Identification of M-cells in the rabbit tonsil by vimentin immunohistochemistry and in vivo protein transport

Does pTis exist in HPV-driven tonsillar carcinomas? An ultrastructural review and examination of two cases

Many tonsillar tumors present clinically as cervical nodal metastases and the primary tumor is often difficult to find. HPV-driven tonsillar carcinoma begins in the reticulated crypt epithelium, possibly through viral integration. The basement membrane is not complete in the reticulated crypt epithelium, which may enhance the immune function. We examined the reticulated crypt epithelium in a normal case and five neoplastic tonsils with cervical metastasis as the presenting symptom to further investigate whether tonsil carcinoma in-situ exists. Our results suggest that in-situ carcinoma may need to be excluded from the future staging for human papilloma virus associated tonsillar tumors.

Roles of M cells in infection and mucosal vaccines

The mucosal immune system plays a crucial part in the control of infection. Exposure of humans and animals to potential pathogens generally occurs through mucosal surfaces, thus, strategies that target the mucosa seem rational and efficient vaccination measures. Vaccination through the mucosal immune system can induce effective systemic immune responses simultaneously with mucosal immunity compared with parenteral vaccination. M cells are capable of transporting luminal antigens to the underlying lymphoid tissues and can be exploited by pathogens as an entry portal to invade the host. Therefore, targeting M-cell-specific molecules might enhance antigen entry, initiate the immune response, and induce protection against mucosal pathogens. Here, we outline our understanding of the distribution and function of M cells, and summarize the advances in mucosal vaccine strategies that target M cells.

Rhinovirus infections and adenoidal hypertrophy: do they interact with atopy in children?

Modern diagnostic methods allow the evaluation of the connection between rhinoviruses and atopy. Recent studies suggest that rhinoviruses are present in the adenoids at higher titers than in other specific sites, after inoculation of nasal mucosa or conjunctiva in volunteers. Therefore, it is possible that they might be responsible for specific local changes, while such changes may be influenced by atopy. This review focuses on the interactions between rhinoviral infection, the host's immune status and adenoidal disease.

Protein transport across the small intestine in food allergy

In view of the imminent deficiency of protein sources for human consumption in the near future, new protein sources need to be identified. However, safety issues such as the risk of allergenicity are often a bottleneck, due to the absence of predictive, validated and accepted methods for risk assessment. The current strategy to assess the allergenic potential of proteins focuses mainly on homology, stability and cross-reactivity, although other factors such as intestinal transport might be of added value too. In this review, we present an overview of the knowledge of protein transport across the intestinal wall and the methods currently being used to measure this. A literature study reveals that protein transport in sensitised persons occurs para-cellularly with the involvement of mast cells, and trans-cellularly via enterocytes, while in non-sensitised persons micro-fold cells and enterocytes are considered most important. However, there is a lack of comparable systematic studies on transport of allergenic proteins. Knowledge of the multiple protein transport pathways and which model system can be useful to study these processes may be of added value in the risk assessment of food allergenicity.

Histological and ultrastructural examinations of porcine tonsils

The histology and ultrastructure of porcine tonsils were studied. The porcine tonsils were lymphoepithelial organs situated at the opening of both the digestive and respiratory tracts. The tonsil of the soft palate in the oropharyngeal tract and the paraepiglottic tonsil in the laryngopharynx were mainly consisted of secondary lymphoid follicles encapsulated by connective tissue. The stratified squamous epithelia covering the tonsils and their crypts were frequently heavily infiltrated by lymphoid cells. The pharyngeal and tubal tonsils (TT) were situated in the nasopharyngeal tract. The cells of the pseudostratified columnar epithelia of the pharyngeal and TT were loosely connected, with large intercellular space. They consisted of scattered lymphoid follicles, aggregations of lymphoid cells and diffuse lymphoid tissues. Many high endothelial venules, specialized for the diapedesis of lymphoid cells into the tonsillar tissue, were detected in the four porcine tonsils. Therefore, the overall structures of the tonsils (the tonsil of the soft palate, the paraepiglottic tonsil, the pharyngeal and the TT) reflect their immune functionality in the oral and intranasal immunity.

Seven kinds of intermediate filament networks in the cytoplasm of polarized cells: structure and function

Intermediate filaments (IFs) are involved in many important physiological functions, such as the distribution of organelles, signal transduction, cell polarity and gene regulation. However, little information exists on the structure of the IF networks performing these functions. We have clarified the existence of seven kinds of IF networks in the cytoplasm of diverse polarized cells: an apex network just under the terminal web, a peripheral network lying just beneath the cell membrane, a granule-associated network surrounding a mass of secretory granules, a Golgi-associated network surrounding the Golgi apparatus, a radial network locating from the perinuclear region to the specific area of the cell membrane, a juxtanuclear network surrounding the nucleus, and an entire cytoplasmic network. In this review, we describe these seven kinds of IF networks and discuss their biological roles.

Low molecular weight chitosan in DNA vaccine delivery via mucosa

It is acknowledged that low molecular weight chitosan (LMWC) is advantageous over high molecular weight chitosan (HMWC) in the biodegradability. In this report, the potential of LMWC in DNA vaccine delivery via mucosa was evaluated. Firstly, the effects of molecular weight of chitosan on the physicochemical properties and in vitro transfection efficiency of chitosan/DNA polyplexes were investigated. Secondly, the capabilities of the polyplexes based on LMWC to elicit serum IgG antibodies and to attenuate the development of atherosclerosis after intranasal vaccination were compared with the polyplexes based on HMWC in the rabbit model. Finally, the intramucosal transport of the double-labeled polyplexes was observed by confocal microscopy. The results indicated that LMWC had lower binding affinity to DNA and mediated higher transfection efficiency. Intranasal vaccination with LMWC/DNA polyplexes could elicit significant systemic immune responses, modulate the plasma lipoprotein profile and attenuate the progression of atherosclerosis. Those aspects were comparable to those obtained by HMWC/DNA polyplexes. As revealed by confocal images, LMWC/DNA polyplexes remained stable during interaction with the nasal mucosa, and were internalized by nasal epithelial cells, which was similar to the case of HMWC/DNA polyplexes. In conclusion, LMWCs have potential applications in DNA vaccine delivery via mucosa.

Keratin 20 expressed in the endocrine and exocrine cells of the rabbit duodenum

The expression of intermediate filaments is sensitively reflected in cell function. To examine the involvement of keratin in a secretory function, 15 kinds of keratin (keratin-2, 3, 4, 5, 6, 7, 8, 10, 13, 14, 16, 17, 18, 19, 20) were detected immunohistochemically and immunoelectron microscopically in the rabbit duodenum. Four types of secretory cells existed in the rabbit duodenum: enteroendocrine cells and goblet cells in the epithelium and mucous and serous cells in the duodenal glands. Among the 15 kinds of keratin, keratin 20 was selectively expressed in all these secretory cells. However, localization of keratin 20 in the endocrine cells differed from that in three types of exocrine cells. In the enteroendocrine cells, keratin 20-containing filaments formed a juxtanuclear network from which they extended to the apical cell membrane. These filaments may play a role in intracellular signal transduction, since the apical cell membrane contains some receptors for binding a specific extracellular signal. In the exocrine cells, on the other hand, keratin 20-containing filaments existed just beneath the cell membrane. These filaments may play some role in maintaining cell shape, which is remarkably changed during the secretory cycle.

Intestinal M cells: The fallible sentinels?

The gastrointestinal tract represents the largest mucosal membrane surface in the human body. The immune system in the gut is the first line of host defense against mucosal microbial pathogens and it plays a crucial role in maintaining mucosal homeostasis. Membranous or microfold cells, commonly referred to as microfold cells, are specialized epithelial cells of the gut-associated lymphoid tissues (GALT) and they play a sentinel role for the intestinal immune system by delivering luminal antigens through the follicle-associated epithelium to the underlying immune cells. M cells sample and uptake antigens at their apical membrane, encase them in vesicles to transport them to the basolateral membrane of M cells, and from there deliver antigens to the nearby lymphocytes. On the flip side, some intestinal pathogens exploit M cells as their portal of entry to invade the host and cause infections. In this article, we briefly review our current knowledge on the morphology, development, and function of M cells, with an emphasis on their dual role in the pathogenesis of gut infection and in the development of host mucosal immunity.

Expression of HIV receptors, alternate receptors and co-receptors on tonsillar epithelium: implications for HIV binding and primary oral infection

Background

Primary HIV infection can develop from exposure to HIV in the oral cavity. In previous studies, we have documented rapid and extensive binding of HIV virions in seminal plasma to intact mucosal surfaces of the palatine tonsil and also found that virions readily penetrated beneath the tissue surfaces. As one approach to understand the molecular interactions that support HIV virion binding to human mucosal surfaces, we have examined the distribution of the primary HIV receptor CD4, the alternate HIV receptors heparan sulfate proteoglycan (HS) and galactosyl ceramide (GalCer) and the co-receptors CXCR4 and CCR5 in palatine tonsil.

Results

Only HS was widely expressed on the surface of stratified squamous epithelium. In contrast, HS, GalCer, CXCR4 and CCR5 were all expressed on the reticulated epithelium lining the tonsillar crypts. We have observed extensive variability, both across tissue sections from any tonsil and between tonsils, in the distribution of epithelial cells expressing either CXCR4 or CCR5 in the basal and suprabasal layers of stratified epithelium. The general expression patterns of CXCR4, CCR5 and HS were similar in palatine tonsil from children and adults (age range 3–20). We have also noted the presence of small clusters of lymphocytes, including CD4⁺ T cells within stratified epithelium and located precisely at the mucosal surfaces. CD4⁺ T cells in these locations would be immediately accessible to HIV virions.

Conclusion

In total, the likelihood of oral HIV transmission will be determined by macro and micro tissue architecture, cell surface expression patterns of key molecules that may bind HIV and the specific properties of the infectious inoculum.

Neutrophil chemokines in epithelial inflammatory processes of human tonsils

CXC chemokines are thought to play an important role at sites of inflammation. Because ELR(+) CXC chemokines are expressed in different types of tonsillitis we investigated the role of the surface/crypt epithelium of human tonsils in producing ELR(+) CXC chemokines: interleukin (IL)-8 (CXCL8), ENA-78 (CXCL5), GRO-alpha (CXCL1) and GCP-2 (CXCL6). Tonsillar tissue was obtained from patients undergoing tonsillectomy and chemokine expression was investigated by means of immunohistochemistry. A549 cells were used as a model to study kinetics of chemokine expression in epithelial cells. Cells were stimulated with tumour necrosis factor (TNF)-alpha, lipopolysaccharide (LPS) and supernatants derived from aerobic/anaerobic Staphylococcus aureus strains. Chemokine expression was measured by quantitative reverse transcription-polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA). We observed epithelial expression of IL-8, GRO-alpha and GCP-2 in different types of tonsillitis, whereas ENA-78 was rarely expressed. In A549 cells abundant expression of ENA-78 was detected. IL-8 and GCP-2 are expressed in an acute type of tonsillitis whereas GRO-alpha was frequently detectable both in chronically and acutely inflamed tonsils. ENA-78 does not seem to play a pivotal role in tonsillitis in vivo.

Rabbit tonsil-associated M-cells express cytokeratin 20 and take up particulate antigen

M-cells are believed to play a pivotal role in initiation of the immune response. These cells, located in the epithelia that overlie mucosal lymphoid follicles, are responsible for the active uptake of particulate antigens and for their translocation to the underlying lymphoid tissue. The identification of reliable markers for M-cells is therefore extremely important for the study of the initial steps that lead to the immune response. For this purpose, we studied cytokeratin 20 (CK20) expression in the epithelium of rabbit palatine tonsils by immunofluorescence, confocal microscopy, and Western blotting. CK20+ cells were observed in all rabbit palatine tonsils examined. By Western blotting, one CK20-immunoreactive band was identified at 46 kD on samples of proteins from the intermediate filament-enriched cytoskeletal fraction of tonsil epithelium. Double labeling of CK20+ cells with cell-specific markers confirmed that such cells were actually M-cells. Moreover, CK20+ M-cells displayed a mature phenotype (they formed pockets harboring lymphoid cells) and were functionally competent because they could take up particulate antigens from the pharyngeal lumen. We conclude that CK20 is an M-cell marker for rabbit palatine tonsils. Moreover, we can hypothesize the use of M-cells as a possible site for antigen delivery of particle-based vaccines.

M cell targeting by lectins: a strategy for mucosal vaccination and drug delivery

Bioadhesins are a recognised method of enhancing the absorption of drugs and vaccines at mucosal surfaces. Additionally, bioadhesins allow for cell specific targeting. Lectin-mediated targeting and delivery exploits unique surface carbohydrates on mucosal epithelial cells. The antigen-sampling M cells offer a portal for absorption of colloidal and particulate delivery vehicles, including bacteria, viruses and inert microparticles. We review work supporting the use of lectins to aid targeting to intestinal M cells. Consideration is also given to lectin-mediated targeting in non-intestinal sites and to the potential application of other bioadhesins to enhance M cell transport. While substantial hurdles must be overcome before mucosal bioadhesins can guarantee consistent, safe, effective mucosal delivery, this strategy offers novel opportunities for drug and vaccine formulation.

Lectin-mediated drug delivery in the oral cavity

The delivery of therapeutic agents to, or via, the oral cavity is limited by the efficient removal mechanisms that exist in this area. Lectins are proteins or glycoproteins that bind to specific sugar residues, and can, therefore, interact with the glycoconjugates present on cell surfaces or salivary mucins. Endogenous lectins could also be used as points of attachment for carbohydrate-containing delivery systems. This review considers the possibility of using lectins as targeting agents within the oral cavity and reports on some of the limited number of studies completed to date. As lectins are multifunctional molecules, the possibility of using them as both targeting and therapeutic agents is considered. Lectin-containing delivery systems are a potential innovation for targeted and prolonged therapy within the oral cavity, but considerations such as toxicity and cost will need to be addressed before their routine use becomes a reality.

Nasal vaccines

The nasal route for vaccination offers some important opportunities, especially for the prophylaxis of respiratory diseases. Vaccination via the respiratory tract is reviewed and the deposition and clearance of antigens in the deep lung and nose are described and contrasted. Lymphoid structures in the respiratory tract differ according to species; the rat and mouse have a well developed nose-associated lymphoid tissue, while in man, the structure known as Waldeyer's ring (that includes the tonsils), is important as an induction site. The immune response following intranasal administration can provide protection at the administration site and at various effector sites as part of the common mucosal immune system. A number of formulation considerations are important when designing novel systems for nasal administration as are physiological factors such as mucociliary clearance.

Lectin-mediated mucosal delivery of drugs and microparticles

Absorption of drugs and vaccines at mucosal surfaces may be enhanced by conjugation to appropriate bioadhesins which bind to mucosal epithelia. Bioadhesins might also permit cell- and site-selective targeting. One approach is to exploit surface carbohydrates on mucosal epithelial cells for lectin-mediated delivery. We review work supporting the use of lectins as mucosal bioadhesins in the gastrointestinal and respiratory tracts, the oral cavity and the eye. The gastrointestinal tract is particularly favoured for mucosal delivery. Many studies have demonstrated that the antigen sampling intestinal M cells offer a portal for absorption of colloidal delivery vehicles. Evidence is presented that M cell targeting may be achieved using M cell-specific lectins, microbial adhesins or immunoglobulins. While many hurdles must be overcome before mucosal bioadhesins can guarantee consistent, safe, effective mucosal delivery, this is an exciting area of research that has important implications for future drug and vaccine formulation.

Further characterization of M cells in gut-associated lymphoid tissues of the chicken

M cells are considered to be the most effective cells for the transport of antigens from the intestinal lumen into the gut-associated lymphoid tissue. M cells are characterized by their ultrastructural appearance, the selective uptake of antigens, the binding of lectins, and the presence of underlying lymphocytes. Little attention has been paid to the interaction of intra-epithelial leucocytes and M cells in chickens; therefore, we have investigated both cell types separately and using double immunocytochemical staining in cecal tonsils and Meckel's diverticulum. In the follicle-associated epithelium (FAE), cells were present that differ from their neighbors by short, irregular microvilli. Ferritin was absorbed by these putative M cells, but also by other epithelial cells. The lectins of Triticum vulgaris (WGA) and Glycine max (SBA) showed a patchy staining of the FAE. The numbers of intra-epithelial leucocytes (IEL) increased rapidly after hatch, reaching innumerable at 6 wk of age. Most IEL were T lymphocytes expressing CD8 and only about 30% of them were B lymphocytes. Nevertheless, double staining of M cells (WGA/SBA) and IEL showed that M cells were much fewer than IEL. These results indicate that M cells are not solely induced by the intra-epithelial localization of leucocytes. Because the phenotype of IEL reflected the content of the adjacent underlying lamina propria, IEL immigrate the FAE locally and do not migrate along with the epithelial cells from the crypts. In conclusion, M cells exist in the chicken, but their phenotype and function are less well demarcated from neighbor epithelial cells than is seen in mammals.

M cells at locations outside the gut

Lymphoid tissue associated with mucosal membranes is found not only along the gastrointestinal tract, but also in the tonsils, the upper and lower airways, and the conjunctiva of the eye. The epithelia overlying this mucosa-associated lymphoid tissue (MALT) contain membranous (M) cells which transport antigenic matter across the mucosal membrane to initiate immune responses. Although the morphology and function of intestinal M cells have been thoroughly studied, relatively little is known about the presence and properties of M cells in MALT outside the gut. The available data on ultrastructure, histochemistry, and antigen sampling function of the epithelia in tonsils, nasal-, larynx-, bronchus-, and conjunctiva-associated lymphoid tissue are reviewed and critically discussed. It is concluded that, in principle, the concepts of mucosal immune protection can be applied to these sites of MALT. However, it is questionable whether a separate cell type similar to intestinal M cells exists and performs antigen sampling in the different MALT epithelia. Further studies combining functional and morphological techniques are essential to understand the initiation of immune reaction at the mucosal membranes.

Simultaneous induction of specific immunoglobulin A--producing cells in major and minor salivary glands after tonsillar application of antigen in rabbits

The immunoglobulin A (IgA)-producing cells in the stroma of major salivary glands are induced by antigenic stimulation of the mucosal immune system. Whether such cells also are induced in minor salivary glands by this stimulation remains to be determined. After application of sheep red blood cells to the palatine tonsils every 3 days for 6 weeks, anti-sheep red blood cell IgA was detected in saliva both by agglutination tests and by enzyme-linked immunosorbent assay. Using enzyme-linked immunospot assay, an increase in the number of anti-sheep red blood cell IgA-producing cells was found in minor as well as in major salivary glands of the sixth week of application; such cells constituted 4.9% to 5.9% of the total number of IgA-producing cells in these tissues. Tonsillar application of whole cells of formalin-killed Streptococcus sobrinus induced anti-S. sobrinus IgA in saliva. The number of anti-S. sobrinus IgA-producing cells in the above glands simultaneously increased over 6 weeks, and reached 5.2-5.6% of the total number of IgA-producing cells.

M cells in Peyer's patches of the intestine

M cells are specialized epithelial cells of the mucosa-associated lymphoid tissues. A characteristic of M cells is that they transport antigens from the lumen to cells of the immune system, thereby initiating an immune response or tolerance. Soluble macromolecules, small particles, and also entire microorganisms are transported by M cells. The interactions of these substances with the M cell surface, their transcytosis, and the role of associated lymphoid cells are reviewed in detail. The ultrastructure and several immuno- and lectin-histochemical properties of M cells vary according to species and location along the intestine. We present updated reports on these variations, on identification markers, and on the origin and differentiation of M cells. The immunological significance of M cells and their functional relationship to lymphocytes and antigenpresenting cells are critically reviewed. The current knowledge on M cells in mucosa-associated lymphoid tissues outside the gut is briefly outlined. Clinical implications for drug deliver, infection, and vaccine development are discussed.