The blood cells of the freshwater snail Planorbis corneus (Gastropoda, Pulmonata)

A Dissenters' View on AppleSnail Immunobiology

We stand as dissenters against the acceptance of scientific knowledge that has not been built on empirical data. With this in mind, this review synthesizes selected aspects of the immunobiology of gastropods and of apple snails (Ampullariidae) in particular, from morphological to molecular and "omics" studies. Our trip went through more than two centuries of history and was guided by an evo-devo hypothesis: that the gastropod immune system originally developed in the mesenchymal connective tissue of the reno-pericardial complex, and that in that tissue some cells differentiated into hematopoietically committed progenitor cells that integrate constitutive hemocyte aggregations in the reno-pericardial territory, whether concentrated in the pericardium or the kidney in a species-specific manner. However, some of them may be freed from those aggregations, circulate in the blood, and form distant contingent aggregations anywhere in the body, but always in response to intruders (i.e., pathogens or any other immune challenge). After that, we reviewed the incipient immunology of the Ampullariidae by critically revising the findings in Pomacea canaliculata and Marisa cornuarietis, the only ampullariid species that have been studied in this respect, and we attempted to identify the effectors and the processes in which they are involved. Particularly for P. canaliculata, which is by far the most studied species, we ask which hemocytes are involved, in which tissues or organs are integrated, and what cellular reactions to intruders this species has in common with other animals. Furthermore, we wondered what humoral factors could also integrate its internal defense system. Among the cellular defenses, we give an outstanding position to the generation of hemocyte nodules, which seems to be an important process for these snails, serving the isolation and elimination of intruders. Finally, we discuss hematopoiesis in apple snails. There have been contrasting views about some of these aspects, but we envision a hematopoietic system centered in the constitutive hemocyte islets in the ampullariid kidney.

Flow cytometric characterization of the hemocytes of sea hares from tidal pools in Jeju Island off the south coast of Korea

The members in the family Aplysidae known as sea hares play a crucial role as a grazer in small tidal pools or shallow subtidal hard bottoms. Like other marine gastropods, hemocyte types and functions of sea hares are limitedly known. This study identified and characterized the hemocytes of common Aplysia species Aplysia kurodai, A. juliana, and A. oculifera in rocky tidal pools in Jeju Island off the south coast of Korea using flow cytometry and light microscopy. The flow cytometry identified three different hemocytes in the hemolymph of the three sea hare species: granulocytes, hyalinocytes, and blast-like cells. The granulocytes exhibited pseudopodia on the cell surface and granules in the cytoplasm. Morphology of the hyalinocyte was similar to that of the granulocytes, while they lack cytoplasmic granules. The blast-like cells were small and round, with very thin cytoplasm. The hyalinocytes were the most abundant in the hemolymph, accounting for 89.8-92.6% of the total hemocytes. Flow cytometry indicated that the granulocytes and blast-like cells were less than 5.6% and 5.4% of the total hemocyte populations. Flow cytometry also revealed that the granulocytes and hyalinocytes are engaged in cellular defensive activities such as intra-cellular lysosomal content, phagocytosis, and ROS production. The mean lysosomal contents of the granulocytes (0.4 × 10⁵-0.2 × 10⁵ A U.) were 2-3 times higher than that of hyalinocytes (0.2 × 10⁵-0.6 × 10⁵ A U.). In addition, the ROS production of the granulocytes (0.98 × 10⁶-1.95 × 10⁶ A U.) was about twice higher than that of the hyalinocytes (0.62 × 10⁶-1.14 × 10⁶ A U.). Of the three species of sea hares, the granulocytes showed comparatively higher phagocytosis capacity (70.4-92.3%) than that of the hyalinocytes (34.8-46.0%). Flow cytometry and microscopy indicated that the hemocyte types and their functions were identical, regardless of the species.

Studies on acute and chronic toxicity of cadmium to freshwater snail Lymnaea acuminata (Lamarck) with special reference to behavioral and hematological changes

Molluscs have long been regarded as promising bioindicator and biomonitoring subjects for heavy metals as molluscs are highly tolerant to heavy metals and exhibit high accumulation in their body. In spite of several previous studies about the impact of cadmium on molluscs, little information exists in literatures concerning the toxic effects of cadmium on Lymnaea acuminata, especially pertaining to behavioral and hematological changes as these are considered effective bioindicators and biomonitoring variables for detecting heavy metals in polluted water bodies. In the present study, the median lethal concentrations of cadmium chloride to snail, Lymnaea acuminata, were estimated to be 9.66, 7.69, 6.26, and 5.54 mg/L at 24, 48, 72, and 96 h, respectively. For behavioral studies, variable test concentrations of cadmium from 0.00 to 10 mg/L were used. The clumping tendency, crawling activity, and touch reflex in the exposed snails were gradually decreased with higher concentrations at 72 and 96 h. For measuring the hemocyte numbers in the circulating hemolymph of snail during chronic cadmium exposure, two sublethal doses of cadmium (10 and 20% 96-h LC₅₀-0.55 and 1.11 mg/L, respectively) were used. A significant variation (p < 0.05) from the control at all exposure times (7, 14, 21, and 28 days) was recorded at 1.11 mg/L concentration. The total count of circulating hemocytes was significantly reduced (p < 0.05) compared to the controls at both concentrations of cadmium exposure at all time periods except 14 and 21 days exposure at 0.55 mg/L where values were non-significantly increased. In comparison between two sublethal doses, blood cells were significantly (p < 0.05) lowered at 1.11 mg/L cadmium treatment. Considering the behavioral and hematological data, it seems possible to forecast the physiological state of snails in cadmium-contaminated water bodies and these findings can be used in determining the safe disposal level of cadmium in aquatic ecosystem.

A prokineticin-like protein responds to immune challenges in the gastropod pest Pomacea canaliculata

The golden apple snail Pomacea canaliculata is an invasive pest originating from South America. It has already been found in Asia, the southern United States and more recently in the EU. Aiming to target the immune system of the snail as a way to control its spreading, we have developed organ-specific transcriptomes and looked for molecules controlling replication and differentiation of snail hemocytes. The prokineticin domain-containing protein Astakine 1 is the only cytokine known thus far capable of regulating invertebrate hematopoiesis, and we analyzed the transcriptomes looking for molecules containing a prokineticin domain. We have identified a prokineticin-like protein (PlP), that we called Pc-plp and we analyzed by real-time PCR (qPCR) its expression. In control snails, highest levels of Pc-plp were detected in the digestive gland, the ampulla (i.e., a hemocyte reservoir) and the pericardial fluid (i.e., the hematopoietic district). We tested Pc-plp expression after triggering hematopoiesis via multiple hemolymph withdrawals, or during bacterial challenge through LPS injection. In both cases a reduction of Pc-plp mRNA was observed. The multiple hemolymph withdrawals caused a significant decrease of Pc-plp mRNA in pericardial fluid and circulating hemocytes, while the LPS injection promoted the Pc-plp mRNA drop in anterior kidney, mantle and gills, organs that may act as immune barrier in molluscs. Our data indicate an important role for prokineticin domain-containing proteins as immunomodulators also in gastropods and their dynamic expression may serve as a biosensor to gauge the effectiveness of immunological interventions aimed at curtailing the spreading of the gastropod pest P. canaliculata.

Circulating phagocytes: the ancient and conserved interface between immune and neuroendocrine function

Immune and neuroendocrine functions display significant overlap in highly divergent and evolutionarily distant models such as molluscs, crustaceans, insects and mammals. Fundamental players in this crosstalk are professional phagocytes: macrophages in vertebrates and immunocytes in invertebrates. Although they have different developmental origins, macrophages and immunocytes possess comparable functions and differentiate under the control of evolutionarily conserved transcription factors. Macrophages and immunocytes share their pools of receptors, signalling molecules and pathways with neural cells and the neuro-endocrine system. In crustaceans, adult transdifferentiation of circulating haemocytes into neural cells has been documented recently. In light of developmental, molecular and functional evidence, we propose that the immune-neuroendocrine role of circulating phagocytes pre-dates the split of protostomian and deuterostomian superphyla and has been conserved during the evolution of the main groups of metazoans.

Immune Defenses of the Invasive Apple Snail Pomacea canaliculata (Caenogastropoda, Ampullariidae): Phagocytic Hemocytes in the Circulation and the Kidney

Hemocytes in the circulation and kidney islets, as well as their phagocytic responses to microorganisms and fluorescent beads, have been studied in Pomacea canaliculata, using flow cytometry, light microscopy (including confocal laser scanning microscopy) and transmission electron microscopy (TEM). Three circulating hemocyte types (hyalinocytes, agranulocytes and granulocytes) were distinguished by phase contrast microscopy of living cells and after light and electron microscopy of fixed material. Also, three different populations of circulating hemocytes were separated by flow cytometry, which corresponded to the three hemocyte types. Hyalinocytes showed a low nucleus/cytoplasm ratio, and no apparent granules in stained material, but showed granules of moderate electron density under TEM (L granules) and at least some L granules appear acidic when labeled with LysoTracker Red. Both phagocytic and non-phagocytic hyalinocytes lose most (if not all) L granules when exposed to microorganisms in vitro. The phagosomes formed differed whether hyalinocytes were exposed to yeasts or to Gram positive or Gram negative bacteria. Agranulocytes showed a large nucleus/cytoplasm ratio and few or no granules. Granulocytes showed a low nucleus/cytoplasm ratio and numerous eosinophilic granules after staining. These granules are electron dense and rod-shaped under TEM (R granules). Granulocytes may show merging of R granules into gigantic ones, particularly when exposed to microorganisms. Fluorescent bead exposure of sorted hemocytes showed phagocytic activity in hyalinocytes, agranulocytes and granulocytes, but the phagocytic index was significantly higher in hyalinocytes. Extensive hemocyte aggregates ('islets') occupy most renal hemocoelic spaces and hyalinocyte-like cells are the most frequent component in them. Presumptive glycogen deposits were observed in most hyalinocytes in renal islets (they also occur in the circulation but less frequently) and may mean that hyalinocytes participate in the storage and circulation of this compound. Injection of microorganisms in the foot results in phagocytosis by hemocytes in the islets, and the different phagosomes formed are similar to those in circulating hyalinocytes. Dispersed hemocytes were obtained after kidney collagenase digestion and cell sorting, and they were able to phagocytize fluorescent beads. A role for the kidney as an immune barrier is proposed for this snail.

Epigenetic modification in neurons of the mollusc Pomacea canaliculata after immune challenge

In human and rodents, the transcriptional response of neurons to stress is related to epigenetic modifications of both DNA and histone proteins. To assess the suitability of simple invertebrate models in studying the basic mechanisms of stress-related epigenetic modifications, we analyzed epigenetic modifications in neurons of the freshwater snail Pomacea canaliculata after the injection of Escherichia coli-derived lipopolysaccharide (LPS). The phospho-acetylation of histone H3, together with the induction of stress-related factors, c-Fos and HSP70, were evaluated in large and small neurons of the pedal ganglia of sham- and LPS-injected snails. Immunocytochemical investigations showed that after LPS injection, the immunopositivity towards phospho (Ser10)-acetyl (Lys14)-histone H3 and c-Fos increases in the nuclei of small gangliar neurons. Western blot analysis confirmed a significant increase of phospho (Ser10)-acetyl (Lys14)-histone H3 in nuclear extracts from 2h LPS-injected animals. c-Fos protein levels were significantly augmented 6h after LPS injection. Immunocytochemistry and western blot indicated that no changes occurred in HSP70 distribution and protein levels. To our knowledge this is the first demonstration of epigenetic changes in molluscan neurons after an immune challenge and indicate the gastropod P. canaliculata as a suitable model for evolutionary and translational studies on stress-related epigenetic modifications.

Comparative analysis of circulating hemocytes of the freshwater snail Pomacea canaliculata

Molluscs are invertebrates of great relevance for economy, environment and public health. The numerous studies on molluscan immunity and physiology registered an impressive variability of circulating hemocytes. This study is focused on the first characterization of the circulating hemocytes of the freshwater gastropod Pomacea canaliculata, a model for several eco-toxicological and parasitological researches. Flow cytometry analysis identified two populations of hemocytes on the basis of differences in size and internal organization. The first population contains small and agranular cells. The second one displays major size and a more articulated internal organization. Light microscopy evidenced two principal morphologies, categorized as Group I (small) and II (large) hemocytes. Group I hemocytes present the characteristics of blast-like cells, with an agranular and basophilic cytoplasm. Group I hemocytes can adhere onto a glass surface but seem unable to phagocytize heat-inactivated Escherichia coli. The majority of Group II hemocytes displays an agranular cytoplasm, while a minority presents numerous granules. Agranular cytoplasm may be basophilic or acidophilic. Granules are positive to neutral red staining and therefore acidic. Independently from their morphology, Group II hemocytes are able to adhere and to engulf heat-inactivated E. coli. Transmission electron microscopy analysis clearly distinguished between agranular and granular hemocytes and highlighted the electron dense content of the granules. After hemolymph collection, time-course analysis indicated that the Group II hemocytes are subjected to an evident dynamism with changes in the percentage of agranular and granular hemocytes. The ability of circulating hemocytes to quickly modify their morphology and stainability suggests that P. canaliculata is endowed with highly dynamic hemocyte populations able to cope with rapid environmental changes as well as fast growing pathogens.

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.

Categorization of hemocytes of three gastropod species Trachea vittata (Muller), Pila globosa (Swainson) and Indoplanorbis exustus (Dehays)

Light microscopic observations were made on the hemocytes of three gastropod species namely Trachea vittata, Indoplanorbis exustus and Pila globosa. It revealed two basic types of hemocytes. They are agranulocytes and granulocytes. Agranulocytes are hyalinocytes which are round, unspread hemocytes and have a large nucleo-cytoplasmic ratio. Granulocytes are spreading hemocytes, forming numerous pseudopodia. For the purpose of differential counting, we present a categorization of the granulocytes into three sub-categories based on cell dimensions, nucleo-cytoplasmic ratio, distribution of granules in the cytoplasm and position of the nucleus. The smaller granulocytes are younger cells, and are termed Granulocytes I (Progranulocytes). The larger ones are fully developed cells that have been differentiated into Granulocyte II (basophilic) and Granulocyte III (eosinophilic).

Neutral endopeptidase-24.11 (NEP)-like activity in molluscan hemocytes

Using a spectrofluorimetric procedure, we found that the plasma membrane from hemocytes of two freshwater snails, Planorbarius corneus and Viviparus ater, shows neutral endopeptidase-24.11 (NEP)-like activity. Moreover, the addition of ACTH(1-24) to the hemolymph provokes an increase in NEP-like activity. This increased NEP-like activity is blocked by phosphoramidon, a potent inhibitor of mammalian NEP. These findings suggest that this peptidase has been well conserved in the course of evolution and plays an important role in immune-neuroendocrine mechanisms.

Presence of casein immunoreactive epitopes in molluscs, fish and frog

The presence of a group of peptides derived from milk proteins (caseins) was examined by immunocytochemistry in various tissues from invertebrates and lower vertebrates. Phagocytic hemocytes from different species of molluscs, and cells located in the intestine wall or in related glands of invertebrates and lower vertebrates showed immunoreactivity to antibodies to whole casein and related fragments. Several functional tests (cell migration, inhibition test, phagocytosis) using these peptides were performed on the mollusc hemocytes. Only ovine caseinoglycopeptide was able to increase the phagocytic activity of the hemocytes towards bacteria.

Induction of ACTH- and TNF-alpha-like molecules in the hemocytes of Calliphora vomitoria (Insecta, Diptera)

Three basic cell types are described in the hemolymph of newly enclosed adult Calliphora vomitoria: prohemocytes, plasmatocytes, and granular cells. In addition, anucleate cellular fragments with some inclusions are observed. Cell division is found only in the prohemocytes. Plasmatocytes and granular cells are capable of in vitro bacterial phagocytosis and take part in capsule formation. Adrenocorticotropin hormone (ACTH)-like molecules are found in both cell types. The staining of the plasmatocytes is related to the functional activation of the cells. Indeed, positive staining is only observed during capsule formation, suggesting an induction of ACTH expression. The behaviour of tumor necrosis factor (TNF)-alpha-like molecules is similar. In conclusion, these data provide further support for the close, evolutionary relationship between the immune and the neuroendocrine systems.

Immunocytochemical evidence of PDGF- and TGF-beta-like molecules in invertebrate and vertebrate immunocytes: an evolutionary approach

Immunoreactive platelet-derived growth factor-AB and transforming growth factor-beta 1 were demonstrated in invertebrate and vertebrate immunocytes by an immunocytochemical procedure. These factors are only present in phagocytic cells among invertebrate immunocytes, whereas in vertebrate immunocytes they are found in monocytes, granulocytes, lymphocytes, thrombocytes and platelets. These results, in agreement with previous reports, represent further evidence in favour of the hypothesis that Nature has followed a conservative strategy in using a common pool of signal molecules that have been highly conserved throughout evolution.

Nitric oxide synthase activity in molluscan hemocytes

The hemocytes of the freshwater snail Viviparus ater have nitric oxide synthase (NOS) activity, as demonstrated by [3H]citrulline and nitrite + nitrate formation. The enzyme is NADPH dependent and is competitively inhibited by the mammalian NOS inhibitor NG-monomethyl-L-arginine (Ki = 4.7 microM). The Km for L-arginine is 2.5 microM. 70% of the total activity is observed at very low free Ca2+ concentration (3 nM). LPS treatment increased total NOS activity 2.4 fold. The activity is partly present in the non-soluble fraction of hemocytes (24% and 8% in non-stimulated and LPS-stimulated snails, respectively). An antiserum to the C-terminal synthetic pentadecapeptide of the rat cerebellar NOS inhibited the enzyme activity in a concentration-dependent manner. This is the first biochemical demonstration of the existence of NOS activity in molluscan hemocytes, the cells responsible for defence mechanisms.

Antagonizing effect of morphine on the mobility and phagocytic activity of invertebrate immunocytes

In the present study we have demonstrated that lipopolysaccharide (LPS) acts as an activator in the immunocytes of molluscs Planorbarius corneus, Mytilus edulis, and the insect Leucophaea maderae. This stimulatory effect, demonstrated by cellular conformational changes, is concentration- and time-dependent, and is antagonized by morphine. The inhibitory effect of morphine can be counteracted by naloxone. Morphine inhibitory action on immunocyte activity is also demonstrated by a decrease in the phagocytic activity. These data suggest that the downregulation of morphine is not limited to vertebrates but is also present in invertebrates.

Relationship between corticotropin-releasing factor and interleukin-2: evolutionary evidence

The addition of corticotropin-releasing factor (CRF) to molluscan hemocytes induces the release of biogenic amines (norepinephrine, epinephrine, dopamine), a phenomenon we have considered as an ancestral type of stress response [(1992) Gen. Comp. Endocrinol. 87, 354-360]. A similar but less significant response was observed following the addition of interleukin-2 (IL-2). Pre-incubation of hemocytes with IL-2 or anti-IL-2 monoclonal antibody significantly reduced or completely eliminated the CRF-induced release of biogenic amines. Further direct evidence of competition between CRF and IL-2 was revealed by immunocytochemical and cytofluorimetric analysis. The data are compatible with the presence of a unique (ancestral?) receptor on molluscan hemocytes, capable of binding both CRF and IL-2, two key molecules of the neuroendocrine and immune system, respectively.

Differential modulation of invertebrate hemocyte motility by CRF, ACTH, and its fragments

Various reports have shown that invertebrate hemocytes are responsive to mammalian neuropeptides and cytokines. In the present study, we demonstrate that corticotropin-releasing factor (CRF) and adrenocorticotropin (ACTH) fragments (1-24), (1-4), (4-9), (1-13), (1-17), and (11-24) significantly stimulate molluscan hemocyte migration, and the whole sequence (1-39) and the fragment (4-11) have an inhibitory effect. Differences between species were found with respect to the response to individual fragments. Additionally, the (4-11) fragment was able to antagonize some of the stimulatory fragments (4-9) as well as tumor necrosis factor (TNF-alpha)-induced chemotaxis. Our results suggest that invertebrate hemocytes are able to respond to CRF and ACTH fragments that in turn provide further evidence of the complexity of intercellular signaling within the immune system in relatively primitive animals. Thus, auto- and neuroimmunoregulatory activities in mammals must have had an earlier beginning than previously believed.

Evidence for nitric oxide production and utilization as a bacteriocidal agent by invertebrate immunocytes

The present study demonstrates that molluscan immunocytes are able to produce a chemical bacteriocidal substance which can be indirectly identified as nitric oxide (NO). The cells were analyzed in vitro on slides using computer-assisted microscopic image analysis to detect changes in cell conformation as well as to quantify the number of bacteria present. Sodium nitroprusside yields NO in solution causing bacterial clumping. The same phenomenon occurs in the presence of invertebrate immunocytes. Escherichia coli lipopolysaccharide also increases the number of bacteria found around the immunocytes, but this effect is selectively prevented by the addition of inhibitors of nitric oxide synthase, suggesting that this bacterial clumping is caused by the cells liberating NO. Interestingly the cells presumably producing NO maintain a round morphology. These findings suggest that immunocytes are able to kill bacteria by two mechanisms, i.e., phagocytosis and NO production.

Morphological aspects of Achacin-treated bacteria

1. The morphology of bacteria treated with the bactericidal glycoprotein, Achacin, purified from the giant African snail, Achatina fulica Férussac, has been studied. 2. Achacin lengthens the bodies of Escherichia coli by three to seven times. 3. Achacin damages the surface of Staphylococcus aureus and sinks the cytoplasmic membranes into the cytoplasm. 4. Achacin causes neither the leakage nor the destruction of cells.

Molecular cloning of the antibacterial protein of the giant African snail, Achatina fulica Férussac

An expression cDNA library was constructed with poly(A)-rich RNA extracted from the collar of the giant African snail, Achatina fulica Férussac. A 1.9-kbp cDNA clone encoding a precursor of antibacterial glycoprotein of the snail, achacin, was isolated from the cDNA expression library. The cDNA sequence contains an open reading frame with 1593-nucleotide residues. The deduced amino acid sequence of this achacin precursor starts with a 29-residue leader peptide followed by a 502-residue mature peptide (56 kDa) with four possible N-glycosylation sites, Asn-Xaa-Ser or Asn-Xaa-Thr. The Northern-blot analysis proved that the achacin precursor was specifically expressed in the tissue of snail collar and processed to mature achacin. cDNA inserts encoding achacin precursor were subcloned into expression plasmids. Three kinds of expressed polypeptides were cross-reacted with rabbit antiserum raised against achacin. The largest polypeptide (M(r) 63,000) should be the achacin precursor.

Stress response in the freshwater snail Planorbarius corneus (L.) (Gastropoda, Pulmonata): interaction between CRF, ACTH, and biogenic amines

Previous studies reported that ACTH molecules influence chemotactic and phagocytic activities of hemocytes in the freshwater snail, Planorbarius corneus. The present study reveals that ACTH and CRF affect the release of biogenic amines. Hemocytes from P. corneus hemolymph incubated in vitro with ACTH for 15, 30, and 45 min released epinephrine, norepinephrine, and dopamine. The greatest release occurred after 15 min, while after 45 min the values were similar to those of the controls. Similar incubations with CRF also provoked a release of biogenic amines, this being mainly mediated by the release of endogenous ACTH. These data suggest that (i) ACTH and CRF provoke the release of biogenic amines; (ii) there is a direct relationship between CRF, ACTH, and biogenic amines, with the hemocytes as the target; (iii) exogenous ACTH can mimic an ancestral type of stress response; (iv) the major pathway of the stress response in P. corneus is mediated by a CRF-ACTH-biogenic amine axis. These data should help to unravel part of the complex molecular signaling mechanisms involved in the physiological/endocrinological reaction of invertebrate organisms to stress, and suggest that a stress response unexpectedly similar to that present in mammalian cells is detectable in invertebrates.

Bactericidal action of a glycoprotein from the body surface mucus of giant African snail

1. Bactericidal action of a glycoprotein, Achacin, purified from the giant African snail, Achatina fulica Férussac, has been studied. 2. Achacin kills both gram-positive and gram-negative bacteria, but only in their growing states. 3. Achacin does not have any bacteriolytic activity. 4. The strain which has no cell wall is a little more sensitive than the native strain and the cell membrane-damaged strain. 5. Achacin was observed on the cytoplasmic membrane and on the cell wall of treated Escherichia coli by immunoelectron microscopy. 6. Achacin attacks the cytoplasmic membrane of the cell.

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.

N-acetylmuramic acid in Mollusca Gastropoda: a histochemical and immunocytochemical study

The presence of N-acetylmuramic acid in glycoconjugates in various mollusc tissues was investigated by histochemical and immunocytochemical techniques. The tissues studied included foot, mantle, digestive gland, ganglia and haemocytes of Helix aspersa, Planorbarius corneus, Murex brandaris and Trunculariposis trunculus. Sialic acid residues were found to be absent. The possibility that N-acetylmuramic acid replaces sialic acid in acid glycoconjugates of gastropods with similar properties is discussed.

Immunocytochemical evidence of vertebrate bioactive peptide-like molecules in the immuno cell types of the freshwater snail Planorbarius corneus (L.) (Gastropoda, Pulmonata)

An immunocytochemical investigation was carried out on round and spreading hemocytes of Planorbarius corneus by using 20 antisera to vertebrate bioactive peptides. The immunotests showed the presence of alpha 1-antichymotrypsin-bombesin-, calcitonin-, CCK-8 (INC)-, CCK-39-, gastrin-, glucagon-, Met-enkephalin-, neurotensin-, oxytocin-, somatostatin-, substance P-, VIP-, and vasopressin-immunoreactive molecules in the spreading hemocytes. The round hemocytes were only positive to anti-bombesin, anticalcitonin, anti-CCK-8 (INC), anti-CCK-39, anti-neurotensin, anti-oxytocin, anti-substance P and anti-vasopressin antibodies. No immunostaining was observed with anti-CCK-8 (Peninsula), anti-insulin, anti-prolactin, anti-thyroglobulin and anti-thyroxin (T4) antibodies. As probably in vertebrates, these bioactive peptides may modulate immuno cell function.

Presence of ACTH and beta-endorphin immunoreactive molecules in the freshwater snail Planorbarius corneus (L.) (Gastropoda, Pulmonata) and their possible role in phagocytosis

The presence of ACTH and beta-endorphin immunoreactive molecules in the cell-free hemolymph and in the hemocytes of the freshwater snail Planorbarius corneus were demonstrated by immunocytochemistry and RIA tests. Only spreading phagocytic hemocytes were positive, in contrast with other hemocytes devoid of phagocytic activity, i.e., round hemocytes. These data were confirmed by flow cytometry. Another cell type with marked phagocytic activity, i.e., digestive cells of digestive gland, were also positive to anti-ACTH. Corticotropin-releasing factor immunoreactive molecules were found in the cell-free hemolymph and hemocytes, by RIA. Our data suggest that cells with phagocytic activity, the oldest immune response, may represent a suitable model to unravel the tangled web of the common ancestor of the immune and the neuroendocrine systems.

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.

Selected decrease of haemocytes of the freshwater snail Planorbarius corneus (L.) (Gastropoda, Pulmonata) after bacteria injection

The decrease of haemolymph phagocytic cells (SH) in Planorbarius corneus after bacterial injection seems to be mediated by humoral factor(s) released into the haemolymph. SH show different adhesiveness in vitro in the presence of bacterial metabolic products.