Heat and moisture exchanger vs heated humidifier during long-term mechanical ventilation. A prospective randomized study

Adequate humidification of inspired gases with HMEs during long-term MV remains controversial. In this study, a comparison is made between tracheal secretions during long-term MV either with HME or conventional HH. Both the HME and HH groups were similar with respect to age, sex, diagnosis, duration of MV, SAPS and mortality. Temperature of gases in the tracheal tube was lower and the amount of tracheal instillations was greater in the HME group than in the HH group. Tracheal secretions became thicker between day 1 (control) and day 5, in the HME group than in the HH group. Four and two tube occlusions occurred in HME and HH groups, respectively. Tracheal bacterial colonization was similar in the two groups. Given the advantages of HME (reduced nurses' work and financial cost), HME could be routinely used under cautious surveillance and replaced by HH if difficulty in suctioning occurs.

Immunoglobulin class- and subclass-specific responses to Mycoplasma pulmonis in sera and secretions of naturally infected Sprague-Dawley female rats

Mycoplasma pulmonis causes chronic murine respiratory mycoplasmosis and genital disease in rats. Specific immunoglobulin M (IgM), IgA, and IgG and its subclasses present in sera and tracheal and uterine lavage samples from 36 naturally infected Sprague-Dawley female rats were tested for reactivity with M. pulmonis in an enzyme-linked immunosorbent assay. Ten specific-pathogen-free Sprague-Dawley female rats served as the negative controls. Tracheal and uterine lavage samples were cultured quantitatively for M. pulmonis. M. pulmonis was isolated from the trachea (35 of 36) and uterus (17 of 36) of naturally infected rats; all rats were infected in at least one of the two sites cultured. M. pulmonis was not isolated from any control rat. There was a significant difference in levels of specific antibody of all classes except IgG2c between control and naturally infected animals (P less than 0.001 for IgM, IgG, IgG1, and IgG2a; P less than 0.002 for IgG2b; and P less than 0.02 for IgA). There was no correlation between numbers of M. pulmonis cells isolated and the amount or class of antibody measured in serum or tracheal lavage specimens. The predominant antibodies to M. pulmonis found in the sera of naturally infected rats were IgG and IgM. The IgG2a subclass was responsible for the majority of IgG-positive animals. There were no differences between rats which were positive by culture for M. pulmonis in the uterus (U+) and rats which were negative by culture for M. pulmonis in the uterus (U-) with respect to distribution or amount of antibody classes and subclasses in the serum. However, tracheal wash samples from U+ rats had significantly higher (P less than 0.03) levels of specific IgG1 and IgG2a than those from U- rats. Conversely, IgG2a was present in higher levels in pooled uterine lavage specimens from U- rats than in those from U+ rats.

Branhamella (Moraxella) catarrhalis: pathogenic significance in respiratory infections

OBJECTIVES

To assess the pathogenic significance of Branhamella catarrhalis isolates in patients with respiratory infections and to define the clinical characteristics of such patients.

DESIGN AND SETTING

Respiratory specimens were assessed in a three-year prospective study performed in a Brisbane metropolitan hospital. Assessment of the pathogenic significance of isolates of B. catarrhalis was based on four predetermined criteria: (i) clinical evidence of respiratory infection based on history, examination and chest x-ray; (ii) isolation of B. catarrhalis as the sole potential pathogen; (iii) absence of antibiotic treatment in the previous two weeks; and (iv) subsequent clinical response to an antibiotic to which the isolate was sensitive.

RESULTS

B. catarrhalis was identified in 118 respiratory samples, 92 (78%) being from patients less than 10 years old. Infection with B. catarrhalis was more commonly seen in winter months and was community-acquired in two-thirds of cases. Isolation of this organism was associated with a broad variety of upper and lower respiratory tract syndromes. Isolates were considered to be of pathogenic significance (all four above criteria satisfied) in 35% of cases and of possible significance (the first and fourth criteria satisfied) in a further 15% of cases. Isolates were more likely to be of pathogenic significance in older patients and in those with pre-existing cardiorespiratory disease; however, a number of serious infections were observed in previously-well children. Expectorated sputum and tracheal aspirates were more likely to yield a clinically significant isolate than nasopharyngeal aspirates. Production of beta-lactamase was demonstrated in 88% of isolates.

CONCLUSION

B. catarrhalis causes respiratory infection more frequently than is generally appreciated. Isolation of this organism from the respiratory tract had pathogenic significance or possible pathogenic significance in 50% of our patients. If therapy is indicated in patients with respiratory infection caused by this organism, traditional beta-lactam regimens cannot be relied upon, as shown by the high rate of beta-lactamase production in this study; a tetracycline, erythromycin, a second or third generation cephalosporin, or the combination of a penicillin derivative and beta-lactamase inhibitor should be considered.

Airway adherence of Pseudomonas aeruginosa: mucoexopolysaccharide binding to human and bovine airway proteins

The ability of Pseudomonas aeruginosa (PA) to adhere to cells of the upper and lower airways is considered the initial step in its colonization and subsequent infection. Many potential adhesins exist, but few eukaryote receptors have been reported. This study evaluates the adherence of PA and the well-recognized adhesin mucoexopolysaccharide, of the mucoid variant, to tracheal epithelial cells and airway secretions. A number of tools were used to systematically examine this process, each in increasing detail. Scanning electron microscopy of infected tracheal cell monolayers showed that although nonmucoid PA adhered most often as individual organisms, mucoid strains frequently were adherent in the form of clusters of microcolonies. Partially purified mucoexopolysaccharide was itself adherent to the tracheal cell monolayers. More quantitative studies of carbon 14-labeled PA adherence to tracheal cell monolayers demonstrated that (1) bacterial adherence was temperature dependent; (2) mucoid PA was more adherent than nonmucoid PA (p less than 0.005); (3) proteinase treatment of the intact monolayers increased adherence of mucoid PA; and (4) adherence of nonmucoid PA was partially inhibited by pretreatment with N-acetylglucosamine, a normal constituent of airway mucus (control, 9.5 +/- 2.0 bacteria/cell; N-acetylglucosamine, 5.8 +/- 1.5 bacteria/cell; p = 0.05). These observations suggest that N-acetylglucosamine may play a role in the epithelial cell receptor for ligands on the surface of nonmucoid strains of PA. Pretreatment of mucoid PA with N-acetylglucosamine, D-arabinose, D-mannose, or N-acetylneuraminic acid did not affect adherence. Partially purified proteins isolated from the apical plasma membrane of bovine tracheal epithelial cells probed in a Western analysis with the iodine 125-labeled PA mucoexopolysaccharide revealed two binding proteins of 45,000 mol wt and 104,000 mol wt. Human airway secretions of patients with chronic PA infection were screened by the dot blot technique and demonstrated selective binding of mucoexopolysaccharide ligand. Western analysis of these biologically important secretions revealed that PA mucoexopolysaccharide bound to a 65,000 mol wt protein in airway secretions of infected individuals. This glycoprotein is similar to a previously described cell receptor for bacterial type 1 fimbriae.

Tracheal antimicrobial peptide, a cysteine-rich peptide from mammalian tracheal mucosa: peptide isolation and cloning of a cDNA

Extracts of the bovine tracheal mucosa have an abundant peptide with potent antimicrobial activity. The 38-amino acid peptide, which we have named tracheal antimicrobial peptide (TAP), was isolated by a sequential use of size-exclusion, ion-exchange, and reverse-phase chromatographic fractionations using antimicrobial activity as a functional assay. The yield was approximately 2 micrograms/g of wet mucosa. The complete peptide sequence was determined by a combination of peptide and cDNA analysis. The amino acid sequence of TAP is H-Asn-Pro-Val-Ser-Cys-Val-Arg-Asn-Lys-Gly-Ile-Cys-Val-Pro-Ile-Arg-Cys-Pr o- Gly-Ser-Met-Lys-Gln-Ile-Gly-Thr-Cys-Val-Gly-Arg-Ala-Val-Lys-Cys-Cys-Arg- Lys-Lys - OH. Mass spectral analysis of the isolated peptide was consistent with this sequence and indicated the participation of six cysteine residues in the formation of intramolecular disulfide bonds. The size, basic charge, and presence of three intramolecular disulfide bonds is similar to, but clearly distinct from, the defensins, a well-characterized class of antimicrobial peptides from mammalian circulating phagocytic cells. The putative TAP precursor is predicted to be relatively small (64 amino acids), and the mature peptide resides at the extreme carboxyl terminus and is bracketed by a short putative propeptide region and an inframe stop codon. The mRNA encoding this peptide is more abundant in the respiratory mucosa than in whole lung tissue. The purified peptide had antibacterial activity in vitro against Escherichia coli, Staphylococcus aureus, Klebsiella pneumonia, and Pseudomonas aeruginosa. In addition, the peptide was active against Candida albicans, indicating a broad spectrum of activity. This peptide appears to be, based on structure and activity, a member of a group of cysteine-rich, cationic, antimicrobial peptides found in animals, insects, and plants. The isolation of TAP from the mammalian respiratory mucosa may provide insight into our understanding of host defense of this vital tissue.

Tracheal granulation tissue. A study of bacteriology

We prospectively examined 19 patients (21 laryngotracheal reconstructions) over a 6-month period to evaluate the bacteriology of granulation tissue present at the time of Teflon stent removal and at the first laryngoscopy several weeks later. The most frequently recovered isolates were viridans streptococci, Pseudomonas aeruginosa, nonhemolytic Streptococcus, and Staphylococcus aureus. All but one positive culture were polymicrobial. The amount of tissue did not correlate with the duration of stenting and the amount of granulation tissue and number of organisms decreased after stent removal. Further prospective study of the most appropriate antimicrobial therapy is needed.

Infection of P388D1 macrophages and respiratory epithelial cells by Histoplasma capsulatum: selection of avirulent variants and their potential role in persistent histoplasmosis

We evaluated P388D1 macrophagelike cells as model host cells for studying the intracellular survival and strain-specific virulence of Histoplasma capsulatum. Previously characterized strains which were virulent for mice destroyed monolayers of these cells within a few days. In contrast, related avirulent "smooth" variants failed to do so even after 20 days, although they persisted within P388D1 cells for at least 7 days. On the basis of this observation, we developed a quantitative radiolabel assay to use as an initial screen for virulence. Another cell type lining the respiratory tract was then examined as a potential host for H. capsulatum. Hamster trachea epithelial (HTE) cells readily internalized a variety of strains lacking alpha-(1,3)-glucan in their cell walls; however, the tracheal cells were only rarely infected by organisms possessing this polysaccharide. We subsequently inoculated HTE cells with alpha-(1,3)-glucan-positive strains and enriched for the few yeasts infecting these cells. The progeny resembled smooth variants in terms of colony morphology, the absence of alpha-(1,3)-glucan in their cell walls, and their inability to kill macrophages. Did the HTE cells select for these variant yeasts from the parent inoculum or instigate a change from the parental phenotype? Following a 3-h uptake period, only 2% of the ingested yeasts lacked alpha-(1,3)-glucan. One day later, nearly half of the intracellular organisms lacked this polymer. This rapid conversion of a large proportion of the inoculum suggests some type of environmentally triggered change, perhaps analogous to phase variation seen in many other pathogens. Infection of epithelial cells or some other nonprofessional phagocyte during natural histoplasmosis might give rise to similar variants, thus establishing a reservoir of organisms capable of causing chronic or latent infections.

Prospective study of nosocomial pneumonia and of patient and circuit colonization during mechanical ventilation with circuit changes every 48 hours versus no change

Circuits on mechanical ventilators with cascade humidifiers are routinely changed every day or every other day, although humidifying cascades have been considered unlikely to increase the risk of respiratory infection because they do not generate aerosols. Moreover, changing ventilator tubings every 24 rather than every 48 h increases the risk of ventilator-associated pneumonia. To study the effects of ventilator circuit changes on the rate of nosocomial pneumonia and on patient and circuit colonization, 73 consecutive patients requiring continuous mechanical ventilation for more than 48 h were randomly assigned to either ventilator circuit changes every 48 h (Group 1, n = 38) or no change (Group 2, n = 35). Patients dying or being weaned before 96 h were not analyzed (Group 1 n = 3; Group 2 n = 7; leaving Group 1 n = 35 and Group 2 n = 28; p = 0.13). Ventilator-associated pneumonia was defined as the occurrence during mechanical ventilation or within 48 h after weaning of a new and persistent infiltrate on chest X-ray, purulent tracheal secretions, and a positive culture of a protected brush specimen (greater than or equal to 10(3) cfu/ml). Bacterial colonization was assessed every 48 h by quantitative cultures of pharyngeal swab, tracheal aspirate, humidifying cascade, and expiratory tubing trap. The two groups were similar in terms of age, indication for and duration of ventilation, and severity of illness.(ABSTRACT TRUNCATED AT 250 WORDS)

Preoperative assessment of the likelihood of infection of the lower respiratory tract after cardiac surgery

Lower-respiratory-tract infections are among the most frequent complications observed in the intensive care unit, leading to delayed postoperative recovery time and increased costs and mortality. We have tried to evaluate the prognostic value of perioperative bacteriology of tracheal aspirates in assessing the risk of such complications. In a prospective study aspirates of 100 patients undergoing cardiac surgery were taken immediately after intubation and were analysed for microorganisms by Gram-stain and microbiological cultures using standard procedures. All patients received perioperative antibiotic prophylaxis with a single dose of 2 g ceftriaxone intravenously. From 26 patients with bacteriologically positive tracheal secretion, 8 (30.7%) developed lower respiratory tract infection whereas only 1 of 72 patients (1.4%) with negative bacteriological results developed this complication. Smoking (p less than 0.01) and abnormal preoperative lung function (p less than 0.01) were significantly more frequent in patients developing postoperative pneumonia. Regarding the results of this study, the risk of developing pulmonary infection in the early postoperative course after cardiac surgery can be estimated from the tracheal aspirates.

Adherence of Actinobacillus pleuropneumoniae to porcine tracheal epithelial cells and frozen lung sections

The ability of 23 different Actinobacillus pleuropneumoniae isolates to adhere in vitro to porcine tracheal epithelial cells and to porcine frozen lung sections was examined. It was found that A. pleuropneumoniae adhered poorly to isolated tracheal epithelial cells. On the other hand, A. pleuropneumoniae adhered to frozen lung sections and marked variations were observed between and within serotypes. Adherence to lung sections did not seem related to the hemagglutinating activity of the isolate. Two noncapsulated variants adhered to lung sections in greater numbers than their capsulated parent strains. Adherence to lung sections was not inhibited by the extracellular matrix components tested namely, laminin, fibronectin, and collagen, but was inhibited by homologous serotype-specific antiserum. The data indicated that the A. pleuropneumoniae isolates tested possess the ability to adhere to porcine lung tissue, a property which did not seem to be related to the serotype and did not seem to involve the capsular material or the hemagglutinins of the isolates.

Sensitivity and specificity of daily tracheal aspirate cultures in predicting organisms causing bacteremia in ventilated neonates

The sensitivity of daily tracheal aspirates in predicting neonatal bacteremia was ascertained from 48 of 354 ventilated neonates who became septic during a 4-year period. Fourteen babies (designated Group A) had a positive blood culture on the first day of life; 28 infants (Group B) and 6 infants (Group C) had bacteremia beyond the first day. Group C infants became septic as a result of intraabdominal pathology. Pathogens isolated from blood were correlated with those from preceding daily tracheal aspirates. The overall sensitivity of tracheal cultures in predicting results of blood cultures was 81% (Group A, 71%; Group B, 93%; Group C, 50%). The specificity of daily tracheal aspirates was ascertained from 28 of 50 ventilated infants who were nonseptic and had negative blood cultures during a 6-month period. Only 18 had consistently sterile tracheal aspirates (specificity, 64%). The mean number of days of intubation was 6.6 for the 10 false positive and 3.6 for the 18 true negative. Because of low positive predictive value (0.26) the role of daily tracheal aspirate culture is limited to providing early information regarding potential pathogens when sepsis occurs rather than to identify babies who are going to become septic.

Detection of infectious laryngotracheitis virus in chickens using a non-radioactive DNA probe

A DNA hybridization assay using a non-radioactive probe has been developed for the detection of infectious laryngotracheitis virus (ILTV) DNA. A 1.4-kilobase pair BamHI fragment of ILTV genomic DNA was cloned and then labeled by one of two methods; nick translation using 32P-dATP or non-radioactive labeling using a commercially available DNA labeling and detection kit. The non-radioactive DNA labeling method proved to be as sensitive as the radioactive method. Using the non-radioactive probe, ILTV DNA was readily detected in tracheal samples from acutely infected chickens and also from convalescent chickens at a time when viral antigen could no longer be detected by the enzyme-linked immunosorbent assay or the virus could no longer be reisolated. This technique provides a safe and effective means of identifying field outbreaks of ILTV and also may detect latent ILTV infections relatively quickly and inexpensively.

An immunohistochemical study of the pneumonia caused by peste des petits ruminants virus

Ten goats were inoculated with peste des petits ruminants virus, a paramyxovirus closely related to rinderpest virus. All goats developed severe clinical disease, 8/10 having coughing or dyspnea as prominent clinical signs. In addition, all of the goats had stomatitis and diarrhea. Histopathologic and immunohistochemical studies were done only on the respiratory tracts. Pathologic changes ranged from mild multifocal bronchiolitis and bronchitis to severe bronchointerstitial pneumonia. Lesions were more severe in anteroventral than caudal lobes. The histologic nature of the viral process in the goat lungs had many features in common with the processes of pneumonia in dogs, due to canine distemper, or pneumonia in human beings, due to measles virus. Immunohistochemical staining of formalin-fixed, paraffin-embedded respiratory tract tissue was performed using an indirect system with rabbit anti-rinderpest virus serum, biotinylated anti-rabbit antibody, streptavidin-alkaline phosphatase, and nitroblue tetrazolium chromogen. Staining was sensitive, highlighting the presence of viral antigen in both lung and trachea of all goats. Viral antigen was found in both cytoplasm and nucleus of tracheal, bronchial, and bronchiolar epithelial cells, type II pneumocytes, syncytial cells, and alveolar macrophages. In general, the amount of staining correlated directly with the severity of the inflammatory process.

Aerobic and anaerobic bacterial isolates from horses with pneumonia or pleuropneumonia and antimicrobial susceptibility patterns of the aerobes

Frequency of aerobic and anaerobic isolates in 327 aspirates and in 123 pleural fluid samples from 327 horses with pneumonia or pleuropneumonia and antimicrobial susceptibility patterns of the aerobes were reported. Of the 327 horses, 75% survived, 20% were euthanatized, and 5% died. Tracheobronchial aspirates or pleural fluid specimens from 25 of the horses did not yield growth. Of the remaining 302 horses, 221 had only aerobic organisms isolated, whereas only anaerobes were isolated from 6 of the 302 horses. The remaining 75 horses had mixed aerobic and anaerobic bacterial infections. The survival rates for horses with aerobic only isolates was twice that of horses with anaerobic isolates. The aerobic bacteria most frequently isolated were beta-Streptococcus spp, Pasteurella spp, Escherichia coli, and Enterobacter spp. The anaerobic species most frequently isolated were Bacteroides spp and Clostridium spp.

Susceptibility of newly established mouse strain MPS to Mycoplasma pneumoniae infection

A newly established mouse strain, MPS, which is more sensitive to Mycoplasma pulmonis than ICR, ddY and other mouse strains was examined for its susceptibility to Mycoplasma pneumoniae. In experimental infections with M. pneumoniae, it was observed that M. pneumoniae attached to tracheas of MPS mice, and M. pneumoniae cells were isolated from tracheas and lungs of MPS mice even after four weeks of infection, while no mycoplasmas were isolated from ICR and ddY mice after one week of infection. Specific antibodies against M. pneumoniae were also observed by the Western blotting in the sera of MPS mice infected with M. pneumoniae. Although any lung lesion could not be observed in this work, this newly established mouse strain MPS may be useful for experiments of M. pneumoniae infection, especially for the analysis of strain differences in susceptibility to M. pneumoniae infection.

The role of polar pili in the adherence of Pseudomonas aeruginosa to injured canine tracheal cells: a semiquantitative morphologic study

Pseudomonas aeruginosa adheres to respiratory epithelial cells in a highly specific fashion. In order to study the role of P. aeruginosa polar pili in the adherence process we conducted a quantitative morphological electron microscopic examination of P. aeruginosa adherence to SO2 injured canine tracheal cells in vitro. A pilin lacking background strain of P. aeruginosa PAK (BLP2) was constructed using a gene replacement and it in turn was engineered to express either the pilin gene of P. aeruginosa PAO, PAK, or no pilin gene. After 30 minutes incubation of these bacterial strains with injured canine tracheal rings the P. aeruginosa strains expressing pili adhered quantitatively more to the injured tracheal cells than did the pili lacking strains. PAO bearing strains adhered in greater numbers than PAK bearing strains. Healthy tracheal cells did not have any bacteria bound to their surfaces. The bacteria bound to the cilia and lateral edge of the exfoliating tracheal cells. Invasion of tracheal cells by piliated P. aeruginosa bacteria and penetration into the submucosa was also demonstrated. These data confirm the role of pili as important adhesins to injured tracheal cells. The difference in the adherence characteristics of pilin types PAK versus PAO may relate to the differences in the primary structure of these two pilin molecules.

Bronchoalveolar lavage and tracheal wash to determine lung involvement in a cat with cryptococcosis

A one-year-old 3-kg female domestic shorthair cat was diagnosed as having cryptococcosis. Although the cat had no clinical signs referable to the pulmonary system and results of thoracic radiography were normal, organisms were recovered by use of tracheal wash and bronchoalveolar lavage. In cases of fungal infections, the latter 2 methods can be more reliable than radiography and evaluation of clinical signs for determining pulmonary involvement.

Use of a protected catheter brush for culture of the lower respiratory tract in horses with small airway disease

A protected catheter brush introduced by fiberoptic bronchoscopy was used to sample the tracheai and bronchial mucosa in 28 horses with small airway disease. Tracheal and bronchial brushings were examined for the presence of fungi, aerobic and anaerobic bacteria, and a cytoiogical evaluation was also done on fluid collected by the bronchoalveolar lavage (BAL) technique. Microorganisms (bacteria and fungi) were isolated more often in tracheal brushings (53.6%) than in bronchial brushings (10.7%). Anaerobic bacteria were not isolated. Results of this study indicate that fiberoptic bronchoscopy using a protected catheter brush is an easy and practical technique to obtain minimally contaminated samples for isolation of microorganisms from the lower respiratory tract of horses. However, no association was observed between isolation of high numbers of microorganisms from the bronchi and severity of small airway disease.

Type A influenza viruses in waterfowl in Ohio and implications for domestic turkeys

Because ducks are considered an important reservoir for type A influenza virus, and type A influenza viruses had not been recovered from ducks in Ohio, a 3-year virus surveillance study was conducted in Ohio waterfowl and waterfowl passing through Ohio to determine if domestic turkeys were at risk of exposure to avian influenza (AI) viruses from the waterfowl reservoir. The prevalence of AI infections in ducks during the fall migration averaged about 5.9%. The 55 waterfowl-origin type A influenza viruses recovered from ducks during fall 1986, 1987, and 1988 represented 23 different hemagglutinin-neuraminidase sub-type combinations of type A influenza viruses. Virus recovery frequencies ranged from 3.6% to 7.8% between years, from 2.0% to 8.2% between study sites, from 0.0% to 16.7% for sampling days, and from 0.0% to 14.3% among species of ducks sampled.

Determination of affinity of Pasteurella multocida isolates for porcine respiratory tract mucus, and partial characterization of the receptors

The ability of 25 Pasteurella multocida isolates to adhere in vitro to porcine respiratory tract mucus was examined. Microplate wells were coated with crude mucus preparation, then bacteria were added. After incubation, unbound bacteria were removed by washing, and the number of mucus-bound bacteria was estimated by quantitation of the adherent colony-forming units and by use of an ELISA. Pasteurella multocida had affinity to respiratory tract mucus, although significant differences were not observed in affinity of capsular type-A and type-D isolates. Preliminary characterization, using ultrafiltration, gel filtration chromatography, electrophoresis, and enzymatic treatments, indicated that the receptors may be a class of protein molecules of low molecular weight (less than 25,000). The origin of these receptors, however, is not known at this time.

Infection of cultured human tracheal epithelial cells by human parainfluenza virus types 2 and 3

Despite growing information of the effects of human respiratory virus infection on airway physiology, little information is available on the mechanisms of pathology and pathophysiology in these infections. The human respiratory pathogens, parainfluenza virus types 2 and 3 (hPIV2, hPIV3, respectively), clinically cause laryngotracheobronchitis (infection of the large proximal airways). In order to examine the pathobiology of these viruses in airway cells of human origin, we exposed primary cultures of human tracheal epithelial cells. Primary cultures of human tracheal epithelial cells were readily infected by these agents: cells exposed to hPIV2 and hPIV3 expressed viral antigens (demonstrated by indirect immunofluorescence assay), produced infectious virus, and demonstrated cytopathic effects (including early syncytium formation). Peak viral titers of 2 x 10(7) plaque-forming units per milliliter were obtained, similar to titers from permissive CV-1 cells. Trypan blue staining and direct cell counts demonstrated no difference in the viability of the control and infected cells until the infected cells began to detach from the culture substrate. However, infected cells release significantly more LDH than control cells by 48 h following infection at a multiplicity of infection of 1 virus/target cell. This system provides a model for studying the effects of infection of the human tracheal epithelium by human respiratory viral pathogens without confounding interactions with other cell and tissue types.

Infection of cultured human airway epithelial cells by influenza A virus

The lack of an adequate in vitro model has hampered study of the cellular basis by which influenza A virus causes disease in the human airway. We report in vitro infection of human airway epithelial cells by influenza A virus. Fetal and adult human tracheal and bronchial epithelial cells cultured from explants and SV40 transformed adult human tracheal epithelial cells were exposed to a recently isolated strain of influenza A virus (H1N1) and a laboratory passaged strain (WSN) of influenza A virus at similar multiplicity of infection. All cultures derived from explants showed hemadsorption (approximately 30% of the cells) with the H1N1 virus. No hemadsorption was detected with the WSN virus. One of two transformed cell lines showed a 5-10% hemadsorption to cells after H1N1 exposure and none following exposure to WSN. Immunofluorescent staining for influenza A-specific antigens in virus-exposed, explant-derived cells indicated viral infection and replication in these cells. Hemagglutinating material in the growth medium of infected, explant-derived cell lines, increased as a function of time, indicating the production of virus proteins. Exposure of rhesus monkey kidney cells and new human tracheal epithelial cultures to supernatant from these cells resulted in hemadsorption, indicating the presence of infectious virus in the supernatant. Light microscopic examination of virally infected bronchial epithelial cells demonstrated that the common types of cytopathic changes were rarely seen while cell proliferation continued over time. The data indicate that influenza A virus can infect, replicate, and produce infectious virus in cultured human tracheal and bronchial epithelial cells.