Infection with the protozoan parasite Bonamia ostreae modifies in vitro haemocyte activities of flat oyster Ostrea edulis

Abstract

Bonamia ostreae is an intracellular protozoan parasite, infecting haemocytes of the European flat oyster Ostrea edulis. Oyster defence mechanisms mainly rely on haemocytes. In the present study in vitro interactions between parasites and flat oyster haemocytes were investigated using flow cytometry and light microscopy. Haemocyte parameters including: non specific esterase activity, reactive oxygen species (ROS) production and phagocytosis were monitored using flow cytometry after 2 h cell incubation with live and dead B. ostreae. Two ratios of parasites per haemocyte were tested (5:1 and 10:1), haemocytes alone were used as controls and the experiment was carried out three times. Flow cytometry revealed a decrease of non specific esterase activities and ROS production by haemocytes after incubation with live parasites, while there was little difference in phagocytosis activity when compared with controls. Similarly, dead parasites induced a decrease in haemocyte activities but to a lesser extent compared to live parasites. These results suggest that B. ostreae actively contributes to the modification of haemocyte activities in order to ensure its own intracellular survival.

Disseminated neoplasia in cockles Cerastoderma edule: ultrastructural characterisation and effects on haemolymph cell parameters

“…Flow cytometry makes it possible to analyse different parameters simultaneously in a large number of cells in a short time, thus improving the efficiency and capacity of more traditional immunological methods (Fisher & Ford 1988). Flow cytometry has been used to analyse size, organelle contents, viability, phagocytosis capacity, enzyme activities and ROI production of haemocytes in various bivalve mollusc species (Gagnaire et al 2004, 2006, Samain et al 2007, Morga et al 2009 The aim of the present work was to characterise the ultrastructure of neoplastic cells of cockles through transmission electron microscopy (TEM) and to evaluate the effect of disease at different severity stages on various haemolymph cell parameters using flow cytometry. The cell parameters studied were cell mortality, non-specific esterase activities, lysosome biovolume, ROI production, phagocytosis ability, and intracellular Ca 2+ and actin levels.…”

Bonamia parasites: a rapidly changing perspective on a genus of important mollusc pathogens

“…Flow cytometry was used to demonstrate that live parasites are phagocytosed at higher rates than fluorescent beads . Numbers of infected haemocytes were similar after the contact with live and heatinactivated parasites; however, the mean number of parasites per infected haemocyte was higher in the first treatment (Morga et al 2009). Moreover, examination of naturally infected flat oysters revealed that the number of tissue-infiltrating haemocytes increased with infection intensity, suggesting a recruitment process at the site of infection whereas circulating haemocyte densities were not statistically different between infected and non-infected oysters (Cochennec-Laureau et al 2003a).…”

“…Post-internalization interactions have notably been investigated by flow cytometry: contrary to heatinactivated parasites, live B. ostreae induced a decrease of reactive oxygen species (ROS) production and esterase activities between 1 and 4 h post infection and phagocytosis activity decreased at 2 h (Morga et al 2009(Morga et al , 2011. In addition, the expression of an extracellular superoxide dismutase (Oe-EcSOD) decreased after 1 h of contact.…”

“…Recent studies have focused on gaining a greater understanding of the response of oysters to B. ostreae infection (Morga et al 2009, 2011, 2012, Comesaña et al 2012, Martín-Gómez et al 2012. Functional studies combining more sophisticated genetic methodology, proteomics and cellular and ultrastructural approaches will be required to better characterize how these mechanisms allow an oyster host to resist Bonamia infection and the parasite to escape host responses.…”

“…Recently, mechanisms of interaction between Bonamia spp. and their hosts, including mechanisms involved in the resistance to the disease, have been investigated in more depth at cellular and molecular levels (Morga et al 2009(Morga et al , 2011. Furthermore, it seems that in some cases, after their introduction, the parasites are only present at a low prevalence and with presumably limited effects on the population .…”