[Structure and antigenicity of the glycopeptidolipid antigen of Mycobacterium avium-intracellulare complex (MAC) serovar 16].

The characteristic lipids and specific surface antigens which typify serotypes of Mycobacterium avium-intracellulare complex (MAC) serogroup have been examined. The characteristic lipids are recognized as glycopeptidolipid (GPL) antigen consisted of short-chain acylated oligosaccharides linked to long-chain fatty acyl-D-Phe-D-allo Thr-D-Ala-L-alaninol-O-3, 4-di-O-methyl rhamnose 'core'. The lack of information on the properties of GPL antigen from serovar 16 and a large number of patients infected with MAC serovar 16 have prompted an examination of the chemical structures utilizing the analytical techniques of alditol acetates with GC or GC/MS, and making use of FAB/MS and 1H-NMR to analyze the intact GPLs. The following structure of serovar 16 GPL antigen was proposed with molecular weight: 1933, main fatty acyl component: OH-C32:0, and oligosaccharides: 3-amido (2'-methyl, 3'-hydroxy, 4'-methoxy pentanoyl) 3, 6-dideoxy hexose-->4-O-methyl-L-rhamnose-->L-rhamnose-->L-rhamnose-->6-deoxy-L-talose The unique structure may be an important factor in physiological and pathological roles. The GPL antigens were highly reactive in ELISA against sera from rabbits hyperimmunized with MAC strains, indicating its basic antigenicity. The type-specific antigen of serovar 16 was also specifically reactive against sera from patients infected with MAC serovar 16, but invariant core was not. Apparently, the epitope of GPL antigen of serovar 16 was specific oligosaccharides, 3-amido (2'-methyl, 3'-hydroxy, 4'-methoxy pentanoyl) 3, 6-dideoxy hexose. It was found that the ELISA using GPL antigens was particularly useful for the serovar diagnosis of human infections with MAC.