Visceral leishmaniasis (VL) is caused by protozoa belonging to the Leishmania donovani complex and is considered the most serious and fatal form among the different types of leishmaniasis, if not early diagnosed and treated. Among the measures of disease control stand out the management of infected dogs and the early diagnosis and appropriate treatment of human cases. Several antigens have been characterized for use in the VL diagnosis, among them are the recombinant kinesin-derived antigens from L. infantum, as rK39 and rKDDR. The main difference between these antigens is the size of the non-repetitive kinesin region and the number of repetitions of the 39 amino acid degenerate motif (6.5 and 8.5 repeats in rK39 and rKDDR, respectively). This repetitive region has a high antigenicity score. To evaluate the effect of increasing the number of repeats on diagnostic performance, we designed the rKDDR-plus antigen, containing 15.3 repeats of the 39 amino acid degenerate motif, besides the absence of the non-repetitive portion from L. infantum kinesin. Its performance was evaluated by enzyme-linked immunosorbent assay (ELISA) and rapid immunochromatographic test (ICT), and compared with the kinesin-derived antigens (rKDDR and rK39). In ELISA with human sera, all recombinant antigens had a sensitivity of 98%, whereas the specificity for rKDDR-plus, rKDDR and rK39 was 100%, 96% and 71%, respectively. When evaluated canine sera, the ELISA sensitivity was 97% for all antigens, and the specificity for rKDDR-plus, rKDDR and rK39 was 98%, 91% and 83%, respectively. Evaluation of the ICT/rKDDR-plus, using human sera, showed greater diagnostic sensitivity (90%) and specificity (100%), when compared to the IT LEISH (79% and 98%, respectively), which is based on the rK39 antigen. These results suggest that the increased presence of repetitive motifs in the rKDDR-plus protein improves the diagnostic performance of serological tests by increasing the specificity and accuracy of the diagnosis.

中文翻译：

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KDDR-plus 重组蛋白（一种来自婴儿利什曼原虫的驱动蛋白衍生抗原）中重复基序的增加，提高了人类和犬内脏利什曼病血清学检测的诊断性能。

内脏利什曼病 (VL) 由属于多诺瓦利什曼原虫复合体的原生动物引起，如果不及早诊断和治疗，则被认为是不同类型利什曼病中最严重和最致命的形式。在疾病控制措施中，最突出的是感染犬的管理以及人类病例的早期诊断和适当治疗。几种抗原已被表征可用于 VL 诊断，其中包括来自婴儿乳杆菌的重组驱动蛋白衍生抗原，如 rK39 和 rKDDR。这些抗原之间的主要区别在于非重复驱动蛋白区域的大小和 39 个氨基酸简并基序的重复次数（在 rK39 和 rKDDR 中分别为 6.5 和 8.5 次重复）。该重复区域具有高抗原性评分。为了评估增加重复次数对诊断性能的影响，我们设计了 rKDDR-plus 抗原，除了不存在来自婴儿乳杆菌驱动蛋白的非重复部分之外，还包含 39 个氨基酸简并基序的 15.3 个重复。通过酶联免疫吸附试验（ELISA）和快速免疫层析试验（ICT）评估其性能，并与驱动蛋白衍生抗原（rKDDR和rK39）进行比较。在人血清 ELISA 中，所有重组抗原的灵敏度为 98%，而对 rKDDR-plus、rKDDR 和 rK39 的特异性分别为 100%、96% 和 71%。评估犬血清时，ELISA 灵敏度对所有抗原均为 97%，对 rKDDR-plus、rKDDR 和 rK39 的特异性分别为 98%、91% 和 83%。使用人类血清评估 ICT/rKDDR-plus，与基于 rK39 抗原的 IT LEISH（分别为 79% 和 98%）相比，显示出更高的诊断敏感性（90%）和特异性（100%）。这些结果表明，rKDDR-plus 蛋白中重复基序的增加通过提高诊断的特异性和准确性来提高血清学检测的诊断性能。