Salivary fibronectin in man: an immunoblotting, radioimmunoassay and immunohistochemical study

Immunocytochemistry of myoepithelial cells in the salivary glands

MECs are distributed on the basal aspect of the intercalated duct and acinus of human and rat salivary glands. However, they do not occur in the acinus of rat parotid glands, and sometimes occur in the striated duct of human salivary glands. MECs, as the name implies, have structural features of both epithelial and smooth muscle cells. They contract by autonomic nervous stimulation, and are thought to assist the secretion by compressing and/or reinforcing the underlying parenchyma. MECs can be best observed by immunocytochemistry. There are three types of immunocytochemical markers of MECs in salivary glands. The first type includes smooth muscle protein markers such as alpha-SMA, SMMHC, h-caldesmon and basic calponin, and these are expressed by MECs and the mesenchymal vasculature. The second type is expressed by MECs and the duct cells and includes keratins 14, 5 and 17, alpha 1 beta 1 integrin, and metallothionein. Vimentin is the third type and, in addition to MECs, is expressed by the mesenchymal cells and some duct cells. The same three types of markers are used for studying the developing gland. Development of MECs starts after the establishment of an extensively branched system of cellular cords each of which terminates as a spherical cell mass, a terminal bud. The pluripotent stem cell generates the acinar progenitor in the terminal bud and the ductal progenitor in the cellular cord. The acinar progenitor differentiates into MECs, acinar cells and intercalated duct cells, whereas the ductal progenitor differentiates into the striated and excretory duct cells. Both in the terminal bud and in the cellular cord, the immediate precursors of all types of the epithelial cells appear to express vimentin. The first identifiable MECs are seen at the periphery of the terminal bud or the immature acinus (the direct progeny of the terminal bud) as somewhat flattened cells with a single cilium projecting toward them. They express vimentin and later alpha-SMA and basic calponin. At the next developmental stage, MECs acquire cytoplasmic microfilaments and plasmalemmal caveolae but not as much as in the mature cell. They express SMMHC and, inconsistently, K14. This protein is consistently expressed in the mature cell. K14 is expressed by duct cells, and vimentin is expressed by both mesenchymal and epithelial cells. After development, the acinar progenitor and the ductal progenitor appear to reside in the acinus/intercalated duct and the larger ducts, respectively, and to contribute to the tissue homeostasis. Under unusual conditions such as massive parenchymal destruction, the acinar progenitor contributes to the maintenance of the larger ducts that result in the occurrence of striated ducts with MECs. The acinar progenitor is the origin of salivary gland tumors containing MECs. MECs in salivary gland tumors are best identified by immunocytochemistry for alpha-SMA. There are significant numbers of cells related to luminal tumor cells in the non-luminal tumor cells that have been believed to be neoplastic MECs.

Subcellular localization of epidermal growth factor in human parotid gland

The intracellular distribution of epidermal growth factor was investigated in human parotid gland by immunogold cytochemistry at the electron-microscopy level. Epidermal growth factor immunoreactivity was demonstrated in both acini and ducts. In acinar cells, secretory granules appeared moderately stained, clearly indicating that parotid gland contributes to salivary epidermal growth factor through granule exocytosis. In ductal cells, gold particles were found to decorate numerous cytoplasmic vesicles, particularly abundant in striated duct cells. Since epidermal growth factor reactive vesicles were seen not only at the cellular apex, but nearby lateral plasma membranes as well, it leads to the hypothesis that epidermal growth factor may be discharged both apically into the saliva, and basally into the interstitium.

Fibronectin in saliva inhibits Porphyromonas gingivalis fimbria-induced expression of inflammatory cytokine gene in mouse macrophages

The aim of this study was to examine whether fibronectin in saliva plays a regulatory role in Porphyromonas gingivalis fimbria-mediated pathogenesis in adult periodontal disease. Our previous study demonstrated that fibronectin is one of the binding proteins of P. gingivalis fimbrillin. In the present study, we observed that fibronectin in saliva binds specifically to the fimbrillin. The fibronectin content in saliva of adult periodontal patients was significantly lower than that of healthy subject. In addition, the inhibitory action of salivary fibronectin from adult periodontal patients toward P. gingivalis fimbria-induced expression of the neutrophil chemoattractant KC gene in mouse macrophages was clearly weak compared with that of the fibronectin from healthy subjects. These results suggest that fibronectin in saliva plays an important role as a regulator in the pathogenesis of P. gingivalis fimbriae in adult periodontal disease.

Reverse transcription-polymerase chain reaction and immunohistochemical study of the expression of fibronectin mRNA in human submandibular salivary gland

The alternative expression of fibronectin mRNA in submandibular salivary glands was analysed using three groups of polymerase chain reaction probes to amplify the cell-binding domain (CBD), and the extra domain (ED)-A and ED-B exon regions in five normal human adults. The fibronectin CBD region was fairly well expressed in the salivary gland while less than trace amounts of ED-A and ED-B exons were expressed. Immunohistochemical staining with an antihuman plasma fibronectin monoclonal antibody, which recognized specifically the CBD region, demonstrated definite positive cytoplasmic staining in the duct-cell area. On the other hand, an anticellular fibronectin ED-A-specific monoclonal antibody was very low positive in duct cells. The results suggest that salivary fibronectin is synthesized in the submandibular salivary gland only, and does not include the ED-A segment. Furthermore, duct cells also produced fibronectin without ED-A.

The pathogenesis of ventilator-associated pneumonia: I. Mechanisms of bacterial transcolonization and airway inoculation

Ventilator-associated pneumonia (VAP) is an infection of the lung parenchyma developing in patients on mechanical ventilation for more than 48 h. VAP is associated with a remarkably constant spectrum of pathogenic bacteria, most of which are aerobic Gram-negative bacilli (AGNB) and, to a lesser extent Staphyloccus aureus. Most authorities agree that VAP develops as a result of aspiration of secretions contaminated with pathogenic organisms, which appear to be endogenously acquired. These pathogens gain access to the distal airways by mechanical reflux and aspiration of contaminated gastric contents and also by repetitive inoculation of contaminated upper airway secretions into the distal tracheobronchial tree. Persistence of these organisms in the upper airways involves their successful colonization of available surfaces. Although exogenous acquisition can occur from the environment, the rapidity at which critically ill patients acquire AGNB in the upper airways in conjunction with the low rate of AGNB colonization of health-care workers exposed to the same environment favors the presence of endogenous proximate sources of AGNB and altered upper airway surfaces that are rendered receptive. Proximate sources of AGNB remain unclear, but potential sites harboring AGNB prior to illness include the upper gastrointestinal tract, subgingival dental plaque, and the periodontal spaces. Following illness or antibiotic therapy, competitive pressures within the oropharynx favor AGNB adherence to epithelial cells, which lead to oropharyngeal colonization. Similar dynamic changes in contiguous structures (oropharynx, trachea, sinuses, and the upper gastrointestinal tract) lead to the transcolonization of these structures with pathogenic bacteria. Following local colonization or infection, these structures serve as reservoirs of AGNB capable of inoculating the lower airways. As the oropharynx becomes colonized with AGNB, contaminated oropharyngeal secretions reach the trachea, endotracheal tube, and ventilator circuit. Contaminated secretions pooled above the endotracheal tube cuff gain access to the trachea and inner lumen of the endotracheal tube by traversing endotracheal tube cuff folds. Amorphic particulate deposits containing AGNB form along the endotracheal tube and are capable of being propelled into the distal airways by ventilator-generated airflow or by tubing manipulation. Bacteria embedded within this type of amorphous matrix are particularly difficult for the host to clear. If host defenses fail to clear the inoculum, then bacterial proliferation occurs, and the host inflammatory response progresses to bronchopneumonia.(ABSTRACT TRUNCATED AT 400 WORDS)

Saliva-bacterium interactions in oral microbial ecology

Saliva is thought to have a significant impact on the colonization of microorganisms in the oral cavity. Salivary components may participate in this process by one of four general mechanisms: binding to microorganisms to facilitate their clearance from the oral cavity, serving as receptors in oral pellicles for microbial adhesion to host surfaces, inhibiting microbial growth or mediating microbial killing, and serving as microbial nutritional substrates. This article reviews information pertinent to the molecular interaction of salivary components with bacteria (primarily the oral streptococci and Actinomyces) and explores the implications of these interactions for oral bacterial colonization and dental plaque formation. Knowledge of the molecular mechanisms controlling bacterial colonization of the oral cavity may suggest methods to prevent not only dental plaque formation but also serious medical infections that may follow microbial colonization of the oral cavity.

The functions of saliva

Oral health is determined to a considerable extent by our ability to produce saliva. Not only must adequate amounts be produced, but a large number of specific proteins also must be secreted for the mouth to function properly. This brief review is directed at describing (1) how saliva is secreted, (2) the consequences of decreased salivary function, (3) the components necessary for oral homeostasis, and (4) the common causes of salivary hypofunction.