Mosser D M, Edelson P J
J Immunol. 1984 Mar;132(3):1501-5.
When exposed to normal human or guinea pig sera, promastigotes of Leishmania enriettii and L. tropica activate the complement cascade by the alternative pathway and fix C3 on their surfaces. In high (25%) serum concentrations, the result of complement activation is parasite lysis. At lower concentrations (4%), complement fixation results in enhanced parasite binding and uptake into murine peritoneal macrophages. Parasites are lysed in normal guinea pig, C4-deficient guinea pig, normal human, and C2-deficient human sera when they are incubated at 37 degrees C for 30 min. Fetal calf and normal mouse sera are poorly lytic. Lysis requires Mg++ but not Ca++, is mediated by heat labile (56 degrees C, 30 min) component(s), and does not occur when the incubations are maintained at 4 degrees C. Guinea pig serum preadsorbed with promastigotes of L. tropica in EDTA at 4 degrees C for 30 min is fully lytic. Immunofluorescence studies with anti-C3 antibodies show that under these conditions C3 is deposited on the surface of the parasite. The serum-dependent binding of parasites to macrophages is also mediated by heat-labile, nonadsorbable factor(s) present in normal guinea pig and mouse sera, as well as C2-deficient and C4-deficient sera. The serum-dependent macrophage recognition mechanism is trypsin sensitive but relatively resistant to chymotrypsin. Parasites but not macrophages can be presensitized at room temperature with low levels (8%) of serum to enhance their binding to macrophages. Presensitization does not occur at 4 degrees C. These results show that Leishmania promastigotes of several species can fix complement by activating the alternative complement pathway. This may then result either in parasite lysis or in an accelerated uptake of the parasite into phagocytic cells. In vivo, the biologic outcome of infection may reflect a balance between extracellular lysis and enhanced uptake into phagocytic cells.
当利什曼原虫恩氏亚种和热带利什曼原虫的前鞭毛体暴露于正常人血清或豚鼠血清时，它们通过替代途径激活补体级联反应，并在其表面固定C3。在高血清浓度（25%）下，补体激活的结果是寄生虫裂解。在较低浓度（4%）下，补体固定导致寄生虫与小鼠腹腔巨噬细胞的结合和摄取增强。当寄生虫在37℃孵育30分钟时，它们在正常豚鼠血清、C4缺陷型豚鼠血清、正常人血清和C2缺陷型人血清中会被裂解。胎牛血清和正常小鼠血清的裂解能力较差。裂解需要Mg++而不是Ca++，由热不稳定成分（56℃，30分钟）介导，当孵育维持在4℃时则不会发生裂解。在4℃下用EDTA处理30分钟的热带利什曼原虫前鞭毛体预吸附的豚鼠血清具有完全的裂解能力。用抗C3抗体进行的免疫荧光研究表明，在这些条件下C3沉积在寄生虫表面。寄生虫与巨噬细胞的血清依赖性结合也由正常豚鼠和小鼠血清以及C2缺陷型和C4缺陷型血清中存在的热不稳定、不可吸附因子介导。血清依赖性巨噬细胞识别机制对胰蛋白酶敏感，但对胰凝乳蛋白酶相对抗性。寄生虫而非巨噬细胞可以在室温下用低水平（8%）的血清进行预致敏，以增强它们与巨噬细胞的结合。在4℃下不会发生预致敏。这些结果表明，几种利什曼原虫前鞭毛体可以通过激活替代补体途径来固定补体。这随后可能导致寄生虫裂解或加速寄生虫被吞噬细胞摄取。在体内，感染的生物学结果可能反映细胞外裂解和增强被吞噬细胞摄取之间的平衡。
