Cilia in children with recurrent upper respiratory tract infections: ultrastructural observations

Functional analysis and evaluation of respiratory cilia in healthy Chinese children

BACKGROUND

To aid in the diagnosis of Primary Ciliary Dyskinesia (PCD) and to evaluate the respiratory epithelium in respiratory disease, normal age-related reference ranges are needed for ciliary beat frequency (CBF), beat pattern and ultrastructure. Our aim was to establish reference ranges for healthy Chinese children.

METHODS

Ciliated epithelial samples were obtained from 135 healthy Chinese children aged below 18 years by brushing the inferior nasal turbinate. CBF and beat pattern were analysed from high speed video recordings. Epithelial integrity and ciliary ultrastructure were assessed using transmission electronic microscopy.

RESULTS

The mean CBF from 135 children studied was 10.1 Hz (95% CI 9.8 to 10.4). Approximately 20% (ranged 18.0-24.2%) of ciliated epithelial edges were found to have areas of dyskinetically beating cilia. Normal beat pattern was observed in ciliated epithelium from all subjects. We did not find any effect of exposure to second hand smoke on CBF in our subjects. Microtubular defects were found in 9.3% of all of the cilia counted in these children, while other ciliary ultrastructural defects were found in less than 3%.

CONCLUSIONS

We established the reference range for CBF, beat pattern and ultrastructure in healthy Chinese children. Using similar methodology, we found a lower overall mean CBF than previously obtained European values. This study highlights the need to establish normative data for ciliary function in different populations.

Chronic cough in preschool children

Cough may be the first overt sign of disease of the airways or lungs when it represents more than a defense mechanism, and may by its persistence become a helpful pointer of potential disease for both patient and physician. On the other hand, impairment or absence of the coughing mechanism can be harmful and even fatal; this is why cough suppression is rarely indicated in childhood. Pediatricians are concerned more with the etiology of the cough and making the right diagnosis. Whereas chronic cough in adults has been universally defined as a cough that lasts more than 8 weeks, in childhood, different timing has been reported. Many reasons support defining a cough that lasts more than 4 weeks in preschool children as chronic, however; and this is particularly true when the cough is wet. During childhood, the respiratory tract and nervous system undergo a series of anatomical and physiological maturation processes that influence the cough reflex. In addition, immunological response undergoes developmental and memorial processes that make infection and congenital abnormalities the overwhelming causes of cough in preschool children. Cough in children should be treated on the basis of etiology, and there is no evidence in support of the use of medication for symptomatic cough relief or adopting empirical approaches. Most cases of chronic cough in preschool age are caused by protracted bacterial bronchitis, tracheobronchomalacia, foreign body aspiration, post-infectious cough or some combination of these. Other causes of chronic cough, such as bronchiectasis, asthma, gastroesophageal reflux, and upper respiratory syndrome appear to be less frequent in this age group. The prevalence of each depends on the population in consideration, the epidemiology of infectious diseases, socioeconomic aspects, and the local health system.

Establishment of a reverse genetics system for studying human bocavirus in human airway epithelia

Human bocavirus 1 (HBoV1) has been identified as one of the etiological agents of wheezing in young children with acute respiratory-tract infections. In this study, we have obtained the sequence of a full-length HBoV1 genome (including both termini) using viral DNA extracted from a nasopharyngeal aspirate of an infected patient, cloned the full-length HBoV1 genome, and demonstrated DNA replication, encapsidation of the ssDNA genome, and release of the HBoV1 virions from human embryonic kidney 293 cells. The HBoV1 virions generated from this cell line-based production system exhibits a typical icosahedral structure of approximately 26 nm in diameter, and is capable of productively infecting polarized primary human airway epithelia (HAE) from the apical surface. Infected HAE showed hallmarks of lung airway-tract injury, including disruption of the tight junction barrier, loss of cilia and epithelial cell hypertrophy. Notably, polarized HAE cultured from an immortalized airway epithelial cell line, CuFi-8 (originally derived from a cystic fibrosis patient), also supported productive infection of HBoV1. Thus, we have established a reverse genetics system and generated the first cell line-based culture system for the study of HBoV1 infection, which will significantly advance the study of HBoV1 replication and pathogenesis.

Human bocavirus 1 (HBoV1) has been identified as one of the etiological agents of wheezing in young children with acute respiratory-tract infections. HBoV1 productively infects polarized primary human airway epithelia. However, no cell lines permissive to HBoV1 infection have yet been established. More importantly, the sequences at both ends of the HBoV1 genome have remained unknown. We have resolved both of these issues in this study. We have sequenced a full-length HBoV1 genome and cloned it into a plasmid. We further demonstrated that this HBoV1 plasmid replicated and produced viruses in human embryonic kidney 293 cells. Infection of these HBoV1 progeny virions produced obvious cytopathogenic effects in polarized human airway epithelia, which were represented by disruption of the epithelial barrier. Moreover, we identified an airway epithelial cell line supporting HBoV1 infection, when it was polarized. This is the first study to obtain the full-length HBoV1 genome, to demonstrate pathogenesis of HBoV1 infection in human airway epithelia, and to identify the first cell line to support productive HBoV1 infection.

Recovery of the ciliated epithelium following acute bronchiolitis in infancy

BACKGROUND

Little is known about the longitudinal changes in the ciliated respiratory epithelium of infants following viral bronchiolitis. A study was undertaken to investigate the time required for the ciliated epithelium to return to normal following bronchiolitis in infants treated with inhaled steroids or placebo.

METHODS

Thirty one previously healthy term infants were studied as part of a clinical trial to determine the effect of 12 weeks of treatment with inhaled fluticasone (FP) or placebo via a spacer device (17 FP, 14 placebo). Nineteen healthy children aged 0-6 years previously studied in our department were used as controls. Nasal biopsy specimens were taken from infants with bronchiolitis and ciliary beat frequency (CBF) was measured before treatment and repeated 3, 6, 12, and 24 weeks later. The epithelial ultrastructure was examined by transmission electron microscopy and a normal errors mixed model based on normal controls was used to examine the time for cilia to return to normal in bronchiolitic infants.

RESULTS

The mean CBF of infants with bronchiolitis (in Hz) at weeks 0, 3, 6, 12, and 24 were 0.5 (n = 4), 10.9 (n = 4), 12.0 (n = 9), 11.9 (n = 8), and 12.1 (n = 7) in the placebo group and 10.6 (n = 6), 11.4 (n = 9), 8.8 (n = 8), 10.9 (n = 4), and 13.2 (n = 7) in the FP group. The time for the epithelial ultrastructure to normalise was as follows: epithelial integrity score (13.1 weeks), % ciliated cells with loss of cilia (14.0 weeks), and % epithelial cells with abnormalities in projection (16.7 weeks) or mitochondria (15.9 weeks). Inhaled steroids had no significant effects on CBF or epithelial ultrastructure.

CONCLUSION

Ciliary loss and epithelial abnormalities persist on average for 13-17 weeks following acute bronchiolitis in infancy.

Nitric oxide levels and ciliary beat frequency in indigenous New Zealand children

New Zealand children's morbidity from respiratory disease is high. This study examines whether subclinical ciliary abnormalities underlie the increased prevalence of respiratory disease in indigenous New Zealand children. A prospective study enrolled a group of healthy children who were screened for respiratory disease by questionnaire and lung function. Skin-prick tests were performed to control for atopy. Exhaled and nasal NO was measured online by a single-breath technique using chemiluminescence. Ciliary specimens were obtained by nasal brushings for assessment of structure and function. The ciliary beat frequency (CBF) (median CBF, 12.5 Hz; range, 10.4-16.8 Hz) and NO values (median exhaled NO, 5.6 ppb; range, 2.3-87.7 ppb; median nasal NO, 403 ppb; range, 34-1,120 ppb) for healthy New Zealand European (n=58), Pacific Island (n=61), and Maori (n=16) children were comparable with levels reported internationally. No ethnic differences in NO, atopy, or CBF were demonstrated. Despite an apparently normal ciliary beat, the percentage of ciliary structural defects was 3 times higher than reported controls (9%; range, 3.6-31.3%), with no difference across ethnic groups. In conclusion, it is unlikely that subclinical ciliary abnormalities underlie the increased prevalence of respiratory disease in indigenous New Zealand children. The high percentage of secondary ciliary defects suggests ongoing environmental or infective damage.

Functional analysis of cilia and ciliated epithelial ultrastructure in healthy children and young adults

BACKGROUND

There are very few data on normal ciliary beat frequency, beat pattern, and ultrastructure in healthy children and adults. A study was undertaken to define ciliary structure, beat frequency and beat pattern in a healthy paediatric and young adult population.

METHODS

Ciliated epithelial samples were obtained from 76 children and adult volunteers aged 6 months to 43 years by brushing the inferior nasal turbinate. Beating cilia were recorded using a digital high speed video camera which allowed analysis of ciliary beat pattern and beat frequency. Tissue was fixed for transmission electron microscopy.

RESULTS

The mean ciliary beat frequency for the paediatric population (12.8 Hz (95% CI 12.3 to 13.3)) was higher than for the adult group (11.5 Hz (95% CI 10.3 to 12.7 Hz), p<0.01, t test); 10% (range 6-24%) of ciliated edges were found to have areas of dyskinetically beating cilia. All samples had evidence of mild epithelial damage. This reflected changes found in all measurements used for assessment of epithelial damage. Ciliary ultrastructural defects were found in less than 5% of cilia.

CONCLUSION

Normal age related reference ranges have been established for ciliary structure and beat frequency. In a healthy population localised epithelial damage may be present causing areas of ciliary dyskinesia.

Plasma membrane polarity of polymorphonuclear leucocytes from children with primary ciliary dyskinesia

BACKGROUND

Polymorphonuclear leucocytes (PMN) from subjects with primary ciliary dyskinesia (PCD) can have abnormal locomotory systems. The locomotory activity of PMN is the result of biochemical events mediated by the plasma membrane. In this study we investigated plasma membrane polarity of PMN from children with PCD.

DESIGN

Membrane polarity was studied in 11 children with PCD and in healthy controls by measuring the steady-state fluorescence excitation and emission spectra of 2-dimethylamino[6-lauroyl]naphthalene (Laurdan), which is known to be incorporated at the hydrophobic-hydrophilic interface of the bilayer, displaying spectral sensitivity to the polarity of its surroundings. Laurdan shows a marked steady-state emission red shift in polar solvents, with respect to nonpolar solvents. Moreover, the effect of the microtubule disassembling agent colchicine on PMN membrane polarity was evaluated.

RESULT

Our results show a red shift of the fluorescence excitation and emission spectra of Laurdan in PMN from the PCD group with respect to the control group. These data indicate an increase in membrane polarity of PMN from the PCD group. Treatment of PMN with colchicine induced a red shift in the Laurdan excitation and emission spectra with the same trend observed in PMN from the PCD group.

CONCLUSION

PMN from children with PCD are characterized by an increased plasma membrane polarity. These changes could be the basis of the modifications in the locomotory activities of PMN. The observed alterations may be attributed to abnormalities in the cytoskeleton.

Tannic acid supplemented fixation improves ultrastructural evaluation of respiratory epithelium in children with recurrent respiratory tract infections

Samples of the respiratory mucosa of children with recurrent respiratory infections suspected of having primary ciliary dyskinesia are routinely fixed with glutaraldehyde before ultrastructural examination. This standard technique, however, may not be optimal for visualizing ciliary components or for preserving several cellular and extracellular structures during dehydration and embedding procedures. In this study, brushes of nasal (28 samples) and/or tracheal (9 samples) mucosa from 32 children with recurrent respiratory tract infections were examined. Twenty-nine samples were fixed with glutaraldehyde supplemented with tannic acid to determine if the ultrastructural analysis of respiratory epithelium and bronchial secretions could be improved. Eight samples were conventionally fixed with glutaraldehyde alone. Lesions of the cellular membrane and damaged cells were easily visualized using tannic acid supplemented fixation. Internal ciliary structures including individual microtubules and dynein arms were also more clearly observed. In addition, the internal structure of microvilli of the respiratory epithelium could be studied and the presence of phospholipid-rich surfactant-like material within nasal and tracheal secretions were visualized after tannic acid supplemented fixation. We suggest that addition of tannic acid during fixation is useful for accurate ultrastructural evaluation of respiratory mucosa in both clinical and experimental situations.

Polymorphonuclear leukocyte-generated oxygen metabolites decrease beat frequency of human respiratory cilia

We investigated the effect of polymorphonuclear leukocyte (PMN)-generated oxygen metabolites on the ciliary beat frequency. PMNs were incubated with human respiratory cilia obtained by nasal brushing. The oxidative metabolism was stimulated by opsonized zymosan, and ciliary beat frequency was evaluated before and after activation of PMNs. Ciliary beat frequency was studied using video microscopy. Our results demonstrate a significant decrease in ciliary beat frequency after activation of PMNs. This effect was reduced by catalase. These data suggest that the PMN-generated oxygen metabolites, particularly H2O2, decrease beat frequency of human respiratory cilia.

Ultrastructure of human nasal epithelium during an episode of coronavirus infection

The nasal epithelium from a young girl was examined by electron microscopy and found to be infected by coronavirus. Virions are seen within and outside the ciliated cells, but not outside or within the goblet cells or other cells of the nasal mucosa. Some virions are located near the microvilli, others in pockets in the apical cell membrane. The cytoplasm contains many small vesicles with a single virion, large apical vesicles containing hundreds of virions, and lysosome-like cytosomes with a moderate number of virions. Some virus-like particles devoid of an electron-dense interior are seen both in the cytosomes and extracellularly. Virus budding was observed in the Golgi apparatus but nowhere else in the cell. The ciliated cells seem not to be destroyed by the viruses, although in many cases the cilia are withdrawn into the cell body. The loss of cilia is likely to cause rhinorrhoea.