Aims: Determine how membrane vesicles from bacterial lung pathogens affect alveolar macrophage (AM) function.
Methods: Bone-marrow derived alveolar macrophages (BMDAMs) were challenged with bacterial vesicles derived from K. pneumoniae, S. aureus, P. aeruginosa, and E. coli. Immune responses were assessed using multiplex cytokine assays, western blotting, and flow cytometry and compared to commonly used bone-marrow derived macrophages (BMDM). Host responses including cell death, apoptotic caspase activation, and mitochondrial health were examined through real-time analysis using live cell imaging. To investigate the role of BCL-2 family members in AMs, A1-deficient AMs and BH3 mimetics, such as ABT-737, and S63845, were used.
Results: Bacterial vesicles induced pro-inflammatory cytokine secretion in both BMDM and BMDAMs. However, vesicles caused higher levels of cell death in BMDMs compared to BMDAMs. Treatment with P. aeruginosa vesicles led to increased expression of anti-apoptotic proteins A1 and MCL-1 in AMs. Live cell imaging of A1-deficient cells, combined with the MCL-1 inhibitor S63845, resulted in higher levels of cell death compared to wild type.
Conclusions: Alveolar macrophages show increased survival rates and secretion of pro-inflammatory cytokines in responses to P. aeruginosa membrane vesicles. Anti-apoptotic proteins A1, and MCL-1 play crucial roles in alveolar macrophages by promoting macrophage survival when challenged with P. aeruginosa vesicles. These findings highlight the intricate interplay between macrophages and bacterial vesicles, shedding light on their role in modulating inflammation during infections.