Histological characteristics of intestinal inflammation in SAMP1/Yit mice. (a) An early aphthous inflammatory lesion involving a Peyer’s patch. A pre-existing submucosal lymphoid aggregate is involved by a mixed inflammatory infiltrate of PMNs and macrophages. The epithelium overlying this lesion is infiltrated by PMNs and is focally eroded. ×80; inset, ×125. (b) Inflamed small intestinal mucosa showing partial villous blunting and epithelial phenotypic changes. Compared with normal uninflamed mucosa (Figure 1d), there are increased numbers of Paneth cells in the crypts and mucin-secreting goblet cells in the crypts and on the villi. ×200. (c) Transmural inflammation. PMNs and mononuclear cells infiltrate the full thickness of the muscularis propria to involve the serosal surface. ×200. (d) Mucosal granuloma. A collection of epithelioid histiocytes is present within the lamina propria between intestinal crypts. ×400. (e) Active inflammation. PMNs can be seen within the lamina propria, infiltrating between epithelial cells (“cryptitis”) and present in aggregate within a crypt lumen (“crypt microabscess”). ×200. (f) Basal plasmacytosis. The base of the inflamed mucosa contains numerous plasma cells, characterized by large cells with eccentrically placed cytoplasm and coarse nuclear chromatin clumping in a “clock face” pattern. All panels show staining with hematoxylin and eosin. ×800.