Interferon and (2'-5')oligoadenylate enhance the expression of low affinity receptors for IgE (Fc epsilon R2/CD23) on the human monoblast cell line U937

Low affinity IgE receptors: regulation and functional roles in cell activation

The low affinity IgE receptors (Fc epsilon RII/CD23) homologous to animal lectins have the unique property of cleaving-off the extracytoplasmic portion as the soluble form (IgE binding factor; IgE-BF). Molecular analysis using Fc epsilon RII/CD23 cDNA proved that Fc epsilon RII is not unique to B lymphocytes but is expressed on a variety of cell lineages including T lymphocytes, macrophages and eosinophils. In these cell types, IL-4 is a general inducer of this molecule while IFN-gamma down-regulates B cell Fc epsilon RII/CD23 and up-regulates Fc epsilon RII/CD23 on macrophage and eosinophil cell lines. As predicted by the expression of Fc epsilon RII/CD23 in some HTLV-1(+) T cell lines, Fc epsilon RII/CD23 proved to be induced on normal peripheral T lymphocytes by IL-4 or IL-2 in the presence of additional permissive signals. As indicated by IL-2-dependent Fc epsilon RII/CD23 induction, there is an interesting bilateral co-regulation between Fc epsilon RII/CD23 and the 55 kDa chain of the IL-2 receptor complex with Tac antigen (IL-2R/p55(Tac]. Triggering of Fc epsilon RII/CD23 resulted in the enhanced expression of IL-2R/p55(Tac), whereas IL-2 enhanced the expression of Fc epsilon RII/CD23 in some systems. It is suggested that the triggering of cell surface Fc epsilon RII/CD23 by natural ligands is effectively buffered by soluble Fc epsilon RII/CD23 (IgE-BF).

Molecular cloning of a macrophage-derived, interferon-inducible secreted immunoglobulin-binding protein

We describe the molecular cloning of a 1803-bp cDNA coding for a product termed interferon-induced immunoglobulin-binding protein (IIBP) from a library of IFN-alpha-induced primary bone marrow macrophages. The open reading frame encodes a protein of 26-kDa containing two immunoglobulin-like and one Fc receptor-like domain. Due to the constitutive release of low amounts of IFN-beta, the IIBP mRNA is already present in macrophage-colony-stimulating factor-cultured macrophages. Its expression could be blocked in the presence of either anti-IFN-beta or interleukin-4, which down-regulates the endogenous IFN-beta production. Upon addition of rIFN-alpha4 a 3-5-fold superinduction of IIBP mRNA was observed. Rat monoclonal antibodies detected a protein of the predicted size exclusively in cell culture supernatants of primary bone marrow macrophages and a B-cell line. In immunoprecipitation experiments an unknown 30-kDa protein co-precipitated. The secreted IIBP showed considerable binding to nonspecific rat IgG2a and could be precipitated using mouse IgG2a, IgG2b and IgG3 antibodies of irrelevant specificities, indicating that this gene product is a novel secreted immunoglobulin-binding protein with a new IgG isotype binding pattern that differs to that of known Fc receptors.

Mechanism of interferon-gamma down-regulation of the interleukin 4-induced CD23/Fc epsilon RII expression in human B cells: post-transcriptional modulation by interferon-gamma

It has been reported that the interleukin 4 (IL-4) specific induction of cell surface CD23 (Fc epsilon RII) is down-regulated by interferon-gamma (IFN-gamma) in monocytes and B cells. However, the molecular level at which the inhibition occurs seems to vary depending on the cell types. In normal human B cells, IFN-gamma inhibits the IL-4 induced de novo synthesis of CD23 at the level of gene expression. Analysis of inhibition kinetics suggested a rapid signal transmission by IFN-gamma. Yet the inhibitory action of IFN-gamma on CD23 mRNA accumulation appeared as a secondary response requiring a new protein synthesis. Through nuclear run-on transcription and mRNA stability studies, we further demonstrate that the IL-4 induced CD23 gene expression is down-regulated by IFN-gamma mainly at post-transcriptional levels by decreasing mRNA stability.

EoL-1, a human eosinophilic cell line

EoL-1 cells, a recently established human eosinophilic leukemia cell line, have cytological features of myeloblasts under normal culture conditions, and differentiate not only phenotypically but also functionally into eosinophils by a number of stimuli. EoL-1 cells are particularly useful for analyzing leukemic cell differentiation and the properties of malignant eosinophils. EoL-1 cells are also a useful in vitro model for studying human eosinophil functions and their regulation.

Interferon-gamma potentiates the antiviral activity and the expression of interferon-stimulated genes induced by interferon-alpha in U937 cells

Binding of type I interferon (IFN-alpha/beta) to specific receptors results in the rapid transcriptional activation, independent of protein synthesis, of IFN-alpha-stimulated genes (ISGs) in human fibroblasts and HeLa and Daudi cell lines. The binding of ISGF3 (IFN-stimulated gene factor 3) to the conserved IFN-stimulated response element (ISRE) results in transcriptional activation. This factor is composed of a DNA-binding protein (ISGF3 gamma), which normally is present in the cytoplasm, and other IFN-alpha-activated proteins which preexist as latent cytoplasmic precursors (ISGF3 alpha). We have found that ISG expression in the monocytic U937 cell line differs from most cell lines previously examined. U937 cells express both type I and type II IFN receptors, but only IFN-alpha is capable of inducing antiviral protection in these cells. Pretreatment with IFN-gamma potentiates the IFN-alpha-induced protection, but IFN-gamma alone does not have any antiviral activity. ISG15 mRNA accumulation in U937 cells is not detectable before 6 h of IFN-alpha treatment, peaks at 24 h, and requires protein synthesis. Although IFN-gamma alone does not induce ISG expression, IFN-gamma pretreatment markedly increases and hastens ISG expression and transcriptional induction. Nuclear extracts assayed for the presence of ISRE binding factors by electrophoretic mobility shift assays show that ISGF3 is induced by IFN-alpha within 6 h from undetectable basal levels in untreated U937 cells. Activation of ISGF3 alpha, the latent component of ISGF3, occurs rapidly. However, the increase in ISGF3 activity ultimately correlates with the accumulation of ISGF3 gamma induced by IFN-alpha or IFN-gamma.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of Fc gamma receptor subtype expression on a human eosinophilic leukemia cell line EoL-3: participation of cAMP and protein kinase C in the effects of interferon-gamma and phorbol ester

We investigated the effects of interferon-gamma (IFN-gamma), phorbol myristate acetate (PMA), and dibutyryl cAMP (Bt2cAMP) on Fc gamma R subtype expression on a human eosinophilic leukemia cell line, EoL-3. Unstimulated EoL-3 cells expressed Fc gamma RII as determined by monoclonal antibody (mAb) IV-3, whereas there was little or no Fc gamma RI and Fc gamma RIII expression as determined by mAbs 32.2 and 3G8, respectively. IFN-gamma induced Fc gamma RI expression, and Bt2 cAMP, which did not induce Fc gamma RI expression by itself, showed an additive effect on IFN-gamma-induced Fc gamma RI expression. Fc gamma RII expression was augmented by IFN-gamma, PMA, and Bt2 cAMP. Bt2 cAMP also showed an additive effect on IFN-gamma-augmented Fc gamma RII expression. Fc gamma RIII expression could be induced only by IFN-gamma plus Bt2 cAMP. H-7, a protein kinase C (PK-C) inhibitor, suppressed the enhancement of Fc gamma R subtype expression induced by these reagents. These results show that Fc gamma R subtype expression on EoL-3 cells is regulated differently in each subtype and that cAMP and PK-C play important roles in the regulation.

Transforming growth factor beta and dexamethasone suppress the expression of Fc epsilon receptor 2 (CD23) on a human eosinophilic cell line EoL-3

The effects of interferon-alpha (IFN-alpha), INF-gamma, transforming growth factor beta (TGF-beta) and dexamethasone on low-affinity Fc receptors for IgE (Fc epsilon R2/CD23) expression on a human eosinophilic leukemia cell line, Eol-3, were examined. Fc epsilon R2/CD23 expression was enhanced by both IFN-alpha and IFN-gamma, and suppressed by TGF-beta and dexamethasone. Northern blot analysis revealed that these reagents regulate the Fc epsilon R2/CD23 expression from mRNA level: both IFN-alpha and IFN-gamma increased the amount of Fc epsilon R2/CD23 mRNA, while both dexamethasone and TGF-beta decreased Fc epsilon R2/CD23 mRNA, where the effect of dexamethasone was much stronger than that of TGF-beta. In comparison with IFN-alpha, IFN-gamma seemed to enhance preferentially the release of surface Fc epsilon R2/CD23, which resulted in the increase of soluble Fc epsilon R2/CD23. These results suggest that these reagents may play important regulatory roles in allergy and in helminth infections via their effects on Fc epsilon R2/CD23 expression on eosinophils.

Regulation of Fc epsilon receptor 2 (CD23) expression on a human eosinophilic cell line EoL3 and a human monocytic cell line U937 by transforming growth factor beta

Regulation of low-affinity receptors for IgE (Fc epsilon R2/CD23) on a human eosinophilic cell line EoL3 and a human monocytic cell line U937 was studied using an anti-Fc,R2/CD23 monoclonal antibody H107 by flow cytometry. While platelet-activating factor, interleukin 4, and interferon gamma significantly augmented Fc epsilon R2/CD23 expression on both cell lines, transforming growth factor beta (TGF beta) inhibited both the basal level of Fc epsilon R2/CD23 expression and the enhanced Fc epsilon R2/CD23 expression induced by these reagents in dose- and time-dependent manners. However, TGF beta did not significantly suppress the high basal level of Fc epsilon R2/CD23 expression on RPMI 8866 cells. These results suggest that Fc epsilon R2/CD23 expression on EoL3 and U937 cells is regulated by various cytokines and growth factors, and that TGF beta plays an important regulatory role in IgE-mediated immune responses.