DEFECTS IN BACTERIAL KILLING
The best example of an immunodeficiency characterized by failure of phagocyte-mediated bacterial killing is chronic granulomatous disease (CGD). In normal neutrophils (and monocytes), bacterial phagocytosis result in the activation of the nicotineamide adenine dinucleotide phosphate (NADPH) oxidase complex, which produces superoxide and generates a millieu within the phagosome that activate the proteolytic enzymes, cathepsin, and elastase. The activity of the proteolytic enzymes is bactericidal. The NADPH oxidase complex comprises two membrane-associated proteins, p91phox and p22phox (also called the α and β units of cytochrome B558, respectively), complexes with three cytosolic cofactors, p47phox, p40phox and p67phox. Mutations have been identified in four out of five components (p91phox, p22phox, p47phox, p67phox), resulting in defective NADPH oxidase activity, leading to impairment of bacterial killing by phagocytic cells. The results is a clinical syndrome, called CGD, characterized by failure of bacterial degradation in vivo, resulting in the persistence of tissue inflammation with granuloma formation in a variety organs. CGD due to p91phox defiociency is x-linked, while the other variants of CGD are inherited in an autosomal recessive manner.