Recombinant polypeptide of Mycobacterium leprae as a potential tool for serological detection of leprosy

Marcelo Dos Santos Barbosa,Silvana Beutinger Marchioro,Sibele Borsuk,Iara Beatriz Andrade De Sousa,Simone Simionatto

doi:10.1186/s13568-019-0928-9

Marcelo Dos Santos Barbosa, Silvana Beutinger Marchioro + Show 3 more

Open Access

https://doi.org/10.1186/s13568-019-0928-9

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Abstract

Current prevention methods for the transmission of Mycobacterium leprae, the causative agent of leprosy, are inadequate as suggested by the rate of new leprosy cases reported. Simple large-scale detection methods for M. leprae infection are crucial for early detection of leprosy and disease control. The present study investigates the production and seroreactivity of a recombinant polypeptide composed of various M. leprae protein epitopes. The structural and physicochemical parameters of this construction were assessed using in silico tools. Parameters like subcellular localization, presence of signal peptide, primary, secondary, and tertiary structures, and 3D model were ascertained using several bioinformatics tools. The resultant purified recombinant polypeptide, designated rMLP15, is composed of 15 peptides from six selected M. leprae proteins (ML1358, ML2055, ML0885, ML1811, ML1812, and ML1214) that induce T cell reactivity in leprosy patients from different hyperendemic regions. Using rMLP15 as the antigen, sera from 24 positive patients and 14 healthy controls were evaluated for reactivity via ELISA. ELISA-rMLP15 was able to diagnose 79.17% of leprosy patients with a specificity of 92.86%. rMLP15 was also able to detect the multibacillary and paucibacillary patients in the same proportions, a desirable addition in the leprosy diagnosis. These results summarily indicate the utility of the recombinant protein rMLP15 in the diagnosis of leprosy and the future development of a viable screening test.

Highlights

The chronic infectious disease leprosy is caused by the intracellular, acid-fast bacillus known as Mycobacterium leprae (Araújo 2003)
A receiver operating characteristic (ROC) curve was constructed for the 24 patients and 14 healthy endemic controls (HCs) (Fig. 3), the cutoff value was based on the highest likelihood ratio (11.08) and the Youden index J was calculated (0.7203). rMLP15 showed an antibody response in 19 of 24 patients (79.17%) and 1 of 14 HCs (7.14%) from the sera evaluated in Enzyme‐linked immunosorbent assay (ELISA) (Fig. 3a), thereby yielding a specificity rate of 92.86%, a sensitivity rate of 79.17%, and an area under the ROC curve (AUC) of 0.83 (Fig. 3b)
It has been established that the combined detection of humoral and cellular markers is efficient in diagnosing MB and PB leprosy patients

Summary

Introduction

The chronic infectious disease leprosy is caused by the intracellular, acid-fast bacillus known as Mycobacterium leprae (Araújo 2003). Other diagnostic methods like bacilloscopy and histopathology lack adequate sensitivity and rely on well-trained technicians as well (Cheng et al 2019). Molecular diagnostic methods like PCR and qPCR are difficult and expensive to perform in the field, despite having high levels of sensitivity (Martinez et al 2014; Cheng et al 2019). Serological tests based on M. leprae antigens are available, they lack adequate sensitivity and are only for supporting clinical diagnosis (Kim et al 2013). Primarily used for detecting MB patients, the phenolic glycolipid I (PGL-I) (Roche et al 1999) and the Leprosy IDRI Diagnostic-1 (LID-I) tests stand out (Duthie et al 2007; Hungria et al 2012). Of significance is the NDO-LID® test, a rapid serological, lateral flow test designed with two proteins, ND-O (a synthetic PGL-I mimetic) and LID-I (a fusion protein of ML0405 and ML2331) (Reece et al 2006; Hungria et al 2017; van Hooij et al 2018)

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