PGL-I leprosy serology.

Mycobacterium leprae is the causative agent of leprosy, a disease that, despite having an effective cure with multidrug therapy (MDT), leaves millions of cured patients with sequelae as a consequence of the nerve damage that forms the hallmark of leprosy. A number of diagnostic issues hamper the correct and timely diagnosis of leprosy and the correct classification of patients for treatment purposes: (i) bacterial examinations are often not used; (ii) there is a tendency to over-diagnose single lesion PB leprosy; and (iii) early (borderline) lepromatous often goes unnoticed due to the absence of sensibility loss and lesions. Approximately 70% of leprosy patients can be diagnosed on the basis of the single clinical sign of skin patches with sensory loss, but 30% of patients, including many MB patients, do not present this symptom. The delayed detection of this latter group of patients may be a major cause of continued transmission. Most mycobacteria have specific, highly antigenic glycolipids that can be used as tools for the serodiagnosis of distinct mycobacterial infections. As the mycobacterium enters the human body, the cell wall is the first barrier encountered by the immune system. The cell wall of Mycobacterium leprae consists mainly of lipids, including a considerable glycolipid fraction with a unique carbohydrate composition. One of the first Mycobacterium leprae-specific antigens to be isolated and characterized was phenolic glycolipid-I (PGL-I), the major antigenic glycolipid in the bacterium. The PGL-I molecule is composed of a unique trisaccharide, 3,6-di-O-methyl-β-Dglucopyranosyl-(1→4)-2,3-di-O-methyl-α-L-rhamnopyranosyl(1→2)-3-O-methyl-α-L-rhamnopyranose. The principal antigenic determinant of PGL-I is the ultimate diand trisaccharide part of the molecule . Monoclonal antibodies were used to further analyze this antigenic determinant of PGL-I. It was shown that removal of the terminal sugar residue resulted in loss of binding of most antibodies, while removal of the long chain fatty acids of the molecule had no effect on antibody binding. These and other results suggested that chemical synthesis of the ultimate disaccharide part would provide an antigenic epitope that would be specific enough for application in the serology of leprosy. The sugar part of PGL-I was synthesized and conjugated to bovine serum albumin (BSA) either directly or through different linkers, namely an octyl (O) or phenyl (P) linker arm. More recently it was conjugated to human serum albumin. Since the identification of PGL-I, the following neoglycolipids have been produced: monosaccharide-octyl-BSA (M-O-BSA), disaccharide-BSA (D-BSA), natural disaccharide-octyl-BSA (ND-O-BSA), natural trisaccharide-phenyl-BSA (NT-P-BSA) and natural disaccharide-octyl-HSA (ND-O-HSA). Based on native PGL-I and its semi-synthetic derivatives, numerous serological assays have been developed to detect the presence of antibodies of the immunoglobulin IgM, IgG and IgA classes. Since the semi-synthetic antigens can be produced in larger quantities and can be applied more easily than native PGL-I, a wide variety of applications ranging from clinical diagnosis to large epidemiological studies became feasible. The techniques used to develop tests include the enzyme-linked immunosorbent assay (ELISA), the passive hemagglutination test (PHA), a gelatin particle agglutination test (MLPA), the dipstick and the lateral flow test. An expressive part of the studies published so far have used the ELISA, dipstick and lateral flow techniques. However, the question remains as to which technique is the most suitable for a specific study. There are advantages and potential pitfalls that may occur when using each technique.