The Journal of Immunology TLR6-Driven Lipid Droplets in Mycobacterium leprae-Infected Schwann Cells: Immunoinflammatory Platforms Associated with Bacterial Persistence Katherine A. Mattos,* ,1 Viviane G. C. Oliveira,* ,1 Heloisa D’Avila, † Luciana S. Rodrigues,* Roberta O. Pinheiro, ‡ Euzenir N. Sarno, ‡ Maria Cristina V. Pessolani,* ,2 and Patricia T. Bozza †,2 The mechanisms responsible for nerve injury in leprosy need further elucidation. We recently demonstrated that the foamy phenotype of Mycobacterium leprae-infected Schwann cells (SCs) observed in nerves of multibacillary patients results from the capacity of M. leprae to induce and recruit lipid droplets (LDs; also known as lipid bodies) to bacterial-containing phagosomes. In this study, we analyzed the parameters that govern LD biogenesis by M. leprae in SCs and how this contributes to the innate immune response elicited by M. leprae. Our observations indicated that LD formation requires the uptake of live bacteria and depends on host cell cytoskeleton rearrangement and vesicular trafficking. TLR6 deletion, but not TLR2, completely abolished the induction of LDs by M. leprae, as well as inhibited the bacterial uptake in SCs. M. leprae-induced LD biogenesis correlated with increased PGE 2 and IL-10 secretion, as well as reduced IL-12 and NO production in M. leprae-infected SCs. Analysis of nerves from lepromatous leprosy patients showed colocalization of M. leprae, LDs, and cyclooxygenase-2 in SCs, indicating that LDs are sites for PGE 2 synthesis in vivo. LD biogenesis Inhibition by the fatty acid synthase inhibitor C-75 abolished the effect of M. leprae on SC production of immunoinflammatory mediators and enhanced the mycobacterial-killing ability of SCs. Altogether, our data indicated a critical role for TLR6-dependent signaling in M. leprae–SC interactions, favoring phagocytosis and subsequent signaling for induction of LD biogenesis in infected cells. Moreover, our observations reinforced the role of LDs favoring mycobacterial survival and persistence in the nerve. These findings give further support to a critical role for LDs in M. leprae pathogenesis in the nerve. The Journal of Immunology, 2011, 187: 2548–2558. L eprosy is an ancient infectious scourge caused by Myco- bacterium leprae that remains a public health problem in several countries (1). Leprosy constitutes an excellent model for deciphering the mechanisms that regulate innate and adaptive immunity in humans, because the disease presents as a clinical spectrum that correlates with the level of the immune response to the pathogen (2–4). At one end of the spectrum, individuals with polar tuberculoid leprosy (TT) develop a strong cellular immune response against M. leprae that restrains the growth of the pathogen. At the opposite end of the spectrum, failure of the immune system to kill or inhibit M. leprae is a conspicuous characteristic of polar lepromatous leprosy (LL). In the absence of antibiotic treatment, a large proportion of LL patients suffer lifelong debilitating disease in which the myco- bacteria are able to reproduce to very high numbers, mainly inside dermal macrophages and Schwann cells (SCs) of the peripheral nerve system. In these patients, M. leprae can live for years inside cells and has developed various, but poorly understood, mecha- nisms for escaping the host immune defenses. Markedly, the presence of collections of highly infected macrophages/SCs ac- cumulating large amounts of lipids, described as foamy cells, are characteristic in LL, but not in TT, lesions (5). The mecha- nisms that disturb the lipid homeostasis of M. leprae-infected cells remain nebulous. These lipids were initially thought to be derived from M. leprae, such as phthiocerol dimycocerosate/ dimycocerosate and phenolic glycolipid-1 (PGL-1) (6, 7). How- ever, very recently, a more detailed analysis of the lipid metabo- lism in LL lesions indicated that the foamy aspect is due mostly to the accumulation of host-derived lipids, such as oxidized phos- pholipids and cholesterol ester (8, 9).These lipids were shown to be stored in nonmembrane-bound cytoplasmic organelles known as lipid bodies or lipid droplets (LDs) (9). LDs are dynamic lipid-storage organelles found in all cell types that constitute rapidly mobilized lipid sources for many important *Laboratory of Cellular Microbiology, Oswaldo Cruz Institute, Oswaldo Cruz Foun- dation, Rio de Janeiro, RJ 21045-900, Brazil; † Laboratory of Immunopharmacology, Oswaldo Cruz Institute, Oswaldo Cruz Foundation, Rio de Janeiro, RJ 21045-900, Brazil; and ‡ Laboratory of Leprosy, Oswaldo Cruz Institute, Oswaldo Cruz Founda- tion, Rio de Janeiro, RJ 21045-900, Brazil 1 K.A.M. and V.G.C.O. contributed equally to this work as co-first authors. 2 M.C.V.P. and P.T.B. contributed equally to this work as co-senior authors. Received for publication May 9, 2011. Accepted for publication July 1, 2011. This work was supported by the Conselho Nacional de Desenvolvimento Cientı ´fico e Tecnolo ´gico, Programa Estrate ´gico de Apoio a ` Pesquisa em Sau ´de-Fundac ¸a ˜o Oswaldo Cruz, the Programa de apoio a Nu ´cleos de Excele ˆncia, and the Fundac ¸a ˜o de Amparo a ` Pesquisa do Estado do Rio de Janeiro. P.T.B. is a Guggenheim Fellow. K.A.M. and V.G.C.O. were recipients of a fellowship from the Fundac ¸a ˜o de Amparo a ` Pesquisa do Estado do Rio de Janeiro. Address correspondence and reprint requests to Dr. Patricia T. Bozza or Dr. Maria Cristina V. Pessolani, Laborato ´rio de Imunofarmacologia, Instituto Oswaldo Cruz, Fundac ¸a ˜o Oswaldo Cruz, Avenue Brasil 4365, Manguinhos, Rio de Janeiro, RJ 21045-900, Brazil (P.T.B.) or Laborato ´ rio de Microbiologia Celular, Instituto Oswaldo Cruz, Fundac ¸a ˜o Oswaldo Cruz, Avenue Brasil 4365, Manguinhos, Rio de Janeiro, RJ 21045-900, Brazil (M.C.V.P.). E-mail addresses: pbozza@ioc.fiocruz.br (P.T.B.) or cpessola@ioc.fiocruz.br (M.C.V.P.) The online version of this article contains supplemental material. Abbreviations used in this article: ADRP, adipose differentiation-related protein; BCG, bacillus Calmette-Gue ´rin; COX-2, cyclooxygenase-2; CytB, cytochalasin B; CytD, cytochalasin D; EIA, enzyme immunoassay; ER, endoplasmic reticulum; FAS, fatty acid synthase; LAM, lipoarabinomannan; LD, lipid droplet; LL, lepromatous leprosy; MFI, mean fluorescence intensity; MOI, multiplicity of infection; MSM, Mycobacterium smegmatis mc2 155; ORO, oil red O; PGL-1, phenolic glycolipid- 1; SC, Schwann cell; TT, tuberculoid leprosy; WT, wild-type. Copyright Ó 2011 by The American Association of Immunologists, Inc. 0022-1767/11/$16.00 www.jimmunol.org/cgi/doi/10.4049/jimmunol.1101344