A modified spectrophotometric test for nitroblue-tetrazolium reduction of granulocytes and monocytes and its application for testing inhibition of monocytes by serum components in tumor patients

A Quantitative Nitroblue Tetrazolium Assay for Determining Intracellular Superoxide Anion Production in Phagocytic Cells

Conventionally, a semi-quantitative microscopic nitroblue tetrazolium (NBT) assay is used to determine the production of superoxide anion (O2(-)) in various phagocytic cells. This microscopic assay is conducted by counting the cells containing blue NBT formazan deposits, which are formed by reduction of the membrane permeable, water-soluble, yellow-colored, nitroblue tetrazolium (Y-NBT) by O2(-). However, this assay is semi-quantitative and is prone to observer bias. In the present study, we modified the NBT assay by dissolving the blue formazan particles using 2M potassium hydroxide and dimethylsulfoxide and then measured its absorbance using a microplate reader at 620nm. The absorbance of dissolved NBT increased in proportion to cell number (r = 0.9907), incubation time, and stimulus concentration. To test the usefulness of this modified assay, we compared the abilities of a number of types of phagocytic cells to produce O2(-). The cells examined included murine macrophage cell lines (RAW 264.7 and J774), freshly prepared murine peritoneal macrophages and neutrophils, a human myeloid cell line (PLB-985), and freshly prepared human peripheral blood neutrophils. In addition, we demonstrate that nitric oxide produced by RAW 264.7 cells does not interfere with the modified colorimetric NBT assay. Taken together, our results indicate that the modified colorimetric NBT assay is simple, sensitive, and quantitative, and that it can be used to determine the amounts of intracellular O2(-) produced by phagocytic cells. Thus, this assay is sensitive enough to measure, quantitatively, even the small amounts of O2(-) produced in monocytes and macrophages that are not detectable by the conventional microscopic NBT assay.

Retinoids and myelomonocytic growth factors cooperatively activate RARΑ and induce human myeloid leukemia cell differentiation via MAP kinase pathways

Use of all-trans-retinoic acid (ATRA) in combinatorial differentiation therapy of acute promyelocytic leukemia (APL) results in exceptional cure rates. However, potent cell differentiation effects of ATRA are so far largely restricted to this disease and long-term survival rates in non-APL acute myelogeneous leukemia (AML) remain unacceptably poor, requiring development of novel therapeutic strategies. We demonstrate here that myelomonocytic growth factors (granulocyte colony-stimulating factor [G-CSF] and/or granulocyte macrophage colony-stimulating factor [GM-CSF]) potentiate differentiation effects of ATRA in different AML cell lines and primary cells from patients with myeloid leukemia. The ligand-dependent activities of endogenous and transiently expressed retinoic acid receptor alpha (RARα) isoforms can be potentiated by G/GM-CSF in U-937 cells and correlate with increased expression of ATRA-inducible RARα2 isoform. Specific inhibitors of mitogen mitogen-activated protein kinase (MAPK) (MEK)-1/-2 or p38 extracellular signal-related kinase (ERK) kinase diminish the ATRA as well as ATRA and G/GM-CSF-induced activation of the RARα proteins and decreased the differentiation-induced decline in cell numbers. Our data demonstrate that acting, at least in part, via the MAP kinase pathways, myelomonocytic growth factors enhance ATRA-dependent activation of the RARα isoforms and maturation of myeloid leukemia cells. These results suggest that combinatorial use of these agents may be effective in differentiation therapy of AML. (Blood. 2005;105:341-349)

Ionophore-induced functional changes in macrophages

Ca ionophore A 23187 and valinomycin known to induce Ca2+ influx, i.e. K+ efflux, appeared to induce activation-related changes in rat peritoneal macrophages (PM) at 10(-5)-10(-7) M concentrations as revealed by aggregation, nitro blue tetrazolium (NBT) reduction, superoxide anion production as well as beta glucuronidase release; however, lactate dehydrogenase (LDH) activity was measured in supernatants only after treatment with 10(-5) M of A 23187. The PM-activating effect of A 23187 was abolished in the presence of 5 mM EGTA, whereas the activating effect of K ionophore did not depend on the extracellular Ca2+. Fc receptor (FcR) mediated incorporation, intracellular killing as well as the antibody dependent cytotoxicity (ADCC) were markedly inhibited upon incubation with Ca ionophore or valinomycin. C3bR mediated phagocytosis was found to be more resistant to the cation transport affecting drugs. The impairment of effector functions was elicited by nontoxic concentrations of ionophores, however, their inhibiting effects did not require extracellular Ca2+ at the time of ionophore-exposition.

Cleavage of IgG by elastase-like protease (ELP) of human polymorphonuclear leukocytes (PMN): isolation and characterization of Fab and Fc fragments and low-molecular-weight peptides. Stimulation of granulocyte function by ELP-derived Fab and Fc fragments

The elastase-like protease (ELP) from human polymorphonuclear granulocytes (PNM) is able to split human IgG into Fab and Fc-like fragments and smaller peptides. These fragments are similar but not identical to those produced by papain. They differ in their electrophoretical mobility as well as in their molecular weights. Both ELP-Fab and papain-Fab show antigen-binding capacity. In contrast to papain-derived split products of IgG, the ELP-generated Fab and Fc fragments could enhance granulocyte function. Both ELP-Fab and ELP-Fc increase the spontaneous reduction of nitroblue-tetrazolium (NBT) in granulocytes dose-dependent in a homologous as well as in an autologous system. Furthermore, the ELP-derived Fab and Fc induce an active release of ELP by PMN. It could also be demonstrated that Fab as well as Fc increased the peroxidase activity in granulocytes.

A microassay for nitroblue tetrazolium reduction by human neutrophils

By adapting the nitroblue tetrazolium reduction test (NBT test) of neutrophil function to microtiter plates with correspondingly small incubation and dye extraction volumes, it has been possible to develop a microassay with the following advantages: 1. The cell number required for single standard assay has been reduced five- to tenfold to 1 X 105 PMN. 2. If little blood or few cells are available, this number can be further reduced to 1-5 X 104. 3. The test is rapid (less than 6 hours overall) and highly reproducible. 4. A single technician can process at least six plates = 576 single assays at a time. 5. Due to the small incubation volume, test substances can be saved. NBT reduction in this test is a function of both cell number and concentration of the stimulus (here: zymosan). Addition of serum, Mg+/-+/-, or EGTA/Mg enhances the response to zymosan while Ca+/- +/- at greater than or equal to 2 mM is inhibitory.