to the change in physicochemical characteristics of colloid and the inflammation induced in the lung by gadolinium.

Silica deposition in the lung during epithelial injury potentiates fibrosis and increases particle translocation to lymph nodes

Increased respiratory disease and daily mortality rates are associated with higher levels of fine particulate air pollutants. We examined the possibility that deposition of particles to previously injured lungs might accentuate pulmonary damage, by investigating how the lung handled silica deposited during a phase of epithelial injury. A low dose of intratracheal (i.t.) bleomycin (BL) was used to induce epithelial damage in mice; 3 days later, 0.2 mg silica was instilled. Lung injury, measured by cell numbers and protein levels in bronchoalveolar lavage, was increased at 1 week and many silica particles translocated to the interstitium. At 12 weeks, the silica plus BL group showed increased pulmonary fibrosis biochemically and morphologically, and had significantly higher retained-silica content in the lung. In addition, these mice showed enlarged hilar lymph nodes with many granulomas-containing macrophages and silica. The results indicate that instillation of fine particulates to the alveoli at a time of epithelial damage potentiates the lung injury and increases translocation of particles to the interstitium. In the case of silica, deposition of particles into injured lungs resulted in increased fibrosis. The demonstration of enhanced translocation of silica to lymph nodes suggests that inhaled fine particulates may induce more distal effects following transport across an injured epithelium and subsequent entrance to the lymphatic system.

Particle clearance from the gills of rainbow trout (Oncorhynchus mykiss)

The rate of particle clearance from the gills was assessed in healthy rainbow trout (Oncorhynchus mykiss), challenged with the formalin-killed bacterium Flavobacterium branchiophilum, as well as in fish with altered ventilation levels produced by varying the concentrations of dissolved oxygen (DO) in the water. The clearance of F. branchiophilum from the gills was quantified by means of an enzyme-linked immunosorbent assay. Fish held under normoxic conditions (DO = 9.5 mg/l) showed an initial rapid reduction in bacterial antigen, with 50% of the bacteria being cleared in the first 12 h after exposure, followed by slower clearance for the remaining bacteria; total elimination was achieved by 40 h. Fish with reduced ventilation rates (hyperoxia; DO = 25 mg/l) and elevated ventilation rates (hypoxia; DO = 4.5 mg/l) had significantly impaired particle clearance (r < 0.05), achieving only 60 and 20% reduction, respectively, at 72 h after challenge.

Induction of procoagulant activity in virus infected bovine alveolar macrophages and the effect of lipopolysaccharide

Three viruses known to be associated with the bovine respiratory disease complex were evaluated in vitro for potential impact upon the procoagulant activity (PCA) of bovine alveolar macrophages (bAM). Cultures of bAM were inoculated with bovine parainfluenza virus Type 3 (PI-3), cytopathic bovine viral diarrhea virus (cpBVDV), non-cytopathic BVDV (ncpBVDV), or bovine herpes virus Type 1 (BHV-1) and incubated for several time periods (24, 48, 72, 96 h). BAM were then exposed to E. coli lipopolysaccharide (LPS), or LPS with bovine serum. The amount of PCA expressed was quantified using a chromogenic assay. Viral inoculation increased bAM expression of PCA (P < 0.01). The increase in PCA expression was larger at higher rates of viral inoculation (P < 0.01). LPS enhanced PCA expression by bAM at low rates of viral inoculation (P < 0.01). The effect of LPS-serum treatment was greater than the LPS alone (P < 0.01). At high rates of viral inoculation, LPS had no enhancing effect on PCA expression. The effect of LPS on virus inoculated bAM varied with virus type, rate of inoculation, and duration of virus exposure (P < 0.01). The results suggest that these four viruses initiate the production of PCA by bAM independently of LPS. In the field situation, an initial viral infection may induce fibrin deposition in the pulmonary alveoli prior to the establishment of a secondary gram negative bacterial infection.

Patterns of particle deposition and retention after instillation to mouse lung during acute injury and fibrotic repair

Studies on particle deposition, clearance, and translocation to the interstitium and lymph nodes have mostly been carried out on normal animals. This study evaluates changes in these parameters after inert particles are deposited in lungs during acute inflammatory injury and during fibrotic repair. Three days after instilling bleomycin to mouse lungs, there is an inflammatory response and necrosis of type 1 epithelium. When carbon is instilled in these lungs, particles appear uniformly distributed, some are engulfed by the increased phagocytes, but many particles cross the denuded epithelial surface to reach interstitial macrophages. Subsequently much carbon remains in the connective tissue and some reaches hilar lymph nodes. After 16 weeks, particle retention in the lung is significantly greater than in a carbon-only control group. Other mice received carbon 4 weeks after bleomycin when epithelial repair had occurred and many areas of the lung were fibrotic. Very little carbon reached these regions; most was deposited in less fibrotic areas of lung. Few particles crossed the epithelium so that retained carbon in lung and lymph nodes was equivalent to that in the carbon-only group. The results show that a fibrotic lung structure alters the patterns of particle deposition in the lung. However, the major factor determining enhanced particle retention is the integrity of the epithelium. Particle deposition at a time of epithelial injury is associated with enhanced translocation to interstitium and lymph nodes. This may result in pathologic changes if a normally nonreactive low dose of toxic particles is deposited when the epithelium is breached.

Impaired tracheobronchial clearance of bacteria in calves infected with Mycoplasma dispar

Infection of tracheal organ cultures with Mycoplasma dispar results in degeneration of respiratory epithelial cells with loss of ciliary activity. To assess the effect of these changes on the clearance of bacteria from the respiratory tract, the tracheobronchial clearance of a suspension of Serratia marcescens was determined in calves before and after infection with M. dispar. Tracheobronchial samples were obtained at various times after deposition of the marker bacteria. Clearance of S. marcescens was significant by 3 h after inoculation and only few colonies were detected 4 h after challenge. By contrast, in the same animals 5 days after intratracheal exposure to M. dispar, clearance of S. marcescens did not decrease significantly 4 h after inoculation. Histopathological and scanning electron microscopy (SEM) studies of infected lungs revealed that, as a result of infection with M. dispar, areas of degeneration and destruction of the respiratory ciliated epithelium occur in intermediate and small airways. These lesions may be responsible for the altered clearance observed in these mycoplasma-exposed calves.

Persistence of respiratory syncytial virus genome and protein after acute bronchiolitis in guinea pigs

Children with acute respiratory syncytial virus (RSV) bronchiolitis often develop sequelae of recurrent wheezing and asthma. To determine whether RSV persists within the lung after resolution of acute bronchiolitis, we examined the lungs of guinea pigs 60 days after intranasal inoculation with either human RSV (n = 10) or uninfected cell culture supernatant (n = 11). Evidence of viral persistence within the lung was determined by viral culture to test for replicating virus, immunohistochemistry to test for viral protein, and the reverse transcriptase-polymerase chain reaction (RT-PCR) to test for viral genomic RNA. Lungs were also examined histologically for evidence of bronchiolar inflammation or increased numbers of mast cells in the airway walls. All viral cultures were negative; however, there was positive immunohistochemical staining of occasional alveolar macrophages in six of ten RSV-inoculated guinea pigs while RT-PCR was positive in seven of ten RSV-inoculated animals. The six guinea pigs with evidence of RSV by immunohistochemistry and RT-PCR showed excess bronchiolar polymorphonuclear cell infiltrates (p < 0.005) but no increase in the number of airway wall mast cells. These results show that RSV protein and genomic RNA can persist in the lungs of experimentally inoculated guinea pigs for at least 60 days after infection and that persistence of the virus within alveolar macrophages might contribute to the pathogenesis of chronic bronchiolar inflammation.

Bronchoalveolar lavage fluid cytology reflects airway inflammation in beagle puppies with acute bronchiolitis

Beagle puppies infected with both canine parainfluenza virus type 2 (CPI2) and Bordetella bronchiseptica (Bb) develop more severe acute bronchiolitis and airways hyperresponsiveness than do those infected with CPI2 or Bb alone. The aim of our study was to characterize the inflammatory response associated with airway hyperresponsiveness, and to determine whether the inflammatory cell response of bronchoalveolar lavage fluid (BALF) reflected changes in the bronchioles in this model. We investigated 25 beagle puppies (ages 76 +/- 5 days, mean +/- SEM) in four groups: controls (n = 6), or puppies inoculated with both CPI2 and Bb (CPI2-Bb) (n = 11), with only CPI2 (n = 4), or only Bb (n = 4). The puppies were killed 3-4 days after inoculation, the lungs excised, the intermediate lobe lavaged, and BALF and the bronchiolar wall tissue examined for neutrophils and other inflammatory cells. Control puppies had no evidence of inflammation. However, the CPI2-Bb puppies had developed cough and rhinitis, positive cultures for CPI2 and Bb, and a neutrophilic cellular response in both the bronchioles and the BALF. Puppies inoculated with only CPI2 or Bb had milder illnesses and no significant bronchiolar and BALF neutrophilic response. For all groups, the severity of bronchiolar wall inflammation correlated with the total number of BALF inflammatory cells, and bronchiolar wall neutrophil counts correlated with the percentage of neutrophils in the BALF. The illness and the airway hyperresponsiveness observed in the CPI2-Bb group were associated with airway neutrophilia. Our studies support the hypothesis that neutrophils are associated with airway dysfunction in this model, and the use of BALF to study the process.