A Listeria monocytogenes strain with a constitutively active phospholipase C is susceptible to intracellular killing by neutrophils through an MPO-dominant mechanism 2677

Abstract Description Listeria monocytogenes, a facultative intracellular pathogen, causes listeriosis, a serious illness that particularly affects immunocompromised individuals. Once inside host cells, the bacterium escapes from phagosomes by employing an enzyme, phospholipase PC-PLC, enabling it to multiply in the cytosol. Normally secreted as an inactive pro-protein, PC-PLC becomes functional after cleavage. A mutant strain of Listeria, Δpro-PC-PLC, lacks the pro-peptide, resulting in a consitutively active enzyme. Mouse studies have shown that this mutant strain is significantly weakened, with neutrophils playing a critical role in clearing the infection. We hypothesized that neutrophils are directly responsible for eliminating the Δpro mutant strain. To test this, we isolated human neutrophils and exposed them to both wild-type (WT) and Δpro bacteria, measuring bacterial killing rates. Results revealed that Δpro bacteria were eliminated more effectively than WT bacteria. Further analysis showed increased release of myeloperoxidase (MPO) by neutrophils infected with Δpro bacteria. Western blot experiments also indicated elevated levels of PKC and LC3A/B proteins in Δpro-infected neutrophils. Additionally, fluorospectrometry demonstrated higher calcium ion levels in neutrophils exposed to Δpro bacteria following fMLP receptor activation. Our data suggest that Δpro bacteria lose their ability to regulate intracellular signaling pathways, leading to enhanced anti-bacterial neutrophil responses. Funding Sources Internal funding. Topic Categories Innate Immune Responses and Host Defense: Cellular Mechanisms (INC)