Kathleen H. Jeong

The ultrastructure of the amebocyte-producing organ in Biomphalariaglabrata

The amebocyte-producing organ (APO) in normal and echinostome-sensitized Biomphalaria glabrata was studied at the ultrastructural level. The APO in unexposed snails consists of small clusters of primary ameboblasts resting on the epithelial cells lining the pericardium. The ameboblasts are held in a loose reticulum formed by extensions from smooth muscle and few fibroblastic cells. Secondary ameboblasts and amebocytes constitute further stages of this cell line. Amebocytes, resembling cells in the snails circulation, appear in the blood sinus coursing through the interior of the APO. Exposure of snails to echinostome miracidia results in significant morphological changes in the organ. Large clusters of primary and and secondary ameboblasts appear, many of these cells undergoing mitosis. Fully activated APOs consist of masses of cells loosely arranged in zones of progressive maturation. Blood cells in activated APOs were significantly larger than those seen in normal APOs.

Tissue reactions induced by Schistosoma mansoni in Biomphalaria glabrata.

In Biomphalaria glabrata with a strong natural resistance, Schistosoma mansoni sporocysts are rapidly encapsulated by granulocytes and killed, mainly by the strong phagocytic activity of the cells. Irradiated Echinostoma paraensei sporocysts seem able to suppress the function of the granulocytes. Tissue reactions in snails with self-cure demonstrate: involvement of two types of cells, granulocytes and hyalinocyte-like cells; formation of amoeba-fibrous capsules; limited tendency of granulocytes to become attracted to the parasites; a slow process of parasite destruction; and a possible involvement of humoral factors. It seems that there is partial suppression of the granulocyte function in smails with self-cure.

Studies on resistance in snails. 7. Evidence of interference with the defense reaction in Biomphalaria glabrata by trematode larvae.

Echinostoma lindoense sporocysts that develop from irradiated miracidia normally are destroyed by amebocyte capsules in the ventricle of Biomphalaria glabrata within 10 days postexposure. The survival period of these ventricular sporocysts was considerably longer in snails that also harbored normal sporocysts of E. lindoense, Paryphostomum segregatum, or Schistosoma mansoni. Protection of irradiated E. lindoense sporocysts by the same of different trematode species is presumed to be the result of an active process by which normal sporocysts interfere with capsule formation and protect themselves and other trematode larvae from encapsulation. Homologous protection was stronger than heterologous.

Leucocytosis in Biomphalaria glabrata sensitized and resensitized to Echinostoma lindoense

Leucocytosis was shown to occur in the pulmonate gastropod Biomphalaria glabrata exposed to the trematode Echinostoma lindoense. In these sensitized snails, the leukocyte count in the hemolymph was elevated 3 to 5 days postexposure to miracidia, and prior to complete encapsulation of sporocysts. This increase continued 1 to 5 days after destruction of sensitizing, irradiated E. lindoense sporocysts. Counts returned to normal levels after this period. A significant and more rapid increase in numbers of circulating leukocytes occurred 1 to 6 hr after reexposure of snails to a sensitizing dose of nonirradiated E. lindoense sporocysts. The leukocyte counts usually returned to normal levels after this period, except in snails in which some resensitizing sporocysts remained alive.

Acquired resistance in snails. Induction of resistance to Schistosoma mansoni in Biomphalaria glabrata

Abstract Acquired resistance to Schistosoma mansoni PR-I strain has been induced in Biomphalaria glabrata 442132 strain by infecting the snails with irradiated homologous miracidia. Present and previous results support the hypothesis that acquired resistance to trematodes in snails is an enhancement of the hosts natural resistance to the parasite.

FURTHER CHARACTERIZATION OF ACQUIRED RESISTANCE IN BIOMPHALARIA GLABRATA

The albino strain of Biomphalaria glabrata is capable of developing an acquired resistance to echinostomes that is relatively specific, i.e., strong against Echinostoma lindoense, challenged by the homologous species, moderate or weak against closely related E. paraensei and E. liei, and nonexistent against Paryphostomum segregatum and Schistosoma mansoni. The present results show that acquired resistance induced by E. paraensei is much stronger against the heterologous E. lindoense than against the homologous species. These observations indicate that although the response of snails with acquired resistance to a challenge exposure is relatively specific, the stimuli for inducing that resistance may be nonspecific.

SELECTIVE INTERFERENCE WITH GRANULOCYTE FUNCTION INDUCED BY ECHINOSTOMA PARAENSEI (TREMATODA) LARVAE IN BIOMPHALARIA GLABRATA (MOLLUSCA)

Various trematode larvae can interfere with the host snails resistance to the same or unrelated trematode species, chiefly, it appears by interference with the function of the hosts granulocytes. In Biomphalaria glabrata infected with the trematodes, Echinostoma paraensei, granulocytes lose their ability to encapsulate the larvae of trematodes to which the hosts were previously resistant. However, the granulocytes in these snails retain their ability to encapsulate injected latex spheres, or larvae of the metastrongyle nematode, Angiostrongylus malaysiensis, and to phagocytose epidermal plates cast off by miracidia of the trematode, Schistosoma mansoni. Cellular infiltration in injured preputial tissue of the snail also was not suppressed by the presence of E. paraensei larvae. Interference with the granulocyte function in B. glabrata induced by E. paraensei infection therefore appears to be a selective phenomenon.

Distribution and variation of hemagglutinating activity in the hemolymph of Biomphalaria glabrata.

Abstract A sensitive hemagglutination assay utilizing glutaraldehyde-fixed trypsinized calf erythrocytes (GTC) is described to test for agglutinin levels in hemolymph and albumen gland extracts from nine populations of Biomphalaria glabrata , and from B. straminea and B. obstructa . High levels of GTC-reactive hemagglutinin were found in all snail populations. There was no correlation between hemagglutinin titer and innate resistance of B. glabrata strains to Schistosoma mansoni . However, an increase in hemagglutinin titer occurs in B. glabrata M-RLc snails infected with Echinostoma lindoense and in snails sensitized and reexposed to this parasite.

Enzyme histochemical comparison of biomphalaria glabrata amebocytes with human granuloma macrophages.

In fresh water snails, amebocytes are the principal cells that react to parasitic infection. Ultrastructurally, amebocytes resemble mammalian macrophages. To clarify the relationship between amebocytes and macrophages, we compared the histochemical staining for seven enzymes in Biomphalaria glabrata snail amebocytes, both in the amebocyte‐producing organ (APO) and in the encapsulation reaction formed around parasite sporocysts with the staining in macrophages from the lymph nodes of patients with sarcoid or tuberculosis. Snails were infected with Echinostoma paraensei and Schistosoma mansoni miracidia. APOs and ventricular tissue with encapsulated parasites were fixed and embedded in glycol methacrylate monomer. Hardened blocks were sectioned at 2 μ m and stained for alkaline phosphatase, acid phosphatase, α‐ naphthyl acetate esterase (ANAE), ATPase, peroxidase, 5′nucleotidase, and chloroacetate esterase. The amebocyte‐producing organ contained cells that were positive for acid phosphatase, ANAE, and ATPase. Amebocytes in the capsules formed around echinostome sporocysts showed stronger staining for the same three enzymes. Capsules did not form around schistosome sporocysts, but the connective tissue around them contained numerous amebocytes that were also positive for these three enzymes. The amebocyte enzyme histochemistry resembled that in human granuloma macrophages, but differed from that in neutrophils. The increased expression of enzymes in amebocytes involved in the encapsulation reaction as compared to those in the APO was reminiscent of the alterations observed when human monocytes convert to tissue macrophages. These studies support the hypothesis that the amebocyte is an “invertebrate macrophage.”

Inducement of miracidia-immobilizing substance in the hemolymph of Biomphalaria glabrata

Abstract Lie K. J. , Jeong K. H. and Heyneman D. 1980. Inducement of miracidia-immobilizing substance in the hemolymph of Biomphalaria glabrata . Intemational Journal for Parasitology 10 : 183–188. More than 85% of echinostome-infected albino B. glabrata laboratory strain snails develop miracidia-immobilizing substance(s) (MIS) in the hemolymph, while less than 5% of control uninfected snails show this ability. Snails infected with Echinostoma lindoense show a strong miracidial immobilizing test (MIT) when homologous miracidia are exposed to the hemolymph and a moderate response when E. liei and Paryphostomum segregatum miracidia are used. Infection with E. paraensei results in a high level of hemolymph MIS with E. lindoense miracidia, a moderate one with P. segregatum miracidia, and a weak one when hemolymph is tested against E. liei as well as the homologous E. paraensei miracidia. Infection with E. liei induces a strong MIT with E. lindoense miracidia whereas only a moderate one was observed when using homologous or P. segregatum miracidia. Infection with P. segregatum gives a moderate MIT reaction to miracidia of the homologous species, as well as to E. lindoense and E. liei , and only a weak response to E. paraensei miracidia. Infection with S. mansoni fails to induce hemolymph that shows MIS to any of the parasites tested. Production of hemolymph MIS is temporary. It begins one day postexposure, reaches its maximum 10–14 days postexposure, and declines to the preinfection level several weeks later. Infection of snails with irradiated parasites also results in a temporary production of hemolymph MIS. Uninfected snails show a tissue-extract MIS, which is especially strong when digestive gland extracts are used. However, these snails give little or no evidence of a hemolymph MIS.