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

GP2-expressing cells: a new guardian with divergent functions in the intestine, eyes, and nose

GP (glycoprotein)-2, originally identified as a predominant membranous component of pancreatic acinar cells, has attracted the interest of researchers in mucosal immunology for its role as a functional molecule specific for antigen-sampling cells in the intestinal Peyer's patches. GP2 is involved in the detection of pathological bacteria and is also histologically useful for the identification of the M cell lineage and their differentiation in lymphoid tissues. Subsequent immunohistochemistry for GP2 has revealed a broad distribution of M cells and related cells in the nasopharyngeal lymphoid tissues, conjunctiva, tear duct, and airway. Especially, GP2 cells in the paranasal sinuses and tear duct have been identified as novel types of epithelial cells. The systematic administration of RANKL can induce extra-M cells in conventional epithelia of body. The production and release of GP2 by conjunctival goblet cells and several mucous glands suggests leading roles for mucous cells in protection, including the entrapment of microorganisms for infections. The ocular surface and conjunctiva are connected to the lacrimal sac, nasolacrimal duct, and further nasal cavity, comprising another canal that passes through the body. The broad distribution of GP2-expressingcells may indicate its function as a new guardian in the intestine, eyes, and nose, all of which are exposed to external milieu.

Molecular insights into the mechanisms of M-cell differentiation and transcytosis in the mucosa-associated lymphoid tissues

Microfold cells (M cells), which are located in the follicle-associated epithelium (FAE) covering mucosal lymphoid follicles, are specialized epithelial cells that initiate mucosal immune responses. These cells take luminal antigens and transport them via transcytosis across the FAE to the antigen-presenting cells underneath. Several intestinal pathogens exploit M cells as their portal for entry to invade the host and cause disease conditions. Recent studies have revealed that the uptake of antigens by M cells is essential for efficient antigen-specific IgA production and that this process likely maintains the homeostasis of mucosal tissues. The present article reviews recent advances in understanding the molecular mechanism of M-cell differentiation and describes the molecules expressed by M cells that are associated with antigen uptake and/or the transcytosis process. Current efforts to augment M-cell-mediated uptake for use in the development of effective mucosal vaccines are also discussed.

Effect of intratonsillar injection of steroids on the palatine tonsils of rabbits

OBJECTIVES/HYPOTHESIS

Nasal steroids may significantly improve nasal obstructive symptoms with a reduction of adenoid size in children, but they do not consistently yield the same concurrent effect on enlarged palatine tonsils. Failure of nasal steroids to decrease the size of palatine tonsils is believed to be attributable to location and washout by saliva. The purpose of this study was to determine if direct application of steroid via intratonsillar injection would reduce the size of palatine tonsils in the rabbit model.

STUDY DESIGN

Prospective animal study.

METHODS

Eight rabbits (16 tonsils) were administered intratonsillar injections of fluticasone (n = 8, 1 mg/ml) or saline (n = 8, 0.1 ml) on days 0, 3, 7, 10, 14, and 17. Two rabbits (4 tonsils) received a single steroid injection to compare single versus multiple steroid injections. The rabbit's tonsil size was measured before each injection. After the fifty injections, the tonsils were harvested for histologic analysis.

RESULTS

A total of 16 tonsils were analyzed. After five steroid injections, the reduction (-7.7 mm(2)  ± 4.27) in size was statistically significant when compared to reduction (6.12 mm(2)  ± 6.57) in the saline injected group (P = 0.001). Repeated steroid injection was more potent than a single injection (-3.00 mm(2)  ± 3.08) in reducing the size (P = 0.006). In histologic analysis, tonsils after repeated steroid injections were significantly smaller than saline-injected tonsils (P = 0.014), without obvious lymphoid follicles.

CONCLUSION

Repeated focal tonsillar injections of corticosteroids significantly reduced the size of palatine tonsils as compared to saline-injected controls. A single injection of corticosteroids appears to be effective, but not as effective, as multiple injections.

LEVEL OF EVIDENCE

N/A.

Regulation of tight junctions in upper airway epithelium

The mucosal barrier of the upper respiratory tract including the nasal cavity, which is the first site of exposure to inhaled antigens, plays an important role in host defense in terms of innate immunity and is regulated in large part by tight junctions of epithelial cells. Tight junction molecules are expressed in both M cells and dendritic cells as well as epithelial cells of upper airway. Various antigens are sampled, transported, and released to lymphocytes through the cells in nasal mucosa while they maintain the integrity of the barrier. Expression of tight junction molecules and the barrier function in normal human nasal epithelial cells (HNECs) are affected by various stimuli including growth factor, TLR ligand, and cytokine. In addition, epithelial-derived thymic stromal lymphopoietin (TSLP), which is a master switch for allergic inflammatory diseases including allergic rhinitis, enhances the barrier function together with an increase of tight junction molecules in HNECs. Furthermore, respiratory syncytial virus infection in HNECs in vitro induces expression of tight junction molecules and the barrier function together with proinflammatory cytokine release. This paper summarizes the recent progress in our understanding of the regulation of tight junctions in the upper airway epithelium under normal, allergic, and RSV-infected conditions.

Epithelial barrier and antigen uptake in lymphoepithelium of human adenoids

Invasion of antigens through the mucosal surface can be prevented by the common mucosal immune system, including Peyer's patches (PPs) and nasopharyngeal-associated lymphoreticular tissue (NALT). The adenoids (nasopharyngeal tonsils) comprise one of the NALTs and constitute the major part of Waldeyer's lymphoid ring in humans. However, the role of the lymphoepithelium, including M cells and dendritic cells (DCs), in the adenoids is unknown compared with the epithelium of PPs. NALTs also have unique functions such as the barrier of epithelial cells and uptake of antigens by M cells and DCs, and may play a crucial role in airway mucosal immune responses. The lymphoepithelium of adenoids has well-developed tight junctions that play an important role in the barrier function, the same as nasal epithelium but not palatine tonsillar epithelium. Tight junction molecules are expressed in both M cells and DCs as well as epithelial cells, and various antigens may be sampled, transported, and released to lymphocytes through the cells while they maintain the integrity of the epithelial barrier. This review summarizes the recent progress in our understanding of how M cells and DCs control the epithelial barrier in the adenoids.

Cytoskeletal proteins in thymic epithelial cells of the Australian lungfish Neoceratodus forsteri

The vertebrate thymus consists of distinctive subpopulations of epithelial cells that contain a diverse repertoire of cytoskeletal proteins. In this study of the thymus in the Australian lungfish, Neoceratodus forsteri, immunohistochemistry was used to distinguish the cytoskeletal proteins present in each class of thymic epithelial cell. A panel of antibodies (Abs), each specific for a different cytoskeletal polypeptide (keratins, vimentin, desmin, actin and tubulins), was used on paraffin and ultrathin resin sections of thymus. Ab AE I (reactive against human type I cytokeratins (CK) 14, 16 and 19) selectively stained the cytoplasm of capsular, trabecular and the outermost epithelial cells of Hassall's corpuscles. Anti-CK 10 Abs strongly labelled the capsular epithelial cells and less than 20% of cortical and medullary epithelial cells. The anti-50-kDa desmin Ab did not react with any thymic cells, whereas the anti-53-kDa desmin Ab labelled some capsular, cortical and medullary thymic epithelial cells. The anti-vimentin Ab stained most of the capsular and ~60% of the cortical epithelium. Thymic nurse cells and Hassall's corpuscles were found to be devoid of actin, which was strongly detected in medullary and perivascular epithelium. Both alpha and beta tubulins were detected in all thymic cells. This study extends the concept of thymic epithelial heterogeneity. The complexity of thymic epithelium in N. forsteri may indicate a relationship between thymic epithelial subpopulations and the thymic microenvironment. These data identify anti-keratin Abs as a valuable tool for studying differentiation and ontogeny of the thymic epithelium in N. forsteri.

An appraisal of intermediate filament expression in adult and developing pancreas: vimentin is expressed in alpha cells of rat and mouse embryos

Intermediate filaments are frequently used in studies of developmental biology as markers of cell differentiation. To assess whether they can be useful to identify differentiating pancreatic endocrine cells, we examined the pattern of expression of nestin, cytokeratin 20, and vimentin on acetone-fixed cryosections of rat adult and developing pancreas. We also studied vimentin expression in mouse embryonic pancreas at E19. Cytokeratin 20 was found in all pancreatic epithelial cell lineages during the entire development of the rat gland and in the adult animals. Under our experimental conditions, therefore, cytokeratin 20 is not an exclusive marker of rat duct cells. Nestin was detected exclusively in stromal cells either in the adult or developing rat pancreas. Vimentin was observed within cells located in the primitive ducts of rat pancreas starting from E12.5. Their number rapidly increased, reaching its highest level in newborn animals. Vimentin was also spotted in alpha cells starting from E12.5 but disappeared soon after birth, likely identifying immature or recently differentiated alpha cells. In addition, vimentin was observed in duct and alpha cells of mouse developing pancreas showing that its expression in such cells is not an event restricted to the rat. This manuscript contains online supplemental material at http://www.jhc.org. Please visit this article online to view these materials.

Expression of tight junction proteins in epithelium including Ck20-positive M-like cells of human adenoids in vivo and in vitro

The human adenoid epithelium forms a continuous barrier against a wide variety of exogenous antigens. In this study, to elucidate the structures of the epithelial barrier in the human adenoid, including M-cells, we identified M-cells using an anti-cytokeratin 20 (Ck20) antibody and investigated expression of tight junction proteins in human adenoid epithelium in vivo and in vitro. In human adenoid epithelium and primary cultures, mRNAs of occludin, junctional adhesion molecule-A, ZO-1, and claudin-1, -4, -7, and -8 were detected by reverse transcription-polymerase chain reaction, whereas claudin-2 and -9 were expressed in vitro. In the epithelium in vivo, some Ck20-positive cells were randomly observed and indicated pocket-like structures, whereas Ck7 was positive in almost cells. Transmission electron microscopy revealed that Ck20-associated gold particles could be identified in M-like cells which had short microvilli and harboured the lymphocyte in the pocket-like structure. In primary cultures in vitro, Ck20-positive cells were also detected and had a function to take up fluorescent microparticles. In Ck20-positive cells in vivo and in vitro, expression of occludin, ZO-1, claudin-1 and -7 were observed at cell borders. These results indicate that the epithelial barrier of the human adenoid is stably maintained by expression of tight junction proteins in the epithelium including Ck20-positive M-like cells.

Nestin expression in adult and developing human kidney

Nestin is considered a marker of neurogenic and myogenic precursor cells. Its arrangement is regulated by cyclin-dependent kinase 5 (CDK5), which is expressed in murine podocytes. We investigated nestin expression in human adult and fetal kidney as well as CDK5 presence in adult human podocytes. Confocal microscopy demonstrated that adult glomeruli display nestin immunoreactivity in vimentin-expressing cells with the podocyte morphology and not in cells bearing the endothelial marker CD31. Glomerular nestin-positive cells were CDK5 immunoreactive as well. Western blotting of the intermediate filament-enriched cytoskeletal fraction and coimmunoprecipitation of nestin with anti-CDK5 antibodies confirmed these results. Nestin was also detected in developing glomeruli within immature podocytes and a few other cells. Confocal microscopy of experiments conducted with antibodies against nestin and endothelial markers demonstrated that endothelial cells belonging to capillaries invading the lower cleft of S-shaped bodies and the immature glomeruli were nestin immunoreactive. Similar experiments carried out with antibodies raised against nestin and alpha-smooth muscle actin showed that the first mesangial cells that populate the developing glomeruli expressed nestin. In conclusion, nestin is expressed in the human kidney from the first steps of glomerulogenesis within podocytes, mesangial, and endothelial cells. This expression, restricted to podocytes in mature glomeruli, appears associated with CDK5.