Trehalose 6,6′-Dimycolate (Cord Factor) ofMycobacterium tuberculosisInduces Foreign-Body- and Hypersensitivity-Type Granulomas in Mice

Abstract

Granulomatous inflammation is characterized morphologically by a compact organized collection of macrophages and their derivatives. It is classified as either a hypersensitivity type or a foreign-body type. Lipid components of the Mycobacterium tuberculosis cell wall participate in the pathogenesis of infection. Strains of M. tuberculosis have cord factor (trehalose 6,6-dimycolate [TDM]) on their surface. To clarify host responses to TDM, including immunogenicity and pathogenicity, we have analyzed the footpad reaction, histopathology, and cytokine profiles of experimental granulomatous lesions in immunized and unimmunized mice challenged with TDM. In the present study, we have demonstrated for the first time that TDM can induce both foreignbody-type (nonimmune) and hypersensitivity-type (immune) granulomas by acting as a nonspecific irritant and T-cell-dependent antigen. Immunized mice challenged with TDM developed more severe lesions than unimmunized mice. At the active lesion, we found monocyte chemotactic, proinflammatory, and immunoregulatory cytokines. The level was enhanced in immunized mice challenged with TDM. This result implies that both nonimmune and immune mechanisms participate in granulomatous inflammation induced by mycobacterial infection. Taken together with a previous report, this study shows that TDM is a pleiotropic molecule against the host and plays an important role in the pathogenesis of tuberculosis.The pathogenesis of tuberculosis is a function of the pathogen, Mycobacterium tuberculosis, and of the immune response of the host to the pathogen (5, 14). Tuberculosis is a chronic infection with M. tuberculosis complex, including M. tuberculosis and Mycobacterium bovis, that is characterized morphologically by granulomatous inflammation, a compact organized collection of macrophages and their derivatives, such as epithelioid and giant cells, at the site of infection (19). The pathogenicity of M. tuberculosis is related to its ability to escape killing by macrophages and induce delayed-type hypersensitivity (DTH) (5,14,19).Granulomatous inflammation can be broadly classified as either a hypersensitivity (immunologic, T-cell-dependent) type or a foreign-body (nonimmunologic, T-cell-independent) type (19,20). There is much known, but we still have a long way to go to understand the mechanism of M. tuberculosis pathogenicity. Mycobacteria are rich in lipids. Lipid components of the M. tuberculosis cell wall participate in pathogenesis. Cord factor (trehalose 6,6Ј-dimycolate [TDM]), a surface glycolipid, causes M. tuberculosis to grow in serpentine cords in vitro. Virulent strains of M. tuberculosis have TDM on their surface (2), and injection of purified TDM into experimental animals induces lesions characterized by chronic granulomatous inflammation (6,29).To clarify host responses to mycobacterial TDM, including immunogenicity and pathogenicity, we have analyzed the footpad reactions, histopathology, and cytokine profiles of experimental granulomatous lesions in immunized and unimmunized mic...

Mycobacterial glycolipid trehalose 6,6′-dimycolate-induced hypersensitive granulomas: contribution of CD4+ lymphocytes

“…Mice were immunized according to previously published methods (Guidry et al, 2004(Guidry et al, , 2006Yamagami et al, 2001). Briefly, mice received 100 ml of a water/oil emulsion containing 100 mg TDM (Sigma) emulsified in complete Freund's adjuvant (Sigma) and 100 mg methylated BSA (Promega) administered by subcutaneous injection at the base of the tail.…”

“…Two days after adoptive transfer, mice were injected with 100 ml of a water/oil/water emulsion prepared as described previously (Guidry et al, 2004;Yamagami et al, 2001), administered by intravenous tail vein injection. To prepare 100 ml of sample, 100 mg TDM was added to 3.2 ml incomplete Freund's adjuvant (Sigma) and ground in a homogenizer tube with a Teflon pestle.…”

“…In mice, hypersensitive granulomas produced in response to TDM produce pathology which mimics in many ways that seen in M. tuberculosis infection in man. Previous studies suggested a role for T cells in this response; however, antigen specificity still remained to be shown (Seggev et al, 1982(Seggev et al, , 1984Yamagami et al, 2001). Recently, it was demonstrated that a T cell-mediated response could be generated in cells recovered from mice immunized with TDM.…”

“…Relative to surface-associated TDM, organisms genetically altered to produce less TDM, or irregular TDM, exhibit reduced growth and survival both in vivo and in vitro (Armitige et al, 2000;Copenhaver et al, 2004;Glickman et al, 2000;Rao et al, 2005). Perhaps TDM's most interesting attribute is its ability to induce cytokine and chemokine production leading to granuloma formation in the lungs of responsive mice (Behling et al, 1993;Bekierkunst, 1968;Guidry et al, 2004;Lima et al, 2001;Perez et al, 2000;Yamagami et al, 2001). In mice, hypersensitive granulomas produced in response to TDM produce pathology which mimics in many ways that seen in M. tuberculosis infection in man.…”

In Vivo Activity of Released Cell Wall Lipids ofMycobacterium bovisBacillus Calmette-Guérin Is Due Principally to Trehalose Mycolates

“…Mycobacterial cell wall glycolipids induce foreign body-type granulomas in mice (2,3), and we have shown that glycolipids of Mycobacterium bovis bacillus Calmette-Guérin (BCG) 3 traffic within the host macrophage and spread to uninfected bystander macrophages (4). Released glycolipids included phosphatidylinositol dimannosides (PIM2), phosphatidylglycerol and cardiolipin (CL), phosphatidylethanolamine, trehalose monomycolate (TMM), trehalose dimycolate (TDM), and mycoside B (MycB) (5).…”