Nocardia brasiliensis Cell Wall Lipids Modulate Macrophage and Dendritic Responses That Favor Development of Experimental Actinomycetoma in BALB/c Mice

Abstract

ABSTRACTNocardia brasiliensisis a Gram-positive facultative intracellular bacterium frequently isolated from human actinomycetoma. However, the pathogenesis of this infection remains unknown. Here, we used a model of bacterial delipidation with benzine to investigate the role ofN. brasiliensiscell wall-associated lipids in experimental actinomycetoma. Delipidation ofN. brasiliensiswith benzine resulted in complete abolition of actinomycetoma without affecting bacterial viability. Chemical analyses revealed that trehalose dimycolate and an unidentified hydrophobic compound were the principal compounds extracted fromN. brasiliensiswith benzine. By electron microscopy, the extracted lipids were found to be located in the outermost membrane layer of theN. brasiliensiscell wall. They also appeared to confer acid-fastness.In vitro, the extractable lipids from theN. brasiliensiscell wall induced the production of the proinflammatory cytokines interleukin-1β (IL-1β), IL-6, and CCL-2 in macrophages. TheN. brasiliensiscell wall extractable lipids inhibited important macrophage microbicidal effects, such as tumor necrosis factor alpha (TNF-α) and nitric oxide (NO) production, phagocytosis, bacterial killing, and major histocompatibility complex class II (MHC-II) expression in response to gamma interferon (IFN-γ). In dendritic cells (DCs),N. brasiliensiscell wall-associated extractable lipids suppressed MHC-II, CD80, and CD40 expression while inducing tumor growth factor β (TGF-β) production. Immunization with delipidatedN. brasiliensisinduced partial protection preventing actinomycetoma. These findings suggest thatN. brasiliensiscell wall-associated lipids are important for actinomycetoma development by inducing inflammation and modulating the responses of macrophages and DCs toN. brasiliensis.