A new type of glycolipid possessing trehalose and mycolic acids has been identified in the lipids of Rhodococcus aurantiacus (Gordona aurantiaca), a psychrophilic acid-fast bacterium. Gas chromatographic and gas chromatographic-mass spectrometric analysis of hydrolysis products of the most abundant glycolipid class (GM) (containing approx. 50% of the total lipids) showed that the hydrophilic moiety was composed essentially of trehalose, while the hydrophobic moiety contained Chr-74 polyunsaturated mycolic acids only. Permethylation study revealed that the new glycolipid possessed three mycolic acid residues for each trehalose molecule and was identified as trehalose 2,3,6'-trimycolate. Trehalose trimycolate Asymmetric ester Mycolic acidCord factor Acid-fast bacillus

As previously reported (I. Yano, I. Tomiyasu, S. Kitabatake, and K. Kaneda, Acta Leprologica 2:341-349, 1984), Nocardwa rubra, one of the nonpathogenic actinomycetes, possesses three classes of mycolic acidcontaining glycolipid, i.e., glucose mycolate, trehalose dimycolate, and trehalose monomycolate. The carbon chain length of their mycolic acids is shorter (C_3&,a) than that in mycobacteria (longer than C70), and the glycolipid consists of only a-mycolic acid. One intravenous administration of 500 ,Ig of each purified glycolipid to ICR mice in the form of water-in-oil-in-water emulsion without any protein antigens caused prominent granuloma formation in the lungs, spleen, and liver. The lung index in the treated mice was about 3.5 times larger than that in the control mice (given water-in-oil-in-water emulsion only) at 1 week after the injection and then rapidly declined, while spleen and liver indices peaked at 2 weeks after the injection and persisted longer. The granuloma consisted of macrophages, some of which phagocytized glycolipid micelles, lymphocytes, monocytes, and neutrophils. In addition, many small hemopoietic islands were observed in the liver sinusoids, where various immature blood cells were trapped by the prominent cytoplasmic projections of Kupffer cells. The granuloma formation and hemopoiesis observed here are considered to be the most characteristic morphological expression of macrophage activation in these organs. This is the first report to show that such histological changes can be induced by chemically defined and homogeneous mycolic acid-containing glycolipids other than those of mycobacteria.