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Inhibition of neutrophil myeloperoxidase activity by selected tissues
Abstract:
Myeloperoxidase, a polymorphonuclear leukocyte-specific enzyme, has been used previously to quantify the number of polymorphonuclear leukocytes in tissue. When this method was employed in an attempt to measure polymorphonuclear leukocyte numbers in infected kidneys, it was found that myeloperoxidase could not be demonstrated, although significant numbers of neutrophils were present in the pyelonephritic lesions. Further studies were carried out to determine the effect of other tissues on free and cell-bound exogenous myeloperoxidase. We have shown that while skin had little effect on enzyme levels, liver and spleen totally destroyed myeloperoxidase activity within 30 sec. Cardiac and striated muscle had an intermediate effect. When intact neutrophils were added to fresh cardiac tissue 72.5% myeloperoxidase activity was destroyed during the enzyme solubilization procedure. These findings indicate that the technique can only be used for the quantification of polymorphonuclear leukocytes in selected tissues and that appropriate controls are essential. Previous studies in which myeloperoxidase levels have been used to estimate polymorphonuclear leukocyte numbers in cardiac tissue will need reevaluation.
Insights
Myeloperoxidase (MPO) enzyme activity is destroyed by certain tissues, limiting its use for quantifying neutrophils in infected kidneys. Careful tissue selection and controls are essential for accurate neutrophil quantification.
Area of Science:
- Biochemistry
- Immunology
- Pathology
Background:
- Myeloperoxidase (MPO) is an enzyme specific to polymorphonuclear leukocytes (neutrophils).
- MPO activity has been used to quantify neutrophil numbers in various tissues.
- Previous studies have relied on MPO levels to estimate neutrophil infiltration.
Purpose of the Study:
- To investigate the impact of different tissues on myeloperoxidase (MPO) activity.
- To determine the reliability of MPO quantification for neutrophils in infected kidneys.
- To assess the influence of tissue environment on MPO enzyme stability.
Main Methods:
- Assessing MPO activity in infected kidney tissue.
- Incubating exogenous MPO with various tissue homogenates (skin, liver, spleen, cardiac, striated muscle).
- Evaluating MPO activity after incubation with intact neutrophils and fresh cardiac tissue.
Main Results:
- MPO was undetectable in infected kidney lesions despite neutrophil presence.
- Liver and spleen completely abolished MPO activity within 30 seconds.
- Cardiac and striated muscle partially reduced MPO activity, with significant loss even with intact neutrophils.
Conclusions:
- MPO quantification is not universally applicable for neutrophil enumeration due to tissue-specific enzyme degradation.
- The presence of certain tissues, particularly liver and spleen, inactivates MPO.
- Accurate neutrophil quantification using MPO requires careful consideration of tissue type and appropriate controls, necessitating reevaluation of previous cardiac tissue studies.