Radix lagotis is an intermediate snail host of the nasal bird schistosome Trichobilharzia regenti. Changes in defence responses in infected snails that might be related to host-parasite compatibility are not known. This study therefore aimed to characterize R. lagotis haemocyte defence mechanisms and determine the extent to which they are modulated by T. regenti. Histological observations of R. lagotis infected with T. regenti revealed that early phases of infection were accompanied by haemocyte accumulation around the developing larvae 2-36 h post exposure (p.e.) to the parasite. At later time points, 44-92 h p.e., no haemocytes were observed around T. regenti. Additionally, microtubular aggregates likely corresponding to phagocytosed ciliary plates of T. regenti miracidia were observed within haemocytes by use of transmission electron microscopy. When the infection was in the patent phase, haemocyte phagocytic activity and hydrogen peroxide production were significantly reduced in infected R. lagotis when compared to uninfected counterparts, whereas haemocyte abundance increased in infected snails. At a molecular level, protein kinase C (PKC) and extracellular-signal regulated kinase (ERK) were found to play an important role in regulating these defence reactions in R. lagotis. Moreover, haemocytes from snails with patent infection displayed lower PKC and ERK activity in cell adhesion assays when compared to those from uninfected snails, which may therefore be related to the reduced defence activities of these cells. These data provide the first integrated insight into the immunobiology of R. lagotis and demonstrate modulation of haemocyte-mediated responses in patent T. regenti infected snails. Given that immunomodulation occurs during patency, interference of snail-host defence by T. regenti might be important for the sustained production and/or release of infective cercariae.

Charles University Prague Faculty of Science Department of Parasitology Prague Czech Republic

Charles University Prague Faculty of Science Department of Parasitology Prague Czech Republic; Charles University Prague 1st Faculty of Medicine Institute of Immunology and Microbiology Prague Czech Republic

Charles University Prague Faculty of Science Department of Parasitology Prague Czech Republic; Institute of Haematology and Blood Transfusion Prague Czech Republic

Charles University Prague Faculty of Science Department of Parasitology Prague Czech Republic; Masaryk University Faculty of Science Department of Botany and Zoology Brno Czech Republic

Charles University Prague Faculty of Science Institute of Applied Mathematics and Information Technologies Prague Czech Republic

Molecular Parasitology Laboratory School of Life Sciences Kingston University Kingston upon Thames Surrey United Kingdom

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