The presence of different derivatives of sialic acids (SA) on Leishmania donovani instigated us to investigate their status on different strains of Leishmania sp. causing different forms of the disease. Leishmaniatropica (K27), Leishmaniamajor (JISH118) and Leishmaniamexicana (LV4) responsible for cutaneous, Leishmaniabraziliensis (L280) and Leishmaniaamazonensis (LV81) causing diffuse and Leishmaniainfantum (MON29) responsible for visceral leishmaniasis were included in this study. The strains showed a differential distribution of SA in spite of their close resemblance in pathogenesis. K27, JISH118, L280 and MON29 were categorized as high SA-containing strains having enhanced 9-O-acetyl sialic acid (9-O-AcSAhigh) whereas LV4 and LV81 evidenced considerably reduced SA. Interestingly, 9-O-AcSAhigh promastigotes showed significant viability as compared to their de-O-acetylated forms after exposure to NaNO2 suggesting the involvement of 9-O-AcSA in conferring nitric oxide (NO) resistance. Enhanced intracellular survivability was demonstrated following infection of human macrophages with 9-O-AcSAhigh promastigotes in contrast to their de-O-acetylated forms indicating their contribution in bestowing a survival benefit. Additionally, reduced accumulation of NO, interleukin-12 and interferon-γ in the supernatant of macrophages infected with 9-O-AcSAhigh promastigotes indicated suppression of leishmanicidal host responses. However, LV4 and LV81 with least 9-O-AcSA, before and after de-O-acetylation, showed unaltered NO resistance, multiplicity and host responses signifying the probable involvement of other determinants which may be a function of their inherent parasitic attribute. Hence, enhanced levels of 9-O-AcSA serve as one of the potential determinants responsible for increased NO resistance and survivability of parasites by inhibition of host responses.
由于在多诺万利什曼原虫(Leishmania donovani)上发现了不同的
唾液酸(
SA)衍
生物,因此我们研究了它们在引起不同形式疾病的不同利什曼原虫菌株上的状况。本研究包括引起皮肤利什曼病的 Leishmaniiatropica (K27)、Leishmaniiamajor (JISH118) 和 Leishmaniamexicana (LV4),引起弥漫性利什曼病的 Leishmaniabraziliensis (
L280) 和 Leishmaniaamazonensis (LV81),以及引起内脏利什曼病的 Leishmaniainfantum (MON29)。尽管这些菌株的致病机理十分相似,但它们的
SA 分布却各不相同。K27、JISH118、
L280和MON29被归类为高
SA含量菌株,它们的9-O-乙酰基Sialic酸(9-O-Ac
SAhigh)含量较高,而LV4和LV81的
SA含量则大大降低。有趣的是,在暴露于 NaNO2 后,9-O-Ac
SAhigh 原核细胞的存活率明显高于其去 O-乙酰化形式,这表明 9-O-Ac
SA 参与了
一氧化氮(NO)抗性的赋予。与去 O-乙酰化形式相比,9-O-Ac
SA 高原生体感染人类巨噬细胞后,细胞内存活率提高,这表明它们有助于提高存活率。此外,感染了 9-O-Ac
SAhigh 原鞭毛虫的巨噬细胞上清液中 NO、白细胞介素-12 和干扰素-γ 的积累减少,这表明利什曼杀宿主反应受到抑制。然而,9-O-Ac
SA含量最低的LV4和LV81在去O-乙酰化前后的NO抗性、繁殖能力和宿主反应都没有改变,这表明可能有其他决定因素的参与,而这些因素可能是其固有寄生属性的一个功能。因此,9-O-Ac
SA 水平的提高是通过抑制宿主反应来增强寄生虫对 NO 的抗性和存活能力的潜在决定因素之一。