Jansen A M, Leon L, Machado G M, da Silva M H, Souza-Leão S M, Deane M P
Department of Protozoology, Institute Oswaldo Cruz, Rio de Janeiro, Brazil.
Exp Parasitol. 1991 Oct;73(3):249-59. doi: 10.1016/0014-4894(91)90096-f.
The opossum Didelphis marsupialis is known to be among the most important wild reservoirs of Trypanosoma cruzi and one in which the trypanosome may go through both the usual vertebrate intracellular cycle in its tissues and an extracellular cycle in the lumen of its scent glands. The species is highly resistant to heavy inocula and, depending on the parasite strain, experimental infections may be permanent or self limited. Aiming to understand the mechanisms involved in this parasite-host interaction we made a study of the acute phase of infection with different T. cruzi strains. Strains F, G-49 and G-327 produced durable infections with relatively high parasitemia and invasion of the scent glands, while equivalent inocula of the Y strain resulted in scanty parasitemia of short duration, no invasion of the SG, and no evidence of persistent parasitism. A smaller inoculum of G-49 produced only subpatent though persistent parasitemia and no invasion of the scent glands. The humoral immune response was less marked in the Y group; among the other groups IgM and IgG antibodies increased to high levels, higher in the G-49 group. The increase in IgG coincided with a drop of parasitemia to subpatent levels. Two opossums inoculated directly in the scent glands with culture forms of the Y strain had a short-lived subpatent parasitemia, but the parasites remained in the glands and serum Ig antibodies reached high levels. Immunoblot analysis showed that the sera of the inoculated opossums recognized few T. cruzi antigens (more in the F strain) in comparison with those of mice. However, with the only exception of those subcutaneously inoculated with the Y strain and including two naturally infected specimens, all the opossum's sera recognized a 90-kDa peptide in all T. cruzi strains. Our results confirm that opossums are able to selectively eliminate some strains of T. cruzi and indicate that the mechanism involved in this selection is probably not related to the humoral immune response. In infections by strains that are able to establish a permanent foothold in opossum tissues, there are indications that IgG antibodies participate in the control of the parasite population of the acute phase but are unable to prevent the chronic phase. It was once more demonstrated that the opossum infected scent glands function as diffusion chambers for parasite antigens but that, on the other hand, the parasites are here protected against the mechanisms developed by the host to control their population.
负鼠（Didelphis marsupialis）是已知的克氏锥虫最重要的野生宿主之一，在其体内，锥虫可在组织中经历常见的脊椎动物细胞内循环，并在其气味腺管腔内经历细胞外循环。该物种对大量接种具有高度抗性，根据寄生虫菌株的不同，实验性感染可能是永久性的或自限性的。为了了解这种寄生虫与宿主相互作用的机制，我们对不同克氏锥虫菌株感染的急性期进行了研究。F、G - 49和G - 327菌株产生了持久感染，伴有相对较高的寄生虫血症和气味腺的侵袭，而等量接种的Y菌株导致短暂的少量寄生虫血症，没有气味腺的侵袭，也没有持续寄生的证据。较小剂量的G - 49接种仅产生亚临床但持续的寄生虫血症，且没有气味腺的侵袭。Y组的体液免疫反应不太明显；在其他组中，IgM和IgG抗体升高到高水平，G - 49组更高。IgG的增加与寄生虫血症降至亚临床水平同时发生。两只直接用Y菌株培养形式接种到气味腺的负鼠出现了短暂的亚临床寄生虫血症，但寄生虫留在腺体内，血清Ig抗体达到高水平。免疫印迹分析表明，与小鼠相比，接种负鼠的血清识别的克氏锥虫抗原较少（F菌株中较多）。然而，除了皮下接种Y菌株的负鼠（包括两个自然感染的标本）外，所有负鼠的血清在所有克氏锥虫菌株中都识别一种90 kDa的肽。我们的结果证实负鼠能够选择性地清除一些克氏锥虫菌株，并表明参与这种选择的机制可能与体液免疫反应无关。在能够在负鼠组织中永久立足的菌株感染中，有迹象表明IgG抗体参与急性期寄生虫数量的控制，但无法预防慢性期。再次证明，感染的负鼠气味腺起到寄生虫抗原扩散室的作用，但另一方面，寄生虫在此受到保护，免受宿主为控制其数量而产生的机制的影响。
