Pulmonary Clearance Mechanisms Research Articles

MULTI-CHAMBER MODEL AS AN INSTRUMENT FOR ANALYSIS OF THE TOXICOKINETIC ROLE OF SOLUBILITY OF ELEMENT OXIDE NANOPARTICLES AND PHAGOCYTIC REACTION TO THEIR DEPOSITION IN LUNGS IN CHRONIC INHALATION EXPOSURE

The paper retraces the development of a mechanistic multi-chamber model describing particle retention in lungs in chronic inhalation exposures. This model was first developed and experimentally tested for various conditions of exposure to polydisperse dusts of SiO 2 or TiO 2 , and later successfully used as a basis for analyzing patterns in the retention of nanoparticles (NP) having different chemical compositions (Fe 2 O 3 , SiO 2 , NiO). The most significant adaptation of this model for exposure to element oxide NPs was due to the need to take into account not only the physiological mechanisms of their elimination, but also their solubility « in vivo ». It has been found that the relative contribution of the latter might be different for nanoparticles of different nature and predominant in some cases. The modeling of NiO-NPs retention also suggests that damage to the physiological pulmonary clearance mechanisms by particularly toxic nanoparticles might result in lung toxicokinetics becoming nonlinear.

Consequent stages of developing a multi-compartmental mechanistic model for chronically inhaled nanoparticles pulmonary retention.

The paper retraces the development of a mechanistic multicompartmental system model describing particle retention in lungs under chronic inhalation exposures. This model was first developed and experimentally tested for various conditions of exposure to polydisperse dusts of SiO2 or TiO2. Later on it was successfully used as a basis for analyzing patterns in the retention of nanoparticles having different chemical compositions (Fe2O3, SiO2, NiO). This is the first publication presenting the outcomes of modeling lung retention of nickel oxide nano-aerosols under chronic inhalation exposure. The most significant adaptation of the above-mentioned model to the conditions of exposure to metal-oxide nanoparticles is associated with the need to describe mathematically not only the physiological mechanisms of their elimination but also their solubilization "in vivo" bearing in mind that the relative contribution of the latter may be different for nanoparticles of different nature and predominant in some cases. Using nickel oxide as an example, it is suggested as well that damage to the physiological pulmonary clearance mechanisms by particularly toxic nanoparticles may result in lung toxicokinetics becoming nonlinear.

Critical Parameters for Particle-Based Pulmonary Delivery of Chemotherapeutics.

Targeted delivery of chemotherapeutics through the respiratory system is a potential approach to improve drug accumulation in the lung tumor, while decreasing their negative side effects. However, elimination by the pulmonary clearance mechanisms, including the mucociliary transport system, and ingestion by the alveolar macrophages, rapid absorption into the blood, enzymatic degradation, and low control over the deposition rate and location remain the main complications for achieving an effective pulmonary drug delivery. Therefore, particle-based delivery systems have emerged to minimize pulmonary clearance mechanisms, enhance drug therapeutic efficacy, and control the release behavior. A successful implementation of a particle-based delivery system requires understanding the influential parameters in terms of drug carrier, inhalation technology, and health status of the patient's respiratory system. This review aims at investigating the parameters that significantly drive the clinical outcomes of various particle-based pulmonary delivery systems. This should aid clinicians in appropriate selection of a delivery system according to their clinical setting. It will also guide researchers in addressing the remaining challenges that need to be overcome to enhance the efficiency of current pulmonary delivery systems for aerosols.

Abstract 28: Extracellular Matrix Coating Enhances Nanoparticle Uptake by Lung Epithelial Cells

Introduction: Rapid uptake of drug-loaded nanoparticles (NPs) by lung cells is critical for effective pulmonary delivery of therapeutic agents because of the rapid pulmonary clearance mechanisms. We tested the possibility that coating NPs with extracellular matrix (ECM) derived from lung tissue enhances nanoparticles uptake by lung cells. Methods and Results: Fresh adult porcine lung tissue obtained from a local slaughterhouse was decellularized using detergent (sodium dodecyl sulfate) and then enzymatically digested into a soluble solution. The double emulsion method was utilized to fabricate core-shell poly(lactic-co-glycolic) (PLGA) nanoparticles loaded with bovine serum albumin (BSA) for protein release studies, 6-coumarin for cellular uptake studies, or human erythropoietin receptor (hEPOR) cDNA co-expressing green fluorescent protein (GFP) for in vivo gene expression studies. The ECM was coated onto the nanoparticle surface by physical adsorption using the ECM solution (100 μg/ml). There is no significant difference in the diameter, blood compatibility or cell toxicity between coated and uncoated NPs. ECM-coated NPs showed slower protein release rate than uncoated NPs as the ECM coating hindered protein diffusion into the solution. ECM-coated NPs showed significantly higher cellular uptake by human lung epithelial cells than collagen-coated or uncoated NPs. In addition, ECM-coated and uncoated NPs loaded with hEPOR-GFP cDNA were aerosolized and delivered by inhalation into rat lung. Following single inhalation using uncoated NPs, GFP expression in lung tissue progressively increased for up to 21 days. Using the ECM-coated NPs EPOR expression peaked at 14 days, then declined thereafter. Conclusions: Coating NPs with lung-derived ECM markedly enhances NP uptake by lung cells, delays the release of encapsulated protein or DNA, and shortens the duration of peak tissue gene expression compared to uncoated NPs. This NP formulation may be useful where more precise timing of delayed payload release is desired.

51. Rapid and Long Term Protection to Pseudomonas aeruginosa Using a Platform Vaccine Concept That Mediates Both Passive and Active Immunity

We have developed a platform technology against infectious agents that mediates both passive and active immunity, with rapid, passive protection through the genetic delivery of an anti-pathogen monoclonal antibody together with long term protective active immunity evoked through the presentation of a defined pathogen neutralizing epitope. Both strategies are incorporated into an E1 E3 adenovirus (Ad) vector through the coding of an antibody in the transgene and incorporation of a pathogen antigenic sequence into the hexon capsid protein, respectively. As a model to evaluate the vaccine, we have applied this to a public health-important infectious agent, Pseudomonas aeruginosa, a gram-negative ubiquitous pathogen associated with persistent pulmonary infection in hosts with bronchiectasis, such as cystic fibrosis, compromised immune function or who have pulmonary clearance mechanisms disrupted by endotracheal tubes. Although P. aeruginosa is susceptible to antibiotic therapy, chronic colonization of the respiratory tract with frequent exacerbations is typical of high risk populations. Pathogenicity linked to P. aeruginosa infection results from the release of numerous virulence factors that can degrade tissues such as proteases and phospholipase and others that diminish cellular functions via exotoxins. The passive vaccine mediates expression of an antibody to an exotoxin secreting protein, PcrV, a known P. aeruginosa a neutralizing target. Antibody expression is mediated by the nonhuman C7 serotype Ad to avoid the highly prevalent preexisting immunity to serotype 5 Ad. In parallel, the Ad capsid hexon protein has a short epitope, Epi8, derived from the outer membrane protein F of P. aeruginosa, an established neutralizing epitope for long term active immune protection to P. aeruginosa. Western analysis confirmed the expression of the anti-PcrV antibody and ELISA assays of anti-Epi8 antibodies evoked from the hexon modified Ad confirmed the active response. In vivo challenge assays in mice used agar-encapsulated P103 strain of P. aeruginosa titered for lethality. The passive vaccine significantly reduced colonization of the lung of mice intranasally challenged with a lethal dose of P. aeruginosa at 3, 5 and 10 days after vaccination in comparison to mice vaccinated with a control Ad vector, whereas the active vaccine significantly reduced colonization at 5 wk post-vaccination. The combination of the active and passive vaccines therefore provides immediate and long term protection to exposure of P. aeruginosa. The concept of a combined passive and active vaccine to provide immediate protection with long-term immunity could be an important tool for public health, particularly for bioterror-related infectious agents.

Inhaled nano- and microparticles for drug delivery.

The 21st century has seen a paradigm shift to inhaled therapy, for both systemic and local drug delivery, due to the lung's favourable properties of a large surface area and high permeability. Pulmonary drug delivery possesses many advantages, including non-invasive route of administration, low metabolic activity, control environment for systemic absorption and avoids first bypass metabolism. However, because the lung is one of the major ports of entry, it has multiple clearance mechanisms, which prevent foreign particles from entering the body. Although these clearance mechanisms maintain the sterility of the lung, clearance mechanisms can also act as barriers to the therapeutic effectiveness of inhaled drugs. This effectiveness is also influenced by the deposition site and delivered dose. Particulate-based drug delivery systems have emerged as an innovative and promising alternative to conventional inhaled drugs to circumvent pulmonary clearance mechanisms and provide enhanced therapeutic efficiency and controlled drug release. The principle of multiple pulmonary clearance mechanisms is reviewed, including mucociliary, alveolar macrophages, absorptive, and metabolic degradation. This review also discusses the current approaches and formulations developed to achieve optimal pulmonary drug delivery systems.

Visualization of pulmonary clearance mechanisms via noninvasive optical imaging validated by near-infrared flow cytometry.

In vivo optical imaging with near-infrared (NIR) probes is an established method of diagnostics in preclinical and clinical studies. However, the specificities of these probes are difficult to validate ex vivo due to the lack of NIR flow cytometry. To address this limitation, we modified a flow cytometer to include an additional NIR channel using a 752 nm laser line. The flow cytometry system was tested using NIR microspheres and cell lines labeled with a combination of visible range and NIR fluorescent dyes. The approach was verified in vivo in mice evaluated for immune response in lungs after intratracheal delivery of the NIR contrast agent. Flow cytometry of cells obtained from the lung bronchoalveolar lavage demonstrated that the NIR dye was taken up by pulmonary macrophages as early as 4-h post-injection. This combination of optical imaging with NIR flow cytometry extends the capability of imaging and enables complementation of in vivo imaging with cell-specific studies.

Some Peculiarities of Pulmonary Clearance Mechanisms in Rats after Intratracheal Instillation of Magnetite (Fe3O4) Suspensions with Different Particle Sizes in the Nanometer and Micrometer Ranges: Are We Defenseless against Nanoparticles?

We studied differences between phagocytic responses to nanoparticles (NPs) versus microparticles in the pulmonary region by synthesizing magnetite of different sizes and instilling suspensions of these particles intratracheally into rats' lungs. Ten and 50 nm particles caused a greater increase in cell counts of the bronchoalveolar lavage fluid (BALF) than the instillation of microparticles. The response to 10 nm particles was weaker than to 50 nm ones, and the smaller NPs were more cytotoxic; both were more cytotoxic than the microparticles. Phagocytic activity was also studied using optical and atomic force microscopy. Phagocytes were more "loaded" in the lungs instilled with 10 nm particles as compared with those instilled with 50 nm particles; NPs of both sizes were engulfed more avidly than microparticles. We found in a separate comparative experiment that magnetite NPs were more cytotoxic than titanium dioxide and quartz suspensions having particle size distribution typical of industrial dusts.

Some Peculiarities of Pulmonary Clearance Mechanisms in Rats after Intratracheal Instillation of Magnetite (Fe3O4) Suspensions with Different Particle Sizes in the Nanometer and Micrometer Ranges: Are We Defenseless against Nanoparticles?

Some Peculiarities of Pulmonary Clearance Mechanisms in Rats after Intratracheal Instillation of Magnetite (Fe₃O₄) Suspensions with Different Particle Sizes in the Nanometer and Micrometer Ranges: Are We Defenseless against Nanoparticles?

Inhalative nanomedicine—Opportunities and challenges

Inhalation therapy is still limited by the low bioavailability of the administered drugs. Advantages of the pulmonary administration site like large resorption area, low enzymatic equipment, and circumvention of the first pass effect are set into perspective by the rigid barrier properties of the alveolar region. As a consequence, the systemic bioavailability of peptides and proteins is still relatively limited, even when administered by modern pharmaceutical aerosol technologies. In the context of advanced pulmonary drug therapy the use of nanoparticles as alternative to micronsized drug formulation could be of special interest, because nanoparticles seem to overcome some cellular barriers quite efficiently. Besides such outstanding permeation properties, nanoparticles may also hold promises to escape from pulmonary clearance mechanisms and to allow for cell-specific targeting within the lung. Such opportunities and challenges of inhalative nanomedicine are reviewed in this short review.

Reduced alveolar macrophage migration induced by acute ambient particle (PM10) exposure

Increased levels of particulate air pollution (PM10) have been implicated as a causal agent in pulmonary disease exacerbation and increased deaths from respiratory and cardiovascular disorders. The exact mechanism by which PM10 drives toxicity in the lung is still unknown, but studies have focused on inhibition of macrophage function and impaired alveolar clearance mechanisms. To assess the effects of PM10 on pulmonary macrophage clearance mechanisms ex vivo, Wistar rats were instilled with 125 or 250 microg of PM10 collected from the North Kensington, London. Control rats were instilled with sterile saline. The rats were sacrificed after 18 h and a bronchoalveolar lavage (BAL) was performed. Macrophages isolated from the BAL fluid were assessed for ability to migrate towards a positive chemoattractant (ZAS) ex vivo and to perform phagocytosis. Macrophages isolated from the PM10-exposed rats showed inhibition of potential to migrate. Macrophage phagocytic ability ex vivo was also significantly reduced by the presence of PM10 inside the cells. This study indicates that acute PM10 exposure diminishes macrophage motility and phagocytosis in a manner that could prove deleterious to particle clearance from the alveolar region of the lung. Decreased particle clearance promotes inflammation, and hence, warrants further investigation in relation to the effects of chronic PM10 exposure on macrophage clearance mechanisms and establishing the mechanisms behind decreased macrophage migration.

Methylmercury and the Brain: Griffiths et al. Respond

Methylmercury and the Brain: Griffiths et al. Respond

Fundamentals of pulmonary drug delivery

Aerosol administration of peptide-based drugs plays an important role in the treatment of pulmonary and systemic diseases and the unique cellular properties of airway epithelium offers a great potential to deliver new compounds. As the relative contributions from the large airways to the alveolar space are important to the local and systemic availability, the sites and mechanism of uptake and transport of different target compounds have to be characterized. Among the different respiratory cells, the ciliated epithelial cells of the larger and smaller airways and the type I and type II pneumocytes are the key players in pulmonary drug transport. With their diverse cellular characteristics, each of these cell types displays a unique uptake possibility. Next to the knowledge of these cellular aspects, the nature of aerosolized drugs, characteristics of delivery systems and the depositional and pulmonary clearance mechanisms display major targets to optimize pulmonary drug delivery. Based on the growing knowledge on pulmonary cell biology and pathophysiology due to modern methods of molecular biology, the future characterization of pulmonary drug transport pathways can lead to new strategies in aerosol drug therapy.

Bronchiectasis: current clinical and imaging concepts.

B RONCHIECTASIS should not be considered a single diagnostic entity. Rather, it should be treated as a morphologic abnormality representing the final common pathway of a variety of conditions that cause long-standing inflammation or infection of the bronchial tree.1 Pathologically, bronchiectasis is manifest as dilation of one or more branches of the bronchial tree; usually the dilation is such that multiple bronchi can be followed to within 1 cm of the pleural surface (as opposed to normal bronchi, which usually cannot be seen grossly within 2 cm of the pleura). 2 Historically the gross appearance of bronchiectatic airways has been divided into three different categories: cylindrical, saccular, and varicose (Fig 1). 3 Cylindrical bronchiectasis represents relatively uniform dilation of segments of the bronchial tree, usually involving sixthto eighthgeneration branches. Saccular bronchiectasis indicates balloon-like dilation of bronchial branches and usually involves thirdto fourth-generation branches. Finally, varicose bronchiectasis indicates an intermediate form between cylindrical and saccular bronchiectasis in which focally dilated bronchial segments are interposed between normal or narrowed bronchial segments. The dilation of the bronchial tree seen in bronchiectasis is essentially due to the destruction of the elastic and muscular layers of the bronchial wall. Occasionally a single prolonged infection, in conjunction with the severe inflammatory response that it elicits, may be sufficient to cause the bronchial injury necessary to elicit bronchiectasis. More typically, however, bronchiectasis is caused by a vicious cycle of recurrent infection and chronic inflammation. 4 The pathway to bronchiectasis classically begins in a host with impaired pulmonary clearance mechanisms; this impairment may be in-born and generalized as in patients with cystic fibrosis, or focal and acquired as in patients with bronchial obstruction. The subsequent stagnation of secretions within the tracheobronchial tree increases endoluminal pressure and predisposes to infection. Once an endobronchial infection begins, pathogens tend to remain within the bronchial tree for prolonged periods of time, leading to an exaggerated inflammatory response. The combination of prolonged infection and inflammation initially leads to destruction of the ciliated respiratory epithelium and submucosa before the infection is cleared. This mucosal and submucosal injury increases the risk of the host for future infection; thus the entire cycle will usually repeat itself, causing subsequent destruction of the elastic, muscular, and cartilaginous layers of the bronchial tree. This progressive bronchial injury eventually leads to bronchial dilation. 5 Table 1 lists selected predisposing factors for bronchiectasis. Although the list is long, it is far from comprehensive. However, the most common causes of bronchiectasis can be easily remembered through a systematic approach. The best method for approaching the differential diagnosis for bronchiectasis separates the list into two basic categories: causes of focal bronchiectasis and causes of diffuse bronchiectasis. The primary cause of focal bronchiectasis, especially in developing countries and among the disadvantaged in the United States, remains recurrent childhood infections. This includes undertreated bacterial infections as well as viral pneumonias caused by viral organisms, such as adenovirus and respiratory syncystial virus. Measles, whooping cough, and tuberculosis, although historically common causes of bronchiectasis, have decreased in importance with the advent of immunizations and chemoprophylaxis (Fig 2). 6 After childhood infection, endobronchial obstruction is probably the next most frequent cause of focal bronchiectasis on a worldwide basis. This includes obstruction from an endobronchial mass, such as a carcinoid or foreign body, intrinsic obstruction due to an airway stenosis or congenital defect, and extrinsic compression of the airway due to adenopathy or a large lung mass. 7 Aspiration should also be considered whenever one identifies focal bronchiectasis, especially if obstruction and childhood infection have been ruled out. On the other hand, diffuse bronchiectasis is usually due to a congenital or acquired deficiency

Inhalation of High Concentrations of Low Toxicity Dusts in Rats Results in Impaired Pulmonary Clearance Mechanisms and Persistent Inflammation

This study was carried out to assess the time course of pulmonary clearance impairment and persistence of inflammation following high-dose inhalation exposures to titanium dioxide (TiO2) or carbonyl iron (CI) particles. Male rats were exposed to air, TiO2or CI particles 6 hr/day, 5 days/week, for 4 weeks at concentrations of 5, 50, and 250 mg/m3and evaluated at selected intervals through 6 months postexposure. Indices of pulmonary inflammation as well as alveolar macrophage clearance functions (i.e., morphology,in vivoandin vitrophagocytosis, and chemotaxis), cell proliferation, and histopathology endpoints were measured at several postexposure time periods through 6 months. In addition, amounts of TiO2or CI in lungs and tracheobronchial lymph nodes were measured to allow an evaluation of particle clearance and translocation patterns. Four-week exposures to TiO2or CI particles at concentrations of 250 mg/m3resulted in lung burdens of 12 mg titanium and 17 mg iron, respectively, with particle retention half-times ranging from 68 days for 5 mg/m3TiO2to approximately 330 days for 250 mg/m3. The impact of this TiO2dust load and similar lung burdens of CI particles produced a sustained pulmonary inflammatory response measured through a period of 3–6 months postexposure concomitant with increases in BrdU cell labeling of terminal airway and pulmonary parenchymal cells. The impairment of particle clearance mechanisms was accounted for by deficits inin vitrophagocytic and chemotactic potential of alveolar macrophages recovered from the lungs of high-dose, TiO2- or CI-exposed rats. Free granular pigment (TiO2or CI) was present on the hypertrophic mucosal surfaces of bronchioles and bronchi, and particle-laden macrophages, found individually, were numerous throughout alveoli and within lymphoid tissues immediately after exposure. Aggregates of particle-laden macrophages were present within alveoli and alveolar ducts from 1 week postexposure through the entire 6-month recovery period. Macrophage accumulations increased in size and number from 1 week through 1 month postexposure and then appeared to remain constant through the remaining 5-month postexposure period. Minimal cellular hypertrophy and hyperplasia were evident at alveolar duct bifurcations adjacent to macrophage aggregates, and this effect was most prominent at 3 to 6 months postexposure. The results of this study clearly demonstrate that exposure to high dust concentrations of two different innocuous particle types produced sustained pulmonary inflammation, enhanced proliferation of pulmonary cells, impairment of particle clearance, deficits in macrophage function, and the appearance of macrophage aggregates at sites of particle deposition. In addition, the mass deposition rate determination appears to be a less sensitive indicator of “overload” when compared to biomarkers of pulmonary toxicity, such as macrophage function and cellular inflammation and proliferation indices.

Increased Content of Chromium and Nickel in Lung Tissues from Patients with Bronchial Carcinoma

Epidemiological studies have shown that occupational exposure to certain chromium and nickel compounds is followed by an increased lung cancer incidence. However, few data exist on the content of these metals in lung cancer patients in general. In the present study, central and peripheral lung tissue, bronchial tissue and hilar lymph nodes were collected from 20 patients with bronchial carcinoma and 21 control individuals, and the tissue concentration of chromium and nickel was measured by use of atomic absorption analysis. Increased levels of both metals were found in cancer patients as compared to controls. Lung tissue concentration of chromium was two-fold increased, while the bronchial wall content of nickel was three times the level in control individuals. Smokers showed a dose-related increase in the deposition of both chromium and nickel. Furthermore, in cancer patients an inverse relationship between smoking and the tissue level of chromium in regional lymph nodes was found, possibly indicating a depressive effect on pulmonary clearance mechanisms. Our results emphasize the possible role of small amounts of chromium and nickel as agents in bronchial carcinogenesis, unrelated to occupation and probably related to tobacco smoking.

Alveolar macrophage phagocytic kinetics following pulmonary parainfluenza-3 virus infection.

Qualitative and quantitative evaluations of the cellular components of bronchoalveolar washings of calves with experimental parainfluenza-3 virus pneumonitis and control calves were made. Calves were exposed to 10(9) TCID50 of PI-3 by intranasal aerosol exposure and bronchoalveolar cells obtained 7 days after infection by volume-controlled bronchopulmonary lavage. Transient tachypnea and pyrexia occurred in all infected calves, and virus was recoverable at 7 days from nasal swabs and lung tissue. Pulmonary lesions were typical of viral pneumonitis, characterized by patchy alveolitis and bronchiolitis with accumulations of cells and inflammatory debris. The mean total lavage cell yield was elevated in the virus-infected calves, and the percentage of neutrophils was elevated (P less than 0.05). Increased numbers of pulmonary alveolar macrophages (PAM) were also recovered but the difference was not significant. Linear regression equations showed that a decreased proportion of PAM from virus-infected animals were phagocytic. The mean initial phagocytic rates of macrophages from calves with viral pneumonitis were significantly decreased (P less than 0.05) over controls. This difference was concentration dependent and required a phagocytic stimulus in excess of 12.5 X 10(6) beads/ml. Studies of phagocytic kinetics showed that PAM from calves with viral pneumonitis had a lower Vmax than PAM from control calves, but that Km values were comparable. No differences in PAM beta-glucuronidase and acid phosphatase activity were observed. These results indicate depressed phagocytic function in PI-3 virus-inflamed lungs relative to controls. In concert with virus-induced airway lesions, such in vivo depression of PAM phagocytic functions would be expected to depress pulmonary particulate clearance and lung defense mechanisms.

Inhalation studies of Mt. St. Helens volcanic ash in animals: III. Host defense mechanisms

The effects of inhalation exposure of mice or rats to 9.4 mg/m3 volcanic ash, 2.5 mg/m3 SO2, or both on host defense mechanisms were assessed. Cytologic changes in pulmonary lavage fluid included an increase in percentage polymorphonuclear leukocytes due to SO2 exposure and an increase in eosinophils due to ash. SO2 and ash also produced decreases in percentage alveolar macrophages. In the case of ash-exposed animals, this decrease was offset by an increase in lymphocytes. Total cell counts and viability were not affected by any of the exposures. Pulmonary clearance mechanisms were affected in that there were both decreased alveolar macrophage phagocytic capability following ash and ash + SO2 exposures and depressed ciliary beat frequency attributable to ash exposure. None of the inhalation exposures caused increases in susceptibility to an immediate or 24 hr postexposure aerosol challenge with Streptococcus. However, intratracheal instillation of both fine- and coarse-mode volcanic ash caused slight but significant increases in mortality due to bacterial challenge 24 hr after the instillation. The phytohemagglutinin-induced blastogenic response of splenic lymphocytes from exposed animals did not differ significantly from that of control lymphocytes, although the lipopolysaccharide-induced blastogenic response was enhanced. Ash exposure had no effect on susceptibility to murine cytomegalovirus. In summary, volcanic ash alone or in combination with SO2 had only minimal effects on certain host defense mechanisms.

Hypothesis: the role of the lung in stomach carcinogenesis.

It is proposed that pulmonary defense mechanisms play an important role in stomach carcinogenesis. Inhaled carcinogens reach the stomach by normal pulmonary clearance and account for the association of stomach cancer with dusty occupations. We postulate that although familial and other factors determine the susceptibility to endothelial cancer (both stomach and lung), those persons whose pulmonary clearance mechanisms are more susceptible to impairment by cigarette smoke retain carcinogens and other particulate matter in the lungs and are at increased risk for lung cancer. Those whose clearance mechanisms are not impaired continue to clear these particles from their lungs, unconsciously swallow the cleared particles, receive more of these substances in the stomach, and are at increased risk for stomach cancer. This accounts for: first, the very striking dose-response relationship between the amount of smoking and lung cancer mortality and the relatively weak relationship between smoking and stomach cancer, and second, for observed reciprocal relationships in time trends of mortality between stomach cancer and lung cancer.

Lung clearance of Staphylococcus aureus strains with differing protein A content: protein A effect on in vivo clearance.

We have studied the clearance from murine lungs of two strains of Staphylococcus aureus, one possessing high and the other possessing low levels of protein A.S. aureus FDA 209 and S. aureus Wood 46 were assayed for their ability to bind mouse immunoglobulin G, using an indirect radioimmunoassay. S. aureus FDA 209 binding of mouse immunoglobulin was significantly greater than that of S. aureus Wood 46 (118,909 versus 37,845 cpm). Clearance of these two strains from the lung after a 30-min aerosol inoculation period was not significantly different. The percentage of bacteria remaining in the lung was 49.2 and 55.0% at 2h, 31.8 and 33.2% at 3 h, and 25.4 and 17.2% at 4 h for protein A-rich and protein A-poor strains, respectively (P greater than 0.20 at each time). These data suggest that the previously demonstrated in vitro antiphagocytic effect of protein A may not be relevant to pulmonary clearance mechanisms.