Isolation of mycolic acid-containing glycolipids in Nocardia rubra and their granuloma forming activity in mice.

Three classes of glycolipids (TMM (trehalose monomycolate), TDM (trehalose dimycolate) and GM (glucose mycolate] containing mycolic acids as hydrophobic components were isolated from a strain of Nocardia rubra (Rhodococcus rubrum) and their structures have been partially characterized using infrared spectrometry, gas-liquid chromatography and gas chromatography-mass spectrometry. Acid or alkaline hydrolysis of isolated glycolipids revealed that trehalose was the sole water soluble component in TMM and TDM, while glucose was the hydrophilic component in GM. On the other hand, saturated, monoenoic and dienoic mycolic acids with carbon atoms ranging from C36 to C50 contained constituents of fatty acid moiety at C44. From the analytical results, TMM, TDM and GM were tentatively identified as trehalose monomycolate, trehalose dimycolate and glucose monomycolate, respectively. The mycolic acid composition differed significantly by the glycolipid classes: the highest amount of saturated mycolic acids were detected in TMM and GM, while a significant amount of dienoic mycolic acids have been found in TDM and the cell wall bound lipid fraction (BL). All these three classes of glycolipids containing mycolic acids showed strong granuloma forming activity in lungs and spleen of ICR mice 1 week after intravenous injection of 100 to 500 micrograms glycolipid in W/O/W micelles containing Freund's incomplete adjuvant. These results indicated that glycolipids containing shorter carbon chain mycolic acids ranging C40-50, corresponding to less acyl numbers or monosaccharides such as glucose, can also produce foreign body-type granuloma in mice without protein antigens.