Evaluation of a rapid serological test for leprosy classification using human serum albumin as the antigen carrier.

The presence of anti-BSA antibodies may interfere in serological tests, as ELISA or immunochromatographic assays. BSA is frequently used as a blocking agent or as "inert" carrier of antigens, such as the NT-P-BSA, the semi-synthetic trisaccharide analogue of the PGL-I (phenolic glycolipid-I) antigen from the cell wall of the Mycobacterium leprae. PGL-I was prepared and linked to human serum albumin based in the hypothesis that replacing BSA by a human protein carrier would enhance the performance of leprosy serological tests. A total of 1162 serum samples were tested by ELISA and by the ML Flow rapid test using NT-P-BSA or NT-P-HSA antigens. When grouping leprosy patients as paucibacillary (PB) or multibacillary (MB) according to the Ridley & Jopling classification, ML Flow BSA and ML Flow HSA tests correctly allocated 70.9% and 68.6% of patients in the PB group, and 87% and 81% of patients in the MB group, respectively. Concordant results were found in 82.0% (953/1162) (kappa value=0.637; sd=0.023) of samples between ML Flow tests and 85.7% (996/1162) (kappa value=0.703; sd=0.021) between ELISA tests. ML Flow results were statistically similar and the same was true for ELISA tests using HSA or BSA. However, we noticed a tendency to decreased capacity to detect MB patients and an increased positivity among PB patients, HHC, TB patients and healthy controls by the HSA carrier in both ML Flow and ELISA. The PGL-I serology performed by the ML Flow test with BSA or HSA as antigen carriers can be a useful, friendly auxiliary tool to identify patients with higher bacterial load.

Serological diagnosis of leprosy in patients in vietnam by enzyme-linked immunosorbent assay with Mycobacterium leprae-derived major membrane protein II.

A serological diagnostic test using phenolic glycolipid-I (PGL-I) developed in the 1980s is commercially available, but the method is still inefficient in detecting all forms of leprosy. Therefore, more-specific and -reliable serological methods have been sought. We have characterized major membrane protein II (MMP-II) as a candidate protein for a new serological antigen. In this study, we evaluated the effectiveness of the enzyme-linked immunosorbent assay (ELISA) using the MMP-II antigen (MMP-II ELISA) for detecting antibodies in leprosy patients and patients' contacts in the mid-region of Vietnam and compared to the results to those for the PGL-I method (PGL-I ELISA). The results showed that 85% of multibacillary patients and 48% of paucibacillary patients were positive by MMP-II ELISA. Comparison between the serological tests showed that positivity rates for leprosy patients were higher with MMP-II ELISA than with PGL-I ELISA. Household contacts (HHCs) showed low positivity rates, but medical staff members showed comparatively high positivity rates, with MMP-II ELISA. Furthermore, monitoring of results for leprosy patients and HHCs showed that MMP-II is a better index marker than PGL-I. Overall, the epidemiological study conducted in Vietnam suggests that serological testing with MMP-II would be beneficial in detecting leprosy.