Cytometric, morphologic and enzymatic characterisation of haemocytes in Anodonta cygnea

Low-level ionizing radiation-induced DNA responses in the Asian green mussel Perna viridis

Cesium-137 (Cs-137) is a radioactive isotope present in marine environments due to the operation of nuclear power plants and weapons testing. Radiocesium poses a potential risk to marine life due to its long half-life and bioaccumulation. This study evaluated the genotoxicity of low doses of Cs-137 in the Asian green mussel Perna viridis, a sentinel species for marine pollution monitoring, by performing the comet assay and micronucleus test on hemolymph samples. Genotoxicity was assessed after exposing mussels to Cs-137 at dose rates of 0, 5, 10, and 15 μGy/h for 48 h. Cs-137's organ-specific distribution was also determined using HPGe gamma spectrometry. Even at low radiation doses, Cs-137 was found to exert genotoxic effects. Significant increases in DNA strand breaks (%Tail DNA) and micronucleus formation (MNF) were observed at all tested dose rates compared with the levels in controls, with dose-dependent responses. Cs-137 predominantly accumulated in the soft tissues, specifically the gills and digestive gland. The findings support the recommended safety level of 10 μGy/h for aquatic organisms, suggesting its appropriateness as a fundamental criterion for developing the national marine water quality standard for Cs-137 in Thailand.

Specification of hemocyte subpopulations based on immune-related activities and the production of the agglutinin MkC1qDC in the bivalve Modiolus kurilensis

Bivalves, such as Modiolus are used as indicator organisms to monitor the state of the marine environment. Even though hemocytes are known to play a key role in the adaptive and protective mechanisms of bivalves, these cells are poorly studied in horse-mussel Modiolus kurilensis. In this paper, we present classification of horse-mussel hemocytes based on their immune functions, including the production of specific immune-related molecules, as well as their morphological composition after isolation by density gradient centrifugation. An effective fractionation protocol was adapted to separate four hemocyte subpopulations with distinct morphofunctional profiles. First subpopulation consisted of small under-differentiated hemoblasts (2.20 ± 0.85%) with a bromodeoxyuridine positive nucleus, and did not show any immune reactivity. Second was represented by agranulocytes (24.11 ± 2.40%), with evenly filled cytoplasm containing a well-developed protein-synthesizing apparatus, polysomes, smooth endoplasmic reticulum and mitochondria, and positively stained for myeloperoxidase, acidic proteins, glycogen and neutral polysaccharides. Third subpopulation consisted of eosinophilic granulocytes (62.64 ± 9.32%) that contained the largest number of lysosomes, peroxisomes and vesicles with contents of different density, and showed the highest phosphatase, reactive oxygen species (ROS) and phagocytic activities. Lastly, fourth group, basophilic granulocytes (14.21 ± 0.34%), are main producers of lectin-like protein MkC1qDC, recently discovered in M. kurilensis and characterized by pronounced antibacterial and anticancer activity. These cells characterized by intracytoplasmic of the MkC1qDC localization, forming granule-like bodies visualized with specific antibody. Both granulocytes and agranulocytes showed phagocytic activity and ROS production, and these reactions were more pronounced for eosinophilic granulocytes, suggesting that this group is the key element of the cell-mediated immune response of M. kurilensis. Our results support a concept of bivalve's hemocyte specification with distinct phenotypes.

Cellular and humoral immune response between snail hosts and their parasites

In invertebrates, the innate immune system protects against a wide range of microbiological infections. Several immunological processes are involved in the interactive immune response between snails and their parasites, including phagocytosis, nitric oxide synthesis, phenol oxidase activity, lysozymes, and lectin formation. The immunological responses connected to the interaction between snails and parasites are discussed in detail in the current research. Understanding the nature of these interactive reactions will enable scientists to explore approaches to eliminate and cure parasitic infections.

Bivalve Haemocyte Subpopulations: A Review

Bivalve molluscs stand out for their ecological success and their key role in the functioning of aquatic ecosystems, while also constituting a very valuable commercial resource. Both ecological success and production of bivalves depend on their effective immune defence function, in which haemocytes play a central role acting as both the undertaker of the cellular immunity and supplier of the humoral immunity. Bivalves have different types of haemocytes, which perform different functions. Hence, identification of cell subpopulations and their functional characterisation in immune responses is essential to fully understand the immune system in bivalves. Nowadays, there is not a unified nomenclature that applies to all bivalves. Characterisation of bivalve haemocyte subpopulations is often combined with 1) other multiple parameter assays to determine differences between cell types in immune-related physiological activities, such as phagocytosis, oxidative stress and apoptosis; and 2) immune response to different stressors such as pathogens, temperature, acidification and pollution. This review summarises the major and most recent findings in classification and functional characterisation of the main haemocyte types of bivalve molluscs.

Effects of Bacillus lincheniformis feeding frequency on the growth, digestion and immunity of Haliotis discus hannai

To study the effects of Bacillus lincheniformis feeding frequency on the survival and growth of Haliotis discus hannai abalone, we measured the expression levels of nonspecific immune genes and monitored the anti-Vibrio parahaemolyticus immune reaction. H. discus hannai (shell length: 32.75 ± 2.63 mm, body weight: 4.91 ± 0.34 g) was selected to perform a 70 d laboratory culture experiment including a 14 d V. parahaemolyticus artificial infection experiment. The control group (C) was fed normal commercial feed every day. The M1 experimental group was given experimental feed and basal feed on alternating days until the end of the experiment. The M2 experimental group was given experimental feed for 4 d and basal feed for 3 d, and this cycle was repeated every 7 d until the end of the experiment. The M3 experimental group was given experimental feed for 2 d and basal feed for 5 d, and this cycle was repeated every 7 d until the end of the experiment. The M4 group was continuously given experimental feed for the duration of the experiment. The concentration of added B. lincheniformis in each experimental group was 10⁵ cfu/g (according to the quantity of viable bacteria). The specific growth rate (as measured by body weight) and the feed conversion efficiency of the abalone in M1 and M2 were significantly higher than those in M4 and C (P < 0.05). The cellulose and lipase activities of abalone in M1, M2 or M4 were significantly higher than those in M3 or C (P < 0.05). The acid phosphatase, superoxide dismutase, total haemocyte counts, O₂^- levels generated by respiratory bursts, and the expression levels of Mn-SOD, TP_x, GST_s and GST_m in abalone in the M2 group were significantly higher than those in any other feeding frequency group (P < 0.05). At the end of the V. parahaemolyticus infection, the cumulative mortality of the abalone in M2 was significantly lower than that in any other group (P < 0.05). Consequently, given the growth advantages and the enhancement of immune function, the feeding plan in which B. lincheniformis was applied for 4 d per week, and basal feed was then applied for 3 d, did not lead to a high level of immune reaction, immune fatigue or waste of resources, but increased the growth rate of individuals and their resistance to V. parahaemolyticus infection.

Effects of the probiotic Bacillus amyloliquefaciens on the growth, immunity, and disease resistance of Haliotis discus hannai

The effects of a diet containing the probiotic Bacillus amyloliquefaciens on the survival and growth of Haliotis discus hannai were evaluated by measuring growth and hematological parameters and the expression levels of nonspecific immune genes. In addition, the abalone's response to Vibrio parahaemolyticus infection was assessed. H. discus hannai (shell length: 29.35 ± 1.81 mm, body weight: 4.28 ± 0.23 g) were exposed to an 8-week culture experiment in indoor aquariums and a 2-week V. parahaemolyticus artificial infection experiment. In each experiment, the control group (C) was fed daily with the basal feed; the experimental groups were fed daily with the experimental feed, prepared by spraying B. amyloliquefaciens onto the basal feed at final concentrations of 10³ (group A1), 10⁵ (A2), and 10⁷ (A3) cfu/g. The survival rate, body weight specific growth rate, and food conversion efficiency in A2 and A3 were significantly higher than those in A1 and C (P < 0.05). The total number of blood lymphocytes, the O₂^- and NO levels produced from respiratory burst, the activities of acid phosphatase, superoxide dismutase, and catalase, and the expression levels of catalase and thiol peroxidase in A2 were not significantly different from those in A3, but these factors were significantly higher in A2 compared to A1 and C (P < 0.05). The total antioxidant capacity and expression levels of glutathione S-transferase in A1, A2 and A3 were significantly higher than those in C (P < 0.05). At day 9 after infection with V. parahaemolyticus, all abalone in C were dead; at the end of the experiment, the cumulative mortality of abalone in A2 was significantly lower than that in any other group (P < 0.05). Thus, the experimental feed containing 10⁵ cfu/g B. amyloliquefaciens not only facilitated the food intake and growth of abalone, but also effectively enhanced their non-specific immunity and resistance to V. parahaemolyticus infection. In this regard, B. amyloliquefaciens may be a useful probiotic strain for abalone aquaculture.

Differential proteomic profiles and characterizations between hyalinocytes and granulocytes in ivory shell Babylonia areolata

The haemocytes of the ivory shell, Babylonia areolata are classified by morphologic observation into the following types: hyalinocytes (H) and granulocytes (G). Haemocytes comprise diverse cell types with morphological and functional heterogene and play indispensable roles in immunological homeostasis of invertebrates. In the present study, two types of haemocytes were morphologically identified and separated as H and G by Percoll density gradient centrifugation. The differentially expressed proteins were investigated between H and G using mass spectrometry. The results showed that total quantitative proteins between H and G samples were 1644, the number of up-regulated proteins in G was 215, and the number of down-regulated proteins in G was 378. Among them, cathepsin, p38 MAPK, toll-interacting protein-like and beta-adrenergic receptor kinase 2-like were up-regulated in G; alpha-2-macroglobulin-like protein, C-type lectin, galectin-2-1, galectin-3, β-1,3-glucan-binding protein, ferritin, mega-hemocyanin, mucin-17-like, mucin-5AC-like and catalytic subunit of protein kinase A were down-regulated in G. The results showed that the most significantly enriched KEGG pathways were the pathways related to ribosome, phagosome, endocytosis, carbon metabolism, protein processing in endoplasmic reticulum and oxidative phosphorylation. For phagosome and endocytosis pathway, the number of down-regulation proteins in G was more than that of up-regulation proteins. For lysosome pathway, the number of up-regulation proteins in G was more than that of down-regulation proteins. These results suggested that two sub-population haemocytes perform the different immune functions in B. areolata.

Seawater acidification and emerging contaminants: A dangerous marriage for haemocytes of marine bivalves

The combined effects of seawater acidification and the non-steroidal anti-inflammatory drug diclofenac on haemocyte parameters of the mussel Mytilus galloprovincialis and the clam Ruditapes philippinarum were investigated for the first time. Animals were maintained for one week (T0) in natural pH condition (8.1) and two reduced pH values (pH -0.4 units and pH -0.7 units). Bivalves were then exposed for additional 14 days (T1 and T2) to the three experimental pH values in both the presence and absence of environmentally realistic concentrations of diclofenac (0.05 and 0.50 μg/L). To assess potential impairment in immunosurveillance, haemocyte parameters (total haemocyte count, haemocyte volume and diameter, Neutral Red uptake, haemocyte proliferation and lysozyme activity) were measured after 7, 14 and 21 days of exposure to differing pH value or pH/diclofenac combinations. In both species, pH affected the whole haemocyte data set at all sampling times, influencing most of the parameters measured at T0 and T1 in clams, and at T2 in mussels. Conversely, in both species diclofenac affected the overall haemocyte response at T2 only. However, in R. philippinarum a higher number of haemocyte parameters were significantly influenced even at T1. A significant interaction between pH and diclofenac was mainly evident in mussels, affecting haemocyte size and lysozyme activity at both T1 and T2. Overall, the results obtained demonstrated that the experimental conditions tested can alter markedly haemocyte parameters in marine bivalves.

The effects of feeding Lactobacillus pentosus on growth, immunity, and disease resistance in Haliotis discus hannai Ino

To study the effects of probiotic-added food on the survival and growth of abalone (Haliotis discus hannai Ino), the expression levels of nonspecific immune genes and the anti-Vibrio parahaemolyticus infection were examined. During an 8-week culturing experiment in an indoor aquarium and a 2-week V. parahaemolyticus artificial infection experiment, the control group was fed with untreated food once a day, while the experimental groups (L1, L2 and L3) were fed with Lactobacillus pentosus added food. The concentration of probiotics in the experimental food was 10³ cfu/g (L1), 10⁵ cfu/g (L2) and 10⁷ cfu/g (L3), respectively. The results showed that the survival rate, shell length-specific growth rate, and the food conversion rate (FCR) of abalones in L1 and L2 were significantly higher than the control group. The food intake of abalones in L3 was significantly lower than that in L1, L2 and the control group, but there was no significant difference in FCR identified between L1, L2 and L3. In the L. pentosus-added groups, the total number of blood lymphocytes, lysozyme activity, acid phosphatase, superoxide dismutase, and expression levels of Mn-superoxide dismutase (Mn-SOD) and thioredoxin peroxidase (TP_x) were significantly higher than the control group, while the malondialdehyde (MDA) content was significantly lower than the control group. The phagocytic activity of blood lymphocytes, catalase activity and the expression levels of heat shock protein 70 (HSP70) of abalones in the control group were significantly lower than that in L1 and L2, but there was no significant difference when compared with L3. The levels of O₂^-, NO produced by respiratory burst of blood lymphocytes and the expression levels of catalase (CAT) in L1 and L2 were significantly higher than both L3 and the control group. Seven days after infection with V. parahaemolyticus, all abalones in the control group were dead. After 14 days the cumulative mortality rate of abalones in the L. pentosus-added groups was significantly lower than that in the control group. Therefore, the 10³ cfu/g and 10⁵ cfu/g L. pentosus-added food not only promoted food intake and growth of abalones, but also improved their non-specific immunity and reduced V. parahaemolyticus infection, indicating that this strain is a good potential candidate for probiotic added food in the aquaculture industry.

Identification of distinct haemocyte populations from the freshwater bivalves swan mussel (Anodonta cygnea) and duck mussel (Anodonta anatina) using wheat-germ agglutinin

Haemocytes play a major role in molluscs immunity. Functional studies are, however, impaired by limited available experimental tools to identify and sort distinct haemocyte populations. Therefore, using nonlethal methods, we aimed at evaluating whether lectin staining combined with flow cytometry could be used to distinguish circulating haemocyte populations from two freshwater bivalves of the family Unionidae, the duck mussel (Anodonta anatina (L., 1758)) and the swan mussel (Anodonta cygnea (L., 1758)). Based on classical classification, haemocytes were distinguished as granulocytes and hyalinocytes and cytological features were visualized using transmission microscopy and staining techniques. Size, granularity, viability, and surface staining using lectins as specific probes were analysed by flow cytometry and fluorescence microscopy. The microscopic proportions of granulocytes and hyalinocytes significantly differed, being of 70% and 30% for A. cygnea and of 85% and 15% for A. anatina, respectively. Two haemocyte populations were sorted by flow cytometry based on size and granularity and confirmed as granulocytes and hyalinocytes. Interestingly, two different granulocyte populations could be further discriminated in A. cygnea according to their binding affinity to wheat-germ agglutinin (WGA), whereas granulocytes of A. anatina all stained similarly. Our results show that WGA labelling combined with flow cytometry can be used to better discriminate Anodonta haemocyte populations and obtain purified populations for functional studies.

Waterborne cadmium impacts immunocytotoxic and cytogenotoxic endpoints in green-lipped mussel, Perna canaliculus

Mussels are sentinel species that can be used to monitor coastal metal pollution through the application of biomarkers. Among the several important metal toxicants in coastal settings, cadmium (Cd) is of particular concern, being a non-essential metal that is known to cause harmful impacts in aquatic organisms at low concentrations. The aim of the present study was to examine the immunocytotoxic and cytogenotoxic effects of Cd on the green-lipped mussel, Perna canaliculus, under laboratory conditions. The acute (96 h; 0, 2000 and 4000 μg Cd L(-1)) and subchronic (28 d; 0, 200 and 2000 μg Cd L(-1)) toxic effects of waterborne Cd were measured in haemocytes and gill cells using differential haemocyte cell count, the micronucleus test and the comet assay. During subchronic exposure to Cd the relative counts of eosinophils and hyalinocytes increased significantly in Cd-exposed mussels while the proportion of basophils decreased. All of these effects were time- and concentration-dependent. Conversely, the relative numbers of basophils and eosinophils increased significantly during acute Cd exposure. Nuclear aberrations such as the formation of micronuclei, nuclear buds, fragmented-apoptotic cells and binuclei were observed in gill cells of Cd-exposed mussels. All of these parameters increased significantly at 2000 μg Cd L(-1) during subchronic exposure to Cd, and all showed a strong and significant correlation to gill Cd accumulation. Comet assay results demonstrated a significant increase in DNA damage in the haemocytes of mussels exposed to subchronic Cd concentrations. The results indicate that Cd has the capacity to induce immune system and genotoxic damage in green-lipped mussels, an impact that may have implications such as reduced disease resistance and compromised survival. These data also suggest that immunocytotoxic and cytogenotoxic biomarkers would be a valuable addition to environmental monitoring programmes using green-lipped mussels.

Monitoring of DNA damage in haemocytes of freshwater mussel Sinanodonta woodiana sampled from the Velika Morava River in Serbia with the comet assay

This study was undertaken to investigate the potential of the freshwater mussel Sinanodonta woodiana for detection of genotoxic pollution of the environment. Study was performed at two sites in the Velika Morava River, from May 2010 to February 2011. The alkaline comet assay on haemocytes was used, and the olive tail moment (OTM) was chosen as a measure of DNA damage. The specimens held on acclimation under controlled laboratory conditions for 10d were used as a control. Chemical analysis revealed the presence of phosphates and increased concentrations of zinc, copper and nickel at both sites during the entire sampling period. The values of OTM in mussels collected from the environment, significantly correlated with the concentration of zinc (r=0.6248), temperature (r=0.7006) and dissolved oxygen (r=0.7738). Seasonal variations in genotoxic response were observed, with the highest OTM values obtained during summer months. Preliminary results of the in vitro study indicated the effect of water temperature on genotoxic response to zinc and cadmium in S. woodiana suggesting that the presence of genotoxic pollutants during months with lower temperature could be under-estimated. Obtained results indicate that S. woodiana could be a valuable tool for active biomonitoring of aquatic environments and emphasizes the importance of seasonal genotoxic monitoring with this organism.

Phagocytosis and respiratory burst activity of haemocytes from the ivory snail, Babylonia areolata

Haemocytes from the ivory snail, Babylonia areolata phagocytized Saccharomyces cerevisiae and Vibrio parahaemolyticus after 30 min. Haemocytes phagocytized V. parahaemolyticus at a greater rate than they phagocytized S. cerevisiae. The phagocytic rate (PP) of V. parahaemolyticus by granulocytes to was a little higher than that of S. cerevisiae. The phagocytic index (PI) of V. parahaemolyticus by granulocytes was significantly higher than that of S. cerevisiae. The same was true of hyalinocytes. The PP of granulocytes was significantly higher than that of hyalinocytes for each pathogen. No difference in PI was observed in granulocytes and hyalinocytes. Two defense mechanisms of B. areolata were quantified using flow cytometry. Haemocyte phagocytosis was quantified using fluorescent microbeads and respiratory burst activity was measured using H2O2 increases detected by 2', 7'-dichlorofluorescein diacetate. Both phagocytosis and respiratory burst activity of the haemocytes increased over time. After 90 min the phagocytic rate no longer increased. In the case of respiratory burst, the greatest increase in fluorescence occurred between 30 and 120 min, no further increase was seen after 120 min. These results showed unequivocally that a native (unstimulated) haemocyte oxidative burst was active in B. areolata. The aim of this study was to further the knowledge of immunology in gastropods.

Association between environmental microbiota and indigenous bacteria found in hemolymph, extrapallial fluid and mucus of Anodonta cygnea (Linnaeus, 1758)

Bivalves filter and accumulate large numbers of microorganisms present in the harvesting water. A complete understanding of the balance between Anodonta cygnea and the microbiota present in their surrounding environment remains incomplete. Therefore, the aim of this study was to quantify and identify the indigenous bacteria in the biological fluids of A. cygnea collected from Mira Lagoon in northern Portugal. The results showed Vibrio metschnikovii and Aeromonas sobria as the dominant groups. The median for total bacteria from mucus was 3.1 × 10(3) CFU g(-1), whereas the range in means from fluids was 1.5 × 10(2) to 6.5 × 10(2) CFU ml(-1). During the experimental work, Escherichia coli and enterococci were not detected in healthy A. cygnea. However, the periodic detection of E. coli and enterococci in Mira lagoon revealed its presence in the water. Our observations suggest that A. cygnea has the ability to filter and eliminate E. coli, present in the surrounding environment, through an active phagocytic process conducted by hemolymph circulating cells, the hemocytes.

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

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.

Persistence of DNA damage in the freshwater mussel Unio pictorum upon exposure to ethyl methanesulphonate and hydrogen peroxide

An important endpoint in assessing pollution-related toxicity is genotoxicity. To obtain insight into the time-course of oxidative- and alkylation-induced DNA damage in the freshwater mussel, Unio pictorum, mussels were exposed for 24 hr to concentration gradients of pro-oxidant hydrogen peroxide (H(2)O(2)) and a mono-functional alkylating agent, ethyl methanesulfonate (EMS). DNA damage was assessed in haemocytes immediately upon exposure and over the recovery period of up to 72 days by means of comet and micronucleus assays. Following exposure to H(2)O(2), DNA damage as detected by the comet assay returned to control values after one day, except for the mussels exposed to the highest dose when damage was detectable for the next 3 days. In contrast, alkylation-induced DNA damage was detectable even after 72 days of recovery in de-chlorinated water, with a dose-response relationship observable throughout the whole recovery period. Micronucleus frequency was the highest on Day 3 after exposure to EMS; it decreased considerably by Day 7 and returned almost to the control levels 19 days after exposure, while no significant induction of micronuclei was observed in mussels exposed to H(2)O(2). Although the comet assay is considered a biomarker of recent genotoxic exposure, detecting DNA damage of shorter longevity than with the micronucleus assay, results presented here show that in the case of alkylation damage the comet assay reveals genotoxic exposure of U. pictorum in a dose-dependent manner even after 2 months.

Immune responses of mussel hemocyte subpopulations are differentially regulated by enzymes of the PI 3-K, PKC, and ERK kinase families

Various hemocyte cell types have been described in invertebrates, but for most species a functional characterization of different hemocyte cell types is still lacking. In order to characterize some immunological properties of mussel (Mytilus galloprovincialis) hemocytes, cells were separated by flow cytometry and their capacity for phagocytosis, production of reactive oxygen species (ROS), and production of nitric oxide (NO), was examined. Phosphatidylinositol 3-kinase (PI 3-K), protein kinase C (PKC), and extracellular signal-regulated kinase (ERK) inhibitors were also used to biochemically characterize these cell responses. Four morphologically distinct subpopulations, designated R1-R4, were detected. R1, R2, and R3 cells presented different levels of phagocytosis towards zymosan, latex beads, and two bacteria species. Similarly, R1 to R3, but not R4, cells produced ROS, while all subpopulations produced NO, in response to zymosan. Internalization of all phagocytic targets was blocked by PI 3-K inhibition. In addition, internalization of latex particles, but not of bacteria, was partially blocked by PKC or ERK inhibition. Interestingly, phagocytosis of zymosan was impaired by PKC, or ERK inhibitors, only in R2 cells. Zymosan-induced ROS production was blocked by PI 3-K inhibition, but not by PKC, or ERK inhibition. In addition, zymosan-stimulated NO production was affected by PI 3-K inhibition in R1 and R2, but not in R3 or R4 cells. NO production in all cell types was unaffected by PKC inhibition, but ERK inhibition blocked it in R2 cells. These data reveal the existence of profound functional and biochemical differences in mussel hemocytes and indicate that M. galloprovincialis hemocytes are specialized cells fulfilling specific tasks in the context of host defense.

Sydney rock oyster (Saccostrea glomerata) hemocytes: Morphology and function

In this study, three major hemocyte types were identified in the Sydney rock oyster. They were characterized primarily by light and electron microscopy based on the presence or absence of granules and nucleus to cytoplasm ratios. Hemoblast-like cells were the smallest cell type 4.0+/-0.4microm and comprised 15+/-3% of the hemocyte population. They had large nuclei and scanty basic cytoplasm. This cell type also had some endoplasmic reticuli and mitochondria. The second major type were hyalinocytes. Hyalinocytes represented 46+/-6% of all hemocytes. They were large cells (7.1+/-1.0microm) that had low nucleus:cytoplasm ratios and agranular basic or acidic cytoplasm. Hyalinocytes had the ability to phagocytose yeast cells and formed the core of hemocyte aggregates associated with agglutination. Four discrete sub-populations of hyalinocytes were identified. The third major cell type were the granulocytes, comprising 38+/-1% of the hemocyte population. These cells were large (9.3+/-0.3microm) and were characterized by cytoplasm containing many acidic or basic granules. Granulocytes were more phagocytic than hyalinocytes and they formed the inner layer of hemocytes during the encapsulation of fungal hyphae. Five discrete sub-populations of granulocytes were identified based on the types of granules in their cytoplasm. Flow cytometry showed that the hemocytes of rock oysters could be divided into between two and four major cell types based on their light scattering properties. The most common of the cell types identified by flow cytometry corresponded to hyalinocytes and granulocytes. Cytochemical assays showed that most enzymes associated with immunological activity were localized in granulocytes. Their granules contained acid phosphatase, peroxidase, phenoloxidase, superoxide and melanin. Hyalinocytes were positive only for acid phosphatase. All of these observations suggest that Sydney rock oysters have a broad variety of functionally specialized hemocytes, many of which are involved in host defense.

Studies on a PMCA-like protein in the outer mantle epithelium of Anodonta cygnea: insights on calcium transcellular dynamics

Early studies on the outer mantle epithelium (OME) cells of the freshwater bivalve Anodonta cygnea (Linnaeus, 1758) revealed high ionic calcium concentrations by electrophysiological methods and subsequently a high tendency to reach an intracellular toxic condition. This toxicity could be neutralized by specific mechanisms in the cytosol of OME cells of A. cygnea. The present immunocytochemistry studies of OME cells by light and transmission electron microscopy (TEM) clearly showed a positive reaction of an antibody directed against the human plasma membrane Ca(2+)-ATPase 1 (PMCA-1) in the cytoplasm of OME cells. Also, western blot analysis of different fractions of OME cells with anti human PMCA-1 and C28R2 antibodies confirmed the presence of a PMCA-like protein with an unusual topographical localization and a molecular weight of only 70-80 kDa. These results lead us to speculate that this PMCA-like protein is distributed either in the plasma membrane or in the entire cytosol, where it eventually regulates intracellular calcium levels. Interestingly, the antibody reactions showed seasonal variations, being highest in OME samples prepared during summer when A. cygnea live under natural acidosis and absent in samples taken in winter conditions, which is in accordance with the seasonal variation of shell calcification rates. During winter, PMCA-1 antibody reaction was also detected in OME cells of animals kept only under experimentally induced acidosis conditions. Therefore, we assume that a functional role for this PMCA-like protein in the intracellular calcium regulation of OME cells during the mineralization of the shells of A. cygnea can be speculated.

Peroxidase activity and inducibility in the sea fan coral exposed to a fungal pathogen

The enzymatic defense mechanisms of Gorgonia ventalina to the fungal pathogen Aspergillus sydowii may play important roles in colony resistance to infection. In this study, we examined the role of the superfamily of peroxidase enzymes in the coral response to a naturally occurring pathogen. We examined the inducibility of peroxidases by experimentally exposing corals to A. sydowii and found that peroxidase activity was induced after an 8 day incubation period. In contrast, naturally infected corals collected from the reef had lower peroxidase activity when compared to healthy corals. Infected sea fans from the field also had less measurable protein in their tissues and increased purple sclerites near infection sites and it is likely that these infections are months old. Using native-PAGE activity gels, we detected 5 peroxidase isozymes in healthy corals, indicating that multiple isoforms of peroxidase with a plurality of possible functions are present in this coral. The role of the peroxidase enzymes in disease resistance was examined by testing anti-fungal activity of commercially available and partially purified sea fan peroxidases. In both cases there was significant, dose-dependent anti-fungal activity. While peroxidases are ubiquitous enzymes involved in many cellular pathways, we also hypothesize that G. ventalina utilizes these enzymes as an integral component in disease resistance pathways. As such, they may also contribute to the initiation of physiochemical defenses such as melanization and lipid soluble anti-fungal metabolites.

Flow cytometry as a tool to quantify oyster defence mechanisms

The fast growing oyster aquaculture industry is greatly hindered by Perkinsus marinus and Haplosporidium nelsoni which can kill up to 80% of the production. The relationship between parasites and oyster defence mechanisms is unclear. Two defence mechanisms of the Eastern Oyster (Crassostrea virginica) were quantified at the single cell level utilising flow cytometry. Phagocytosis was measured using fluorescent beads. Respiratory burst activity was quantified as the H2O2-specific increase in dichlorofluorescein-associated fluorescence upon stimulation. These two assays distinguished three populations of haemocytes (granulocytes, hyalinocytes and intermediate cells) with unique functional characteristics. Granulocytes were most active at phagocytosis and H2O2 production while hyalinocytes were relatively inactive. The intermediate cells had moderate phagocytic and respiratory burst activity. Flow cytometry can rapidly, accurately and directly quantify the morphology and function of a large number of individual cells, and will lead to a better understanding of the bivalve immune system.