Rainbow trout leucocyte activity: influence on the ectoparasitic monogenean Gyrodactylus derjavini

The ectoparasitic monogenean Gyrodactylus dejavini from rainbow trout Oncor hynchus mykiss was exposed in vitro to macrophages isolated as peritoneal e xudate cells or as pronephros cells from the host. Cells colonized the para site especially in the mannose-rich regions in the cephalic ducts where cil iated structures were abundant. Opsonization with fresh serum, in contrast to heat-inactivated serum, enhanced Colonization also on other body parts. The adverse effect of the activated macrophages towards G, dejavini was ass ociated with a heat-labile component released from these cells to the cultu re medium. Analysis of substances released from the cells showed reactivity for a number of enzymes, complement factor C3, interleukin (II-1) and reac tive oxygen metabolites. Chemotaxis assays with pronephric leucocytes showe d chemoattractants in G, dejavini, and the respiratory burst level of macro phages was slightly elevated due to parasite exposure. It is suggested that skin leucocytes contribute to an increased level. of complement factors in the trout skin during the host response, whereby a hostile microenvironmen t for the parasites is created. In addition, the IL-l production could affe ct mucous cell secretion and hyperplasia and add to the antiparasitic actio n of the epithelium. Likewise, reactive oxygen metabolites and various enzy mes are Likely to be involved in the skin response.