Invasion of Metagonimus yokogawai into the submucosal layer of the small intestine of immunosuppressed mice.

Metagonimus yokogawai was found deeply invaded into the submucosa of the small intestine of mice (ICR) when they were immunosuppressed by prednisolone injection. Experimental groups consisted of control, fluke infection (1,800 metacercariae per mouse), and fluke infection plus immunosuppression. In fluke infection group, many worms were found sectioned in the intervillous space of the jejunum and ileum at 6 hrs, 12 hrs, and 1 day after infection, and pathological changes characterized by villous atrophy and crypt hyperplasia were observed. After 3 days, only a few worms were found in intestinal sections, and after 7 days, the pathological changes became minimal. No worm was found penetrated beyond the mucosal layer. On the other hand, in immunosuppressed mice, numerous worms were found sectioned in the duodenum and jejunum, irrespective of the infection period up to 14 days. Pathological changes of the mucosa were minimal until 3 days after infection, but at 5 days marked destruction of the mucosal layer was observed. At this time many flukes were found invaded deeply into the submucosa facing the muscular layer. Despite continuous immunosuppression, the mucosal damage was gradually recovered at 7-21 days post-infection. The results showed that immunosuppression of ICR mice can induce, for a short period of time, severe mucosal damage, and allow deep invasion of M. yokogawai into the submucosa of the small intestine.