Myeloperoxidase

🔬 What is Myeloperoxidase (MPO)?

Myeloperoxidase (MPO) is a heme-containing enzyme present in the azurophilic granules of neutrophils and to a lesser extent in monocytes.

It catalyzes the reaction:

H₂O₂ + Cl⁻ → HOCl (hypochlorous acid)

HOCl is a powerful antimicrobial agent used in innate immunity.

1️⃣ Role in Acute Leukemia Diagnosis

MPO is clinically important in distinguishing:

• Acute Myeloid Leukemia (AML) → MPO positive

• Acute Lymphoblastic Leukemia (ALL) → MPO negative

Cytochemical Staining:

• MPO stain is positive in myeloblasts.

• Helps confirm myeloid lineage.

👉 Very important in hematology lab diagnosis.

2️⃣ Cardiovascular Disease Marker

Elevated plasma MPO is associated with:

• Atherosclerosis

• Plaque instability

• Acute coronary syndrome

MPO contributes to:

• LDL oxidation

• Endothelial dysfunction

• Plaque rupture

📌 Considered an early marker of cardiac risk, sometimes rises before troponin.

3️⃣ Inflammatory Disorders

Increased MPO levels seen in:

• Sepsis

• Chronic inflammatory diseases

• Rheumatoid arthritis

• Inflammatory bowel disease

Because MPO reflects neutrophil activation.

4️⃣ Vasculitis

MPO is a major target antigen in:

• MPO-ANCA (p-ANCA) associated vasculitis

Seen in:

• Microscopic polyangiitis

• Some cases of glomerulonephritis

5️⃣ Oxidative Stress Marker

MPO contributes to:

• Tissue damage

• Lipid peroxidation

• Protein modification

Thus used in research as a marker of oxidative stress.