Induction of Reactive Intermediates and Autophagy-Related Proteins upon Infection of Macrophages withRhodococcus equi

Abstract

Rhodococcus equi (R. equi)is an intracellular macrophage-tropic pathogen with potential for causing fatal pyogranulomatous pneumonia in foals between 1 and 6 months of age. In this study, we sought to determine whether infection of macrophages withR. equicould lead to the induction of autophagy. Murine bone marrow derived macrophages (BMDM) were infected withR. equifor various time intervals and analyzed for upregulation of autophagy proteins and accumulation of autophagosomes relative to uninfected controls. Western blot analysis showed a progressive increase in LC3-II and Beclin1 levels in a time-dependent manner. The functional accumulation of autophagosomes detected with monodansylcadaverine further supported the enhanced induction of autophagy in BMDM infected withR. equi. In addition, infection of BMDM withR. equiinduced generation of reactive oxygen species (ROS) in a time-dependent manner. These data are consistent with reports documenting the role of ROS in induction of autophagy and indicate that the infection of macrophages byR. equielicits innate host defense mechanisms.