Immunocytochemical study of agglutinin synthesis in the haemocytes of the freshwater snailplanorbarius comeus(L.) (Gastropoda, Pulmonata)

Tissue distribution and levels of natural and induced serum lysozyme immunoreactive molecules in a freshwater snail

Lysozyme immunoreactive molecules (irLm) in Planorbarius corneus was demonstrated by an immunocytochemical method in oocytes, the kidney, spreading phagocytic hemocytes (SH), digestive phagocytic cells, and epithelial cells of the stomach and intestine. Three hr after the injection of a variety of bacteria or substances (S. aureus, E. coli, E. coli LPS, latex particles, PBS) a statistically significant increase in irLm serum level was detected by the microELISA method. Twenty-four hr later, this increase was detected only in specimens which had been injected with bacteria. A similar response was observed 14 days later, following a second injection of the above-mentioned substances in the same snails. The results suggest that: 1) irLm appears to be an inducible molecule responding non-specifically to foreign challenge; 2) no anamnestic response is observed for irLm; 3) a relationship exists between irLm and phagocytosis; indeed, irLm have chemotactic activity towards SH; 4) serum irLm probably originates from different sources; in fact, they are released from SH and the kidney. The increase in the serum irLm level is responsible, at least in part, for the lytic attack and death of bacteria, but it is probably also involved in unspecific inflammatory reactions.

Haemocytes of the cockle Cerastoderma glaucum: morphological characterisation and involvement in immune responses

For the first time, morpho-functional characterisation of haemocytes from the cockle Cerastoderma glaucum was performed to identify circulating cell types and to study their involvement in immune responses. Haemocyte mean number was 5.5 (x 10(5)) cells/mL haemolymph. Two main haemocyte types were found in haemolymph: granulocytes (85%), about 10 microm in diameter and with evident cytoplasmic granules, and hyalinocytes (15%), 8 to 14 microm in diameter, with a few or no granules. Most of the cytoplasmic granules stained in vivo with Neutral Red, indicating that they were lysosomes. On the basis of haemocyte staining properties, granulocytes and hyalinocytes were further classified as basophils and acidophils. Acidophil hyalinocytes were the largest haemocyte type (about 14 microm in diameter) and had an eccentric nucleus and a large cytoplasmic vacuole. Both granulocytes and hyalinocytes (except acidophils) were able to phagocytise yeast cells, although the basal phagocytic index was very low (about 2%). It increased significantly (up to 26%) after pre-incubation of yeast in cell-free haemolymph, suggesting that haemolymph has opsonising properties. Haemocytes also produced superoxide anion. Moreover, both granulocytes and hyalinocytes (except acidophils) were positive for some important hydrolytic and oxidative enzymes. Lysozyme-like activity was recorded in both cell-free haemolymph and haemocyte lysate, although enzyme activity in cell lysate was significantly higher. Results indicate that haemocytes from C. glaucum are effective cells in immune responses.

Air exposure and functionality of Chamelea gallina haemocytes: effects on haematocrit, adhesion, phagocytosis and enzyme contents

The Venus clam Chamelea gallina is fairly common along the western coasts of the Adriatic and is subjected to intense fishing. Since over the last 20 years extensive hypoxic and anoxic conditions have repeatedly damaged this natural resource, we decided to study the effects of anoxic stress on the functionality of clam haemocytes and the consequences on immune responses. Clams, exposed to air, close their valves and tissues become anoxic and metabolism processes switch to anaerobiosis. In these conditions, a significant decrease in the haematocrit value and in the percentage of acid phosphatase-positive haemocytes was observed, while the number of cells with beta-glucuronidase significantly increased after day 1. The above indices generally returned to control values when clams were re-immersed in seawater after 1 day of treatment. Clams exposed to air for 2 days and then re-immersed, attempted to recover in the subsequent 3 days. Animals had fully recovered on day 4. Three-day-exposed clams did not recover. Phagocytic and adhesion indices decreased significantly after the first day of air exposure. The change in frequency of three types of circulating cells (spreading, round, apoptotic) was also monitored.

Haemocytes of the clam Tapes philippinarum (Adams & Reeve, 1850): morphofunctional characterisation

Tapes philippinarum is a bivalve mollusc of the Pacific Ocean, successfully imported for human consumption into the northern Adriatic Sea (Europe). For better knowledge of its considerable adaptive ability in comparison with similar autochthonous species, a morpho-functional characterisation of its haemocytes was carried out with the establishment of short-term cell cultures (60 min at 25 degrees C). Various methods of cytochemical staining identified four cell types in the haemolymph: granulocytes (48.05% +/- 1.43), hyalinocytes (32.18% +/- 0.99), haemoblasts (18.97% +/- 0.63) and serous cells (0.8% +/- 0.19). The granulocytes, possessing cytoplasmic granules with differing dye affinity, included basophils, neutrophils and acidophils. Such granules stained vitally with Neutral Red, and correspond to lysosomes. Hydrolytic and oxidative enzymes were mainly detectable after stimulation in the presence of yeast cells. Both granulocytes and hyalinocytes were positive for alkaline phosphatase, non-specific esterase, peroxidase, and cytochrome C oxidase, whereas only granulocytes were positive for beta-glucuronidase, acid esterase, and arylsulphatase. Both cell types were competent phagocytes towards yeast and plasma had an opsonising effect. Moreover, the respiratory burst accompanied phagocytosis with superoxide anion production, recognisable through cytoplasmic deposits of formazan after treatment with nitro blue tetrazolium. Haemoblasts were small undifferentiated cells which, due to their morphology and positivity to the anti-CD34 antibody, show the typical features of stem cells. Serous cells, probably arising from Keber's gland and belonging to another differentiation pathway, contained non-sulphate acid mucopolysaccharides and play an important role in early defence mechanisms, taking part in the formation of clots.

Cytotoxicity and immunocyte markers in cells from the freshwater snail Planorbarius corneus (L.) (Gastropoda pulmonata): implications for the evolution of natural killer cells

The hypothesis that natural killer (NK) cells represent an important form of cell recognition and cytotoxicity leads to the prediction that NK-like activity should be preserved throughout phylogenetic development. This was tested in the invertebrate Planorbarius corneus. Two types of cells can be identified and separated from the hemolymph of this mollusc, i.e. glass-adherent macrophage-like spreading hemocytes (SH) and nonadherent round hemocytes (RH). Only RH are able to lyse the K-562 human target cell line in a short-term NK cytotoxicity test. This NK-like activity, severely reduced after 18 h incubation at 24 degrees C, is preserved by human recombinant interleukin 2. A further analysis of P. corneus hemocytes has been performed by using several mouse anti-human monoclonal antibodies and cytofluorimetric analysis. Unexpectedly, both SH and RH react with several monoclonal antibodies, including those directed against epitopes typical of mammalian NK cells and cell adhesion molecules. On the whole, these data support the hypothesis that a primitive NK-like activity appeared early in evolution and is not shared by phagocytic cells.

Immune mechanisms in trematode-snail interactions

Digenetic trematodes, including several species of medical and veterinary significance, nearly all depend on molluscs (usually gastropods) as hosts for asexual reproduction. The molluscan internal defence system, although lacking many of the familiar features of the vertebrate immune system, may pose a substantial obstacle to digenean development. In this article, Wil van der Knaap and Eric Loker discuss the manner in which this system is mobilized to kill larval trematodes and the real and putative mechanisms of digenean evasion of molluscan immune responses. These two possible outcomes of trematode-snail associations make them intriguing model systems for exploring processes of parasite infectivity and host resistance.

Immunodetection of haemocyte subpopulations by N-acetylmuramic acid antibody in Planorbarius corneus (L.) (Gastropoda, Pulmonata)

The cell subpopulations in the haemolymph of Planorbarius corneus were distinguished by means of flow cytometry. An antibody against N-acetylmuramic acid was prepared and used as a cellular marker to recognize the cell types forming the subpopulations. The spreading haemocytes showed a positive reaction for anti-N-acetylmuramic acid; round haemocytes gave a negative reaction.