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At least 523 records · Page 29Linked to original sources
PubMed1995

Low-molecular-weight GTP-binding proteins and leukocyte signal transduction.

Recent progress on the understanding of leukocyte signal transduction pathways indicates that many of these pathways are modulated by low-molecular-weight GTP-binding proteins (LMWGs). LMWGs are members of a growing family of GTP-binding proteins known as the Ras superfamily and act as molecular switches for regulating a wide range of signal-transduction pathways in virtually all cells. In leukocytes, LMWGs have been shown to participate in essential cellular functions such as growth control, differentiation, cytoskeletal organization, cytokine and chemoattractant-induced signaling events, reduced nicotinamide adenine dinucleotide phosphate oxidase activity, phospholipid metabolism, and intracellular vesicle transport and secretion, and many more of these functions will certainly be identified as we gain a further understanding of regulatory pathways modulating leukocyte signal transduction. This review will summarize our current understanding of this rapidly advancing area of research.

Animals↗
PubMed1991

Cross-linking a maturation-dependent ram sperm plasma membrane antigen induces the acrosome reaction.

ESA152 is a highly hydrophobic 18 kDa sialoglycoprotein, which becomes expressed on ram sperm in the proximal cauda epididymis. ESA 152 is expressed on all regions of the sperm surface, most strongly on the posterior region of the head, most weakly on the anterior region of the head. In this paper, we show that induction of the acrosome reaction with Ca2+ ionophore causes ESA152 to be redistributed from the posterior to the anterior region of the head plasma membrane. Cross-linking ESA152 with bivalent antibody causes similar redistribution and induces the acrosome reaction. Induction of the acrosome reaction with ESA152 antibody requires Ca2+ but is insensitive to (10 ng/ml) pertussis toxin.

Acrosome↗
PubMed1993

CD45 mAb induces cell adhesion in peripheral blood mononuclear cells via lymphocyte function-associated antigen-1 (LFA-1) and intercellular cell adhesion molecule 1 (ICAM-1).

A novel cell aggregation-inducing characteristic of the leukocyte common antigen, CD45, is described and its underlying molecular mechanisms investigated. Formation of strong cell clusters was consistently observed in human PBMCs after crosslinking CD45 molecules with antibodies, directed to epitopes common for all CD45 isoforms (e.g., mAb ROS220 or NIH45-2) or the CD45RA (e.g., mAb Alb11) or the CD45RO isoform (e.g., mAb UCHL1). This phenomenon was not seen after PBMC treatment with CD45RA mAb HB11 or CD2 mAb 39C1.5. Identical to phorbol 12-myristate 13-acetate (PMA)-induced clustering, CD45-mediated aggregation was also suppressed by EDTA, by cytochalasin B, and by incubation at 4 degrees C, all characteristics of adhesion mediated by integrins. The involvement of LFA-1 and ICAM-1 in CD45-mediated adhesion was supported by the observation that CD11a (LFA-1 alpha) mAb R7.1, CD18 (LFA-1 beta) mAb R3.3, and CD54 (ICAM-1) mAb R6.1 or RR/l all strongly inhibited CD45- and PMA-induced aggregation. Interestingly, highly pure T lymphocytes did not aggregate in response to CD45 mAb, but did after PMA treatment. These results indicate that triggering human PBMCs via CD45 can cause strong cell aggregation, largely through LFA-1/ICAM-1 interactions. Our findings support an important role of the CD45 antigen in signal transduction and intercellular interaction in human PBMCs.

Antibodies, Monoclonal↗
PubMed1999

Activation of Vav and Ras through the nerve growth factor and B cell receptors by different kinases.

Engagement of the B-cell antigen receptor (BCR) or the nerve growth factor receptor (NGFR/TrkA) induces activation of multiple tyrosine kinases, resulting in phosphorylation of numerous intracellular substrates. We show that addition of NGF or anti-IgM antibody leads to the early tyrosine phosphorylation of p95(vav), which is expressed exclusively in hematopoietic cells; NGF, similar to crosslinking the BCR, also results in the rapid activation of Ras. The phosphorylation of Vav and activation of Ras triggered by NGF is mediated through Trk tyrosine kinase, whereas signaling through the BCR uses a different tyrosine kinase. We also show that NGF induces tyrosine phosphorylation of Shc and its association with Grb2. Vav and Ras with the adaptor proteins Shc and Grb2 appear to serve as a link between different receptor-mediated signaling pathways and, in human B cells, may play an important regulatory role in neuroimmune interactions.

Adaptor Proteins, Signal Transducing↗
PubMed1999

The cytoplasmic and the transmembrane domains are not sufficient for class I MHC signal transduction.

Class I MHC molecules deliver activation signals to T cells. To analyze the role of the cytoplasmic and the transmembrane (TM) domains of class I MHC molecules in T cell activation, Jurkat cells were transfected with genes for truncated class I MHC molecules which had only four intracytoplasmic amino acids and no potential phosphorylation sites or native molecules or both. Cross-linking either the native or the truncated molecules induced IL-2 production even under limiting stimulation conditions of low engagement of the stimulating mAb. Moreover, direct comparison of transfected truncated and native class I MHC molecules expressed on the same cell revealed significant stimulation induced by cross-linking the truncated molecules, despite low expression. In addition, truncated class I MHC molecules were as able to synergize with CD3, CD2, or CD28 initiated IL-2 production as native molecules. In further experiments, hybrid constructs made of the extracellular portion of the murine CD8 alpha chain and of the TM and the intracytoplasmic domains of H-2Kk class I MHC molecule were transfected into Jurkat T cells. The expression of the transfected hybrid molecules was comparable to that of the native HLA-B7 molecules. Cross-linking the intact monomorphic HLA-A,B,C epitope or the polymorphic HLA-B7 epitope induced IL-2 production upon costimulation with PMA. In contrast, cross-linking the hybrid molecules generated neither an increase in intracellular calcium concentration ([Ca2+]i) nor stimulated IL-2 production. By contrast, cross-linking intact murine class I MHC molecules induced [Ca2+]i, signal and IL-2 production in transfected Jurkat cells. The data therefore indicate that unlike many other signaling molecules, signaling via class I MHC molecules does not involve the cytoplasmic and the TM portions of the molecule, but rather class I MHC signal transduction is likely to be mediated by the extracellular domain of the molecule.

Animals↗
PubMed1999

Protein kinase C-alpha is essential for Ramos-BL B cell survival.

The Ramos-Burkitt lymphoma (BL) B cell line is driven into growth arrest and apoptosis by cross-linking surface immunoglobulin. We demonstrate that protein kinase C (PKC) activity is required for Ramos B cell proliferation and survival. A variety of PKC inhibitors trigger a significant decrease in [(3)H]thymidine incorporation with a concomitant increase in cell death. Antisense depletion of expression of the PKC-alpha isoform is sufficient to trigger cell death in the absence of any other signal, demonstrating a requirement for this isoform for survival of Ramos-BL B cells. Cross-linking surface immunoglobulin also leads to depletion of PKC-alpha levels, suggesting that this may be one mechanism by which this signals for cell death in Ramos-BL B cells.

Antibodies, Anti-Idiotypic↗
PubMed2000

Effect of allotype on activation of neutrophils by FcgammaRIIIB cross-linking.

Human neutrophils constitutively synthesize two receptors for the constant region of IgG, FcgammaRII, and FcgammaRIIIB. Fluo-3-loaded neutrophils were treated with biotinylated Fab fragments of anti-FcgammaR antibodies and cross-linked with streptavidin, and intracellular calcium ([Ca2+](i)) was monitored by flow cytometry. Polymerization of filamentous actin was quantitated by NBD-phallacidin using flow cytometry. Cross-linking of FcgammaRII by monoclonal antibody (mAb) IV.3 induces an increase in [Ca2+](i), superoxide generation, and the polymerization of actin. [Ca2+](i) responses from cross-linking of FcgammaRIIIB by mAb 3G8 varied from minimal to no release. To determine whether discrepancies in 3G8-induced [Ca2+](i) release were due to allotype variation, we selected five donors who were homozygous for the NA1 allotype of FcgammaRIIIB and five who were either heterozygous or homozygous for the NA2 allotype and compared their [Ca2+](i) response and actin polymerization induced by FcgammaRIIIB cross-linking. Cross-linking of FcgammaRIIIB by 3G8 produced minimal [Ca2+](i) release and polymerization of actin irrespective of donor allotype.

Actins↗
PubMed2000

The CD40-inducible Bcl-2 family member A1 protects B cells from antigen receptor-mediated apoptosis.

CD40 activation is necessary for thymus-dependent humoral immune responses and rescuing both phenotypically immature WEHI-231 B lymphoma cells from B cell antigen receptor-induced cell death and germinal center B cells from spontaneous apoptosis. As some effects of CD40 are probably mediated by differences in gene expression, cDNA expression arrays and RNase protection assays were used to identify the anti-apoptotic Bcl-2 homolog A1 as a CD40-inducible gene in B cell lines and purified germinal center B cells. Sustained CD40-induced A1 upregulation correlated with CD40-mediated rescue of WEHI-231 cells from anti-IgM-induced apoptosis. Moreover, overexpression of A1 specifically protected WEHI-231 cells from anti-IgM-induced apoptosis but not cell death triggered by certain other stimuli.

Animals↗
PubMed2000

The epithelial mucin, MUC1, is expressed on resting T lymphocytes and can function as a negative regulator of T cell activation.

MUC1 is a mucinous glycoprotein which is normally expressed on the surface of a variety of epithelia and aberrantly overexpressed on some human tumors. In this report, we demonstrate that the epithelial mucin, MUC1, is expressed on resting human peripheral blood T cells and two leukemia T cell lines, Jurkat and Hut 78. Crosslinking of MUC1 on peripheral blood T cells by plate-bound anti-MUC1 (DF3-P) antibody inhibits cell proliferation, IL-2 and GM-CSF production, and up-regulation of the IL-2 receptor upon anti-CD3 stimulation. Induction of IL-2 production by Jurkat and HUT 78 is also suppressed and cannot be reversed by the addition of anti-CD28 mAb. These findings suggest that MUC1 can be a potent negative regulator for T cell activation at the resting stage.

CD28 Antigens↗
PubMed2000

Neutrophil chemotaxis and superoxide production are induced by cross-linking FcgammaRII receptors.

Neutrophils express two types of receptor for the Fc region of IgG, FcgammaRII and FcgammaRIIIB. Via these receptors, neutrophils bind IgG complexes that contain more than one IgG molecule. This binding activates functional processes, such as the respiratory burst and chemotaxis. Neutrophils were treated with biotinylated anti-Fc receptor monoclonal antibodies and chemotaxis toward streptavidin, a cross-linking agent, was determined. Cross-linking FcgammaRII and not FcgammaRIIIB induced neutrophil chemotaxis. Superoxide production in response to immobilized anti-Fc receptor antibodies was also examined. Anti-FcgammaRII Fab bound to ELISA plates induced superoxide production, while anti-FcgammaRIIIB Fab did not. Pretreatment of neutrophils with anti-FcgammaRII Fab reduced superoxide generated by immobilized anti-FcgammaRII antibody. The data demonstrate that FcgammaRII and not FcgammaRIIIB are responsible for neutrophil chemotaxis and superoxide production upon Fc receptor activation.

Antibodies, Monoclonal↗
PubMed1998

Treatment with progesterone analogues decreases macrophage Fcgamma receptors expression.

Macrophage Fcgamma receptors (FcgammaRs) are critical for host defense against infection and have an important role in immune cytopenias. Modulation of macrophage FcgammaRs expression is a potential therapeutic approach to immune disorders. Glucocorticoids and synthetic progesterone analogues decrease macrophage FcgammaRs expression. We assessed the effect of treatment with commonly employed progestins on the expression of macrophage FcgammaRs using an experimental model in the guinea pig. Eight clinically available progesterones, medroxyprogesterone acetate (P3), megestrol acetate (P4), medrogestone (P5), alylestrenol (P6), linestrenol (P7), didrogesterone (P8), norethisterone (P9), and gestonorone caproate (P10) and two endogenous progesterones, progesterone (P1) and 17 alpha-hydroxyprogesterone (P2), were studied. Following in vivo treatment of guinea pigs, we determined the clearance of IgG-sensitized erythrocytes in vivo, the binding of IgG-sensitized erythrocytes by isolated splenic macrophages, and splenic macrophage Fcgamma receptor cell surface expression. All progesterones impaired the clearance of IgG-sensitized erythrocytes by decreasing splenic macrophage Fcgamma receptor expression. P5, P6, P7, and P8 were less effective. Flow cytometry and fluorescence microscopy with monoclonal antibodies demonstrated that progesterones decreased the cell surface expression of FcgammaR2 more than that of FcgammaR1,2. Clinically employed progestins impair the clearance of IgG-coated cells by decreasing splenic macrophage FcgammaRs expression. Thus, progesterones are candidate drugs for the treatment of immune disorders.

Animals↗