Microparticles released by Listeria monocytogenes-infected macrophages contribute to the generation of protective immunity: insight into interaction between macrophages and dendritic cells (100.33)

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Abstract Mutual interaction among immune cells is of paramount importance to an efficient protective immunity against bacterial infection. However, the interplay between macrophages and dendritic cells (DC) in the processing and presentation of bacterial antigens for T cell immune responses remains poorly understood. In this report, using Listeria monocytogenes (Lm) infection model, we demonstrate that DCs require the support of macrophages to elicit the protective immunity against Lm infection. We found that DCs themselves were inefficient at taking up Lm but capable of taking up microparticles released by Lm-infected macrophages. These microparticles transferred Lm antigens to DCs, allowing DCs to present Lm antigen to effector T cells. Such microparticles-mediated Lm antigen transfer required MHC class I participation, since MHC class I deficiency in macrophages resulted in a significant reduction of T cell activation. Moreover, the vaccination of mice with microparticles from Lm-infected macrophages produced strong protective immunity against the challenge of Lm. Thus, we have identified an intrinsic antigen transfer program between macrophages and DCs during Lm infection, and emphasized that macrophages also play an essential role in DC-elicited Lm-specific T cell responses.