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.