Interferon‐γ independent formation of pulmonary granuloma in mice by injections with trehalose dimycolate (cord factor), lipoarabinomannan and phosphatidylinositol mannosides isolated from Mycobacterium tuberculosis

Summary The mechanisms by which pulmonary granuloma formation is caused by administration of mycobacterial glycolipids such as trehalose dimycolate (TDM), lipoarabinomannan (LAM) and phosphatidylinositol mannosides (PIM) were investigated. When peritoneal and alveolar macrophages were stimulated with TDM, LAM and PIM in vitro, TDM exhibited the strongest tumour necrosis factor (TNF)‐inducing activity. Responsiveness of macrophages from mice defected Toll‐like receptor 4 (TLR4) was much higher than that of the wild‐type mice. Although PIM and LAM also had a significant activity, LAM rather than PIM stimulated higher TNF‐α production by alveolar macrophage. When mycobacterial glycolipids were injected as water‐in‐oil‐in‐water emulsion into mice via the tail vein, development of pulmonary granuloma in response to glycolipids were related closely to their TNF‐inducing activity and TDM exhibited the strongest activity. Granuloma formation was observed not only in mice lacking interleukin (IL)‐12 signalling but also interferon (IFN)‐γ knock‐out mice. Granuloma formation caused by glycolipids correlated with TNF‐α levels in lungs. Administration of anti‐TNF‐α monoclonal antibody into TDM‐injected IFN‐γ knock‐out mice decreased in granuloma formation, suggesting that development of pulmonary granuloma by mycobacterial glycolipids such as TDM is due to IFN‐γ‐independent and TNF‐α‐dependent pathway.