Animal model of neutropenia suitable for the study of dual-phagocyte systems

Essential role for neutrophils but not alveolar macrophages at early time points following Aspergillus fumigatus infection

Alveolar macrophages and neutrophils mediate innate immune defense against the opportunistic fungal pathogen Aspergillus fumigatus and are believed to be essential for host survival following inhalation of fungal spores (conidia). Although alveolar macrophages are postulated to kill inhaled conidia and neutrophils are believed to act against hyphae, the relative contribution of alveolar macrophages and neutrophils to early defense against A. fumigatus remain incompletely defined. To more precisely characterize the contributions of alveolar macrophages and neutrophils in antifungal host defense, we selectively depleted each cell population at different times following pulmonary challenge with conidia. Mice depleted of alveolar macrophages prior to pulmonary A. fumigatus infection recruited neutrophils normally and restricted hyphal tissue invasion. In contrast, neutrophil depletion prior to or within 3 h after infection was associated with high mortality. Neutrophil depletion at later time points, however, was associated with nearly normal survival rates. Our studies suggest that neutrophils, but not alveolar macrophages, provide essential anticonidial defense and that a brief period of influx into the respiratory tree is sufficient to prevent conidial germination and invasive disease.

Effects of depletion of neutrophils or macrophages on development of cigarette smoke-induced emphysema

The aim of this study was to ascertain the putative roles of neutrophils or macrophages in the pathogenesis of cigarette smoking-induced emphysema on the basis of effects of anti-neutrophil (anti-PMN) antibody or anti-monocyte/macrophage (anti-MoMac) antibody on the development of emphysema in cigarette smoke-exposed rats. Rats were treated with rabbit anti-PMN or anti-MoMac antibody and exposed 7 days/wk for 2 mo to cigarette smoke inhalation; rats treated with nonimmunized rabbit IgG (control antibody) and exposed to cigarette smoke or normal room air served as controls. Antibody treatments began 24 h before the start of smoke or air exposure and was continued with 1 treatment/wk. Total and differential cell counts in bronchoalveolar lavage fluid and collagenase-dissociated lung and determinations of the elastinolytic activity of lung neutrophils or macrophages in [(3)H]elastin-coated wells indicated specific suppression of neutrophil accumulation and neutrophil-related elastinolytic burden in the lungs of the anti-PMN antibody-treated smoke-exposed rats, in contrast to specific suppression of macrophage accumulation and macrophage-related elastinolytic burden in the lungs of the anti-MoMac antibody-treated smoke-exposed rats. Cigarette smoke exposure-induced lung elastin breakdown (quantitated by immunologic assay of levels of elastin-derived peptides and desmosine in lavage fluid) and emphysema in the lungs (based on morphometric analysis of alveolar mean linear intercepts and alveolar tissue density in fixed lungs) were not prevented in the lungs of anti-PMN antibody-treated smoke-exposed rats but was clearly prevented in lungs of the anti-MoMac antibody-treated smoke-exposed rats. These findings implicate macrophages rather than neutrophils as the critical pathogenic factor in cigarette smoke-induced emphysema.

A quantitative measurement of the effect of avian influenza virus on the ability of turkeys to eliminate Pasteurella multocida from the respiratory tract

The effect of avian influenza virus (AIV) infection on the ability of turkeys to eliminate Pasteurella multocida from the respiratory tract was evaluated. Four-week-old turkeys were experimentally infected with an apathogenic AIV subtype (H5N2) by the oculonasal route and subsequently superinfected with P multocida (Urbach strain) by the intranasal route three days after infection with AIV. Quantitative clearance of P multocida from the trachea and lung was determined using a pour plate technique on samples collected at intervals after infection. Samples from turkeys which had been infected with AIV were found to yield more P multocida than those from turkeys which had not been infected with AIV. The numbers of P multocida increased in infected birds to a greater extent than in birds which had not been infected with the virus. The present study suggests that AIV infection may contribute to the increased numbers and a decreased clearance of P multocida in turkeys.

Suppression and recovery of the alveolar macrophage phagocytic system during continuous exposure to 0.5 ppm ozone

Short-term exposures to ozone (O3) are known to impair pulmonary antibacterial defenses and alveolar macrophage (AM) phagocytosis in a dose-related manner. To determine the effect of prolonged O3 exposure, Swiss mice were exposed continuously to 0.5 ppm O3. At 1, 3, 7, and 14 days, intrapulmonary killing was assessed by inhalation challenge with Staphylococcus aureus or Proteus mirabilis and by comparing the number of viable bacteria remaining in the lungs at 4 h between O3-exposed and control animals. To evaluate the effects of O3 on the functional capacity of the AMs, Fc-receptor mediated phagocytosis was assessed. Ozone exposure impaired the intrapulmonary killing of S. aureus at 1 and 3 days; however, with prolonged exposure, the bactericidal capacity of the lungs returned to normal. This trend of an initial suppression followed by recovery was reflected in the phagocytic capacity of the AMs. In contrast to S. aureus, when P. mirabilis was used as the challenge organism, O3 exposure had no suppressive effect on pulmonary bactericidal activity, which correlated with an increase in the phagocytic cell population in the lungs. Morphologic examination of the lavaged macrophages showed that after 1 day of O3 exposure, the AMs were more foamy, and contained significantly more vacuoles. There was also a significant increase in binucleated cells at 3 days. These studies demonstrate that continuous exposure to O3 modulates AM-dependent lung defenses and points to the importance of the challenge organism and exposure protocol in establishing the adverse effect of O3.

Intrapulmonary growth of Staphylococcus aureus in rats during induced atelectasis

Intrinsic pulmonary antibacterial defenses are mediated by alveolar macrophages and by noncellular factors. Mechanical ventilation in the resting tidal volume range leads to alterations in the physical characteristics of alveolar surfactant, alveolar instability, regional hypoxia, and systemic hypoxemia. While a number of experimental manipulations diminish the activity of the intrinsic antibacterial defense system, the effects of mechanical ventilation per se have not been systematically evaluated previously. We found that normal rats ventilated without sighing (periodic large breaths) manifested severe defects in pulmonary clearance of Staphylococcus aureus during 6-h experiments, such that growth of the inoculum occurred. Addition of a timer-controlled mechanism to cause the animals to sigh every 2 min, without other modifications in the experimental conditions, caused significant improvement in clearance. Analysis of cellular response, compartmentalization of viable bacteria, surfactant quantities and sedimentation characteristics, and protein influx indicated that the defect in clearance paralleled alterations in the physical state of surfactant and alveolar stability but was not strongly correlated with alterations in the other parameters we measured. The data show that defective pulmonary bacterial clearance is rapidly induced by measures which alter alveolar stability and suggest that intrinsic pulmonary defenses require maintenance of normal air-liquid interfaces for optimal function.

The effect of parainfluenza virus type 3 on the phagocytic cell response of the ovine lung to Pasteurella haemolytica

Groups of Caesarean-derived, colostrum-deprived lambs were inoculated by the intratracheal route with Pasteurella haemolytica 4 to 6 days after the inoculation of parainfluenza virus type 3 (PI3). Some were killed immediately (0 h) and others 24 h later. Control groups were inoculated with PI3 alone, P. haemolytica alone or media alone. Pulmonary phagocytic cells, P. haemolytica and PI3 were recovered by pulmonary lavage. The phagocytes were separated into alveolar macrophage (AM) and neutrophil fractions by density gradient centrifugation and examined biochemically and microbiologically. Twenty-four hours after the inoculation of P. haemolytica bacterial proliferation to greater than 0 h levels had occurred in four of six animals inoculated with P. haemolytica alone, two of eight inoculated with P. haemolytica 4 days after PI3 and all of eight inoculated with P. haemolytica 6 days after PI3. Mean bacterial numbers in animals inoculated with P. haemolytica 6 days after PI3 and killed at 24 h (10(9.1 +/- 1.9)) were significantly higher than they were in the other two groups killed at this time (PI3 4 days, P. haemolytica 24 h, mean = 10(5.3 +/- 1.7); P. haemolytica alone 24 h, mean = 10(4.5 +/- 2.9)). Pneumonic lesions were also more severe in the first group. This defect in pulmonary clearance and increase in the severity of pneumonia in animals inoculated with P. haemolytica 6 days after PI3 coincided with a 1000-fold decrease in virus titres in the lung between Day 6 and Day 7 after virus inoculation and the first detectable evidence of the host's immune response. The virus infection resulted in a significant increase in the number of AM that could be recovered from the lung and an increase in the number of AM with cytoplasmic vacuolation. However, there was no difference in the total number of AM or the number of vacuolated AM between animals that controlled the P. haemolytica infection and those in which proliferation of P. haemolytica occurred. The inoculation of P. haemolytica resulted in a 100-fold increase in the number of neutrophils in the lavage fluid, but there were no differences between virus-infected and uninfected animals, nor was there a difference between animals that controlled the P. haemolytica infection and those that did not.(ABSTRACT TRUNCATED AT 400 WORDS)

The role of neutrophils in the development of cadmium chloride-induced emphysema in lathyrogen-fed hamsters

This study was designed to evaluate the role of neutrophils (PMNs) in the pathogenesis of emphysema. After administration of CdCl2 intratracheally to hamsters fed a lathyrogen, beta-amino propionitrile fumarate (BAPN), the classic lesions of emphysema developed. Administration of specific antineutrophil serum markedly reduced the PMN influx into the lungs which followed CdCl2 exposure and produced a substantial decrease in elastase and collagenase content of bronchoalveolar lavage fluid (BAL). The degree of emphysema in PMN-depleted hamsters given BAPN and CdCl2 was not different from that in hamsters given BAPN and CdCl2. Furthermore, the degree of acute lung injury following CdCl2, as determined by hydroxyproline content of BAL and by lung lipid peroxidation, was the same in PMN-depleted and non-depleted groups. Thus, PMNs were not necessary for the induction of emphysema in BAPN-CdCl2-treated hamsters. The results suggest that PMNs may not be obligate mediators of emphysema.

Modulation of pulmonary clearance of bacteria by antioxidants

To further delineate the mechanisms underlying murine pulmonary defenses against bacterial infection, we studied the effects of antioxidant enzymes and hydroxyl radical scavengers on pulmonary clearance processes. Intratracheal injection of catalase and superoxide dismutase resulted in prolonged intraalveolar residence of the enzymes, but caused no decrease in rates of clearance of either Staphylococcus aureus 502A or Pseudomonas aeruginosa PAO1. In contrast, dimethylsulfoxide and dimethylthiourea caused significant depression of clearance of P. aeruginosa without altering clearance of S. aureus. These results provide further differentiation between clearance processes affecting gram-negative and gram-positive bacteria and suggest that murine clearance of gram-negative organisms may be in part mediated by reactions which generate hydroxyl anion. In vivo administration of agents which inhibit hydrogen peroxide-, superoxide-, or hydroxyl anion-mediated reactions do not alter normal clearance of S. aureus.

Comparative role of complement in pneumococcal and staphylococcal pneumonia

To evaluate the role of complement in pneumococcal and staphylococcal pneumonia, we decomplemented rats with cobra venom factor and inoculated them intratracheally with Staphylococcus aureus or type 25 pneumococci. S. aureus produced a patchy bronchopneumonia in normal Sprague-Dawley or Lewis rats, and decomplementation did not increase the severity of staphylococcal infection in either rat strain as judged by quantitative cultures of the lungs and blood at 6, 24, and 48 h after inoculation. In contrast, decomplementation markedly increased the severity of pneumonia caused by type 25 pneumococci in Sprague-Dawley and Lewis rats. In Sprague-Dawley rats, decomplementation significantly increased the number of bacteria in the lungs at 3, 6, and 24 h of infection. Bacteremia developed early in decomplemented Sprague-Dawley rats, but the higher pulmonary bacterial counts did not appear to be caused by bacteremic seeding of the lungs. Decomplemented Sprague-Dawley rats inoculated intravenously with pneumococci failed to develop the very high levels of bacteria in the lungs that were observed when the rats were inoculated intratracheally. Moreover, decomplemented Lewis rats inoculated intratracheally with pneumococci developed significantly increased numbers of pneumococci in the lungs early in infection (3 and 6 h) when they had no detectable bacteremia. These data indicate that in murine models complement plays a major protective role against type 25 pneumococci in the lung, whereas complement is not important to host defense in staphylococcal pneumonia.

Early bacterial clearance from murine lungs. Species-dependent phagocyte response

Two sets of phagocytic cells are available to defend the lung against inhaled bacteria. Both resident alveolar macrophages and granulocytes from the circulation have been observed in pulmonary air spaces after the deposition of bacteria; their functional roles, however, have been defined. We rendered mice selectively granulocytopenic with heterologous antiserum in order to ascertain the relative contributions of these two groups of cells in intrapulmonary bacterial killing. The clearance of Staphylococcus aureus was unimpaired in granulocytopenic animals, confirming the primary role of the alveolar macrophages in the killing of these organisms. In contrast, granulocytopenic animals cleared only 10.0+/-7.0% of an inoculum of Klebsiella pneumoniae compared with 33.0+/-4.0% clearance in normal animals (P < 0.02), and Pseudomonas aeruginosa proliferated to 513% of baseline levels in granulocytopenic animals, whereas normal mice cleared 26.8+/-10.6% of the inoculum. These findings indicate that circulating granulocytes play a major role in the clearance of the latter two organisms. This variation in cellular response to different bacterial species suggests that the defense of the lung against pathogenic bacteria is more complex than has been previously assumed.