Immunohistochemical study on the secretory host defense system with lysozyme and secretory phospholipase A2 throughout rat respiratory tract

The host defense system with lysozyme and secretory phospholipase A2 (sPLA2) was immunohistochemically investigated in rat respiratory tract under healthy conditions. In the nasal epithelium, a large number of non-ciliated and non-microvillous cells (NC) and a small number of goblet cells (GC) were immunopositive for lysozyme and sPLA2. A few acinar cells and almost all epithelial cells of intercalated ducts were immunopositive for both bactericidal substances in the nasal glands. In the laryngeal and tracheal epithelia, few NC and GC were immunopositive for both bactericidal substances. In the laryngeal and tracheal glands, a few acinar cells and most ductal epithelial cells were immunopositive for both bactericidal substances. In extra-pulmonary bronchus, small numbers of NC and GC were immunopositive for lysozyme and sPLA2, whereas few NC and no GC were immunopositive in the intra-pulmonary bronchus. No secretory source of either bactericidal substance was located in the bronchioles. In the alveolus, many glandular epithelial cells and alveolar macrophages were immunopositive for lysozyme but immunonegative for sPLA2. Moreover, lysozyme and sPLA2 were detected in the mucus layer and in the periciliary layer from the nose to the extra-pulmonary bronchus. These findings suggest that secretory sources of lysozyme and sPLA2 are distributed in almost all the respiratory tract. Their secretory products are probably transported to the pharynx and contribute to form the first line of defense against inhaled bacteria throughout the respiratory tract

Mechanism of M-cell differentiation accelerated by proliferation of indigenous bacteria in rat Peyer’s patches

The mechanism by which indigenous bacteria on the follicle-associated epithelium (FAE) of lymphatic follicles (LFs) accelerate the differentiation of microvillous columnar epithelial cells (MV) into M-cells was immunohistochemically investigated in rat Peyer's patches. The results showed that the number of Toll-like receptor (TLR) -4(+) M-cells was greater in the FAE with expansion of bacterial colonies (LFs with bacterial colonies on the FAE: b-LF) than the FAE without expansion of bacterial colonies (nb-LF). TLR-4 was also expressed in the striated borders of MV upstream next to M-cells in the FAE of the b-LF. TLR-4(+) vesicles were frequently detected in the cytoplasms of MV with TLR-4(+) striated borders upstream next to TLR-4(+) M-cells in the FAE of b-LF. These findings suggest that TLR-4(+) MV take up TLR-4 ligands and differentiate into M-cells in the b-LF. Neither the distribution of RANK nor that of RANKL was coincident with that of M-cells in the b-LF. Moreover, RANK, but not RANKL, was expressed in intestinal villi, whereas cleaved caspase-3 was immunonegative in the MV and M-cells of the FAE, unlike in villous epithelial cells. Therefore, RANK/RANKL signaling in the LF might contribute to the down-regulation of epithelial apoptosis to facilitate the differentiation of MV into M-cells in rat Peyer's patches

Immunohistochemical study on the distribution of β-defensin 1 and β-defensin 2 throughout the respiratory tract of healthy rats

The distributions of β-defensin 1 and 2 in secretory host defense system throughout respiratory tract of healthy rats were immunohistochemically investigated. In the nasal epithelium, a large number of non-ciliated and non-microvillous cells (NCs) were immunopositive for both β-defensin 1 and 2, whereas a small number of goblet cells (GCs) were immunopositive only for β-defensin 1. Beta-defensin 2-immunopositive GCs were few. In the nasal glands, a small number of acinar cells and a large number of ductal epithelial cells were immunopositive for both β-defensins. In the laryngeal and tracheal epithelia, a very few NCs and GCs were immunopositive for both β-defensins. In laryngeal and tracheal glands, a very few acinar cells and a large number of ductal epithelial cells were immunopositive for both β-defensins. In the extra-pulmonary bronchus, a small number of NCs were immunopositive for both β-defensins. A small number of GCs were immunopositive for β-defensin 1, whereas few GCs were immunopositive for β-defensin 2. From the intra-pulmonary bronchus to alveoli, a very few or no epithelial cells were immunopositive for both β-defensins. In the mucus and periciliary layers, β-defensin 1 was detected from the nose to the extra-pulmonary bronchus, whereas β-defensin 2 was weakly detected only in the nose and the larynx. These findings suggest that the secretory sources of β-defensin 1 and 2 are mainly distributed in the nasal mucosa and gradually decrease toward the caudal airway in healthy rats