Injury of respiratory epithelium

The effects of suctioning techniques on the distal tracheal mucosa in intubated low birth weight infants

Microscopic pathology of the distal trachea at autopsy was retrospectively reviewed in 51 low birth weight infants (less than 1250 g). Twenty-six patients from 1977 who had nasal and/or orotracheal intubation and who underwent suctioning with uncontrolled deep suctioning technique were compared to 25 patients from 1980 who had orotracheal intubation with suctioning to the tube tip only. Clinical diagnoses, duration of intubation and number of intubations were correlated to degree of distal tracheal injury: absent (normal epithelium), mild (focal epithelial loss), moderate (diffuse epithelial loss/some inflammation), or severe (submucosal ulceration/squamous metaplasia). From 1977 to 1980 the mortality rate, mean gestational age and mean birth weight all decreased by 20% (P less than 0.05), 1.1 week (P less than 0.05) and 118 g (P less than 0.01) in both autopsied and non-autopsied infants. In 1977, 15 of 26 autopsies (58%) revealed mild (6), moderate (5) or severe (4) pathology. The mean duration of intubation was 71.3, 11.8, and 265 h. respectively. No history of intubation was obtained in two patients with mild injury. No significant tracheal pathology was seen in 11 patients (42%) in 1977. In 1980, fewer patients, 10 of 24 autopsies (42%), revealed mild (3), moderate (4) or severe (3) pathology. The mean duration of intubation was 19.3, 318.3 and 1391.3 h, respectively. One patient with no history of intubation had mild tracheal injury. No significant tracheal pathology was seen in 15 patients (58%) in 1980. The diagnoses of hyaline membrane disease, anemia, hyperbilirubinemia and coagulation disorder were seen more frequently in patients with moderate and severe tracheal pathology both in 1977 and 1980. Despite factors which should lead to greater tracheal injury--longer duration of intubation, lower birth weights and younger gestational age--less tracheal injury was seen in infants undergoing careful suctioning techniques. Clinical implications for the low birth weight neonate are discussed.

Hamster tracheal organ culture in serum-free media: a quantitative comparison of in vitro epithelial morphology with that of in vivo controls

The epithelial morphology of the hamster trachea in serum-free organ culture was compared with that of age-matched in vivo control tissues by collecting and statistically analyzing several quantifiable parameters. By this technique it was possible to detect both subtle and dramatic epithelial alterations. Midtracheal tissues from 6-wk-old male Syrian golden hamsters were used as the explants. Explants were placed on Gelfoam sponges and cultured for 1,2, and 3 wk in CMRL 1066 alone and in CMRL 1066 to which seven factors were added: insulin and transferrin (5 micrograms/ml); hydrocortisone (5 X 10(-7) M); epidermal growth factor (5 ng/ml); bovine pituitary extract (0.5%); and phosphoethanolamine and ethanolamine (5 X 10(-5) M). The following data were collected and statistically analyzed for each tracheal ring: number of epithelial cells; proportion and number of each cell type; basement membrane length; linear density of epithelial cells; epithelial height; and mitotic index. Compared to controls, ciliated cells decreased by 52% during washes in Leibovitz (L15) medium and tissue manipulation performed before culture and this loss persisted after culture for 1 wk. Explants cultured without the factors showed marked changes after 2 and 3 wk including epithelial thickening and folding, which was associated with increased linear density. Many cells in these specimens could not be categorized by type (22% were unidentifiable after 3 wk). Epithelial migration onto the outside of the explant was inhibited. In contrast, explants cultured with the factors maintained a morphology similar to controls at 2 and 3 wk and epithelial migration onto the outside of the explant was supported. This study shows that explants in CMRL 1066 with the seven factors provide a useful biological model for the in vitro study of mucociliary respiratory epithelium.

Immunohistochemical techniques and their applications in the histopathology of the respiratory system

Subsequent to the first report in the 1940s on incubation of tissue sections with fluorescein-conjugated antibodies for localization of antigens, a great number of modifications were introduced to improve the validity of immunohistochemistry which has become a growingly popular tool. The use of immunoenzymatic techniques eliminates the need for expensive fluorescence microscopy equipment, the lack of permanency of preparations and the lack of electron density required in ultrastructural localization of antigens. Regardless of the technique, it is also important to choose a correct fixation which allows the proper preservation of antigens and morphology and the penetration of antibodies through the entire thickness of the preparation. A variety of immunohistochemical techniques have been applied to study several components of the lung, such as collagen, surface active material, lung specific antigens, and enzymes and the detection of tumor markers, immunoglobulins and infectious agents in the respiratory system which is reviewed. The large surface area and the multiplicity of cell types provided by the respiratory tract epithelium of humans for exposure to microbial as well as toxic substances in the environment make this organ system very vulnerable but a good early indicator of adverse health effects. Immunohistochemistry provides valuable information complementary to the immunochemical and biochemical characterization of this barrier.

Experimental models for study of common respiratory viruses

Numerous epidemiological studies have shown that there is excess respiratory disease morbidity in areas of high atmospheric pollution, implying an interactive effect on the clinical illness associated with these common infections. The principal etiologic agents of human respiratory infections are respiratory syncytial virus (RSV), influenza viruses (IV), parainfluenza virus types 1 and 3 (P1, P3), adenoviruses (AD), rhinoviruses (RV) and Mycoplasma pneumoniae (Mpn). Understanding the pathogenesis of the excess morbidity related to pollutants would facilitate detection of undesirable human health effects and provide a basis for intervention strategies. Through use of experimental model systems the mechanism of toxic effects could be defined (whether microbiological, immunological, pathological or physiological) to provide direction for appropriate studies in the human host. Small animal models of IV and Mpn infections have been available for many years; recently, experimental models of several more common viral diseases have been developed. A parallel to human RSV infections is provided by the ferret: virus replicates in the lungs of infant animals, but only in the noses of adults. The common cotton rat infected with RSV develops small airways lesions which may mimic the pathophysiologic changes of bronchiolitis. Both guinea pigs and Syrian hamsters are susceptible to human P3 virus, developing peribronchiolar and interstitial lesions. Practical small animal models for human AD and RV infections are not available because of the high host-specificity of these agents. Both the RSV and P3 model infections are nonlethal which enables study for long-term sequelae. Recent reports of pulmonary function abnormalities among children suffering bronchiolitis in infancy underscores the importance of defining toxic influences which could play a role by making the initial infections more severe.