Loker E S, Cimino D F, Stryker G A, Hertel L A
Department of Biology, University of New Mexico, Albuquerque 87131.
J Parasitol. 1987 Dec;73(6):1090-8.
M line Biomphalaria glabrata snails of 4-, 6-, 8-, 10-, 12-, or 20-mm shell diameter were individually exposed to 10 miracidia each of Echinostoma paraensei. Snails 10 mm in size or larger were found to be significantly less likely to harbor intraventricular sporocysts than snails in smaller size categories. The percentage of snails with intraventricular sporocysts that also developed hemocyte encapsulation responses generally increased with snail size, whereas the number of snails that ultimately became heavily parasitized with large numbers of daughter rediae decreased significantly with snail size. However, at least some snails in each size category developed such disseminated infections. Comparative histological study of 6- and 12-mm snails revealed that parasites readily penetrated both groups of snails, but were more likely to be encapsulated and destroyed in larger snails. Encapsulation reactions were noted from 1 to 15 days postexposure (dpe) in 12-mm snails, indicating that unlike other commonly studied models of trematode-gastropod interactions, snail resistance is not always manifested during the first few days following exposure. Upon infection with E. paraensei, both 6- and 12-mm snails showed significant increases in the number of circulating hemocytes/mm3 of hemolymph. In 6-mm snails, such increases occurred concurrently with successful parasite development. Hemocyte counts in 6-mm snails were significantly elevated from 4 to 15 dpe whereas in 12-mm snails they were significantly elevated from 2 to 30 dpe. A significant degree of resistance to E. paraensei develops as B. glabrata grows and attains sexual maturity. A mechanistic understanding of this phenomenon awaits further investigation.
M线 将壳直径为4毫米、6毫米、8毫米、10毫米、12毫米或20毫米的光滑双脐螺个体分别暴露于10个来自帕氏棘口吸虫的毛蚴中。发现壳尺寸为10毫米或更大的螺比更小尺寸类别的螺容纳脑室内孢子囊的可能性显著更低。脑室内有孢子囊且还产生血细胞包囊反应的螺的百分比通常随螺的尺寸增加，而最终被大量子雷蚴严重寄生的螺的数量随螺的尺寸显著减少。然而，每个尺寸类别中至少有一些螺发生了这种播散性感染。对6毫米和12毫米螺的比较组织学研究表明，寄生虫很容易穿透这两组螺，但在较大的螺中更有可能被包囊并破坏。在暴露后1至15天（dpe）在12毫米的螺中观察到包囊反应，这表明与其他常见研究的吸虫 - 腹足动物相互作用模型不同，螺的抗性并不总是在暴露后的头几天表现出来。感染帕氏棘口吸虫后，6毫米和12毫米的螺血淋巴中每立方毫米循环血细胞的数量均显著增加。在6毫米的螺中，这种增加与寄生虫的成功发育同时发生。6毫米螺的血细胞计数在暴露后4至15天显著升高，而12毫米螺的血细胞计数在暴露后2至30天显著升高。随着光滑双脐螺生长并达到性成熟，对帕氏棘口吸虫产生了显著程度的抗性。对这一现象的机制理解有待进一步研究。
