Question

1- Immune reaction – standard innate as well as specific humoral response appropriate to the Listeria monocytogenes pathogen

2- Epidemiology – where is it common, among whom, risk factors, vectors and reservoirs

3- Treatment – common resistances and alternative treatments – mechanism of action

Answer 1

1. Listeria monocytogenes is a gram positive bacterium that infects macrophages and epithelial cells. it has a intracellular life cycle and spreads from one cell to another. during innate immune responses, neutrophils and macrophages are recruited to the site of infection. These cells engulf the bacteria and kill them through reactive oxygen and nitrogen species.

this bacterium activates cell-mediated arm of the adaptive immune system. inside the infected macrophages, proteins secreted by L. monocytogenes are degraded through the host proteasome and the peptides are presented along with class I MHC and hence activate cytotoxic T cells or CD8⁺ T cells. the activated cytotoxic T cells kills the infected cells by perforin and granzymes and activates macrophages by secreting interferron-gamma.

since the bacteria remains intracellular during its life cycle, hence it does not activates a significant humoral immune response.