Effects of parasitism and pesticide exposure on characteristics and functions of hemocyte populations in the freshwater snail Lymnaea palustris (Gastropoda, Pulmonata) |
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Authors: | J Russo L Lagadic |
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Institution: | CNRS, UMR 6553 ECOBIO, Université de Rennes, France. jacqueline.russo@univ-rennes1.fr |
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Abstract: | Morphological characteristics and functions of hemocytes were used to compare the immunological effects of biological and
chemical stress in the freshwater snailLymnaea palustris. Animals were either infected by a trematode parasite (Metaleptocephalus sp.), or exposed to environmental contaminants, namely atrazine and hexachlorobenzene (HCB). Three populations of circulating
hemocytes, morphologically and cytochemically distinct (round cells, hyalinocytes, granulocytes), were identified in both
control and parasitized or pesticide-exposed snails. After 6 h of exposure, HCB and atrazine resulted in 8-fold increases
in the mean total number of hemocytes, whereas only a 2.2-fold increase was observed 6 h after cercaria emission in parasitized
snails. The impact of HCB was limited to the first 24 h of exposure, whereas long-lasting effects of atrazine were observed.
Hyalinocytes and, to a lesser extent, round cells contributed most to the increases in hemocyte density in pesticide-exposed
snails. Parasitism and atrazine treatment resulted in significant increases of lectin-stained hemocytes, whereas exposure
to HCB did not affect the percentages of stained and unstained cells. Hemocyte phagocytic activity increased in HCB-exposed
snails but with no concomitant change of the oxidative burst. Opposite results were obtained in atrazine-treated snail hemocytes,
with unchanged phagocytosis and decreased phorbol 12-myristate 13-acetate-stimulated production of reactive oxygen intermediates.
No increase in phagocytosis, or in the production of reactive oxygen intermediates, was observed in hemocytes from parasitized
snails. Infection with the immunologically compatible trematode parasiteMetaleptocephalus sp. and exposure to atrazine generated similar reactions from circulating hemocytes, whereas a different response pattern
was observed in HCB-exposed snails.
This revised version was published online in July 2006 with corrections to the Cover Date. |
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Keywords: | immunotoxicity phagocytosis freshwater snail trematode atrazine hexachlorobenzene |
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