Associations between epidermal thionin-positive cells and skin parasitic infections in brown trout Salmo trutta

Abstract

The dynamics of the densities of epidermal thionin-positive cells (putative mast cells) in the skin of brown trout fry were investigated during experimental infections with the skin parasites Ichthyophthirius multifilus (Ciliophora) and Gyrodactylus derjavini (Monogenea). It was shown that the metachromatic thionin-stained cells were extremely sensitive to parasite exposure, as the density of cells in the skin of trout decreased markedly after exposure to the pathogens. As early as 7 d post infection the cell counts were significantly reduced and almost totally depleted following 9 d infection, which suggests that degranulation of the cells occurs following parasite exposure. No recruitment of new cells was seen during the study period. Some reduction in uninfected control groups indicates that the putative mast cells are sensitive to stress as well. A notable variation in densities of thionin-stained cells between different fins was found and the cornea1 surface was devoid of these cells. The possible implications of these cells in host-parasite interactions are suggested and discussed.

Expression of pro-inflammatory cytokines in rainbow trout (Oncorhynchus mykiss) during an infection with Ichthyophthirius multifiliis

“…It has been speculated that eosinophilic granular cells and thionin-positive cells are identical cells with different staining characteristics following different fixations, and that these cells are fish mast cell homologues [24]. Brown trout thionin-positive putative mast cells were shown to degranulate after 7 days of infection with I. multifiliis [25]. In the infections of carp with I. multifiliis, infiltration of neutrophils and later eosinophilic granular cells was seen in the inflamed skin [9,10].…”

Microhabitat selection of Gyrodactylus salaris Malmberg on different salmonids

“…Because of the low mucous cell density the cornea was associated with parasite colonization during a host response. Further, it has been shown that the epidermis of the brown trout cornea also lacks the putative immunologically relevant mast cells (Sigh & Buchmann 2000).…”

Labile resistance of Atlantic salmon, Salmo salar L., to infections with Gyrodactylus derjavini Mikailov, 1975: implications for host specificity

“…This may well be so (Buchmann 1999; Buchmann & Lindenstrøm 2002) and the predilection of G. derjavini for the corneal surface in unsuitable hosts also points to this. The cornea was suggested by Buchmann & Bresciani (1998) and Sigh & Buchmann (2000) to represent an immuno‐privileged site for gyrodactylids parasitizing responding or unsuitable hosts. The cohabitation system using exposure to a high number of gyrodactylids was suitable, in contrast to the isolated infections with only a few parasites, for analysis of this hypothesis.…”