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Chapter 103 : Neutropenia and Neutrophil Defects
Cutaneous infections with Staphylococcus aureus are often recurrent and can be severe. In neutrophil disorders characterized by inadequate inflammation (neutropenia, leukocyte adhesion deficiency [LAD], Chédiak-Higashi syndrome, and specific granule deficiency), infections can extend locally and subcutaneously with little reaction until marked destruction has taken place. There are three basic mechanisms by which neutropenia can occur: decreased neutrophil production, increased neutrophil destruction, or abnormal neutrophil trafficking (either defective release of neutrophils from the bone marrow or an abnormal increase in the marginated or tissue pools). Recently, an autosomal dominant disorder with mild neutropenia due to neutrophil retention in the bone marrow (myelokathexis) has been molecularly characterized. The determination of a qualitative defect of neutrophil function is more complex than the simple determination of neutropenia, since it requires the demonstration of a dysfunctional phenotype. The major classes of neutrophil defects highlight the major neutrophil functions: adhesion, chemotaxis, phagocytosis, degranulation, and killing. Nitroblue tetrazolium (NBT) reduction and dihydrorhodamine (DHR) oxidation are the simplest tests available and are discussed. Chemiluminescence and staphylococcal killing are also discussed since they not only are used in the demonstration of CGD functional defects but also occasionally may help in diagnosis. Despite the important role of myeloperoxidase (MPO) in the neutrophil, clinical disease from MPO deficiency is quite rare and has been reported mostly for diabetics with disseminated Candida infections. MPO is an important marker of myeloid maturation, appearing at the promyelocyte stage of development.