Structure analysis and immunopharmacological activities of mycolic acid-containing glycolipids in acid fast bacterial cell walls

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The most characteristic component of the cell walls of the acidfast bacteria, such as Mycobacteria and Nocardia, has been known to be "mycolic acid", a very high molecular weight 3-hydroxy fatty acid with a long alkyl chain at the 2-position. These acids are associated with cell wall skeleton via the esterification or with specific glycolipids. Since the cell wall components containing mycolic acids possess unique biological activities between the host and parasite relationships in the infection, such as immunoadjuvant activities, macrophage activating activities and antitumor activities, we have started to examine the structure-activity relationships of various mycolic acid-containing glycolipids in Nocardia, Rhodococcus and Gordona which are closely related taxonomically to Mycobacterium. The detailed structure of mycolic acid molecular species ranging from <C_(30)> to <C_(80)> from the glycolipids were demonstrated by using GC/MS and the granuloma forming activity of the glycolipids was shown to be affected deeply by the structure and acyl numbers of mycolic acids. Neutral glycolipids possessing glucose or trehalose as hydrophilic moiety and mycolic acids longer than <C_(40)> were shown to have a strong activity for the granuloma formation in mice. On the other hand, glycolipids possessing anionic charge or shorter chain mycolic acids did not show significant activity. These results show the both hydrophilic and hydrophobic structures of glycolipids play very important roles in immunopharmacological or biological response-modifiering activities.