Ultrastructural observations on peritoneal exudate cells from the striped bass

Ultrastructural and Cytochemical Properties of Peripheral Blood Cells of Piebald Naked Carp (Gymnocypris eckloni)

The ultrastructural and cytochemical properties of peripheral blood cells of Gymnocypris eckloni were investigated by transmission electron microscopy and a range of cytochemical techniques to provide clear insight into the structure and function of blood cells from this fish. Ultrastructurally, erythrocytes, leucocytes (neutrophils, eosinophils, lymphocytes, monocytes), thrombocytes and plasma cells were identified in the peripheral blood of G. eckloni. The most special ultrastructural characteristics of blood cells in this fish were that neutrophils exhibited only one type of cytoplasmic granules containing an eccentric, spherical or oval electron-dense core, and eosinophils presented two types of granules with non-uniform electronic density and without crystalloids in their cytoplasm. Neutrophils, eosinophils, lymphocytes, monocytes and thrombocytes were positive for periodic acid-Schiff and α-naphthyl acetate esterase staining. Intense peroxidase positive staining was observed in neutrophils and monocytes, but not in eosinophils, lymphocytes and thrombocytes. Neutrophils, eosinophils and monocytes were stained positively for acid phosphatase, whereas lymphocytes and thrombocytes did not stain. Leucocytes and thrombocytes were negative for alkaline phosphatase and Sudan black B staining. Erythrocytes were negative for all cytochemical staining. The cytochemical and ultrastructural features of peripheral blood cells of G. eckloni were similar to those of other fish species. However, some important differences were identified in G. eckloni.

Morphological and cytochemical studies of peripheral blood cells of Schizothorax prenanti

The morphological and cytochemical studies of peripheral blood cells of Schizothorax prenanti were studied by light and electron microscopy. Erythrocytes, thrombocytes and three types of leucocytes, lymphocytes, neutrophils and monocytes, were distinguished and characterized. In addition to mature erythrocytes, immature and dividing erythrocytes were observed. A few organelles such as mitochondria were distributed in the cytoplasm of erythrocytes. Lymphocytes with heavily clumped heterochromatic nucleus and minimal cytoplasm were classified into small and large lymphocytes. Three different populations of granules, with distinctive ultrastructural aspect, were observed in neutrophils. Monocytes were the fewest leucocytes possessing rich organelles, phagocytized materials and vacuoles. Thrombocytes with various types were the most abundant blood cells among leucocytes and contained a prominent nucleus with dense bands of heterochromatin and many cytoplasmic vacuoles. Periodic acid-Schiff staining was positive in neutrophils, monocytes, lymphocytes and thrombocytes, but not in erythrocytes. Peroxidase-positive staining was observed in neutrophils and monocytes, but not in erythrocytes, lymphocytes and thrombocytes. Only neutrophils were positive for oil red O. Except for erythrocytes, the other blood cells stained positively for acid phosphatase. Only neutrophils and monocytes were positive for α-naphthyl acetate esterase. None of the cells studied were positive for alkaline phosphatase. The morphologic and cytochemical features of blood cells of S. prenanti are similar to those of other fish. This investigation may be helpful as a tool to monitor the health status of cultured S. prenanti and will grant early detection of clinical pathology.

Seabream (Sparus aurata) long-term dominant-subordinate interplay affects phagocytosis by peritoneal cavity cells

Fish are sensitive to stressful conditions that affect their innate immune systems and increase their susceptibility to diseases. We examined the social stress of paired gilthead seabream (Sparus aurata). Social hierarchies (dominant/subordinate) were characterised by behavioural changes, such as "aggressiveness" and "feeding order"; hierarchical positions were established within an hour of exposure to social stress and remained unchanged for approximately 1 year. To characterise physiological stress, we measured blood plasma levels of cortisol, glucose, and lactate as well as osmolarity and observed that the levels of these stress markers were higher in subordinate individuals than in dominant ones. The discriminant analysis revealed a separation of the subordinate fish groups, and at 15 days, a significant separation among groups was observed. Moreover, diminished phagocytic and respiratory burst activities revealed that social stress appeared to affect the cellular innate immune response of the subordinate specimens. Finally, to examine the effect of cortisol on phagocytosis, peritoneal cavity cells were treated in vitro, and an inhibitory effect was observed.

Identification of phagocytic cells, NK-like cytotoxic cell activity and the production of cellular exudates in the coelomic cavity of adult zebrafish

Coelomic cavity (CC) cells of mature zebrafish harvested by lavage with media or trypsin-EDTA contained 0.80-1.20 x 10(5) and 2.0-3.5 x 10(5) cells, respectively. Media lavage was composed of granulocytes (60-80%), lymphocytes (10-20%), and NCC (4-10%). Granulocytes had large electron dense cytoplasmic paracrystalline granules and a segmented nucleus; they expressed plastin-1, myeloid specific peroxidase and MCSF mRNA; and they were NCAMP-1(+). Lymphocytes had B- and T-cell specific mRNA and were NCAMP-1(-) and NCCRP-1(-). NCC were 3 microm, NCAMP-1(+) and NCCRP-1(+) and did not express B- and T-cell specific mRNA. Additionally, trypsin lavage contained monocytes (marginated chromatin, low nuclear:cytoplasm ratio, sparse cytosolic granules) and macrophages (non-segmented nuclei, no margination of chromatin, abundant electron dense granules). E. coli injected into the CC were phagocytosed in a dose and time dependent fashion by granulocytes, monocytes and macrophages. NCC lysed mammalian target cells and NCAMP-1 expressing hybridoma cells in redirected lysis assays.

Characterization of blood cells and hematological parameters in Cichlasoma dimerus (Teleostei, Perciformes)

The aim of the present study was to obtain a basic knowledge of the hematology of Cichlasoma dimerus. The morphological features of blood cells were described according to the observations made by light and electron microscopy. Erythrocytes, thrombocytes and four types of leucocytes: lymphocytes, monocytes, heterophils and eosinophils, were distinguished and characterized. Thrombocytes are the most abundant blood cells after erythrocytes and are recognized easily from lymphocytes by morphological features and size. Heterophils and eosinophils are PAS positive. Hematological indices (RBC, WBC, PCV, Hb, MCV, MCH, MCHC and leucocyte differential count) were measured in one blood sample from 30 adult fish captured in Esteros del Riachuelo, Corrientes, Argentina (27 degrees 25'S, 58 degrees 15'W). The reference interval and the mean were determined for each hematological parameter evaluated. Contrary to other species, the percent of heterophils was found to be high in relation to the percent of lymphocytes. Low lymphocyte counts occurred in C. dimerus, as compared to these found in other fishes. Compared to most teleosts, this species has similar mean values for PCV and Hb and slightly higher for RBC. Statistical analysis revealed that differences in hematological parameters between male and female fish were not significant.

In vitro response of the striped bass natural resistance-associated macrophage protein, Nramp, to LPS and Mycobacterium marinum exposure

Mycobacteriosis in Chesapeake Bay (USA) striped bass Morone saxatilis is an ongoing disease problem with important economic implications for a large commercial and recreational fishery. Additionally, striped bass serve as a reservoir of potential mycobacterial zoonoses. Recently, we described a striped bass gene homolog of the natural resistance-associated macrophage protein family (MsNramp), which is responsible for resistance to mycobacterial infections in mice. Striped bass MsNramp is strongly induced in peritoneal exudate cells (PE) in vivo after intraperitoneal injection with Mycobacterium spp. The purpose of the present study was to investigate short-term in vitro MsNramp expression and reactive oxygen intermediate (ROI) production in primary cultures of adherent PE after exposure to bacterial lipopolysaccharide (LPS), or live- or heat-killed (HK) Mycobacterium marinum. PE expressed significantly higher levels of MsNramp at 4 and 24 h post-treatment with live and HK M. marinum. MsNramp response to LPS was dose-dependent in these cells, with maximum expression at 4 h and 20 microg/ml LPS. Treatment of PE with LPS resulted in increased intracellular superoxide anion levels, whereas treatment with live M. marinum caused a significant depression. This study is the first report of induction of a teleost Nramp in vitro by mycobacteria, and supports findings of teleost Nramp induction by LPS.

An in vitro assay to measure phagocytosis in striped bass hybrids (Morone saxatilis x Morone chrysops)

An in vitro phagocytosis assay was developed for hybrid striped bass (Morone saxatilis x Morone chrysops), using cells collected from the peritoneal cavity of this fish. The findings indicated that: (1) 10 days following a single intraperitoneal injection (1 ml) of Freund's incomplete adjuvant (FIA) was an appropriate time for collecting suitable working concentrations (5.3+/-4.0 x 10(7) cells ml(-1)) of peritoneal phagocytes (83.7+/-1.5% macrophages) from these hybrids held at 23 degrees C; (2) these cells phagocytosed latex beads (polystyrene microspheres 3.12 microm in diameter) after 30 min of in vitro incubation at room temperature (25+/-1 degrees C). The phagocytic ability and phagocytic capacity in a washed adherent layer exposure system were 67.2+/-2.76% and 4.14+/-0.35 beads phagocyte(-1), respectively. These results strongly suggest that a simple methodology, including baseline data serving as guidelines, is now available for conducting in vitro phagocytosis assays in this hybrid.

Spontaneous cytotoxic activity of eosinophilic granule cells separated from the normal peritoneal cavity of Dicentrarchus labrax

In this study the spontaneous in vitro cytotoxic activity to tumour cell lines, (K562), by unstimulated sea bass (Dicentrarchus labrax) leukocytes was examined by trypan blue exclusion test and lactate dehydrogenase release assay. A high anti-tumour cell line activity of resident peritoneal leukocytes was found at an effector to target ratio (E:T) of 25:1 after incubation for 2 h at 18 degrees C. Rabbit and sheep erythrocytes were not lysed. A low activity was displayed by head kidney and spleen cell populations whereas blood leukocytes revealed no significant activity. The effect of E:T ratio on cytotoxicity as well as microscopy observations suggested that the cytotoxic reaction required effector-target cell contact. Eosinophilic granule cells, isolated on a Percoll density gradient from a peritoneal wash, appeared to be responsible for the in vitro cytotoxic activity.

Blood cells of sea bass (Dicentrarchus labrax L.). Flow cytometric and microscopic studies

Studies of fish blood cells made to date presented numerous problems derived from both the nomenclature and the techniques used. A combination of quantitative and morphological methods is needed if the classification of fish blood cells is to advance from it present provisional state. The aim of the present paper was first to isolate sea bass blood cell populations by flow cytometry and second to characterize then microscopically. Blood cell populations from sea bass (Dicentrarchus labrax L.) were isolated according to their FSC (size) and SSC (granularity) properties by flow cytometry. The isolated populations were then processed for light and transmission and scanning electron microscopic characterization. Sea bass blood leukocytes isolated by flow cytometry consisted of two main cell subpopulations. Subsequent microscopic study of these cells revealed that the first subpopulation was composed of small cells (3-5 microm) of low granularity and consisted of thrombocytes and lymphocytes whereas, the second subpopulation was formed of 6-9 microm sized cells of high granularity consisting of granulocytes and monocyte/macrophages. The combined use of flow cytometry and electron microscopy makes it possible to characterize the different cell types present in sea bass peripheral blood with a high degree of certainty. Although sea bass basically follows the common vertebrate hematological pattern, significant modifications such as the presence of circulating immature erythrocytes, plasma cells and monocyte/macrophages and different forms of thrombocytes can be established with respect to this pattern.

Immunological system and Schistosoma mansoni: co-evolutionary immunobiology. What is the eosinophil role in parasite-host relationship?

Schistosomes, ancestors and recent species, have pervaded many hosts and several phylogenetic levels of immunity, causing an evolutionary pressure to eosinophil lineage expression and response. Schistosoma mansoni adult worms have capitalized on the apparent adversity of living within the mesenteric veins, using the dispersion of eggs and antigens to other tissues besides intestines to set a systemic activation of several haematopoietic lineages, specially eosinophils and monocytes/macrophages. This activation occurs in bone marrow, spleen, liver, lymph nodes, omental and mesenteric milky spots (activation of the old or primordial and recent or new lymphomyeloid tissue), increasing and making easy the migration of eosinophils, monocytes and other cells to the intestinal periovular granulomas. The exudative perigranulomatous stage of the periovular reaction, which present hystolitic characteristics, is then exploited by the parasites, to release the eggs into the intestinal lumen. The authors hypothesize here that eosinophils, which have a long phylogenic story, could participate in the parasite-host co-evolution, specially with S. mansoni, operating together with monocytes/macrophages, upon parasite transmission.

Factors influencing phagocytic response of macrophages from the sea bass (Dicentrarchus labrax L.): an ultrastructural and quantitative study

BACKGROUND

Although phagocytosis is considered the main nonspecific defense mechanism in fish, the significance of the influence of bacterial properties and assay conditions on this mechanism has not been established. We report the influence of leukocyte source, bacterial species, presence or absence of a bacterial wall, bacterial status (live or dead), and bacterial opsonization on in vitro phagocytosis by sea bass (Dicentrarchus labrax L.) macrophages.

METHODS

Leukocytes were challenged with bacteria under different conditions and ultrastructurally studied. The number of phagocytic macrophages and the number of bacteria ingested per macrophage were quantified by microscopical counting, and the data obtained were statistically analyzed following general linear models.

RESULTS

Macrophages from sea bass peritoneal exudate showed a greater capacity to engulf bacteria than did those isolated from blood, which, in turn, had greater engulfment properties than did those isolated from head-kidney. Greater phagocytic activity was observed in the assays carried out with Escherichia coli than in those carried out with Salmonella typhimurium, especially when the TA1950 S. typhimurium strain (with wall) was used. Macrophages showed greater phagocytic activity against live bacteria. Bacterial opsonization had a variable effect on phagocytosis. Sea bass macrophages did not always ingest the same number of bacteria.

CONCLUSIONS

Sea bass macrophages have strong bacterial phagocytic activity. Significant differences were found that had been influenced by bacterial properties as well as by assay conditions. Positive correlation between the number of phagocytic macrophages and the number of bacteria ingested per phagocyte was observed.

Phagocytic defence mechanism in sea bass (Dicentrarchus labrax L.): an ultrastructural study

BACKGROUND

The ultrastructure of the phagocytic process in fish has not been established in spite of the significant morphofunctional differences detected in the fish immune system with respect to the basic immunological pattern in vertebrates. We report the ultrastructure of the bacterial phagocytic defence mechanism in sea bass (Dicentrarchus labrax L.).

METHODS

Head-kidney, blood, and peritoneal exudate leukocytes were challenged with Aeromonas salmonicida and Escherichia coli and processed for transmission electron microscopic study.

RESULTS

Macrophages challenged with bacteria showed changes in the cell outline, in the chromatin pattern, and in the ultrastructural features of the cytoplasm as a consequence of an activation process. The phagocytic process consists of the following: 1) Bacteria-macrophage contact. One or more spot contacts between the bacterial wall and the phagocyte membrane are observed. 2) Bacteria engulfment. Slight depressions, membrane invaginations, or cytoplasmic processes are formed at the phagocyte surface. Macrophage processes occasionally surround the bacteria, overlapping and roaming parallel, or a single, long pseudopod encircles a bacterium several times. 3) Endocytic vesicle formation. Macrophages show one or more bacteria inside membrane-bound cytoplasmic vesicles. 4) Phagolysosome formation. Some dense granules (lysosomes) fuse with the endocytic vesicle. 5) Intracellular killing/digestion. Bacteria inside the endocytic vesicles are observed both virtually intact or damaged at different digestion stages.

CONCLUSIONS

Sea bass macrophages possess the mechanisms necessary to both engulf and kill bacteria. Cellular and subcellular events in the morphology of phagocytosis and lysosomal dissolution of bacteria fit the general pattern described for mammals.

Cytochemical characterization of leucocytes from the seawater teleost, gilthead seabream (Sparus aurata L.)

The cytochemical characterization of head-kidney and peripheral blood leucocytes of gilthead seabream (Sparus aurata L.) was studied by light and electron microscopy. Neutrophilic granulocytes show some cytoplasmic granules, which are positive for alkaline phosphatase and peroxidase but acid phosphatase negative. The scarce granules found in the cytoplasm of the circulating neutrophils and their cytochemical features seem to be indicative of an immature stage. Acidophils are also alkaline phosphatase and peroxidase positive at pH 11.0. They are strongly positive for acid phosphatase and acid phosphatase activity may thus be considered a cytochemical marker to characterize and differentiate neutrophilic from acidophilic granulocytes in this fish species. Three granule populations are characterized in the cytoplasm of the gilthead seabream acidophils: the first is positive only for peroxidase and the second contains a dense core with acid and alkaline phosphatase activities, surrounded by a thin peroxidase positive electron-dense halo. The third granule type contains an eccentric core, which is strongly positive for acid and alkaline phosphatase and peroxidase. As regards their cytochemical features, the first and second granule types seem to correspond respectively to the azurophilic and specific granules found in acidophils of mammals and could be involved in phagocytic processes, thus playing an important microbicidal role in this species. The monocytes, monocyte-macrophages and macrophages show different cytochemical features. The first have scarce acid phosphatase-positive lysosomes, while blood monocyte-macrophages and macrophages are positive for acid and alkaline phosphatases and for peroxidase; the monocyte-macrophages show scarce lysosomes.

Tropical fish medicine. Fish cytology and hematology

Cytology and hematology can provide valuable information during the evaluation of fish patients. Although more commonly practiced with larger species of fish, hematologic evaluation aids in the identification of diseases that have an effect on the cells in peripheral blood in the same manner as in mammalian and avian patients. Cytology provides clinical diagnostic support in the evaluation of the health status of even the smallest fish.