Assessment of neutrophil function

There are 3 mechanisms for opsonization. Firstly, specific antibody that reacts with the bacterial cell walls will then attach to the surface of neutrophils via their Fc receptors, which are for the heavy chains of antibody molecules. Secondly, the classical pathway of complement activation yields opsonic C3b, which attaches to a complement receptor (CR) on the neutrophil surface; thirdly, the alternative pathway properdin system also generates C3b. In fact each neutrophil has 120,000 receptors for the Fc ofIgG and 38,000 surface receptors for C3b (designated CR1 for C3b and CR3 for iC3b). After ingestion most bacteria cen be killed in the phagosomes by the action of 'reactive oxygen intermediates' (ROTs) or by the action of cationic proteins and lysosomal proteases. There are two types of granule within the neutrophil. The primary azurophilic granules contain acid hydrolases and neutral proteases, and the vital myeloperoxidase (MPO) which generates bactericidal hypochlorite from hydrogen peroxide. The specific granules contain lysozyme, lactoferrin, cathepsin G, a collagenase and a protease that will generate C5a from C5. In the process ofphagocytosis each type ofgranule fuses with the phagosome and releases its contents into it. So the lysozyme can digest the peptidoglycan of gram-positive bacterial cell walls, which it does by digesting the bond between muramic acid and Nacetylglucosamine. Then the generated reactive oxygen intermediates together with cationic proteins aid the killing and disintegration of bacteria.