Serological activity of natural disaccharide octyl bovine serum albumin (ND-O-BSA) in sera from patients with leprosy, tuberculosis, and normal controls.

We studied the natural disaccharide-octyl-bovine serum albumin (ND-O-BSA) enzyme-linked immunosorbent assay (ELISA) in sera from 151 leprosy patients, 20 tuberculosis patients, and 42 normal persons from a nonendemic area. The three ELISAs, whole Mycobacterium leprae (WML), phenolic glycolipid-I (PGL-I), and ND-O-BSA, are all highly sensitive for detecting antibodies against M. leprae. The results indicate that the serological activity has highly significant, positive correlations among the three types of antigens used. Their positivity rates are 100% with PGL-I and 97.4% with WML and ND-O-BSA in leprosy patients, and 0% with any antigen used in normal persons at NV-a (a supposed theoretical normal value). However, all three antigens show crossreactivity with tuberculosis patients at different levels. At NV-c (a supposed practical normal value, PNV), this crossreaction significantly decreased in the WML ELISA (PNV = 0.28) and the PGL-I ELISA (PNV = 0.16), and disappeared in the ND-O-BSA ELISA (PNV = 0.20). Under the same conditions, the positivity rates did not decrease significantly in leprosy patients, especially in multibacillary patients. Therefore, we suggest that the PGL-I ELISA in combination with the ND-O-BSA ELISA may be very useful for clinical applications, serodiagnosis, and for the study of subclinical infection in leprosy.