Delineation

of the phagocyte NADPH oxidase through

studies of chronic granulomatous

diseases of childhood

John I. Callin, Thomas 1. Leto, Daniel Rotrosen, Cheung H. Kwong and Harry 1. Malech National Institute

of Allergy and Infectious

Diseases, Bethesda, Maryland,

USA

The phagocyte NADPH oxidase is a complex system consisting of membrane and cytosolic components that must assemble at the membrane for proper activation. Studies of patients with chronic granulomatous diseases of childhood have enabled the molecular characterization of these components, which has led to studies defining their interaction during NADPH complex assembly. Understanding NADPH oxidase assembly provides an opportunity to develop therapeutics for the regulation of this important reaction of inflammation.

in Immunology

Current Opinion

Introduction When phagocytes are appropriately stimulated by opsonized microorganisms, antigen-antibody complexes, chemotactic factors or other stimuli, an NADPH oxidasedependent respiratory burst is activated resulting in the univalent reduction of molecular oxygen to superoxide anion. This superoxide anion is then converted to hydrogen peroxide by superoxide dismutase [I]. In the presence of iron salts, superoxide anion and hydrogen peroxide may interact further to produce hydroxyl radicals. These toxic oxygen products, particularly hydrogen peroxide, provide the phagocytic cell with a potent mechanism for killing micro-organisms. Recent studies have provided important insights into the components of the NADPH oxidase system required for phagocyte activation. Activation requires cellular components from both the cytosol and the cell membrane (Fig. 1). Following activation, all of the components necessary for superoxide production reside in the phagocyte plasma membrane or phagosome membrane and consist of an electron transport chain driven by a NADPH oxidase. The complete enzyme system appears to involve a klavoprotein and a unique cytochrome b558 [ 2 I. This cytochrome has been purilied and when analyzed by sodium dodecyl sulfate polyacrylamide electrophoresis (SDS PAGE), was found to consist of a highly glycolsylated large 91 kD subunit (gpslpb”“, glycopotein 91 kD phagocyte o&&e) and a small 22kD protein subunit (p2p). Studies of a cell-free system containing plasma membrane and purified proteins have demonstrated that two cytosolic components of 47 kD and 67 kD (p67*) [3,4] form a complex with cytochrome b55s

1991,

4153-56

and interact with a third cytosolic protein, a small GTPbinding protein p21 raCl [5-l. The GDP-dissociation inhibitor rhoGD1 may also be involved in the interaction of p21ra’ with the oxidase complex. Much of what is known about the NADPH oxidase system has come from studies of patients deficient in the system, who have chronic granulomatous diseases of childhood (CGDS).

Cytosol proteins

Membrane protein Cytochrome bSS8

~67~”

IO

Activation

rat-1

II

Large

subunit

Phagosome

Oxygen Assembly

of proteins Electrons a Superoxide anion

Electrons NADPH

Fig.1. Schematic diagram of components (See text for details.)

of the NADPH

oxidase.

Abbreviations AR-autosomal SDS-PACE--sodium

recessive; dodecyl

CGD-chronic sulfate

granulomatous

polyacrylamide

disease of childhood;

gel electrophoresis;

@ Current Biology Ltd ISSN0952-7915

X-x-linked.

53

54

Innate immunity

Chronic granulomatousdiseasesof childhood CGDs are a genetically heterogeneous group of disorders with a common phenotypic defect characterized by failure of phagocytic cells to activate the respiratory burst and produce microbicidal products [&I. CGDs are associated with a serious derangement in the ability to defend against bacterial and fungal infections. There is also excessive granuloma formation, indicating that these oxygen products may be important in negative feedback mechanisms required for normal termination of the iriIammatory response. CGDs occur with a frequency of one out of 1 OOOOOOZ two-thirds of cases are inherited as an X-linked disorder (X-CGD) and a third of the cases are inherited as an autosomal recessive disorder (AR-CGD). In addition to pedigree, the classification of CGDs has been relined by identification of specific abnormalities of the phagocytes associated with different forms of CGDs [7] as indicated in table 1 Table 1. Genetic forms of chronic granulomatous diseases of childhood.*

Defect Abnormal membrane

Abnormal

Chromosomal

Patients

protein

localization

Wo)

gp92@ox*

xp21.1

-60

p22@oxt

16~24