Use of an artificial antigen containing the 3,6-di-O-methyl-beta-D-glucopyranosyl epitope for the serodiagnosis of leprosy.

The coupling of synthetic 3,6-di-O-methyl-beta-D-glucopyranosyl-(1----4)-2,3-di-O-methyl-alpha-L -rhamnopyranose, the hapten determinant of phenolic glycolipid I from Mycobacterium leprae, to bovine serum albumin (BSA) by reductive amination produced the antigen epsilon-N-1-[1-deoxy-2,3-di-O-methyl-4-O-(3',6'-di-O-methyl-beta -D-glucopyranosyl)-rhamnitol]-lysyl-BSA, which proved highly sensitive in ELISA and showed good concordance with the native glycolipid in analysis of serum samples from 223 leprosy patients. Conjugates prepared from 6-O-methyl-beta-D-glucopyranosyl- or beta-D-glucopyranosyl-containing disaccharides were inactive and those containing noncyclic 3,6-di-O-methyl-glucitol showed little activity. Thus 3,6-di-O-methyl-beta-D-glucopyranose in its cyclic hemiacetal form is necessary for binding anti-glycolipid IgM from leprosy patients. Analysis of serum samples from healthy subjects showed a false-positive rate of 2.4% (four of 169) against the glycolipid and 3.6% (six of 169) against the glycoconjugate. Comparable figures for samples of sera of tuberculosis patients were 3.0% (two of 66) and 9.0% (six of 66), respectively. Alternative synthesizing strategies may diminish this cross-reactivity. The prospects of a fully synthetic specific antigen for the worldwide serodiagnosis of leprosy look promising.