[Identification and classification of lysozyme-expressing cells in the mouse small intestinal crypt and their correlation with the morphology of secretory granules and labeling density of immunogold].

The four principal epithelial cell lineages (absorptive enterocytes, goblet cells, enteroendocrine cells and Paneth cells) of the adult mouse small intestine derive from multipotent stem cells. Furthermore, the intermediate cells and granule goblet cells are located near the base of crypts of mouse intestine; the former has the characteristics of goblet and Paneth cells and the latter is transformed from the intermediate cells. However, the grounds and the definition for classifing these three cell types (Paneth, intermediate and granule goblet cells) are vague, making it difficult to discuss the structure and a function of those cells. The purpose of this study was to investigate the identification and classification of lysozyme-expressing cells in the mouse small intestinal crypt and their correlation with the morphology of secretory granules and labeling density of immunogold using quantitative immunoelectron microscopy analysis. The results were follows. (1) Paneth cells, intermediate cells and granule goblet cells showed lysozyme immunoreactivity in the electron-dense core of biphasic secretory granules, and therefore lysozyme-exprssing cells were identified in the mouse small intestinal crypt. The sizes of secretory granules were divided into ten groups (every 10%) according to area ratio (core/granule (%)). (2) This distribution of three type cells was classified statistically into "Paneth cell phase": 61% < or = (core/granule (%)), "intermediate cell phase": (core/granule (%)) 21 < or = 60%, "granule goblet cell phase": (core/granule (%)) < or = 20%. (3) Labeling density for lysozyme was commensurate with the size of the central dense core. The Paneth cells had the highest labeling density among the cells. When the transformation from intermediate to granule goblet cell occurred, it happened at the same time that the core of secretory granules gradually shrinks, and the labeling density for lysozyme disappears. (4) The labeling density of immunogold for lysozyme in the small intestine varied at different sites. The labeling density in the Paneth and intermediate cells of the ileal crypt was lower than those of the duodeal and jejunal crypts. (5) In the lysozyme-expressing cells in small intestinal crypt of 2- and 24-month old mouse, the ultrastructure and labeling density did not change.