Neutrophils- Most abundant leukocyte with major function being phagocytosis
- Destroy pathogens in similar manner to macrophages; reactive intermediates and lysosomal enzymes contained in storage granules and classified as below:
- Azurophil granules (primary): myeloperoxidase, lysozyme, defensins, proteinase-3, canthelicidin, and cathepsin B/D
- Specific granules (secondary): lysozyme, collagenase, alkaline phosphatase, phospholipase A, and lactoferrin
- Small storage granules: gelatinase, plasminogen activator, and cathepsin B/D
- Two enzymes allow formation of reactive oxygen species (ROS) which are needed to efficiently kill engulfed bacteria: myeloperoxidase (MPO) and NADPH oxidase
- MPO: most effective microbicidal mechanism, responsible for green color of pus
- NADPH oxidase: defect results in inability to kill intracellular catalase-positive pathogens; defect seen in chronic granulomatous disease (CGD) where bacteria unable to reduce the dye nitroblue tetrazolium (NBT) during phagocytosis (unable to reduce yellow NBT dye to blue insoluble dye)
- Cells express receptors for IgG and complement
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