Inhaled particle-bound sulfate: effects on pulmonary inflammatory responses and alveolar macrophage function

Acid sulfate-coated solid particles are a significant environmental hazard produced primarily by the combustion of fossil fuels. We have previously described a system for the nascent generation of carbonaceous particles surface coated with approximately 140 microg/m(3) acid sulfate [cpSO(4)(2-); 10 mg/m(3) carbon black (CB) and 10 ppm sulfur dioxide (SO(2)) at 85% relative humidity (RH)]. The effects of inhaled cpSO(4)(2-) on pulmonary host defenses are assessed in the present work. Mice were acutely exposed (4 h) to either 10 mg/m(3) CB, 10 ppm SO(2), or their combination at 10% or 85% RH in a nose-only inhalation chamber. No evidence of an inflammatory response was found following any of the exposures as assessed by total cell counts and differential cell counts from bronchoalveolar lavage fluid. However, alveolar macrophage Fc receptor-mediated phagocytosis decreased only following exposure to 140 microg cpSO(4)(2-), significant suppression occurred after 24 h, maximal suppression occurred at 3 days postexposure, and recovery to preexposure levels required 7-14 days. Intrapulmonary bactericidal activity (IBA) was also suppressed only after exposure to 140 microg cpSO(4)(2-); suppression was maximal at 1 day postexposure and recovered by day 7. To assess the effects of lower cpSO(4)(2-) concentrations, mice were repeatedly exposed to 1 mg/m(3) CB and 1 ppm SO(2) at 85% RH ( approximately 20 microg/m(3) cpSO(4)(2-) for 4 h/day) for up to 6 days. A significant decrement in IBA was observed following 5 and 6 days of exposure. These studies indicated that acute or repeated exposure to cpSO(4)(2-) could alter pulmonary host defense mechanisms.

Interstrain variation in murine susceptibility to inhaled acid-coated particles

Epidemiologic studies have demonstrated a positive correlation between concentration of acid aerosol and increased morbidity and mortality in many urban environments. To determine whether genetic background is an important risk factor for susceptibility to the toxic effects of inhaled particles, we studied the interstrain (genetic) and intrastrain (environmental) variance of lung responses to acid-coated particle (ACP) aerosol in nine strains of inbred mice. A flow-past nose-only inhalation system was used to expose mice to ACPs produced by the cogeneration of a carbon black aerosol-sulfur dioxide (SO(2)) mixture at high humidity. Three days after a single 4-h exposure to ACPs or filtered air, mice underwent bronchoalveolar lavage, and cell differentials and total protein were determined as indexes of inflammation and epithelial permeability, respectively. To determine the effect of ACPs on alveolar macrophage (AM) function, lavaged AMs were isolated from exposed animals and Fc receptor-mediated phagocytosis was evaluated. Compared with air-exposed animals, there was a slight but significant exposure effect of ACPs on the mean number of lavageable polymorphonuclear leukocytes in C3H/HeJ and C3H/HeOuJ mice. ACP exposure also caused a significant decrease in AM phagocytosis. Relative to respective air-exposed animals, Fc receptor-mediated phagocytosis was suppressed in eight of nine strains. The order of strain-specific effect of ACPs on phagocytosis was C57BL/6J > 129/J > SJL/J > BALB/cJ > C3H/HeOuJ > A/J > SWR/J > AKR/J. There was no effect of ACP exposure on AM phagocytosis in C3H/HeJ mice. The significant interstrain variation in AM response to particle challenge indicates that genetic background has an important role in susceptibility. The effects of ACPs on AM function, inflammation, and epithelial hyperpermeability were not correlated (i.e., no cosegregation). This model may have important implications concerning interindividual variation in particle-induced compromise of host defense.

Genetic modeling of susceptibility to nitrogen dioxide-induced lung injury in mice

We investigated the mode of inheritance of susceptibility to nitrogen dioxide (NO2)-induced lung injury in inbred mice. Susceptible C57BL/6J (B6) and resistant C3H/HeJ (C3) mice, as well as F1, F2, and backcross (BX) populations derived from them, were exposed to 15 parts per million NO2 for 3 h. Six hours after exposure, animals were lavaged, and differential cell counts and cell viability (cytotoxicity) were measured. Statistically significant (P < 0.05) differences in numbers of lavageable macrophages, epithelial cells, and dead cells were found between inbred strains. Distributions of cellular responses in F1 progeny overlapped both progenitors, and mean responses were intermediate. In C3:BX progeny, ranges of responses to NO2 closely resembled C3 mice, and means were not significantly different between populations. Ranges of cellular responses to NO2 in B6:BX and intercross progeny overlapped both progenitors; mean responses of both populations were intermediate to progenitors. Segregation analyses tested goodness of fit of phenotyping data with various inheritance models, and the highest likelihood for each cell response to NO2 was for the hypothesis two-unlinked loci general. We conclude that there are likely two major unlinked genes that account for differential susceptibility to acute NO2 exposure. The chromosomal location of the genes is not known.

Inhalation of acid coated carbon black particles impairs alveolar macrophage phagocytosis

A flow-past nose-only inhalation system was used for the co-exposure of mice to carbon black aerosols (CBA) and sulfur dioxide (SO2) at varying relative humidities (RH). The conversion of SO2 to sulfate (SO4(-2)) on the CBA, at a fixed aerosol concentration, was dependent on RH and SO2 concentration. The effect of the aerosol-gas mixture on alveolar macrophage (AM) phagocytosis was assessed three days following exposure for 4 h. Exposure to 10 mg/m3 CBA alone at low RH (10%) and high RH (85%), to 10 ppm SO2 alone at both RH, and to the mixture at low RH had no effect on AM phagocytosis. In contrast, AM phagocytosis was significantly suppressed following co-exposure at 85% RH, the only circumstance in which significant chemisorption of the gas by the aerosol and oxidation to SO4(-2) occurred. The results suggest that fine carbon particles can be an effective vector for the delivery of toxic amounts of SO4(-2) to the periphery of the lung.

The effects of ozone on immune function

A review of the literature reveals that ozone (O3) exposure can either suppress or enhance immune responsiveness. These disparate effects elicited by O3 exposure depend, in large part, on the experimental design used, the immune parameters examined as well as the animal species studied. Despite the apparent contradictions, a general pattern of response to O3 exposure can be recognized. Most studies indicate that continuous O3 exposure leads to an early (days 0-3) impairment of immune responsiveness followed, with continued exposures, by a form of adaptation to O3 that results in a re-establishment of the immune response. The effects of O3 exposure on the response to antigenic stimulation also depend on the time at which O3 exposure occurred. Whereas O3 exposure prior to immunization is without effect on the response to antigen, O3 exposure subsequent to immunization suppresses the response to antigen. Although most studies have focused on immune responses in the lung, numerous investigators have provided functional and anatomical evidence to support the hypothesis that O3 exposure can have profound effects on systemic immunity.

Respiratory aflatoxicosis: suppression of pulmonary and systemic host defenses in rats and mice

Dietary aflatoxin B1 (AFB1) exposure impairs innate and acquired host defenses resulting in increased susceptibility to infections in domesticated animals. Experimental studies have confirmed this observation by demonstrating the immunosuppressive effects of AFB1 ingestion. In addition to being present in dietary components, AFB1 is also found in significant amounts in respirable particles of grain dust. To determine the effect of respiratory tract exposure to AFB1 on host defenses, rats and mice were exposed either by aerosol inhalation or intratracheal instillation to AFB1. Nose-only inhalation exposure of rats to AFB1 aerosols suppressed alveolar macrophage (AM) phagocytosis at an estimated dose of 16.8 micrograms/kg with the effect persisting for approximately 2 weeks. To determine whether another mode of respiratory tract exposure, intratracheal instillation, reflected inhalation exposure, animals were treated with increasing concentrations of AFB1 which also suppressed AM phagocytosis in a dose-related manner albeit at doses at least an order of magnitude more than that obtained by aerosol inhalation. Intratracheal administration of AFB1 also suppressed the release of tumor necrosis factor-alpha from AMs and impaired systemic innate and acquired immune defenses as shown, respectively, by suppression of peritoneal macrophage phagocytosis and the primary splenic antibody response. These findings demonstrate that experimental respiratory tract exposure to AFB1 suppresses pulmonary and systemic host defenses and indicates that inhalation exposure to AFB1 is an occupational hazard where exposure to AFB1-laden dust is common.

Concomitant exposure to carbon black particulates enhances ozone-induced lung inflammation and suppression of alveolar macrophage phagocytosis

The goal of this study was to investigate whether coexposures to carbon black and O3 result in a toxicologic interaction in the lungs as quantitated by the inflammatory response and alveolar macrophage (AM) phagocytosis. This aim was accomplished through inhalation coexposures of Swiss mice for 4 h to target concentrations of 10 mg/m3 of carbon black and 1.5 ppm O3, or exposure to either agent alone. As a control for the coexposure experiments, mice were also exposed for 4 h to carbon black, followed immediately thereafter by exposure for 4 h to O3, or vice versa. At 24 h after exposure, the lungs of the animals were lavaged for quantitation of total and differential cell counts and assessment of AM Fc-receptor-mediated phagocytosis. Exposure to carbon black did not result in an inflammatory response, nor had it any effect on AM phagocytosis. Ozone exposure resulted in an inflammatory response in the lungs and suppression of AM phagocytosis. Both biologic parameters were significantly enhanced following combined exposure to the particle and the gas. Carbon black exposure either before or after O3 had no significant effect on AM phagocytosis as compared to O3 exposure alone. These data demonstrate the toxicologic interaction of coexposures to an inert particle and O3 on well-accepted biologic markers pulmonary toxicity. The mechanism for the enhanced biologic effect may be that the carbon black particle acts as a carrier mechanism for O3 to areas in the distal lung not accessible to O3 in the gaseous phase or that O3 alters the physicochemistry of the particulate from a nontoxic to a toxic form.

The toxicologic interactions resulting from inhalation of carbon black and acrolein on pulmonary antibacterial and antiviral defenses

The goal of this study was to investigate whether coexposures to carbon black and acrolein result in a toxicologic interaction having effects on lung defenses against infectious agents. This aim was accomplished through in vivo studies with inhalation challenges of infectious agents that probe the functional integrity of the multicomponent system that comprises the integrated defenses of the lungs. Staphylococcus aureus was used for the alveolar macrophage (AM) surveillance phagocytic system, Proteus mirabilis for the dual phagocytic system composed of AMs and inflammatory polymorphonuclear leukocytes (PMNs), Listeria monocytogenes for the lymphokine-mediated arm of the acquired cellular immune response, and influenza A virus for the cytotoxic T-cell-mediated effector mechanism of cellular immunity. Exposures of Swiss mice to target concentrations of 10 mg/m3 of carbon black and 2.5 ppm acrolein for 4 hr/day for 4 days suppressed the intrapulmonary killing of S. aureus a day after exposure with a return to control levels by Day 7. In contrast, the coexposure enhanced the intrapulmonary killing of P. mirabilis which correlated with a significant increase in accessory phagocytic PMNs recovered from the lungs. Combined exposure to carbon black and acrolein also resulted in impaired elimination of L. monocytogenes and influenza A virus from the lungs. Neither exposure to carbon black alone nor exposure to acrolein alone had any effect on the functional integrity of lung defenses against the four infectious agents. These data demonstrate the effects of the toxicologic interaction of coexposures to an inert particle and acrolein on innate and acquired defenses of the lungs. The mechanism for the enhanced biologic effect may be that the carbon black particle acts as a carrier mechanism for acrolein to the deep lung.

Use of physical chemistry and in vivo exposure to investigate the toxicity of formaldehyde bound to carbonaceous particles in the murine lung

Knowledge about the health effects of exposure to formaldehyde associated with automotive emissions is of pivotal importance in the risk assessment of this agent. Mobile sources emit many combustion-derived pollutants, including formaldehyde, in association with respirable carbon particles. Because it is hydrophilic, most of the inhaled formaldehyde is absorbed in the upper respiratory tract. However, if the organic vapor is adsorbed on respirable particles, formaldehyde may be deposited in the deep lung with the inhaled particles and may be available to interact adversely with cells along the lung parenchyma. On the respiratory surface, the alveolar macrophage phagocytic system plays the pivotal role in defending the lung against infectious agents. Susceptibility to respiratory infections is a relevant and sensitive indicator of the adverse effects of air pollution because acute and chronic exposures to a variety of air pollutants have been shown to decrease pulmonary antibacterial defenses. The goal of this research was to investigate whether exposure to formaldehyde decreases resistance to respiratory infections through dysfunctions of the alveolar macrophage phagocytic system. The study also explored whether interactions between formaldehyde and respirable carbon black particles alter susceptibility to respiratory infections and impairment of alveolar macrophage phagocytosis by delivering adsorbed formaldehyde to the deep lung with the inhaled particles. A carbon black, Regal GR, was used in these studies as a surrogate for the carbonaceous core of Diesel particulate matter. This material was selected to represent the worst-case scenario because the carbon black was expected to adsorb formaldehyde strongly. To accomplish this goal, mice were exposed to formaldehyde and to carbon black and formaldehyde combinations; increased susceptibility to respiratory infections was quantified by alveolar macrophage-dependent intrapulmonary killing of Staphylococcus aureus after an inhalation challenge with the bacterium. The salient findings of the bactericidal studies are as follows: Fifteen parts per million (ppm)* formaldehyde impaired the intrapulmonary killing of S. aureus when exposure followed the bacterial challenge. One ppm formaldehyde impaired the intrapulmonary killing of S. aureus when exposure preceded and was continued after the bacterial challenge. Coexposures to target concentrations of 3.5 mg/m3 carbon black and 2.5 ppm formaldehyde, or 10 mg/m3 carbon black and 5 ppm formaldehyde after the bacterial challenge had no effect on the intrapulmonary killing of S. aureus. Preexposure for four hours per day for four days to target concentrations of 3.5 mg/m3 carbon black and 2.5 ppm formaldehyde had no effect on the intrapulmonary killing of S. aureus when the assay was performed one day after the cessation of exposure.(ABSTRACT TRUNCATED AT 400 WORDS)

Experimental influenza virus infection, silicon dioxide polymorphs, and pulmonary fibrogenesis

Inhalation exposure to silicon dioxide is known to result in acute lung injury followed by pulmonary fibrosis. Recently it has been shown that the acute lung damage during influenza virus infection is also followed by a fibrogenic process. To investigate the interaction between silicon dioxide and influenza virus infection, mice were intratracheally instilled with either alpha-quartz or cristobalite and 3 d later infected by aerosol inhalation with influenza A/PR8/34 virus. At 30, 60, and 90 d after infection, groups of virus infected and noninfected mice were sacrificed and their lungs assessed for total and differential lavage cell counts, lung hydroxyproline content, and morphometric analysis. The silica polymorphs did not alter the proliferation of virus in the lungs as quantitated by infectious virus titers of lung homogenates at 1, 5, 7, 10, and 13 d after infection. In noninfected animals, cristobalite was more reactive than alpha-quartz. The virus infection, in all parameters measured at all time intervals, enhanced the overall fibrogenic response of the lungs to the mineral dusts, suggestive of an additive fibrogenic model. The data demonstrate that virus infection following silicon dioxide exposure results in an interaction that leads to an enhanced fibrogenic response.

Myeloperoxidase-enhanced formation of (+-)-trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene-DNA adducts in lung tissue in vitro: a role of pulmonary inflammation in the bioactivation of a procarcinogen

Several studies have indicated a correlation between the presence of inflammation and the development of cancer. The aim of our study was to determine if pulmonary neutrophils could transform the proximate respiratory carcinogen (+-)-trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene (B[a]P-7,8-diol), to an ultimate carcinogenic metabolite via myeloperoxidase (MPO). To test this hypothesis, virus-free male DBA/2 mice were exposed by inhalation to the Gram-negative bacteria Proteus mirabilis for 1 h. For various time points post-exposure, bronchoalveolar lavage (BAL) was performed to determine total and differential cell counts, cellular MPO activity and production of superoxide. Twelve hours after the exposure, cellular activity of MPO as well as percentage and total number of polymorphonuclear leukocytes peaked and declined thereafter. At this same time point, cells from BAL exhibited increased release of superoxide, as measured by reduction of cytochrome c, after addition of soluble or particulate stimuli, 12-O-tetradecanoylphorbol-13-acetate (TPA) or opsonized zymosan respectively. These cells also elicited biotransformation of B[a]P-7,8-diol as evidenced by enhanced B[a]P-7,8-diol-derived chemiluminescence, tetraol formation and covalently bound adduct formation to exogenous DNA upon addition of TPA or opsonized zymosan. Moreover, the cell-free BAL fluid of infected mice contained substantial MPO activity in comparison to that of uninfected animals. Also, MPO enhanced the binding of B[a]P-7,8-diol to lung DNA in vitro. Unlike previous work emphasizing the potential roles of oxygen free radicals in tumor promotion, our results indicate a role of neutrophilic MPO in the initiation of carcinogenesis.

Aflatoxin B1--DNA adduct formation in rat liver following exposure by aerosol inhalation

There is growing concern that human exposure to respirable grain dust contaminated with aflatoxin B1 (AFB1), a potent hepatocarcinogen, may be a risk factor for a number of human diseases. The objective of this study was to determine if liver DNA adduct formation occurs in rats following either intratracheal injection or nose-only aerosol inhalation exposure to AFB1. Male Fischer 344 rats were exposed by both routes of administration, and in preliminary data using intratracheal instillation, up to 2% of the administered dose became bound to liver DNA. In the nose-only aerosol inhalation experiments, rats were exposed for up to 120 min. Immediately after exposure, four animals were killed at each time point and their livers removed, DNA isolated and purified and analyzed for aflatoxin-DNA adducts by HPLC. A linear dose-response relationship was observed with a correlation coefficient of 0.96 between increasing length of exposure, and the amount of aflatoxin-N7-guanine adducts formed per mg DNA, the mean values and standard errors were 4.2 +/- 0.18, 15.3 +/- 4.3, 21.6 +/- 2.8 and 56.8 +/- 4.6 pmol aflatoxin-DNA adducts per mg DNA for the 20, 40, 60 and 120 min exposures respectively. The amounts of aflatoxin-DNA adducts formed were statistically significantly different (P less than 0.01) among the treated groups. These results indicate that aerosol inhalation is an effective route of exposure to AFB1 in rats that results in genotoxic damage in the liver.

Ozone reduces murine alveolar and peritoneal macrophage phagocytosis: the role of prostanoids

Continuous ozone exposure (0.5 ppm, 1-14 days) reduced the phagocytic activity of murine alveolar and peritoneal macrophages. The response of peritoneal macrophages to ozone was virtually indistinguishable from the response of alveolar macrophages. When added exogenously, prostaglandin E2 (PGE2) inhibited alveolar and peritoneal macrophage phagocytosis. To test the hypothesis that prostanoids mediated the effects of ozone on macrophages, PGE levels of bronchoalveolar lavage fluid (BALF) and the phagocytic activity of macrophages from ozone-exposed mice pretreated with cyclooxygenase inhibitors were measured. PGE levels in BALF were increased following ozone exposure, with high levels of PGE associated with large decreases in phagocytic activity. Pretreatment with indomethacin and d-naproxen completely inhibited ozone-induced increases in PGE recovered by BAL and the suppression of peritoneal macrophage phagocytic activity. The inactive enantiomer of naproxen, l-naproxen, was without effect. Indomethacin partially inhibited ozone-induced suppression of alveolar macrophage phagocytic activity. These observations suggest that prostanoids play a key role in the response to ozone.

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.

Suppression of alveolar macrophage membrane-receptor-mediated phagocytosis by model particle-adsorbate complexes: physicochemical moderators of uptake

In order to assess the abilities of alveolar macrophages (AMs) to phagocytize adsorbent-adsorbate complexes, rat AMs were incubated in vitro with two carbon blacks that have 15-fold differences in specific surface areas (ASTM classification N339 less than Black Pearls 2000) sorbed with 0.5 and 1.0 monolayer coverages of a polar and semi-polar adsorbate (acrolein and benzofuran, respectively). One-half monolayer coverages of N339 with either adsorbates significantly suppressed the phagocytosis of the carbon black, whereas one monolayer coverage did not. Neither adsorbate at either coverages affected the phagocytosis of Black Pearls 2000. The capacity of macrophages to phagocytize a subsequent particle challenge via the Fc-membrane receptor was quantified following treatment of the macrophages with the carbon black-adsorbate complexes. Treatment of the macrophages with carbon black N339-adsorbates complexes at both coverages impaired Fc-receptor-mediated phagocytosis, whereas no effect was observed when the carbon black was Black Pearls 2000. The results of this study indicate that the surface properties of the particles, the chemical properties of the chemical pollutants, and the interactions between particles and pollutants play a major role in defining the biological effect of particle-pollutant complexes.

Pulmonary antibacterial defenses during mild and severe influenza virus infection

Severe influenza virus infections with pneumonic involvement are known to predispose the lungs to bacterial superinfections due to dysfunctions in the alveolar macrophage (AM) phagocytic system. To determine whether milder forms of influenza without pneumonic involvement have a similar outcome, pulmonary antibacterial defenses and AM phagocytosis were compared in murine models of mild and severe influenza virus A/HK/68 infections. Bactericidal activity was quantitated by the intrapulmonary killing of Staphylococcus aureus following aerosol challenge, whereas the functional capacity of the AMs was determined by Fc-receptor-mediated phagocytosis. With the severe virus infection, maximal suppression of bactericidal activity occurred on day 8 of infection and correlated with impairment of AM phagocytosis. A lesser but significant degree of suppression of pulmonary antibacterial defenses and AM phagocytosis was observed on the third day of the mild virus infection. The data demonstrate that mild influenza virus infections that are limited to the upper respiratory tract also impair pulmonary antibacterial defenses and may predispose the lungs to bacterial superinfections.

Sequential virus infections, bacterial superinfections, and fibrogenesis

Parainfluenza 1 (Sendai) and influenza A virus pneumonitis cause severe lung damage, which, upon resolution, is followed by persistent alveolitis and parenchymal changes characterized by patchy consolidation and collagen deposition in the affected areas. To determine whether these long-term sequelae of the virus pneumonias are cumulative, mice were infected by aerosol inhalation with Sendai virus, influenza A virus, or Sendai followed 30 days later by influenza virus infection. At 90 days after the initial infection, mice were killed for assay of long-term parenchymal changes as quantitated lung hydroxyproline (Hpr) content, morphometric analysis, and total and differential lavage cell counts. Sendai virus infection did not alter the proliferation of influenza virus in the lungs as quantitated by infectious virus titers on Day 1, 3, 5, 7, 9, and 11 of influenza infection. At Day 90, lung Hpr content was cumulative in dual-infected mice, with a concomitant increase in the persistent alveolitis. To determine whether bacterial infections played a similar role in these long-term pulmonary sequelae, mice were infected by aerosol inhalation with either Staphylococcus aureus or Klebsiella pneumoniae or, during the course of influenza virus infection, superinfected with each of the bacteria. Sixty days after infection with K. pneumoniae alone, lung Hpr levels were significantly increased over those in noninfected control mice. Infection with S. aureus had no effect on the quantitated parameters of long-term lung damage. In influenza-infected mice superinfected with K. pneumoniae, lung Hpr content was significantly increased over that of S. aureus did not elevate any quantitated parameter of lung damage when compared with the virus alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Suppression of alveolar macrophage membrane receptor-mediated phagocytosis by model and actual particle-adsorbate complexes. Initial contact with the alveolar macrophage membrane

Alveolar macrophages were treated with carbon blacks and adsorbates in order to evaluate the biologic effect of adsorbate, adsorbent and adsorbate-adsorbent complexes. Their capacity to phagocytize a subsequent challenge via the Fc-membrane receptor was quantified. Phagocytosis was suppressed in a dose-related manner with increasing concentrations of both carbon blacks and adsorbates. Carbon black N339 covered with 0.5 monolayers of the adsorbates suppressed phagocytosis more than N339 without the adsorbates. Increasing the adsorbate acrolein coverage from 0.5 to greater than 2.0 monolayers suppressed phagocytosis in a dose-related manner. Finally, samples of diesel particulate matter collected from an engine operated on a pure hydrocarbon fuel with various oxidizers, air (PSU #1) and an oxidizer free of nitrogen (N-free) were tested. Treatment of the macrophages with PSU #1 had a negligible effect on phagocytosis whereas the N-free sample suppressed phagocytosis in a dose-related manner. The data show that alveolar macrophage Fc-receptor-mediated phagocytosis is affected by: carbon black and adsorbate identity and concentration, coverage of the carbon black with adsorbates, and the oxidizer used in the generation of particles emitted by a diesel engine.

A genetic model for evaluation of susceptibility to ozone-induced inflammation

We examined ozone-induced airway inflammatory responses in inbred mice, and progeny of crosses between them, to investigate genetic susceptibility to ozone. Nine strains of male mice (18-23 g, 5-7 wk) were exposed for 3 h to 2 ppm ozone (O3) or filtered air (control), and pulmonary inflammation was assessed 2, 6, and 24 h after exposure by inflammatory cell counts and total protein content in bronchoalveolar lavage (BAL). The time course of the response to O3 was consistent between the strains. The maximum change in polymorphonuclear leukocytes (PMNs) was detected 6 h after O3, and the maximum increase in BAL protein occurred 24 h postexposure. Air controls exhibited no detectable changes in the parameters of inflammation at any time. The phenotypes of the C57BL/6J (B6, termed susceptible) and C3H/HeJ (C3, termed resistant) strains were easily distinguished by the magnitude of their inflammatory responses to O3. A 22-fold difference in PMNs was detected between the two strains 2 h after O3 (P less than 0.001), and a sixfold difference was found 6 h after O3 (P less than 0.001). Total BAL proteins were also significantly different between the B6 and C3 strains 6 h (P less than 0.01) and 24 h after O3 (P less than 0.001). To further evaluate the potential genetic contribution to the inflammatory response, the F1, F2, and backcross progeny from crosses between B6 and C3 strains were examined. The phenotypes of these progeny were consistent with the hypothesis that a single autosomal recessive gene at the Inf locus confers susceptibility to acute O3-induced influx of PMNs, but the genetic control of altered permeability is not clear.(ABSTRACT TRUNCATED AT 250 WORDS)

Influenza virus infection, ozone exposure, and fibrogenesis

Oxidant exposure following chemically induced lung injury exacerbates the tendency to develop pulmonary fibrosis. Influenza virus pneumonitis causes severe acute lung damage that, upon resolution, is followed by a persistent alveolitis and parenchymal changes characterized by patchy interstitial pneumonia and collagen deposition in the affected areas. To determine whether oxidant exposure exacerbates the virus-induced alveolitis and residual lung damage, mice were infected by aerosol inhalation with influenza A virus and continuously exposed to 0.5 ppm ozone or ambient air. Noninfected control mice were exposed to either ambient air or ozone. On various days during the first month after infection, groups of mice were sacrificed and their lungs assessed for acute injury (lung lavage albumin, total and differential cell counts, wet/dry ratios, and morphometry). At 30, 60, 90, and 120 days after infection, groups of mice were sacrificed for total and differential lavage cell counts, lung hydroxyproline content, and morphometric analysis. Ozone exposure did not alter the proliferation of virus in the lungs as quantitated by infectious virus titers of lung homogenates at 1, 4, 7, 10, and 15 days after virus infection but mitigated the virus-induced acute lung injury by approximately 50%. After Day 30 a shift in the character of the pulmonary lesions was observed in that continuous exposure to ozone potentiated the postinfluenzal alveolitis and structural changes in the lung parenchyma. Additional studies suggest that the mechanism for the enhanced postinfluenzal lung damage may be related to the oxidant impairing the repair process of the acute influenzal lung damage. These data demonstrate that ozone exposure mitigates acute virus-induced lung injury and potentiates residual lung damage.

Modulation of pulmonary defense mechanisms against viral and bacterial infections by acute exposures to nitrogen dioxide

The scientific literature suggests that ambient levels of nitrogen dioxide increase susceptibility to respiratory infections. However, this association has not been conclusively demonstrated. The epidemiologic data regarding this relationship are inconclusive because these studies have used parameters of "acute respiratory illness" that are not necessarily related to infectious episodes. Previous animal studies have used either mortality after bacterial infection with virulent bacteria or decreased rate of intrapulmonary killing of bacteria with low virulence. Studies using appropriate bacterial and viral challenge organisms, with morbidity as an endpoint, provide a better basis for extrapolation to humans. The investigations in animals suggest a relationship between nitrogen dioxide and increased susceptibility to respiratory infection, but studies in which functional parameters of host resistance to such infections have been used are few. The aim of this work was to determine the threshold level of acute nitrogen dioxide exposure that would induce increased susceptibility to, and increased severity of, viral and bacterial infections. Physiologic parameters of host resistance to respiratory infections were used as endpoints. A composite picture was developed of dose-response relationships between nitrogen dioxide and the impairment of a spectrum of defense parameters in the murine respiratory tract against viral and bacterial challenges. The salient findings of this study are as follows: (1) the intrapulmonary killing of Staphylococcus aureus was impaired at 5 ppm of nitrogen dioxide; (2) this effect was found at 2.5 ppm or less when nitrogen dioxide exposure was superimposed on lungs predisposed to lowered resistance through immunosuppression with corticosteroids; (3) the adverse effect of nitrogen dioxide occurred at lower concentrations when exposure followed bacterial challenge; and (4) during the course of murine Sendai virus infection, exposure to nitrogen dioxide for four hours per day did not alter the infection in the lungs, but rather it enhanced lung pathology. The implications of these findings are that the antibacterial defenses of the lungs are susceptible to the inhibiting effects of short acute exposures of lower concentrations of nitrogen dioxide when the lungs are predisposed by bacteria present or, even more so, by immunosuppression. The alveolar macrophage phagocytic system is the defense component of the lungs that is most susceptible to the adverse effects of nitrogen dioxide. The finding that nitrogen dioxide increases virus-associated lung damage suggests that the increased severity of the disease process results from the proliferation of the virus to high titers, rather than from alterations of the infective process.

Reduction of influenza virus pathogenesis by exposure to 0.5 ppm ozone

Continuous exposure to 0.5 ppm ozone during the course of murine influenza A/PR8/34 virus infection reduced the severity of the disease as quantitated by histologic (morphometric), biochemical (serum albumin in lavage fluid), and gravimetric (lung wt/dry weight ratios) parameters of lung injury. The ozone-mediated abatement of the lung injury was independent of peak pulmonary virus titers. However, determination of the sites of virus multiplication indicated that exposure to ozone resulted in a less widespread infection of the lung parenchyma. Furthermore, ozone exposure reduced the antiviral immune response as shown by reduced numbers of phenotypically quantitated T- and B-lymphocytes recovered from lung tissues and reduction of serum antibody titers. Since the pathogenesis of influenza virus infection depends on both the site of viral replication and the antiviral immune response, these studies suggest that redistribution of virus growth in murine lungs and immunosuppressive mechanisms are factors in the ozone-reduced disease severity.

Erythromycin-induced suppression of pulmonary antibacterial defenses. A potential mechanism of superinfection in the lung

Erythromycin is a broad-spectrum antibiotic commonly used in patients with respiratory infections. Certain of these patients become colonized with new microorganisms and develop superinfections. Antibiotics have a number of effects other than simply killing or inhibiting the growth of bacteria and may have direct effects upon host cells, including phagocytes. In vitro and in vivo studies have demonstrated that erythromycin decreases polymorphonuclear leukocyte (PMN) directed migration. To test the hypothesis that erythromycin inhibits normal PMN migration into the alveoli in response to a bacterial challenge, mice were challenged by aerosol inhalation with Proteus mirabilis or Staphylococcus aureus and injected intravenously with erythromycin (50 or 100 mg/kg). Pulmonary bactericidal activity and total lavaged lung cell and differential counts were determined 4 h after bacterial challenge. In control mice, only 24 +/- 2% of the initial inoculum of P. mirabilis was viable at 4 h. At a dose of 100 mg/kg, lung defenses after erythromycin were ablated, allowing the proliferation of P. mirabilis to 113 +/- 5% of the initial inoculum. The number of PMN obtained by lavage after P. mirabilis challenge was also inhibited by erythromycin in a dose-dependent manner. In untreated animals, 5.0 +/- 0.2 x 10(6) PMN were recovered as compared with 3.1 +/- 0.4 x 10(6) and 1.1 +/- 0.3 x 10(6) with increasing doses of erythromycin. Intrapulmonary bactericidal activity against S. aureus was not impaired by erythromycin.(ABSTRACT TRUNCATED AT 250 WORDS)

Impairment of antibacterial defense mechanisms of the lung by extrapulmonary infection

To determine whether extrapulmonary infection alters antibacterial defenses of the lung, we challenged mice with peritonitis due to Escherichia coli by aerosol inhalation with either Staphylococus aureus or Pseudomonas aeruginosa. In animals without peritonitis, 14% +/- 5% and 11% +/- 1% of the initially deposited viable S. aureus and P. aeruginosa, respectively, remained in the lungs at 4 hr. In contrast, in mice with peritonitis, at 4 hr 45% +/- 9% of the staphylococci were recoved, and the P. aeruginosa had increased to 948% +/- 354% of the initial inoculum. Proliferation of P. aeruginosa in mice with peritonitis was associated with impaired recruitment of polymorphonuclear neutrophils (PMNs) into the lungs. In contrast, a noninfectious stimulus induced more PMNs into the peritoneal cavity than did intraabdominal sepsis but only minimally impaired PMN recruitment into the lungs after aerosol challenge with P. aeruginosa. Sterile intraperitoneal stimulation did not significantly impair intrapulmonary killing of P. aeruginosa. Levels of antigenic C3 and functionally active C5 were significantly depleted in mice with peritonitis due to E. coli. We conclude that the systemic effects of sepsis, including complement depletion, contribute to the decreased pulmonary PMN recruitment and to impaired intrapulmonary bacterial killing of animals with peritonitis due to E. coli.

Methylprednisolone impairs the bactericidal activity of alveolar macrophages

Corticosteroid treatment of patients following acid aspiration has been reported to increase the incidence of bacterial pneumonia, with Staphylococcus aureus being a common isolate. We hypothesized that administration of methylprednisolone (MP) to mice with acid-injured lungs would impair pulmonary clearance of S. aureus by compromising the bactericidal oxidative metabolism of pulmonary phagocytes. Using an inhalational bacterial challenge, we established that MP decreased pulmonary clearance of S. aureus. In mice with normal lungs and without MP treatment 14 +/- 2% of all initially deposited Staphylococci remained at 4 hr compared to 28 +/- 2% remaining in the lungs of mice with MP treatment. In mice with acid-injured lungs, MP caused a greater impairment of S. aureus clearance at 4 hr with 44 +/- 10% of all initially deposited bacteria remaining in the lungs of control mice and 210 +/- 24% remaining in the lungs of MP-treated mice. After it was demonstrated that there was no difference in the numbers of phagocytic cells obtained by lung lavage from mice with or without MP treatment, the bactericidal oxidative metabolism of these cells was quantitated using luminol-amplified chemiluminescence. Phagocytic cells from mice not exposed to S. aureus displayed minimal chemiluminescence whether they were treated with saline (22 +/- 14 mV) or MP (14 +/- 8 mV). In contrast, phagocytes from saline-treated mice exposed to S. aureus showed a significant increase in chemiluminescence (159 +/- 22 mV). Pretreatment with MP, however, prevented this response to S. aureus (21 +/- 13 mV), indicating that bactericidal oxidative metabolism of these phagocytic cells had been suppressed.(ABSTRACT TRUNCATED AT 250 WORDS)

Aminophylline-induced suppression of pulmonary antibacterial defenses

Respiratory infections are frequently observed in patients with chronic obstructive pulmonary disease, indicating that host defenses are compromised. Antibacterial defenses of the lung against such infections include the alveolar macrophage and polymorphonuclear leukocytes (PMN) that migrate into the lung to provide auxiliary phagocytic defenses. To test the hypothesis that aminophylline acutely impairs pulmonary antibacterial defenses, mice were challenged by aerosol inhalation with Staphylococcus aureus or Proteus mirabilis and injected intraperitoneally with aminophylline (20, 40, or 80 mg/kg). Pulmonary bactericidal activity and total lavaged lung cell and differential counts were determined 4 h after bacterial challenge. The highest dose of aminophylline suppressed the killing of S. aureus so that 55 +/- 5% of the initial viable bacteria remained as compared with 22 +/- 4% in the control animals. In contrast, there was a dose-related suppression of pulmonary antibacterial defenses against gram-negative bacteria. With doses of 40 and 80 mg/kg, lung defenses were ablated, allowing the proliferation of P. mirabilis to 115 +/- 9% and 253 +/- 9%, respectively, the control value being 26 +/- 3%. The number of PMN obtained by lavage after aerosol challenge with P. mirabilis was also inhibited by aminophylline in a dose-dependent manner. From the lungs of untreated animals 5.0 +/- 0.3 X 10(6) PMN were recovered as compared with 3.3 +/- 0.1 X 10(6), 2.5 +/- 0.2 X 10(6), and 1.8 +/- 0.1 X 10(6), respectively, with increasing doses of aminophylline. The bactericidal activity of lavaged PMN from the lungs of aminophylline-treated rats challenged with the gram-negative bacterium in vivo was significantly depressed when compared with that in control animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanisms of bacterial superinfections in viral pneumonias

Although it was once thought that bacterial infection was merely a function of the virulence of the microbe it is now known that other pathogens can alter host resistance. With respect to bacterial superinfection during viral pneumonias, three important factors must be considered; the role of the virus, the role of the bacterium, and the immune status of the host. The fact that no one bacterial species is responsible for all human cases of postinfluenzal bacterial pneumonia indicates that there is a general impairment of pulmonary antibacterial defenses brought about by the viral infection. The fact that the rate of intrapulmonary killing varies with different bacterial species indicates that the superinfecting organism can itself play a role in the dual disease process. Finally, it has been amply demonstrated that the resistance of the host is dependent on a variety of factors which include innate variables such as genetic endowment and a multitude of imponderable variables acquired through life experiences which can be considered under the general category of "host factors". All three factors interact and collectively impinge upon the resistance of the host. Lastly, as influenza virus infections occur most frequently in epidemic outbreaks, the relationship between influenza virus and secondary bacterial infections is the classic example. However, there is growing evidence that an association exists between other virus groups and bacterial pathogens in respiratory tract infections. Adenovirus, parainfluenza virus, and rhinovirus are among the agents that appear to pave the way for bacterial pneumonias. Mycoplasma pneumoniae, once considered to be a virus and the cause of primary atypical pneumonia, may also render the respiratory tract susceptible to bacterial invasion.

Influenza virus-induced immune complexes suppress alveolar macrophage phagocytosis

Immune complexes in the lungs are capable of inducing adverse responses. Herein we have detailed the formation of immune complexes in the lungs of influenza virus-infected mice and examined their effect on alveolar macrophage defenses. On days 3, 7, 10, 15, and 30 after aerosol infection with influenza A/PR8/34 virus, the acellular pulmonary lavage fluid was tested for viral antigen, specific viral antibody, and immune complexes by immunoassays. Whereas peak viral antigen (day 3) diminished to undetectable levels by day 10, specific viral antibody remained at a low concentration until day 10, after which it rapidly increased. Immune complex concentrations increased through day 7, peaked at day 10, and gradually returned to the control level by day 30. These data demonstrate that immune complexes of detectable size are induced by influenza virus infection during the interface between antigen excess and antibody excess conditions. Since alveolar macrophages are the pivotal phagocytic defense cells in the lung, the ability of normal alveolar macrophages to ingest opsonized erythrocytes was quantitated in the presence of immune complexes from lavage fluid. Immune complexes from day 10 virus-infected lungs caused a dose-dependent suppression of antibody-mediated phagocytosis to 30% of control values. In contrast, although these immune complexes also markedly decreased the phagocytosis of antibody-coated yeast cells, they did not significantly impair the antibody-independent ingestion of unopsonized yeast cells by macrophages. the suppressive effects of immune complexes on alveolar macrophages may, in part, explain the phagocytic dysfunction that occurs 7 to 10 days after influenza virus pneumonia.

Dynamics of viral growth, viral enzymatic activity, and antigenicity in murine lungs during the course of influenza pneumonia

Mice were infected by aerosol inhalation with influenza A/PR8/34 virus, and the kinetics of infection were monitored by the measurement of infectious virus, viral neuraminidase activity, and viral antigen as detected by enzyme immunoassay. Pulmonary levels of neuraminidase activity closely paralleled the infectious titers quantitated by standard egg inoculation techniques. Both viral neuraminidase activity and viral antigen increased in a dose-dependent manner during the early stages of the viral infection. After day 5, however, viral neuraminidase activity precipitously declined, whereas viral antigen levels remained elevated at high concentration for up to 60 days. Immunosuppressive treatment with cyclophosphamide resulted in the prolonged maintenance of peak virus titers without any additional increases in viral antigen. Previously infected mice were resistant to reinfection with homologous virus as evidenced by the lack of detectable viral neuraminidase activity and the lack of generation of additional viral antigen. These data define the temporal relationship between levels of infectious virus, neuraminidase activity, and viral antigen in an experimental model of influenza virus infection.

Alveolitis induced by influenza virus

Previous studies of influenza virus infections have focused on the acute pathologic manifestations associated with the virus pneumonia; however, there is evidence suggestive of persistent pathologic processes with possible long-term consequences. Herein we have examined the long-term outcome of virus pneumonia in mice infected by aerosol inhalation of a sublethal dose of influenza A/PR8/34 virus. At 3, 5, 7, 9, 15, 30, 60, 90, 120 days, and a year thereafter, the lavageable lung cell populations and differential counts were quantitated. Consistent with previous studies we demonstrated an inflammatory cellular response during the acute phase of the infection. However, this inflammatory response did not completely resolve, the pulmonary leukocytosis remaining stable from Day 30 through a year after virus infection. For example, on Day 30, virus-infected lungs yielded 12.4 +/- 0.9 X 10(5) cells per lavage of which 15 +/- 3% were polymorphonuclear leukocytes, 18 +/- 4% were lymphocytes, and 67 +/- 5% were alveolar macrophages. In contrast, 7.2 +/- 0.5 X 10(5) cells per lavage were obtained from uninfected lungs of which more than 98% were alveolar macrophages. Histopathologic examination of virus-infected lungs showed an ongoing inflammatory response resulting in patchy mononuclear interstitial pneumonia, deposition of collagen in the affected areas, and marked hyperplasia of bronchial-associated lymphoid tissue. Infectious virus could not be recovered after Day 9. However, in contrast to loss of infectivity, viral antigen persisted at high concentrations in the lung. We conclude that influenza virus infection induced a long-term alveolitis that is associated with persistence of viral antigen. These data open the possibility that influenza virus infections may play a role in interstitial lung disease.

Pulmonary inflammatory responses during viral pneumonia and secondary bacterial infection

Pulmonary bactericidal mechanisms are reduced during viral pneumonia. It has been proposed that secondary bacterial pneumonia occurs because the host's ability to mount an inflammatory response is suppressed. These studies examine the pathobiology of parainfluenza 1 virus and viral-associated staphylococcal pneumonia in a murine model. The sequence of leukocyte and fluid protein changes were studied in the lung and blood. An influx of polymorphonuclear leukocytes into the lungs occurred early in the viral infection, and coincided with lung macrophages aggregation. Maximal increases in pulmonary leukocytes occurred during the period associated with maximum suppression of lung bactericidal mechanisms (days 7-9). During this period, the host was capable of mounting an additional inflammatory response to staphyloccal challenges. Finally, viral pneumonia resulted in a prolonged elevation in the numbers of pulmonary macrophages, lymphocytes, and granulocytes. Thus, changes in lung biology persisted well after resolution of the initiating infections.

Lung macrophage defense responses during suramin-induced lysosomal dysfunction

Lysosomes form an integral part of the degradative mechanisms of the phagocytic cells. Mice were injected with suramin, a lysosomotrophic drug, to investigate the effects of lysosomal pathology on the cell biology and in situ bactericidal activity of the pulmonary macrophage. Treatment with suramin resulted in marked alterations in the cell biology of the macrophage: (i) increased vacuolization and protein content, (ii) suppressed intracellular phagosome-lysosome fusion, (iii) decreased activity of the lysosomal enzymes beta-glucuronidase and N-acetyl-glucosaminidase, and (iv) enhanced exocytosis of acid phosphatase during phagocytosis. Addition of suramin, in vitro, to cell lysates resulted in a reduction in the catalytic activities of acid phosphatase, beta-glucuronidase, and N-acetyl-glucosaminidase; thereby suggesting that selective interaction, in vivo, between suramin and lysosomes containing beta-glucuronidase and N-acetyl-glucosaminidase may have occurred. Plasma membrane 5'-nucleotide phosphodiesterase activity was increased in macrophages recovered from suramin-treated animals. Although the "resting-state" reduction of nitroblue tetrazolium (NBT) was lower in these macrophages, cells stimulated by a phagocytic challenge demonstrated normal increases in NBT reduction. Phagocytosis, in vitro, and pulmonary bactericidal activity were not altered. These data demonstrate that suramin altered numerous aspects of the phagocyte's lysosomal system. Despite these changes in the cell biology of the pulmonary macrophage, the cell's defense functions were not reduced.

The participation of antiviral immune mechanisms in alveolar macrophage dysfunction during viral pneumonia

Virus infections transiently suppress pulmonary antibacterial defenses by causing dysfunctions in the alveolar macrophage phagocytic system. This impairment of pulmonary bactericidal activity is not associated in time with virus proliferation, but rather with the period of time of rapidly declining virus titers and the expression of the antiviral immune response in the lungs. This temporal relationship suggests that the impairment of pulmonary bactericidal activity might be secondary to the antiviral immune response rather than a direct effect of virus replication. Immune depletion of mice during the course of influenza virus pneumonia ameliorated the virus-induced bactericidal defect and prevented bacterial multiplication in the lungs. In contrast, immune reconstitution reestablished the alveolar macrophage phagocytic defect. These data indicate that virus-induced suppression of pulmonary antibacterial defenses may be, in part, immunologically mediated.

The effects of acrolein exposure on pulmonary antibacterial defenses

Inhalation exposure to acrolein induced a dose-dependent impairment of pulmonary antibacterial defenses in mice. Animals exposed to 3 or 6 ppm of acrolein were increasingly less effective in inactivation of aerogenic challenges of 32P-labeled Staphylococcus aureus. Acrolein concentrations greater than 6 ppm caused increased sensory irritations, but no additional impairment of lung antibacterial resistance. Influenza A viral pneumonia in mice also suppressed pulmonary bacterial activity. Mice convalescing from moderate viral pneumonia became severely deficient in antibacterial defenses when exposed to acrolein. Whether the viral-induced impairment in pulmonary defense delayed the inactivation or allowed the proliferation of bacteria was dependent upon the dose of acrolein. The present study demonstrated that an underlying infectious disease process compounded the pulmonary toxicity of acrolein such that normally moderate toxicity was elevated to a virtual abolition of antibacterial defense mechanisms.

Immune impairment of alveolar macrophage phagocytosis during influenza virus pneumonia

The pathogenesis of viral pneumonia is associated with an intact antiviral immune response. To determine the degree of involvement of the host response in influenza virus-induced impairment of pulmonary antibacterial defenses, mice were immunosuppressed by treatment with antilymphocyte serum (ALS). Eight days after infection, pulmonary defense mechanisms were quantitated by aerogenic challenge with Staphylococcus aureus; the ingestion of opsonized erythrocyte (EA) was used to monitor the phagocytic capability of alveolar macrophages obtained by pulmonary lavage. The ALS treatment alone caused no significant alteration in pulmonary antibacterial defenses or macrophage phagocytosis, nor did it interfere with viral multiplication. In noninfected lungs, less than 1% of the initial viable staphylococci remained viable at 24 h compared with proliferation to 490 +/- 147% in virus-infected lungs. Treatment with ALS prevented staphylococcal multiplication, the bactericidal value being 28 +/- 12% at the same time period. The phagocytic index (EA ingested/100 macrophages) in cells retrieved from normal lungs was 783 +/- 22 compared with 235 +/- 29 in macrophages from virus-infected lungs. The ALS ameliorated the impairment in phagocytic ingestion, the index being 505 +/- 34. Incubation of alveolar macrophages from virus-infected, ALS-treated animals with specific viral antibody reestablished the phagocytic defect in a dose-dependent manner; the index being 215 +/- 30 at the lowest dilution of antiviral globulin. The data demonstrate that the virus-induced suppression of pulmonary antibacterial defenses caused by dysfunction in alveolar macrophage phagocytosis is, in part, immunologically mediated.

Immune-enhanced phagocytic dysfunction in pulmonary macrophages infected with parainfluenza 1 (Sendai) virus

Cultured alveolar macrophages infected with parainfluenza 1 (Sendai) virus were treated with specific antiviral immune serum and their phagocytic activity for opsonized erythrocytes (EA), Candida krusei, and Staphylococcus epidermidis quantitated. Membrane Fc receptor and candida binding activity were unaffected by the viral infection. In contrast, the virus infection decreased the phagocytic ingestion of EA. The addition of immune serum induced new phagocytic defects in that the treatment of virus-infected macrophages decreased the binding of EA and candida and reduced the ingestion of the yeast and the staphylococci. In addition, treatment with immune serum also enhanced the phagocytic defects induced by the virus infection alone, further reducing the binding and ingestion of EA. Neither virus infection nor treatment with immune serum affected the intracellular killing of S. epidermidis. These data demonstrated that virus infection of alveolar macrophages in vitro induce phagocytic defects that are accentuated by the treatment of the macrophages with antiviral antibody.

Alterations of pulmonary defense mechanisms by protein depletion diet

Pulmonary defense mechanisms were quantitated in mice that were fed a protein-free diet (PFD) for periods of 2 and 3 weeks. Despite the severe weight loss and emaciation induced by the diet, the bactericidal mechanisms in their lungs were preserved against aerogenic challenges with staphylococcus aureus, Proteus mirabilis, and Listeria monocytogenes. Phagocytic assays of alveolar macrophages that were retrieved by pulmonary lavage from PFD-fed animals showed a decrease in Fc receptor-mediated binding activity but no alteration in the ingestion of sensitized erythrocytes. In contrast, the PFD induced defects in both the attachment phase and the engulfment phase of the phagocytic process when the challenge organism was Candida krusei. The PFD suppressed the pulmonary inflammatory response after mice were infected with influenza virus strain PR8; such mice also failed to eliminate infectious virus from their lungs. Virus infection in control mice suppressed pulmonary antibacterial defenses against challenges with S. aureus and P. mirabilis, and defect that was ameliorated in the lungs of PFD-fed mice with viral pneumonia. The data demonstrated that pulmonary defense mechanisms were modulated by a PFD but that the observed effect was dependent on the agent used to test host defenses.

Lung defenses against viral and bacterial challenges during immunosuppression with cyclophosphamide in mice

Pulmonary virus infections predispose to secondary bacterial pneumonias by suppressing the antibacterial defenses of the lung. Cyclophosphamide (CY) treatment interferes with antiviral defenses and also impairs pulmonary bactericidal activity. To determine whether CY aggravates secondary bacterial pneumonias, mice were infected by aerosol inhalation with para-influenza 1 (Sendai) virus and injected intraperitoneally with either 0.5, 1.0, 2.5, and 5.0 mg of CY on Days 1 and 5 of the infection. On Day 7, the lungs of control (CY-treated but not infected) and virus-infected mice were lavaged and the total and differential number of free pulmonary cells quantitated. At the same time, other groups of mice were challenged aerogenically with Staphylococcus aureus and the number of initially viable bacteria remaining in their lungs quantitated at 4 and 24 h thereafter. The CY treatment induced a dose-dependent neutropenia, which was paralleled by the number of free pulmonary cells recovered from the lungs. Pulmonary bactericidal activity was also suppressed by CY treatment, with the percentage of staphylococci remaining at 24 h in the lungs of control animals being 0.5 +/- 0.2% and 1.5 +/- 0.5%, 4.0 +/- 1.5%, 8.5 +/- 2%, and 36 +/- 5%, respectively, for the increasing doses of CY. In virus-infected animals, CY treatment suppressed the inflammatory response in a dose-dependent manner, with the total number of free lung cells recovered from the highest dose group being only 5% of that recovered from untreated animals. Virus infection depressed the antibacterial defenses of the lung so that in untreated animals, 80 +/- 9% of the staphylococcal remained at 24 h. Treatment with the 2 higher doses of CY caused the bacteria to proliferate extensively in the lungs to 280 +/- 53% and 792 +/- 112%, respectively, for the 2.5 mg and 5.0 mg CY doses. In contrast, treatment with 0.5 mg and 1.0 mg of CY significantly enhanced the intrapulmonary killing of S. aureus in virus-infected lungs so that the bactericidal values at 24 h were 28 +/- 3% and 21 +/- 2%, respectively. These data demonstrated that immunosuppression modulates virus-induced suppression of pulmonary antibacterial defenses with high doses of CY aggravating and low doses ameliorating the defect.

Alveolar macrophage ingestion and phagosome-lysosome fusion defect associated with virus pneumonia

Virus-induced suppression of pulmonary phagocytic defenses is associated with defects in the intracellular processing of bacteria by alveolar macrophages. To determine whether the intracellular defect is related to a failure in phagosomelysosome fusion, mice were infected with a sublethal dose of Sendai virus, and the capacity of phagocytic cells, obtained by lung lavage, to exhibit phagosomelysosome fusion was quantitated during the course of the viral infection. Lysosomes of alveolar macrophages were prelabeled with acridine orange, the cells were challenged with Candida krusei, and fusion was determined with fluorescence microscopy by the discharge of the dye into the yeast-containing phagosome. Ultrastructural cytochemical studies verified the validity of the fluorescent fusion assay. Simultaneous experiments were performed to determine whether the viral infection also suppressed phagocytic ingestion by alveolar macrophages. Phagosome-lysosome fusion was progressively inhibited during the viral infection, reaching a low at day 7 when only 13 +/- 3% of the phagocytic cells fused as compared with 97 +/- 3% in cells from uninfected control animals; respectively, 55 +/- 5% as compared with 74 +/- 2% of the phagocytic cells contained yeasts. Thereafter, phagosome-lysosome fusion progressively increased reaching near normal levels (92 +/- 3%) on day 17 of the infection. At the same time period, phagocytic uptake was enhanced to a level where 97 +/- 3% of the cells contained yeasts. These data demonstrated that virus-induced suppression of intrapulmonary killing of bacteria involves functional lesions that retard the ingestion of inhaled organisms by alveolar macrophages and inhibit intracellular processing by degradative lysosomal enzymes by interfering with phagosome-lysosome fusion.

Alveolar macrophage dysfunction associated with viral pneumonitis

Viral infections are known to predispose to bacterial infections of the lung. Studies on the virus-induced suppression of pulmonary bactericidal mechanisms have identified the defect with abnormalities in the alveolar macrophage phagocytic system. In the investigation presented herein, we have dissected some of the subcomponents of the phagocytic process and found virus-induced defects in phagocytic ingestion, phagosome-lysosome fusion, and intracellular killing.

Alterations in lung macrophage antimicrobial activity associated with viral pneumonia

Secondary bacterial infections are a common sequelae of viral pneumonias. To study 2 functions of the phagocytic defenses of the lung, macrophages were obtained by lung lavage from parainfluenza 1 virus-infected and noninfected mice. The phagocytic capacities (binding, ingestion, and killing) of these cells were assessed in vitro against viable Candida krusei. Viral pneumonia resulted in a progressive suppression (through day 7 of the infection) of the ability of macrophages to bind candida to their surfaces by nonimmunological or complement receptors; ingestion and intracellular killing of candida were also decreased. After day 7, all these functions returned and, in fact, cells with enhanced activities were present on day 17. After introduction of virus into the lungs, the lung macrophage population increased significantly between days 3 and 7 of infection. This resulted in an increase in the phagocytic potential of the lung, despite the virus-associated suppression of the phagocytic activity in a portion of the macrophages. However, the ability of the macrophages to kill ingested microorganisms was also reduced, resulting in an overall deficiency in the lung macrophage defenses. It was concluded that viral pneumonia was associated with at least two suppressive effects on the lung macrophage-decreased receptor activity and microbicidal activity-resulting in a deficiency in the lung phagocytic defenses represented by these cells. These effects were maximal 1 week after infection and could account for the increased susceptibility of these lungs to secondary bacterial pneumonias. In contrast, during the period of convalescence, the lung macrophage antimicrobial activities were increased and reflected in enhanced resistance of the lungs to infections.

Pulmonary and systemic defenses against challenge with Staphylococcus aureus in mice with pneumonia due to influenza A virus

Pulmonary and systemic defenses against hematogenous challenge with 32P-labeled Staphylococcus aureus were measured 10 min, 8 hr, and 24 hr after intravenous injection of the bacteria in a mouse model of influenza virus pneumonia. Infection with influenza A virus did not alter bactericidal defenses in the liver and spleen, but pulmonary bactericidal activity measured 24 hr after infection was suppressed in virus-infected animals; 20% +/- 3% of the initially injected, viable bacteria were recovered from lungs of pneumonitic mice after 24 hr as compared with 9% +/- 1% from lungs of the uninfected mice. These data demonstrate that pulmonary infection with influenza virus does not alter antibacterial defenses of the liver and spleen but does suppress bactericidal activity in the lung.

Effects of viral pneumonia on lung macrophage lysosomal enzymes

During viral pneumonitis in mice, lung fluid protein and free lysosomal enzyme activity are increased while macrophage lysosomal enzymes are decreased.