INFLAMMATORY RESPONSE TO PSEUDOMONAS AERUGINOSA INCREASES THE ABILITY OF MACROPHAGES TO REMOVE APOPTOTIC CELLS'

JÄGER, AV; ARIAS, P; TRIBULATTI, MV; BROCCO, MA; PEPE, MV; KIERBEL, A

Virtual

Congreso; SAMIGE-SAIB; 2020

SAMIGE-SAIB

Pathogens phagocytosis and the uptake of apoptotic cells (efferocytosis) are essential macrophages tasks, classically considered as mutually exclusive. Macrophages have been described to polarize into either pro-inflammatory/microbicidal or anti-inflammatory/efferocytic phenotypes. However, macrophages function implicates much more complexity. Furthermore, little is known about regulation of efferocytosis under inflammatory conditions. Pseudomonas aeruginosa is an opportunistic pathogen that primarily infects immune-compromised individuals and/or patients with epithelial injury. While the epithelium provides a physical barrier against this gram-negative pathogen, innate immunity and, specifically, phagocytosis by neutrophils and macrophages are key determinants in the ability of the host to control P. aeruginosa infection. Thus, the host inflammatory response is intimately connected to the phagocytic clearance of the bacteria. In this study, we aimed to elucidate the modulation of macrophage efferocytic function during P. aeruginosa inflammatory stimulus. For this purpose, we exposed primary bone marrow-derived macrophages (BMDM) to apoptotic cells, bacteria and bacteria-laden apoptotic cells and examined their internalization (independently or in conjuction) by confocal microscopy and subsequent image analysis in order to investigate the phagocytic and efferocytic efficiencies. To study bacterial clearance, we measured intracellular survival over time. Also changes in cytokine expression levels were measured by real-time RT-PCR. We found that BMDM are very efficient in engulfing both the bacterial pathogen P. aeruginosa and apoptotic cells. BMDM showed a high bactericidal capacity which is not affected by the concomitant presence of apoptotic material. Plasticity in macrophage programming, in response to changing environmental cues, may modulate efferocytic capability. In this work we further showed that, after phagocyting and processing P. aeruginosa, macrophages highly increase their efferocytic capacity without affecting their phagocytic function. Moreover, we demonstrate that P. aeruginosa enhances efferocytosis of these phagocytes through the IL-6 signaling pathway. Our results show that, when confronted to this pathogen, macrophages respond through a pro-inflammatory response and microbicidal action to destroy the infectious agent. But, at the same time, the increase of the pro-inflammatory response that follows the bacterial processing promotes the clearance of apoptotic cells by these macrophages contributing to the resolution of local inflammation.