Innate immune defence mechanisms of tench, Tinca tinca (L.), naturally infected with the tapeworm Monobothrium wageneri

A histochemical and ultrastructural investigation of the cellular inflammatory response within the intestines of tench Tinca tinca L. naturally infected with the caryophyllidean cestode Monobothrium wageneri was conducted and the data obtained compared to those in uninfected counterparts. Cestode infections within the intestines were evident through the appearance of raised inflammatory swellings induced by the deep penetration of their scolices into the intestinal wall. Cestodes typically attached in tight clusters, inducing a massive hyperplastic granulocyte response of mast cells and neutrophils, which were significantly more numerous (P less than 0·01) in the intestines of infected (n = 14) than of uninfected (n = 9) tench. Neutrophils were more abundant than mast cells (P less than 0·01) in host tissues in close proximity to the parasite tegument. In transmission electron microscopy sections, mast cells and neutrophils were frequently observed in contact with or inside capillaries, and in close proximity to the cestode. Degranulation of both cell types was seen in the submucosa and lamina muscularis, notably in the immediate tissues surrounding the scolex of M. wageneri. No tegumental secretions were seen at the host-parasite interface. Occasional rodlet cells were encountered in the submucosa of infected fish