Keratinization of the esophageal epithelium of domesticated mammals.

We studied the esophageal epithelium for keratinization characteristics from samples of domesticated mammals of three nutrition groups (herbivores: horse, cattle, sheep; omnivores: pig, dog, rat; carnivores: cat) using histochemistry (keratins, disulfides), sulfur measurements, and cryo-SEM. Keratins were found in all esophageal layers of all species, except for the equine Stratum corneum. The positive reaction staining of Pan-keratin was remarkable, but decreased in intensity toward the outer layers, whereas in the pig and cat, staining was confined to the corneal layer. The herbivores revealed positive staining reactions in the upper Stratum spinosum, particularly in the sheep. Regarding single keratins, CK6 immunostating was found in most esophageal layers, but only weakly or negatively in the porcine and equine Stratum corneum. CK13 staining was restricted to the sheep and here was found in all layers. CK14 could be detected in the equine and feline Stratum basale, and upper vital layers of the dog and rat. CK17 appeared only in the Stratum spinosum and Stratum granulosum, but in all layers of the dog and cat. Disulfides reacted strongest in the Stratum corneum of the herbivores, as corroborated by the sulfur concentrations in the esophagus. Our study emphasized that keratins are very important for the mechanical stability of the epithelial cells and cell layers of the mammalian esophagus. The role of these keratins in the esophageal epithelia is of specific interest owing to the varying feed qualities and mechanical loads of different nutrition groups, which have to be countered.

Demonstration of substances of innate immunity in the esophageal epithelium of domesticated mammals. Part I--Methods and evaluation of comparative fixation.

The aim of the investigation was to demonstrate that the esophageal epithelium of domesticated mammals exhibits characteristic features of innate immunity. The esophageal samples used were obtained immediately after euthanization from seven species of domesticated mammals of three nutrition groups (herbivores: horse, goat, cattle; omnivores: pig, dog, laboratory rat; carnivores: cat). The experimental basis was immunohistochemistry, which was evaluated in a qualitative and statistically relevant semi-quantitative manner. The first part of the study analyzed the influence of different fixation media on the immunohistochemical reactivities. Two formalin-based routine fixation solutions (Bouin's solution, Ca-acetate formalin) were compared with the recently introduced formalin-free HOPE® fixative. In this context, we clearly demonstrated a diminished immunoreactivity for Ca-formol fixed samples; satisfactory results were obtained, particularly, from samples fixed in Bouin's solution. The HOPE® fixation method offers a relatively cheap alternative, as the antibody amounts can be reduced. An application in routine diagnostic is not advisable, because of several variable parameters. It can be concluded that immunohistochemical results have always to be evaluated and discussed in close relation to the fixation medium used.

Demonstration of substances of innate immunity in the esophageal epithelium of domesticated mammals: Part II--Defence mechanisms, including species comparison.

The second part of our study deals with a comparative evaluation and discussion of the immunohistochemical results that were obtained. The cryoscanning electron microscopy (cryoSEM) observations confirmed a monolayer colonization of the esophageal surface with bacteria and fungi (yeasts); the latter in particular was prominent in the ruminant species studied. We demonstrated the existence of several innate immune parameters, including pathogen recognition receptors (PRRs), such as Toll-like receptor 2, which was primarily expressed in the stratum basale; however, the presence ß-glucan receptors remained inconclusive. Furthermore, the group of cationic antimicrobial peptides (CAPs) was shown, comprising ß-defensins 2 and 3 and cathelicidin. The less keratinized esophageal epithelium of the carnivorous cat was protected by high amounts of CAPs; whereas the more strongly keratinized epithelium of the herbivorous and omnivorous species with its characteristic layer structure exhibited clearly weaker reactions. Moreover, lysozyme could distinctly be demonstrated in the cells of the esophageal epithelium. It can be concluded that a first line of defence mechanisms of the innate immune system contributes to maintaining a microbial homeostasis on the surface of the esophageal epithelium of domesticated mammals. The results are discussed in comparison to findings from studies on the human esophagus.