Induction of basophilic differentiation in the human basophilic cell line KU812

Mast Cell and Basophil Cell Lines: A Compendium

Mast cells and basophils play a crucial role during type I hypersensitivity reactions. However, despite efforts to elucidate their role in the pathogenesis of allergy and inflammation, our understanding of MC and basophil biology is still relatively scarce. The practical difficulty in obtaining a sufficient number of purified primary cells from biological samples has slowed down the process of reaching a full understanding of the physiological role of these functionally similar cell types. The establishment of several immortalized cell lines has been a useful tool to establish and perform sophisticated laboratory protocols that are impractical using primary cells. Continuous cell lines have been extensively used to investigate allergen/IgE-mediated cell activation, to elucidate the degranulation dynamics, to investigate structural and functional properties of the high-affinity receptor (FcεRI), and to test cell-stabilizing compounds. In this chapter, we review the most widely used and better-characterized MC and basophil cell lines, highlighting their advantages and drawbacks. It must be pointed out, however, that while cell lines represent a useful in vitro tool due to their easy manipulability and reduced culture costs, they often show aberrant characteristics which are not fully representative of primary cell physiology; results obtained with such cells therefore must be interpreted with due care.

Allergy Testing and Drug Screening on an ITO-Coated Lab-on-a-Disc

A lab-on-a-disc (LOAD) is a centrifugal microfluidic set-up based on centrifugal force without using micro-pumps to drive reagents and cells to various chambers through channels and valves for reactions. A LOAD coated with conductive transparent indium tin oxide (ITO) for thermal control was developed to screen allergy-blocking agents. When the acridine orange (AO)-loaded KU-812 human basophilic cells were activated in the LOAD by stimuli, AO trapped in the cytoplasmic granules was released externally as an allergic mediator mimetic to report degranulation. This response was monitored by fluorescence when the released AO in supernatant had been transferred, with a higher spinning speed, from the reaction chamber to detection chamber in the LOAD where AO reacted with exogenous DNA. We report here the principles of the system and an improved LOAD set-up with the ITO-coated glass resistive microheater to run assays at 37 °C. By using this platform, we demonstrate here for the first time that triptolide, an active ingredient from the Chinese medicine herb Tripterygium wilfordii Hook f., was able to suppress the fMLP-mediated degranulation in basophils. This serves as an example how LOADs can be used to screen agents to alleviate symptoms of allergy.

A dominant role for FcgammaRII in antibody-enhanced dengue virus infection of human mast cells and associated CCL5 release

Dengue virus is a major mosquito-borne human pathogen with four known serotypes. The presence of antidengue virus antibodies in the serum of individuals prior to dengue virus infection is believed to be an important risk factor for severe dengue virus disease as a result of the phenomenon of antibody-dependent enhancement operating on Fc receptor (FcR)-bearing cells. In addition to blood monocytes, mast cells are susceptible to antibody-enhanced dengue virus infection, producing a number of inflammatory mediators including IL-1, IL-6, and CCL5. Using the human mast cell-like lines KU812 and HMC-1 as well as primary cultures of human cord blood-derived mast cells (CBMC), we aimed to identify the participating FcRs in antibody-enhanced mast cell dengue virus infection, as FcRs represent a potential site for therapeutic intervention. CBMC expressed significant levels of FcgammaRI, FcgammaRII, and FcgammaRIII, and mast cell-like HMC-1 and KU812 cells expressed predominantly FcgammaRII. All four serotypes of dengue virus showed antibody-enhanced binding to KU812 cells. Specific FcgammaRII blockade with mAb IV.3 was found to significantly abrogate dengue virus binding to KU812 cells and CBMC in the presence of dengue-specific antibody. Dengue virus infection and the production of CCL5 by KU812 cells were also inhibited by FcgammaRII blockade.

Development of a functional in vitro assay as a novel tool for the standardization of allergen extracts in the human system

BACKGROUND

Biochemical and immunochemical methods used for batch control of allergen extracts rely on the binding of IgE molecules to allergens. They do not measure the ability of a protein to induce type I allergic reactions. Therefore, a biological assay was established that is based on the cellular mechanisms of allergies in order to assess the cross-linking capacity of allergens.

METHODS

Rat basophilic leukaemia cells were transfected with cDNA coding for the human high affinity IgE receptor chains. The surface expression of the IgE-binding alpha-chain was detected by FACS analysis and the functional integration of the 'humanized' receptors into the signal transduction cascade was addressed by intracellular calcium mobilization. Mediator release was measured in response to human IgE and a variety of cross-linking allergen preparations.

RESULTS

Several clones were obtained that were able to bind allergen-specific human IgE. The results of the biological assay were compared with those obtained by immunochemical methods. The biological assay was used to determine the potency of allergen extracts, including highly diluted products that cannot be analysed by conventional methods.

CONCLUSION

A stable 'humanized' basophil cell line was established that will be a useful tool for the standardization and batch control of allergen extracts. Because of its high sensitivity, it can also be used to detect minute quantities of potentially allergenic proteins, e.g. in processed foods. In addition, the test may support the development of novel allergy vaccines, such as recombinant hypoallergenic molecules.

A comparative study of the FcepsilonRI molecule on human mast cell and basophil cell lines

BACKGROUND

Mast cells and basophils express the high-affinity IgE receptor FcepsilonRI. We have analysed the human mast cell line LAD2 and four subclones of the basophil cell line KU812 in order to reveal possible differences concerning the FcepsilonRI surface regulation, anti-IgE-triggered activation, FcepsilonRIalpha protein stability and the mRNA level of FcepsilonRIalpha-, beta- and the truncated beta-chain (beta(T)), and thereby determine the utility of these cell lines in investigations of the FcepsilonRI biology.

METHODS

The surface expression of FcepsilonRI was assessed by flow cytometry, using the monoclonal antibody CRA1. The FcepsilonRI-induced cellular activation (i.e. cross-linking of FcepsilonRI) was determined by changes in the intracellular level of Ca2+, which was measured by fluorescence of Fura-2. The level of the FcepsilonRIalpha protein was determined by a Western blot technique and by a radioimmunoassay. The mRNA level of FcepsilonRIalpha, beta- and beta(T)-chain was analysed using real-time PCR.

RESULTS

Two KU812 subclones and especially LAD2 had FcepsilonRI surface expression which was capable of inducing cellular activation. Both the FcepsilonRI expression and stability of the FcepsilonRIalpha protein were increased when IgE was present. All the cell lines expressed mRNA of FcepsilonRIalpha-, beta- and beta(T), with LAD2 tending to have the highest expression. However, a determination of the beta/beta(T) ratio demonstrated no difference between any of the cell clones.

CONCLUSION

These cell lines are important tools in the investigation of both the FcepsilonRI molecule and the effects induced by its activation.

Monomeric immunoglobulin E stabilizes FcepsilonRIalpha from the human basophil cell line KU812 by protecting it from natural turnover

BACKGROUND

The high affinity IgE receptor (FcepsilonRI) on mast cells and basophils is up-regulated by its own ligand IgE; however, the mechanism is unknown.

OBJECTIVE

To study the IgE-mediated effect on FcepsilonRI on basophils by using the human basophilic cell line KU812.

METHODS

Expression of cell surface FcepsilonRI was assessed by flow cytometry. Western blot technique was used to illustrate tyrosine-phosphorylation and the Ca2+ level in KU812 was measured by fluorescence of Fura-2. Soluble specimens of the alpha-chain from FcepsilonRI (FcepsilonRIalpha) were obtained by lysing 107 KU812 pr. mL. FcepsilonRIalpha was detected by a sandwich immunoradiometric assay employing the IgE-binding capacity of FcepsilonRIalpha in conjunction with a monoclonal antibody. Polyclonal rabbit anti-FcepsilonRIalpha was used for detection of FcepsilonRIalpha by Western blotting.

RESULTS

We found that monomeric IgE did not induce tyrosine-phosphorylation in KU812, which was the case when stimulating with IgE cross-linked by anti-IgE binding. Further, only cross-linking of IgE, but not monomeric IgE, increased the Ca2+ level. Using the immunoradiometric assay, we found a temperature dependent reduction in the amount of FcepsilonRIalpha. Samples incubated at 37 degrees C for 5 h displayed a 16-fold decrease in the FcepsilonRIalpha level compared with samples incubated at 4 degrees C. In the presence of IgE the reduction at 37 degrees C was only threefold.

CONCLUSION

These results indicate that IgE does not induce intracellular signals in KU812, i.e., tyrosine-phosphorylation or Ca2+ release. Instead it appears that FcepsilonRIalpha is an unstable protein that IgE stabilizes and thereby protects from a temperature dependent turnover.

Dengue virus selectively induces human mast cell chemokine production

Severe dengue virus infections usually occur in individuals who have preexisting anti-dengue virus antibodies. Mast cells are known to play an important role in host defense against several pathogens, but their role in viral infection has not yet been elucidated. The effects of dengue virus infection on the production of chemokines by human mast cells were examined. Elevated levels of secreted RANTES, MIP-1alpha, and MIP-1beta, but not IL-8 or ENA-78, were observed following infection of KU812 or HMC-1 human mast cell-basophil lines. In some cases a >200-fold increase in RANTES production was observed. Cord blood-derived cultured human mast cells treated with dengue virus in the presence of subneutralizing concentrations of dengue virus-specific antibody also demonstrated significantly (P < 0.05) increased RANTES production, under conditions which did not induce significant degranulation. Chemokine responses were not observed when mast cells were treated with UV-inactivated dengue virus in the presence or absence of human dengue virus-specific antibody. Neither antibody-enhanced dengue virus infection of the highly permissive U937 monocytic cell line nor adenovirus infection of mast cells induced a RANTES, MIP-1alpha, or MIP-1beta response, demonstrating a selective mast cell response to dengue virus. These results suggest a role for mast cells in the initiation of chemokine-dependent host responses to dengue virus infection.

Modulation of histidine decarboxylase activity and cytokine synthesis in human leukemic cell lines: relationship with basophilic and/or megakaryocytic differentiation

In the present study, we show that UT7D1 cells, derived from the pluripotent cell line UT7, express high levels of histidine decarboxylase (HDC) mRNA spontaneously. These cells conserve the ability to differentiate into megakaryocytes upon stimulation with PMA, while greatly increasing their HDC activity. We provide evidence that enhanced HDC activity reflects the basophil rather than the megakaryocytic differentiation potential of UT7DI cells. Indeed, in addition to HDC mRNA, they express spontaneously several other mRNA coding for molecules present in basophils (FcepsilonRI, CCR3, IL-4Ralpha, IL-5Ralpha). Furthermore, the basophil antigen Bsp-1 is displayed on the surface of some UT7D1 cells in response to PMA concomitantly with increased histamine synthesis and mRNA expression of typical basophil-derived cytokines (IL-6, IL-4, and IL-13). Nevertheless, PMA cannot sustain the differentiation of this lineage, because mRNAs for basophil markers gradually diminish during long-term culture, whereas molecules associated with the megakaryocytic lineage remain prominent. In support of the notion that HDC activity is not related with megakaryopoiesis, we show that PMA-induced CD41 expression and PDGF transcription occurs in the K562 cells, though neither HDC mRNA nor any known basophil marker are expressed in these conditions. In contrast, all these markers are expressed in the basophilic leukemia cell line KU812F. Interestingly, the megakaryocytic cell line HEL produces also substantial amounts of histamine and expresses FcepsilonRI, thus revealing its basophil differentiation potential. HEL as well as KU812F need not be stimulated with PMA to react with Bsp-1 mAb, suggesting that they are more engaged into the basophil differentiation scheme than UT7D1. Other leukemic cell lines unrelated to the megakaryocyte or basophil lineage, like HL60 and U937 do neither synthesize histamine nor express basophil markers before or after PMA stimulation. To our knowledge, this is the first evidence for a factor-dependent cell line with megakaryocyte/basophil bipotentiality with which early stages of basophil commitment can be analyzed.

Demonstration of specific high-affinity Fc epsilon-receptors on the human basophil-like leukemia cell line KU812 by flow cytometry

The specificity of IgE binding to a human basophil-like cell line (KU812) was studied by flow cytometry. Four IgE myeloma proteins, representing both light-chain types, one chimeric IgE protein, and polyclonal serum IgE blocked the direct binding of FITC-labeled IgE(DES) myeloma protein to KU812 cells in a dose-dependent and nearly equimolar way. Although not as efficiently as human IgE (from five to eight times less on a molar basis), both rat and mouse IgE blocked IgE(DES)-FITC binding to KU812 cells. In sharp contrast, all four human IgG subclasses, both IgA subclasses, and IgM myeloma proteins, as well as monomeric and heat-aggregated polyclonal human IgG, were unable to block significantly IgE(DES)-FITC binding to KU812 cells (< 0.5% on a molar basis). The cytophilic epitope on IgE was heat-susceptible (56 degrees C, 2 h), lost after reduction alkylation, and resident in the papain-derived Fc epsilon-fragment, but not in the papain-derived Fab epsilon- and Fc'epsilon-fragments nor in the pepsin-derived F(ab')2 epsilon- and Fc"epsilon-fragments. Washing and displacement experiments indicated that a major part of IgE reacted with high affinity to KU812 cells. The results indicate that the binding of IgE to KU812 cells is highly specific and involves the classical high-affinity Fc epsilon RI-receptor. Although the density of receptors is low, this human cell line offers a unique model to study IgE/Fc epsilon RI interactions.

Phenotypic characterization of the human mast-cell line HMC-1

The cell line HMC-1, derived from a patient with mast cell leukaemia, is the only established cell line exhibiting a phenotype similar to that of human mast cells. This paper reports on a detailed characterization of the expression of a panel of markers for various types of immature and mature haematopoietic cells in the HMC-1. We also studied the potential of HMC-1 to differentiate upon treatment with conditioned media from the human T-cell line Mo, retinoic acid or DMSO. HMC-1 was found to express several mast cell-related markers. A high expression of Kit, the receptor for stem-cell factor, was detected. The majority of the cells were stained with a MoAb against the mast cell-specific serine protease tryptase. Of particular interest was the finding that beta-tryptase mRNA, but not alpha-tryptase mRNA, was expressed in HMC-1. Using enzyme-histochemistry we were able to show that the beta-tryptase was enzymatically active, indicating that tryptase can form active homotetramers. Both heparin and chondroitin sulfate were found to be present in approximately equal amounts. HMC-1 lacked surface expression of the high-affinity IgE receptor, which was confirmed by the absence of mRNA of the alpha- and beta-chains of the IgE-receptor complex. However, a strong expression of the gamma-chain of the IgE-receptor complex was detected. A positive staining of the monocyte/macrophage marker CD68 was obtained, as well as a strong hybridization signal for the eosinophilic/basophilic-related differentiation marker the Charcot-Leyden crystal. Treatment of HMC-1 with conditioned media from the human T-cell line Mo, retinoic acid or DMSO induced only moderate changes in the surface or intracellular expression of the studied markers. The agents tested neither induced any of the monocyte/granulocyte markers examined, nor expression of the Fc epsilon RI alpha-chain.

Constitutive and inducible expression of PDGF in the human basophilic cell line, KU 812

The human basophilic cell line KU 812, that also has some mast cell characteristics, was found to express the PDGF-A gene and secrete PDGF-A like activity. After treatment with IL-6+ TNF-alpha, the PDGF-A mRNA expression increased as did cytoplasmic immunostaining with anti-PDGF antibodies. Secretion of PDGF-A was visualized by immunoprecipitation. An augmentation of non-secreted PDGF-like activity after IL-6+ TNF-alpha treatment was not accompanied by induction of the long splice variant of the PDGF-A-chain mRNA. Treatment with TPA caused an increase in PDGF-A expression and in addition, an induction of PDGF-B transcripts were seen. Staining of cytospin preparations with anti-PDGF antibodies visualized a substantial increase in immunostaining of the TPA treated cells and both intracellular and secreted PDGF-AA-like activity was substantially increased as compared to untreated control cultures. There was a concomitant induction of exon 6 specific mRNA, corresponding to a cellular retention signal after TPA treatment. Our results show that PDGF can be produced by a cell line of the basophilic/mast cell lineage, i.e. cells involved in allergic disorders and inflammation.

Phenotypic characterization of KU812, a cell line identified as an immature human basophilic leukocyte

The knowledge about the differentiation of basophilic leukocytes is fragmentary. This report discusses a detailed phenotypic characterization of molecular markers for hematopoietic differentiation in a basophilic leukemia cell line, KU812. The expression of markers for lymphoid, erythroid, neutrophil, eosinophil, monocytic, megakaryocytic, mast cell and basophil differentiation was analyzed at the mRNA level by Northern blots in the KU812 cells, and for reference, in a panel of human cell lines representative of the different hematopoietic differentiation lineages. KU812 was found to express a number of mast cell and basophil-related proteins, i.e. mast cell tryptase, mast cell carboxypeptidase A, high-affinity immunoglobulin (IgE) receptor alpha and gamma chains and the core protein for heparin and chondroitin sulphate synthesis. We found no expression of a number of monocyte/-macrophage or neutrophil leukocyte markers except for lysozyme. From earlier studies, it has been shown that lysozyme is not expressed in murine mucosal mast cell lines. This finding, together with the expression of the mast cell carboxypeptidase in KU812 might distinguish the phenotype of this cell line from that typical of mucosal mast cell lines in rodents. We found a low level of expression of the eosinophil and basophil marker, major basic protein, which might indicate a relationship between basophils and eosinophils. No expression is, however, detected with the eosinophil-specific markers eosinophil cationic protein, eosinophil-derived neurotoxin or eosinophil peroxidase. We also report an extensive screening for inducers of basophilic differentiation of the KU812 cells. The most efficient protocol of induction included serum starvation which led to a dramatic increase in a number of markers specific for mast cells and basophils such as tryptase, carboxypeptidase A and the heparin core protein. Finally, diisopropylfluorophosphate analysis of total protein extracts from KU812 show four labeled protein bands with sodium dodecyl sulfate-polyacrylamide gel electrophoresis, indicating that this cell line expresses at least three previously undescribed serine proteases of which one or more could be a potential basophil-specific marker(s).