Spectroscopic interference of hemoglobin with neutrophil cytochrome b-245 and its elimination by carbon monoxide

Spectrophotometric determination of neutrophil cytochrome b558 of chronic granulomatous disease

BACKGROUND

Chronic granulomatous disease (CGD) is an inherited disease characterized clinically by severe recurrent bacterial infections from infancy. This disease is a disorder of the formation of superoxide (O2-) by the neutrophil NADPH oxidase system, mostly due to defects in cytochrome b558 (cyt b558), which is one of the oxidase components. Diagnosis of CGD has been performed by the assay of the O2- forming activity, immunological determination of defects in the oxidase components, and or spectrophotometry of cyt b558. However, spectrophotometric analysis of the b-type heme is difficult with small amounts of blood from infant CGD patients, as the limited amounts of neutrophils are contaminated with a relatively high ratio of hemoglobin (Hb) that interferes with the heme spectrum of cyt b558. This report presents an accurate method for the spectrophotometric analysis of cyt b558 in a small amount of CGD neutrophils that were treated with CO gas in a safe procedure instead of the previously reported CO-bubbling method.

METHODS AND RESULTS

The difference of the reduced minus oxidized cyt b558 spectrum was measured under no interference from oxy Hb at the alpha and beta bands and differentiated as d[delta A]/d lambda (lambda = wavelength) to obtain further evidence for the defects of the cyt b558 heme spectrum. The interference from CO-insensitive met Hb was eliminated by subtracting the absorption peak at the Soret (gamma) band of the contaminating met Hb, which was estimated from the CO-treated and untreated spectra of the same, hemolyzed sample.

CONCLUSIONS

This spectrophotometric method is feasible for the determination of abnormality and heme content of cyt b558 with a small amount of CGD neutrophils in 10-20 mL of blood even in the presence of contaminating Hb.

The measurement of cytochrome b559 in polymorphonuclear leukocytes and macrophages in the presence of hemoglobin or mitochondrial cytochromes

A cyanide-insensitive b-type cytochrome (cytochrome b559) is involved in the respiratory burst of phagocytes. Spectroscopic measurement of its content in polymorphonuclear leukocytes or macrophages is complicated by signals arising from contaminating Hb or mitochondrial cytochromes upon reduction by dithionite. These interferences can be overcome by reducing the sample with dithionite, aerating it, and reducing it a second time with dithionite, in the presence of 10 microM cyanide. Cyanide suppresses the response of the interfering proteins to the second dithionite reduction. This modified method allows an accurate determination of the content of cytochrome b559 using smaller numbers of cells than previously feasible.

Role of cytochrome b-559 in arachidonic acid activation of resting human neutrophils

Whether or not cytochrome b-559 is a necessary component of NADPH oxidase activity in neutrophils is still controversial. In highly purified plasma membranes isolated from resting neutrophils and lacking cytochrome b, addition of arachidonic acid induced an NADPH oxidase activity. This activity was similar to that of plasma membranes isolated from phorbol myristate acetate (PMA)-stimulated cells which possessed cytochrome b. Addition of arachidonic acid to the latter plasma membranes did not alter the oxidase activity. It can be concluded that plasma membranes isolated from resting neutrophils have, in the presence of arachidonic acid, an NADPH oxidase activity similar to that of PMA-stimulated cells, except that it is independent of cytochrome b-559.

Analysis of the nonfunctional respiratory burst in murine Kupffer cells

Murine Kupffer cells (KCs), which constitute one of the largest populations of tissue macrophages, differ from most other cells of the myelomonocytic lineage in lacking the capacity for a respiratory burst. A collagenase perfusion technique followed by adherence to plastic at low temperature yielded pure cultures of KCs uniformly expressing receptors for Fc and C3bi, and containing virtually no morphologically detectable intracytoplasmic debris. Such KCs took up and oxidized glucose via the hexose monophosphate shunt about the same as peritoneal macrophages (PCs). Respiratory burst stimuli failed to enhance the hexose monophosphate shunt in KCs, probably because no H2O2 was produced. Detergent-permeabilized KCs generated no O2- in the presence of 1 mM NADPH, in striking contrast to all PC populations studied. Yet, KCs contained at least one component of the O2(-)-producing oxidase, cytochrome b559, in the same quantities as PCs and neutrophils. Cytochrome b559 was demonstrated by a novel double-reduction spectral technique that eliminated interference from hemoglobin and mitochondrial cytochromes. Consistent with the presence of the oxidase, KCs acquired normal respiratory burst capacity after prolonged incubation in vitro. The defect in triggering the respiratory burst in KCs was selective for the reduction of O2 by NADPH, in that reduction of O2 by endogenous arachidonate was readily demonstrate in response to zymosan. The percent of arachidonate released, the percent oxygenated, and the suppression of prostacyclin and leukotriene C production, as well as the pattern of LFA-1 expression, all resembled the pattern reported with PCs several days after exposure to bacteria. Indeed, exposure of PCs to low numbers of zymosan particles led gradually to complete suppression of respiratory burst capacity and refractoriness to its enhancement by rIFN-gamma, as evident in KCs both before and after their explanation. Thus, the modulation of oxidative metabolism that characterizes KCs probably arises from frequent endocytic encounters. This phenomenon may permit macrophages to act as scavengers without oxidative damage to bystander cells.