Mucosal mast cell responses to experimental Metagonimus yokogawai infection in rats

Intestinal mucosal mast cell (MMC) responses were studied in rats experimentally infected with Metagonimus yokogawai (Digenea: Heterophyidae). Twenty Sprague-Dawley rats were fed each 2,500 metacercariae isolated from the sweetfish and sacrificed on the week 1, 2, 3 and 4 post-infection (PI). Recovery of worms was performed from the small intestine of each rat. To visualize the MMCs, duodenal and jejunal (upper, middle and lower) tissue sections were made and stained with alcian blue/safranine-0. The average worm recovery rates were 16.2% and 13.8% on the week 1 and week 2, respectively, but they decreased rapidly to 4.1% and 4.2% on the week 3 and week 4 PI, respectively, which indicate spontaneous worm expulsion after the week 2. The MMC number in the infected rats was, compared with uninfected controls, significantly increased in the whole small intestine, through the whole period of observation. The peak level of mastocytosis was observed on the week 3 PI. It is strongly suggested that MMCs might be involved in the expulsion process of flukes from the rat intestine.