Robert A. Clark

Two cytosolic components of the human neutrophil respiratory burst oxidase translocate to the plasma membrane during cell activation.

The superoxide-forming respiratory burst oxidase of human neutrophils is composed of membrane-associated catalytic components and cytosolic constituents required for oxidase activation. This study concerns the hypothesis that cytosolic oxidase components translocate to a membrane fraction when neutrophils are stimulated and the oxidase is activated. A polyclonal antiserum that recognizes two discrete cytosolic oxidase components of 47 and 67 kD was used to probe transfer blots of electrophoresed membrane and cytosol fractions of resting and stimulated neutrophils. In contrast to their strictly cytosolic localization in unstimulated cells, both proteins were detected in membrane fractions of neutrophils activated by phorbol esters and other stimuli. This translocation event was a function of stimulus concentration as well as time and temperature of exposure to the stimulus. It was inhibited by concentrations of N-ethylmaleimide that blocked superoxide formation but was unaffected by 2-deoxyglucose. There was a correlation between translocation of the cytosolic proteins and activation of the oxidase as determined by superoxide formation. Quantitative analyses suggested that approximately 10% of total cellular p47 and p67 became membrane-associated during phorbol ester activation of the oxidase. Analysis of Percoll density gradient fractions indicated that the target membrane for translocation of both proteins was the plasma membrane rather than membranes of either specific or azurophilic granules. In the cell-free oxidase system arachidonate-dependent but membrane-independent precipitation of the cytosolic oxidase proteins was demonstrated. The data show that activation of the respiratory burst oxidase in stimulated human neutrophils is closely associated with translocation of the 47- and 67-kD cytosolic oxidase components to the plasma membrane. We suggest that this translocation event is important in oxidase activation.

Genetic Variants of Chronic Granulomatous Disease: Prevalence of Deficiencies of Two Cytosolic Components of the NADPH Oxidase System

Chronic granulomatous disease, a syndrome of recurrent infections and failure of oxidative microbicidal activity in phagocytes, results from defects in the gene for one of several components of an oxidase system that can undergo activation. To determine the relative prevalence of certain of the genetic variants of this disorder, we used immunoblotting to detect two specific neutrophil cytosolic proteins of 47 and 67 kd recently shown to be required for oxidase activation. Chronic granulomatous disease is usually an X-linked disorder associated with the absence of membrane cytochrome b558. Of our 94 patients with chronic granulomatous disease, however, 36 had a phenotype characterized by autosomal inheritance, normal membrane oxidase components (including cytochrome b558), and functionally defective cytosolic activity in a cell-free oxidase system. We studied 25 of these 36 patients and found that 22 lacked the 47-kd cytosolic protein, and the remaining 3 were missing the 67-kd component. Patients with chronic granulomatous disease whose functional defect was localized to the neutrophil membrane (classic X-linked cytochrome b-negative type and two other rare variants) had normal amounts of both cytosolic components. We estimate that approximately 33 percent of all patients with chronic granulomatous disease are missing the 47-kd cytosolic oxidase component and about 5 percent of patients are missing the 67-kd component. Chronic granulomatous disease caused by a defect in any cytosolic factors other than the 47-kd and 67-kd proteins, if it exists, is apparently rare.

Isolation and Functional Analysis of Neutrophils

This unit describes the isolation of high‐purity neutrophils (or polymorphonuclear leukocytes; PMN) and the assays that can be performed to assess their function. An assay for the in vitro study of phagocytic capacity is presented, and microbicidal assays using lysostaphin and differential centrifugation are also described. During phagocytosis or on exposure to soluble agonists, neutrophils exhibit a marked increase in oxidative metabolism which is mediated by activation of NADPH oxidase and results in the formation of superoxide anion as well as hydrogen peroxide and other reactive species. The nitroblue tetrazolium reduction slide test is presented, and is a nonquantitative screening test for the presence of reactive oxygen products. The quantitation of superoxide by the kinetic and static assays are detailed, and a “broken cell” assay is also outlined.Finally, measurement of hydrogen peroxide formation is described.

A cytosolic inhibitor of human neutrophil elastase and cathepsin G

The neutrophil serine proteinases elastase and cathepsin G produce connective tissue injury, the extent of which depends on the balance between these enzymes and their inhibitors. The most important of these inhibitors is α1‐proteinase inhibitor, a member of a superfamily of homologous proteins known as serpins. Neutrophil cytosol inhibited the activities of human neutrophil elastase and cathepsin G in a dose‐dependent fashion. To demonstrate formation of an enzyme‐inhibitor complex, we combined 125l‐elastase or 125l‐cathepsin G with neutrophil cytosol or α1‐proteinase inhibitor and analyzed the products by polyacrylamide gel electrophoresis. Unbound elastase and cathepsin G each migrated to an apparent molecular weight of 25 kDa. In the presence of cytosol from neutrophils both radiolabeled enzymes migrated with a relative size of 68 kDa, whereas in the presence of α1‐proteinase inhibitor the relative size was 85 kDa. Enzyme‐inhibitor complexes were stable in sodium dodecyl sulfate at 100° but were dissociated by hydrolysis in ammonium hydroxide (1.5 mol/L) at 37°. Formation of each complex was prevented by pretreatment of elastase or cathepsin G with diisopropylfluorophosphate, indicating that the inhibitor binds to the active site of the enzyme. Exposure of either α1‐proteinase inhibitor or neutrophil cytosol to the myeloperoxidase‐H2O2‐halide system prevented complex formation, suggesting the presence of an oxidizable amino acid at the binding site of the inhibitor. By electrophoretic analysis, the molecular weight of the cytosolic inhibitor was 43 kDa and neutrophils contained approximately 1 attomol of inhibitor per cell. The isoelectric points of the elastase and cathepsin G inhibitor were 5.5–5.9 and inhibitors of the two proteinases coeluted using size exclusion chromatography. These data demonstrate that human neutrophil cytosol contains a single serpin‐like protein that inhibits elastase and cathepsin G. The inhibitor may be important in protecting the intracellular environment from proteolytic injury during degranulation.