Immunology

Myeloperoxidase (MPO) is an enzyme contained in lysosomal azurophilic granules of neutrophils. MPO activity has been shown to correlate with the number of neutrophils in histological sections of the gastrointestinal tract and is therefore accepted as a biomarker of neutrophil invasion in the gut. This protocol describes an easy, cost-effective kinetic colorimetric assay to quantify myeloperoxidase activity in intestinal tissue samples. It is explained using tissue collected in mice but can also be used for other laboratory animals. In a first step, tissue specimens are homogenized using a phosphate buffer containing 0.5% hexadecyltrimethylammonium bromide (HTAB), which extracts MPO from neutrophils. The obtained supernatant is added to a reagent solution containing o-dianisidine dihydrochloride, which is a peroxidase substrate. Finally, the change in absorption is measured via spectrophotometry and converted to a standardized unit of enzyme activity. The assay is illustrated and compared to a commercially available enzyme-linked immunoassay (ELISA), demonstrating that MPO activity does not necessarily correlate with MPO protein expression in tissue samples.

Key features

• Optimized for use in mice and rats but can also be used for samples of other species.

• Measures enzymatic activity instead of mRNA or protein expression.

• Requires a spectrophotometer.

• Can be performed in duplo using 10 mg of (dry-blotted) gut tissue or more.

Graphical overview

Fungal pathogen Candida albicans is one of the top leading causes of overall healthcare-associated bloodstream infections worldwide. Neutrophil is the major effector cell to clear C. albicans infection. Our study showed that mouse neutrophils utilize two independent mechanisms to kill C. albicans: one is CR3 downstream NADPH oxidase-dependent mechanism that kills opsonized C. albicans; the other one is dectin-2-mediated NADPH oxidase-independent neutrophil extracellular trap (NET) that kills unopsonized C. albicans. Neutrophil killing of opsonized C. albicans requires phagocytosing the organism and production of reactive oxygen species production (ROS). Most existing protocols that assay for neutrophil killing of C. albicans requires a washing step after allowing neutrophils to phagocytose the organism. By definition, NET kills organisms extracellularly. Therefore, it is important to skip the washing step and add an optimal ratio of neutrophils and C. albicans to the wells. To demonstrate the effect of NET, it is necessary to compare killing ability of neutrophils treated with micrococcal nuclease (MNase), an enzyme that digests NET, to that treated with heat-inactivated MNase. MNase is also applied to release NET-bound fungal elements for counting. This protocol can be applied to assay NET killing of other biofilm-forming organisms.

In the recent decade, neutrophil extracellular traps (NETs) have been identified and confirmed as a new anti-microbial weapon of neutrophils. In this protocol, we describe easy methods to demonstrate NET formation by immunofluorescence staining of extracellular chromatin fiber with anti-DNA/Histone H1 antibody and quantification of NETs by using a non-cell-permeable DNA specific dye Sytox orange.

The inflammatory response is essential to the reestablishment of cutaneous homeostasis following injury. In this context, leukocytes arrive at the wound site and orchestrate essential events in the wound healing process. Therefore, the quantification of specific subsets of inflammatory cells in the wound tissue is of considerable interest. The current protocol focus on a quantitative index of neutrophils and macrophages accumulation within skin lesions by measuring the specific activity of the marker enzymes Myeloperoxidase (MPO) and N-acetyl-β-D-glucosaminidase (NAG), respectively. MPO is present in high levels in the azurophilic granules of neutrophils and NAG in lysosomes of activated macrophages. These methods allow the indirect estimation of the abundance of neutrophils and macrophages accumulated into the skin.

Neutrophil extracellular traps (NETs) are extracellular DNAs decorated with nuclear and granular proteins such as histones, neutrophil elastase or myeloperoxidase. They exhibit fibrous mesh-like, web-like, or string-like structures. Here, we describe our protocol regarding visualization of ex vivo NETs released from neutrophils activated by lipopolysaccharide (LPS) using fluorescence microscopy.

Neutrophil extracellular traps (NETs) are fibrous mesh-like, web-like, or string-like structures which are composed of DNA, histones, and granule proteins such as neutrophil elastase or myeloperoxidase. When activated by phorbol myristate acetate, interleukin-8, lipopolysaccharide (LPS), and various pathogens, neutrophils release NETs. We reported that NETs were classified as two distinct forms; cell-free NETs that were released away from neutrophils and anchored NETs that were anchored to neutrophils. In general, extracellular DNAs are used as a surrogate marker of NETs. Here, we describe a protocol regarding quantitative procedures of extracellular DNAs released from ex vivo neutrophils activated by LPS using fluorometric double-stranded DNA (dsDNA) quantification assay.