ELISA-based assay of immunoglobulin G antibodies against mammalian cell entry 1A (Mce1A) protein: a novel diagnostic approach for leprosy

BACKGROUND Leprosy is a chronic infectious disease caused by the obligate intracellular bacillus Mycobacterium leprae. Because leprosy diagnosis is complex and requires professional expertise, new tools and methodologies are needed to detect cases in early stages and prevent transmission. The M. leprae genome contains mce1A, which encodes a putative mammalian cell entry protein (Mce1A). We hypothesised that the presence of Mce1A on the cell surface could be detected by the host's immune system. OBJECTIVE The aim of this study was to evaluate antibody responses against the Mce1A protein in leprosy patients, household contacts of patients, and the general population to present an addition tool for leprosy diagnosis. METHODS A cross-sectional study involving 89 volunteers [55 leprosy cases, 12 household contacts (HHC) and 22 endemic controls (EC)] was conducted at Couto Maia Hospital, in Salvador, Bahia (BA), Brazil. RESULTS The median anti-Mce1A IgA was significantly higher in multibacillary (MB) and paucibacillary (PB) cases than in EC (p < 0.0001). A similar trend was observed in IgM levels, which were significantly higher in both MB (p < 0.0001) and PB (p = 0.0006) groups compared to in EC individuals. The greatest differences were observed for IgG class-specific antibodies against Mce1A. The median levels of MB and PB were significantly higher compared to both controls HHC and EC (MB or PB vs EC, MB vs HHC p < 0.0001; PB vs HHC, p = 0.0013). Among leprosy cases, IgG enzyme-linked immunosorbent assay sensitivity and specificity were 92.7% and 97.1%, respectively. IgG positivity was confirmed in 92.1% and 94.1% of MB and PB patients, respectively. CONCLUSION This novel diagnostic approach presents an easy, non-invasive, and inexpensive method for leprosy screening, which may be applicable in endemic areas.

研究背景：麻风病是由专性胞内分枝杆菌——麻风分枝杆菌（Mycobacterium leprae）引发的慢性传染病。由于麻风病诊断流程复杂且需专业技术支撑，亟需开发新型检测工具与方法，以实现早期病例检出并阻断传播。麻风分枝杆菌基因组携带mce1A基因，其编码一种推定的哺乳动物细胞侵入蛋白（Mce1A）。我们推测宿主免疫系统可识别细胞表面存在的Mce1A蛋白。
研究目的：本研究旨在评估麻风病患者、患者家庭接触者以及普通人群体内针对Mce1A蛋白的抗体应答水平，以期为麻风病诊断提供一款新型辅助工具。
研究方法：本研究于巴西巴伊亚州萨尔瓦多市的库托·马亚医院（Couto Maia Hospital）开展，为一项纳入89名志愿者的横断面研究，其中包括55名麻风病病例、12名家庭接触者（HHC）以及22名流行区对照者（EC）。
研究结果：多菌型（MB）与少菌型（PB）麻风病患者的抗Mce1A IgA中位数水平均显著高于流行区对照者（p < 0.0001）。IgM水平亦呈现相似趋势：多菌型组与少菌型组的IgM水平均显著高于对照人群（多菌型组：p < 0.0001；少菌型组：p = 0.0006）。针对Mce1A的IgG特异性抗体差异最为显著，多菌型组与少菌型组的IgG中位数水平均显著高于家庭接触者与流行区对照两组：多菌型或少菌型与流行区对照相比、多菌型与家庭接触者相比，p值均<0.0001；少菌型与家庭接触者相比，p=0.0013。在麻风病患者中，IgG酶联免疫吸附试验（enzyme-linked immunosorbent assay）的灵敏度与特异度分别为92.7%与97.1%。多菌型与少菌型患者的IgG阳性率分别为92.1%与94.1%。
研究结论：本研究提出的新型诊断方法为麻风病筛查提供了一种简便、无创且低成本的技术方案，有望在麻风病流行地区推广应用。