myeloperoksidase

Myeloperoxidase (MPO) is an enzyme found in high concentrations within the lysosomes of phagocytic cells, particularly neutrophils and monocytes. It is synthesized during the differentiation of myeloid cells. MPO plays a crucial role in the innate immune system by catalyzing the formation of hypochlorous acid (HOCl) from hydrogen peroxide and chloride ions. This potent oxidant is a key component of the reactive oxygen species produced by phagocytes to kill ingested microorganisms.

The activity of MPO is vital for host defense against bacterial and fungal infections. When a phagocyte engulfs a pathogen, it fuses with lysosomes containing MPO. In the presence of hydrogen peroxide, MPO oxidizes chloride ions to generate HOCl, which can directly damage microbial components and kill the pathogen. MPO also contributes to inflammation by generating other reactive species that can signal to other immune cells.

Beyond its antimicrobial functions, MPO has been implicated in various inflammatory and autoimmune diseases. Elevated levels of MPO or its oxidative products are found in conditions such as atherosclerosis, rheumatoid arthritis, and inflammatory bowel disease. In atherosclerosis, MPO can oxidize low-density lipoprotein (LDL), promoting plaque formation. While essential for defense, dysregulated MPO activity can contribute to tissue damage and disease progression. Research continues to explore MPO's complex roles in health and disease.