In histological sections, the occurrence of numerous alcian blue–positive mucous cells was observed among the intestinal epithelial cells of infected fish notably within the epithelia in close proximity to the nodule (Figure 2a). RCs in variable numbers (Figure 3a) were seen among the epithelia of both M. wageneri-infected Ensartinib mouse tench (i.e. in close proximity to the point of cestode attachment and at a distance) and in uninfected specimens. Interestingly, within the parasitized intestines, RCs were found to co-occur with granulocytes within the submucosa of the nodule (Figure 3b) and in close proximity to blood vessels and/or within the capillaries. The inflammatory swellings surrounding the M. wageneri

primarily consisted of fibroblasts but also included a large number of neutrophils and MCs. Neutrophils (Figure 3c) and MCs were seen within the connective tissue surrounding capillaries and within the blood vessels within the submucosa and muscularis layer.

In some intestinal sections taken from infected tench, neutrophils were also observed within the epithelia (not shown). Neutrophils appeared round to oval in shape although their outline was commonly irregular (Figure 3c). These cells also contained a round nucleus and a cytoplasm HDAC inhibitor that contained dark, elongated granules that were fibrous in appearance (Figure 3c). Very few mitochondria and fragments of rough endoplasmic reticulum were observed in the cytoplasm of the neutrophils. The MCs, which were frequently observed within the epithelia of

infected hosts (Figure 3a), were irregular in shape with an eccentric, polar nucleus, and a cytoplasm characterized by numerous large, electron-dense, membrane-bounded granules (Figure 3d). The cytoplasm typically contained two to three mitochondria and an inconspicuous Golgi apparatus. Accurate counts of MCs and neutrophils were obtained from two intestinal grids from each infected fish. Neutrophils were found to be numerous within the nodule, in close proximity to the tegument of the cestode, but their number was seen to decrease towards the periphery of the nodule. Neutrophils were significantly more abundant than MCs (Table 1; anova, P < 0·01) second in host tissue close to the point of cestode attachment. At a distance of 200 μm from the site of parasite attachment, however, the number of neutrophils was significantly lower than the MCs (Table 1; anova, P < 0·01). There were significant differences in the number of neutrophils in close proximity to and at a distance of 200 μm from the point of cestode attachment (Table 1; anova, P < 0·01). Likewise, there were significant differences in the number of MCs at the site of infection and 200 μm away (Table 1; anova, P < 0·01). Commonly, the neutrophils and MCs adjacent to the M. wageneri scolex tegument had a cytoplasm that appeared vacuolized (Figure 4a) and contained very few organelles.