Mast cells enter a teleost's brain by Xth cranial nerve in response toDiplostomum phoxini (Trematoda)

Abstract

Summary. Experimental infection by Diplostomum phoxini of the brain of laboratory hatched and reared Phoxinus phoxinus induces the migration along the Xth cranial nerve of periodic acid Schiff positive granular leucocytes (PAS-GLs).These differentiate and grow into cells that lie between the parasite and the neurones of the host. The transformed ceils are associated with elevated levels of heparin and serotonin in the brain; little histamine was detected. The reactive cell is identified as a mast cell.More than 1000 metacercariae of the trematode Diplostomum phoxini can live in the brain of the teleost Phoxinus phoxinus (the European minnow) and although the parasite is associated with a host response 2 it survives for at least 2 years 3. The host can be induced to encapsulate and kill D.phoxini in the brain 4 but it has not been recorded to do so in natural conditions. The cells of the capsule, but not those of the normal response, were identified as astrocytes 4 but in view of the reported abundance of ependymal cells in the teleost brain 5 the participation of ependymal cells in capsule formation cannot be ruled out. The origin and nature of the cells that contribute to the normal response have not been determined although following an appreciation of the extreme solubility of the cell's contents, some 2 histochemical data was recorded. The course of the normal host cell reponse has now been studied through the experimental infection with D.phoxini of young, laboratory hatched and raised minnows.Materials' and methods. Spermatozoa stripped from 1 male P.phoxinus were used to fertilize ova from a single female minnow collected from Lake Frongoch. This lake has been the source of material used in a number of studies of D.phoxini 6-9. Artificially fertilized eggs were maintained in the laboratory at 18 ~ in running lake water and they hatched in 7 days. The young fish were kept at 18 ~ and they measured 1.4-2.3 cm and weighed 60-123 mg at 89 days of age. The gonads in the young fish at this time were developing and primary oocytes were observed in females; the fish were judged to be physiologically normal. These fish were then infected with about 50 cercariae of D.phoxini from 1 specimen of Lymnaea peregrer collected in Lake Frongoch. The infected fish were kept at 18 ~ and individuals were killed 4, 6, 8, h; 3, 4, 6, 8, 10, 12, 15, 20, 25, 29, 30, 34 days post-infection. The fish were fixed in Rossman's fixative 2, embedded without decalcification in Paraplast (Lancer, Oxford), most serial sections were stained with PAS, the use of aqueous solutions was avoided 2. A few sections were stained in PAS using the standard technique J~ to determine the water solubility of intracellular granules. Because the fish were small it was possible to transversely section whole animals. Furthermore, because they had been kept isolated from other fish in the aquarium they were free of pathogens except

The role of rodlet cells in the inflammatory response in Phoxinus phoxinus brains infected with Diplostomum

“…Activated macrophages, however, have been documented in the eyes of rainbow trout, Oncorhynchus mykiss (Walbaum) infected with D. spathaceum (Rudolphi, 1891) [12] and mast cells in the brains of minnows infected with D. phoxini have also been recorded [13]. A reexamination of D. phoxini infected minnow brains in the current study, however, also noted the presence of rodlet cells, notably in the epithelium lining the ventricles of the optic lobes.…”

“…Although Diplostomum infections are ubiquitous, there is a paucity of information relating to the host's immune reaction in response to infection by species of this enigmatic genus of digenean parasites [12,13,30,31]. Similarly, the host cellular reaction in Diplostomum-based histopathological studies has been largely overlooked (e.g.…”