Ultrastructural characterization of the nasal respiratory epithelium in the piglet

An ex vivo porcine nasal mucosa explants model to study MRSA colonization

Staphylococcus aureus is an opportunistic pathogen able to colonize the upper respiratory tract and skin surfaces in mammals. Methicillin-resistant S. aureus ST398 is prevalent in pigs in Europe and North America. However, the mechanism of successful pig colonization by MRSA ST398 is poorly understood. To study MRSA colonization in pigs, an ex vivo model consisting of porcine nasal mucosa explants cultured at an air-liquid interface was evaluated. In cultured mucosa explants from the surfaces of the ventral turbinates and septum of the pig nose no changes in cell morphology and viability were observed up to 72 h. MRSA colonization on the explants was evaluated followed for three MRSA ST398 isolates for 180 minutes. The explants were incubated with 3×10⁸ CFU/ml in PBS for 2 h to allow bacteria to adhere to the explants surface. Next the explants were washed and in the first 30 minutes post adhering time, a decline in the number of CFU was observed for all MRSA. Subsequently, the isolates showed either: bacterial growth, no growth, or a further reduction in bacterial numbers. The MRSA were either localized as clusters between the cilia or as single bacteria on the cilia surface. No morphological changes in the epithelium layer were observed during the incubation with MRSA. We conclude that porcine nasal mucosa explants are a valuable ex vivo model to unravel the interaction of MRSA with nasal tissue.

Influence of intranasal sterile isotonic sea water applications on xylometazoline administration: an experimental study in pigs

OBJECTIVE

The aim of this study was to investigate how isotonic sea water solution (Physiomer) affects the structure of porcine nasal mucosa when it is applied simultaneously with vasoconstrictors (xylometazoline) for a prolonged period of time.

METHODS

Twenty pigs of the PMR-Landraze breed formed the study group. A solution of xylometazoline 0, 1% (Otrivin spray, Novartis) was sprayed every 8h in both nasal cavities of the pigs, with two applications into each nostril for 28 days. Between the applications (4h later), the right nasal cavity was washed with sterile isotonic sea water (Physiomer Normal, Geomar). Biopsies were taken under endoscopic guidance from the nasal mucosa of each nasal cavity separately at specific times. Five histological parameters were microscopically examined for each biopsy section: (1) inflammation, (2) fibrosis, (3) metaplasia of the epithelium, (4) reactive atypia of the epithelium and (5) necrosis.

RESULTS

Statistically significant differences regarding grade of inflammation on days 7 (p=0.0009), 12 (p=0.01), 20 (p=0.02) and 28 (p=0.0005), regarding grade of fibrosis on day 28 (p=0.026) and regarding epithelial metaplasia on day 5 (p=0.052) were found between the nasal mucosa treated only with vasoconstrictors and the nasal mucosa treated with vasoconstrictors and sea water washing. In all cases, samples from the nasal cavities that had been washed with Physiomer appeared with a lower grade of inflammation, fibrosis and metaplasia compared to the samples from nasal mucosa where no nasal washing was performed.

CONCLUSION

Nasal irrigations with isotonic sea water, when are applied 4h after vasoconstrictors for a long period of time, prevent nasal mucosa from histological damage.

In vitro culture of porcine respiratory nasal mucosa explants for studying the interaction of porcine viruses with the respiratory tract

The mucosal surface of the respiratory tract is a common site of entry of many viruses. Molecular and cellular aspects of the interactions of respiratory viruses with the respiratory nasal mucosa are largely unknown. In order to be able to study those interactions in depth, an in vitro model was set up. This model consists of porcine respiratory nasal mucosa explants, cultured at an air-liquid interface. Light microscopy, scanning electron microscopy and transmission electron microscopy, combined with morphometric analysis and a fluorescent Terminal deoxynucleotidyl transferase mediated dUTP Nick End Labelling (TUNEL) staining were used to evaluate the effects of in vitro culture on the integrity and viability of the explants. The explants were maintained in culture for up to 60 h post-sampling without significant morphometric (epithelial thickness, epithelial morphology, thickness of the lamina reticularis, continuity of the lamina densa, relative amounts of collagen and nuclei) changes and changes in viability. The potential to infect the explants was demonstrated for two porcine respiratory viruses of major importance: suid herpesvirus 1 and swine influenza virus H1N1. In conclusion, this in vitro model represents an ideal tool to study interactions between infectious agents and porcine respiratory nasal mucosa.

Olfactory mucosa of the South American armadillo Chaetophractus villosus: an ultrastructural study

The sense of olfaction in armadillos plays an important role, suggested by the great development of the nasal structures, olfactory bulbs, and related brain regions. The mammalian olfactory mucosa is a privileged site of neuronal death and regeneration during the whole life span. A detailed knowledge of its ultrastructure is convenient for gaining insight into the factors controlling those phenomena. We performed this work in species not previously studied in order to provide a firm basis for further research on those factors. No information is available on the histology and ultrastructure of the olfactory mucosa in the order Xenarthra to which armadillos belong. Samples from the endoturbinals of the armadillo Chaetophractus villosus were prepared for light and electron microscopic examination by the usual conventional means. The olfactory epithelium of Chaetophractus villosus shows the classical three types of cells: supporting cells, olfactory receptor neurons, and basal cells. The olfactory neurons and the basal cells were similar to that described in other species. Two different types of supporting cells are described. An outstanding characteristic of the supporting cells is the normal presence of abundant phagosomes, apical secretory granules, apocrine-like protrusions, and highly developed smooth endoplasmic reticulum. Apoptotic bodies are frequently found in the infranuclear cytoplasm of supporting cells. The ductular epithelium of Bowman's glands reveals secretory activity. The lamina propria shows mixed Bowman's glands. Great development of smooth endoplasmic reticulum is observed in the mucous acinar cells. Evidence for merocrine and apocrine mechanisms in the Bowman's glands is presented. The presence of apoptotic bodies and phagosomes in supporting cells suggests a participation in the cellular events induced by cell death and proliferation of the olfactory epithelium. The variety of characteristics exhibited by the supporting cells of the olfactory mucosa may contribute to a deeper understanding of their scarcely known functions.