Myeloperoxidase (MPO) is a protein produced by certain white blood cells, and a myeloperoxidase assay is a laboratory test designed to measure its presence or activity in the body. These assays serve as tools to understand various biological processes linked to immune responses and inflammation. By quantifying MPO, scientists and healthcare professionals can gain insights into the body’s defensive mechanisms and potential imbalances.
Understanding Myeloperoxidase (MPO)
Myeloperoxidase is an enzyme primarily found within neutrophils, a type of white blood cell that plays a significant role in the immune system. This enzyme is encoded by the MPO gene located on chromosome 17 in humans. Neutrophils store MPO in specialized compartments called azurophilic granules, releasing it when activated, such as during an infection.
The main function of MPO involves its ability to catalyze the conversion of hydrogen peroxide and chloride ions into hypochlorous acid. This powerful antimicrobial agent is similar to bleach and helps neutrophils kill invading bacteria and fungi. MPO also generates other reactive oxygen species, which contribute to the body’s defense against pathogens within cellular compartments called phagosomes.
Purpose of Myeloperoxidase Assays
Myeloperoxidase assays quantify MPO levels in biological samples, providing valuable insights into the body’s inflammatory state and immune system activity. These assays are useful in both research and clinical environments.
In research, MPO assays help scientists investigate the role of inflammation in various diseases and evaluate potential therapeutic interventions. In clinical settings, elevated MPO levels can suggest the presence of an underlying inflammatory condition, guiding further diagnostic steps. Monitoring MPO can also help assess the severity of inflammation or track a patient’s response to treatment.
How Myeloperoxidase Assays Work
Myeloperoxidase assays measure either the amount of MPO protein present or its enzymatic activity. One common method involves a colorimetric reaction where a specific chemical substrate is used. When MPO, in the presence of hydrogen peroxide, acts on this substrate, it causes a noticeable color change.
The intensity of this color change is then measured using a device called a spectrophotometer. A stronger color indicates a higher amount of MPO activity in the sample. Another approach utilizes antibodies that bind to the MPO protein.
These antibody-based assays, such as enzyme-linked immunosorbent assays (ELISA), capture MPO from a sample. After unbound substances are washed away, a detection system quantifies the captured MPO, providing a measure of its concentration. Both activity and concentration measurements offer different but complementary insights into MPO’s presence in the body.
Myeloperoxidase Levels and Health
Elevated levels of myeloperoxidase are associated with various health conditions, particularly those involving inflammation and oxidative stress. High MPO levels have been linked to an increased risk of cardiovascular diseases, including atherosclerosis. MPO contributes to the development of atherosclerosis by modifying low-density lipoprotein (LDL) cholesterol, turning it into a form that can promote plaque buildup in arteries. It also produces hypochlorous acid, which directly damages artery walls and interferes with the protective functions of high-density lipoprotein (HDL) cholesterol.
Increased MPO levels are also observed in certain autoimmune conditions, such as microscopic polyangiitis and systemic lupus erythematosus. While MPO plays a role in the immune system’s defense, its excessive or uncontrolled release can lead to collateral damage to healthy tissues. The reactive molecules generated by MPO, though effective against pathogens, can contribute to tissue injury when misdirected.
Conversely, reduced MPO levels, a condition known as myeloperoxidase deficiency, are hereditary. Individuals with this deficiency may have a mild impairment in their immune response, making them more susceptible to certain fungal infections, particularly those caused by Candida species. While MPO deficiency is often benign, recurrent Candida infections can be a clinical symptom.