The Phosphatidyl-myo-inositol Anchor of the Lipoarabinomannans from Mycobacterium bovis Bacillus Calmette Guérin

Abstract

Lipoarabinomannans are major mycobacterial anti- gens capable of modulating the host immune response; however, the molecular basis underlying the diversity of their immunological properties remain an open ques- tion. In this study a new extraction and purification approach was successfully applied to isolate ManLAMs (lipoarabinomannans with mannosyl extensions) from bacillus Calmette Gue which are isoniazid and ethambutol. Also, from different trials, the efficiency of BCG1 vaccine to prevent tuberculosis was found to range from 0 to 80% (2, 3). Virulent mycobacteria survive and multiply within phago- ´rin leading to the obtention of two types of ManLAMs namely parietal and cellular. Struc- turally, they were found to differ by the percentage of mannooligosaccharide caps, 76 and 48%, respectively, and also, thanks to a new analytical method, by the structure of the phosphatidyl-myo-inositol anchor lipid moiety. A novel fatty acid in the mycobacterium genus assigned to a 12-O-(methoxypropanoyl)-12-hydroxy- stearic acid was the only fatty acid esterifying C-1 of the glycerol residue of the parietal ManLAMs, while the phosphatidyl unit of the cellular ManLAMs showed a large heterogeneity due to a combination of palmitic and tuberculostearic acid. Finally, parietal and cellular ManLAMs were found to differentially affect interleu- kin-8 and tumor necrosis factor- secretion from human dendritic cells. We show that parietal but not cellular ManLAMs were able to stimulate tumor necrosis fac- tor- secretion from dendritic cells. From these studies we propose that the 1-[12-O-(methoxypropanoyl)-12-hy- droxystearoyl]-sn-glycerol part is the major cytokine- regulating component of the ManLAMs. It seems likely that modification of the ManLAM lipid part, which may occur in hostile environments, could regulate macro- phagic mycobacterial survival by altering cytokine stimulation.