| Objective sIgA play an important role in the intestinal mucosal immunity. Secretory component (SC) is not only an important component of sIgA, but also a specific receptor of IgA, which can transport IgA into secretion. In previous immunohistochemical experiments, we found that the positive staining was distinctly at the bottom of Lieberkvihn crypts of rat small intestine. Judged from their anatomical location and morphological characteristic, they were assumed to be Paneth cells. It has been reported that rat Paneth cells contained IgA but no SC could be detected in them. This study aimed to determine the cell origin of SC in rat small intestine, to validate the new discovery that Paneth cells can systhesize SC, and to investigate the relationship between Paneth cells and sIgA. Furthermore, it was reported that long-time sleep deprivation could induce bacterial translocation. Thus, ultrastructure and SC quantities of ileum of sleep-deprived rats were observed to investigate the relationship between SC quantities and bacterial translocation. These experiments aimed to give more evidences to validate the relationship of Paneth cells and SC.Methods Ten Sprague-Dawley rats were affused through hearts with 4% paraformaldehyde. Jejunum and ileum of rats were embedded with paraffin and were prepared. HE staining and lysozyme immunohistochemical experiments were undertaken to identify the characteristic location and the shape of Paneth cells. Two kinds of immunohistochemical technique were used to ensure the location of SC. One is SP method, the other is two-step technique. SP method was also used to determine the location of IgA in rat small intestine. With immunoelectronic miscroscope, the distribution of SC in the ultrastructure of Paneth cells of two rats was detected to find the origin of SC. Furthermore, twenty-four rats were divided into expirmental and control groups. The rats of expirmental group underwent 72h of sleep deprivation. Ultrastructure of ileal mucosa was observed by transmission electron microscope. The numbers of SC-positive crypts were measured with method of immunohistochemistry.Results The results of HE staining, lysozyme immunohistochemical experiment,and immunoelectronic miscroscope all showed that Paneth cells were at the bottom of the crypts of Lieberkiihn in rat small intestine. Their nuclei were located at the base of cells. The especial characteristic of Paneth cells was that a great amount of secretory granules accumulated in their apical cytoplasma. These granules contain plenty of lysozyme. In current research, using immunohistochemical technique, SC was demonstrated in Paneth cells of rat for the first time. Both of immunohistochemical techniques showed that SC was distinctly existed within Paneth cells while no SC could be detected in other epithelium cells, such as absorption, goblet, and endocrine cells. SC could be detected on the endoplasmic reticulum, Golgi complex, basolateral membrane and secretory granules of Paneth cells with immunoelectronic miscroscope. Positive result could also be found in the secretory granules that had been secreted into the crypt lumen. The immunohistochemical experiments showed that rat Paneth cells also contained IgA. Numerous bacteria were found in tissues, blood capillaries, and lymph capillaries in lamina propria of ileal mucosa of sleep-deprived rats. After 72h sleep deprivation, SC-positive crypts were decreased (P<0.05).Conclusion First, it was discovered for the first time that Paneth cells of rat can secrete SC and participate in acquired immunity. Second, the mechanism of sIgA secreting in rat small intestine differs from that of human. It was absorption cells in human small intestine that secrete sIgA. But in rat small intestine, it was Paneth cells that secrete sIgA. Third, the decrease of SC quantity in Paneth cells may have a relationship with sleep deprivation-induced bacterial translocation.
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