Relationship between induction of macrophage chemotactic factors and formation of granulomas caused by mycoloyl glycolipids from Rhodococcus ruber (Nocardia rubra).

Mycoloyl glycolipids cause granulomas in the lungs, liver, and spleen of mice, but the mechanism is not fully understood. To understand the role of macrophage chemotactic factors (MCFs) in granuloma formation, we prepared various mycoloyl glycolipids with different carbohydrate moieties: trehalose dimycolate (TDM), glucose mycolate (GM), mannose mycolate (MM), and fructose mycolate (FM) from Rhodococcus ruber, and examined the relationship between their MCF induction in peritoneal macrophages and the extent of granuloma formation. The molecular mass of each glycolipid was confirmed by fast-atom-bombardment mass-spectrometry. TDM or GM caused granulomas in the lungs, spleen, and liver of ICR mice, but MM and FM did not. The culture supernatant of peritoneal macrophages stimulated with TDM or GM increased macrophage migration, whereas MM and FM had no chemotactic activity. The activity of interleukin-1 (IL-1) in the supernatant was increased equally by each glycolipid and was therefore not related to chemotaxis. Tumor necrosis factor-alpha (TNF-alpha) and granulocyte-macrophage colony-stimulating factor (GM-CSF) were not detected in the four supernatants. The TDM-induced MCF was heat-stable, trypsin-labile, and undialyzable. Furthermore, we separated two MCF active fractions from the supernatant of TDM-stimulated macrophages by gel filtration. These factors acted on macrophages but not on neutrophils. Our results suggested that macrophages recognize the sugar moieties of mycoloyl glycolipids and may, in response, generate a MCF that may play an important role in the macrophage or monocyte recruitment which is essential prior to granuloma formation.