Immunohistochemical Study on the Secretory Host Defense System of Bactericidal Peptides in Rat Digestive Organs

Abstract

ABSTRACT. To clarify the fundamental regulation mechanism against indigenous bacterial proliferation in the alimentary tract, we immunohistochemically examined the localization of 4 bactericidal peptides (BP) in the rat digestive exocrine glands. In the upper alimentary tract, lysozyme was detected in the gustatory, extraorbital lacrimal and parotid glands. Secretory phospholipase A2 (sPLA2) was detected in the extraorbital lacrimal glands. -defensin1 was detected in the gustatory and extraorbital lacrimal glands. -defensin2 was detected in the Harderian glands. In the stomach, -defensins were detected in the gastric superficial epithelial cells. In the small and large intestines, only lysozyme and sPLA2 were detected in the Paneth cells. In the cecum, all 4 BP were detected in the middle to apical portions of the crypts, and only sPLA2 was detected in the basal portion. No BP were localized in other exocrine glands associated with the alimentary tract. In addition, all 4 BP were also detected in the columnar epithelial cells of the apical portions of intestinal villi. In the intestinal superficial epithelial cells, lysozyme and -defensins were detected in the ascending colon, whereas only -defensin1 was detected in the descending colon and rectum. These results suggest that BP are mainly secreted from exocrine tissues in the initial portion of the digestive tract and play a role in host defense against indigenous bacteria throughout the digestive tract. Part of the BP in the chyme might be absorbed by the epithelium at the most inner sites of mucosae in the small and large intestines.KEY WORDS: bactericidal peptides, digestive organs, exocrine glands, immunohistochemistry, indigenous bacteria.

Immunohistochemical and Histoplanimetrical Study on the Spatial Relationship between the Settlement of Indigenous Bacteria and the Secretion of Bactericidal Peptides in Rat Alimentary Tract

“…Both intraluminal bacteria and bacterial lipopolysaccharide can stimulate secretions from rat Paneth cells ex-vivo [22]. Our previous study clarified that lysozyme and sPLA2 are secreted from Paneth cells in the rat small intestine [29]. In the present study, lysozyme and sPLA2 in secretory granules of Paneth cells are most frequently and strongly expressed in the ileum, previously suggested as the most frequent residence site of indigenous bacteria in the rat small intestine [27].…”

“…In the small intestine, the rates of Gram-positive and -negative bacteria were almost intermediate. We have previously clarified that lysozyme, sPLA2, -defensin1 and β-defensin2 are secreted mainly from exocrine glands associated with the upper alimentary tract, but only lysozyme and sPLA2 are also secreted from the Paneth cells in the small intestine [29]. Lysozyme mainly acts against Gram-positive bacteria, and several Gram-negative bacteria [1,12], as well as sPLA2 [13,16].…”

“…We have previously clarified that lysozyme, secretory phospholipase A2 (sPLA2), β-defensin1 and β-defensin2 are secreted by particular exocrine organs associated with the rat alimentary tract [29]. The exact mechanism of bacterial regulation by bactericidal substances, however, has not yet been clarified.…”

“…We have previously clarified that lysozyme, sPLA2, β-defensin1 and β-defensin2 are secreted from salivary glands and lacrimal glands into the upper alimentary tract, but only lysozyme and sPLA2 are secreted from Paneth cells in the lower alimentary tract. The site differences in bactericidal peptides secretion might be one of the effective factors in the compartmentalization of Gram-positive bacteria and Gram-negative bacteria in the rat alimentary tract [29]. However, the site differences in the settlement of Grampositive bacteria and Gram-negative bacteria in the rat alimentary tract have never been histologically clarified.…”

Histoplanimetrical Study on the Relationship between Invasion of Indigenous Bacteria into Intestinal Crypts and Proliferation of Epithelial Cells in Rat Ascending Colon

“…Additionally, numerous indigenous bacteria exist between the mucosal folds in the rat ascending colon [27]. However, the detailed distribution of the settlement sites of indigenous bacteria has not been investigated in the ascending colon.The settlement of indigenous or exogenous bacteria is regulated by various host defense, such as digestive enzymes, bactericidal peptides, physical elimination of epithelial cells and so on [7,14,15,17,37,38]. In the previous studies, the secretions of lysozyme and secretory phospholipase A2 from Paneth cells [38] and the acceleration of epithelial cell migration [26] are induced in the local sites with bacterial hyper-proliferations in the rat ileum.…”