The expansion of human gammadelta T cells in response to Daudi cells requires the participation of CD4+ T cells.

The Burkitt's lymphoma cell line Daudi is a potent inducer of human gammadelta T-cell expansion. Using an in vitro culture system comprised of irradiated Daudi cells as stimulators and normal human lymphocytes as responders, the cellular determinants of this response were investigated. Three of four monoclonal antibodies (mAbs 1-1C4, L243, and 9.3F10) directed against disparate epitopes of human major histocompatibility complex (MHC) class II, as well as a mAb with specificity for CD4 (OKT4), inhibited the expansion of gammadelta T cells in response to Daudi cell stimulators. mAbs with a specificity for CD74 and CD8 were non-inhibitory. Lymphocyte depletion experiments demonstrated a critical role for the CD4+ T-cell subset in the expansion of gammadelta T cells. Other data pointed towards requirements for direct cell contact in this system, and the addition of exogenous recombinant interleukin (IL)-2, IL-4, and IL-12 failed to reconstitute gammadelta T-cell expansion in CD4+ lymphocyte-depleted cultures. These results complement previous findings in murine infectious disease and mycobacterial systems, providing a direct demonstration that CD4+ T cells play a role in gammadelta T-cell expansion through an interaction with human leucocyte antigen (HLA) class II on Daudi cells. The data point towards important functional links between the acquired and natural immune systems.     

Cholesterol depletion inhibits src family kinase-dependent calcium mobilization and apoptosis induced by rituximab crosslinking

The monoclonal antibody (mAb) rituximab produces objective clinical responses in patients with B-cell non-Hodgkin's lymphoma and antibody-based autoimmune diseases. Mechanisms mediating B-cell depletion by rituximab are not completely understood and may include direct effects of signalling via the target antigen CD20. Like most but not all CD20 mAbs, rituximab induces a sharp change in the solubility of the CD20 protein in the non-ionic detergent Triton-X-100, reflecting a dramatic increase in the innate affinity of CD20 for membrane raft signalling domains. Apoptosis induced by rituximab hypercrosslinking has been shown to require src family kinases (SFK), which are enriched in rafts. In this report we provide experimental evidence that SFK-dependent apoptotic signals induced by rituximab are raft dependent. Cholesterol depletion prevented the association of hypercrosslinked CD20 with detergent-insoluble rafts, and attenuated both calcium mobilization and apoptosis induced with rituximab. CD20 cocapped with the raft-associated transmembrane adaptor LAB/NTAL after hypercrosslinking with CD20 mAbs, regardless of their ability to induce a change in the affinity of CD20 for rafts. Taken together, the data demonstrate that CD20 hypercrosslinking via rituximab activates SFKs and downstream signalling events by clustering membrane rafts in which antibody-bound CD20 is localized in a high-affinity configuration.     

Induction of DAP12 phosphorylation, calcium mobilization, and cytokine secretion by Ly49H.

The ability of several Ly49 family members to inhibit natural killer (NK) cell functions through recruitment of SHP-1 phosphatase has been reported. In contrast, the mechanisms underlying the activating signal generated by Ly49D are poorly understood. A homodimeric phosphoprotein (pp16) that physically and functionally associates with Ly49D has been described. In this study, a rabbit anti-mouse pp16 antiserum was generated and used to demonstrate that pp16 corresponds to the recently described DAP12 molecule. In addition, we show that a second Ly49 family member that lacks an immunoreceptor tyrosine-based inhibitory motif and contains a charged residue in the transmembrane domain, Ly49H, also associates with DAP12. Furthermore, we show that engagement of the Ly49H/DAP12 complex results in phosphorylation of DAP12, intracellular calcium mobilization, and tumor necrosis factor secretion in transfected cells. These results thus provide evidence that Ly49H is an activating receptor that associates with DAP12, previously described as a pp16 component of the Ly49D receptor complex.     

Extracellular ATP stimulates interleukin-dependent cultured mast cells and eosinophils through calcium mobilization.

We examined the effect of ATP and related nucleotides on the changes in intracellular calcium ([Ca2+]i) in murine bone marrow-derived mast cells (BMMC) and human cord blood-derived eosinophils (EO) cultured in the presence of interleukins. ATP, ADP and AMP released a substantial amount of histamine and leukotriene C4 from BMMC, and EO showed locomotive activity in response to ATP, ADP and GTP. These reactions were accompanied with an increase in [Ca2+]i in BMMC and in EO. The rise in [Ca2+]i in BMMC induced by ATP or antigen at optimal concentrations was inclined to be persisting. On the other hand, these nucleotides induced a rapid and transient rise in [Ca2+]i in EO. Purified human peripheral EO also exhibited locomotive activity and an increase in [Ca2+]i in response to ATP. These results indicate that extracellular ATP activates interleukin-dependent cultured mast cells and EO through Ca2+ mobilization, and suggest that ATP, which is known to be released from activated platelets or autonomic nerves, may stimulate in vivo counterparts of these cultured inflammatory cells.     

Immunoperoxidase staining of surface and intracellular immunoglobulin in human neoplastic lymphoid cells.

An immunoperoxidase technique for the optical microscopic detection of cellular immunoglobulin has been used to stain fixed smears of human neoplastic B lymphoid cells. Only four out of 28 cases of chronic lymphatic leukaemia (CLL) showed membrane labelling by this technique. In contrast, when 14 samples from other types of B lymphoproliferative disorder (including hairy cell leukaemia, non-Hodgkin's lymphoma, and prolymphocytic leukaemia) were studied, all samples showed membrane immunoglobulin labelling (confirmed by capping experiments). This discrepancy was attributed to the greater density of surface immunoglobulin present on neoplastic cells in the latter group of disorders compared to CLL. This immunoperoxidase technique is therefore less sensitive than immunofluorescent staining of cells in suspension for the demonstration of neoplastic cell surface immunoglobulin. However, it offers a number of advantages (eg, excellent visualisation of cell morphology, permanence of stained preparations, and applicability to stored samples) which recommend it as the method of choice in certain clinical haematological contexts.     

Proteolysis of lymphocytic surface immunoglobulin.

Limited proteolysis of lymphocytic surface immunoglobulins in guinea-pig, rabbit and man was investigated by immunofluorescence using conjugated antisera specific for immunoglobulin fragments. The cell surface IgM of guinea pig L2C leukaemic lymphocytes and rabbit blood lymphocytes was cleaved in situ at its hinge region by papain. The Fcmicron fragment remained attached to the membrane and could be stained with the appropriate anti-Fc conjugate. The surface IgD and IgM of human chronic lymphocytic leukaemia cells was cleared from the cell surface by papain, as shown by reagents directed against both Fab and Fc region determinants. This could be due either to proteolytic degradation of membrane bound Fc or to initial cleavage of Ig from the membrane at some point other than the hinge region.     

Tyrosine phosphatase CD45 regulates hydrogen peroxide-induced calcium mobilization in B cells

By taking advantage of established CD45-deficient DT40 cells, the roles of CD45 in oxidative stress signaling were investigated. Using p-nitrophenyl phosphate as substrate, it was found that CD45 constituted nearly 40% of the total protein-tyrosine phosphatase activity. Almost 90% of the phosphatase activity was rapidly inactivated upon hydrogen peroxide treatment. Hydrogen peroxide-induced tyrosine phosphorylation of cellular proteins and c-Jun N-terminal kinase activation were markedly enhanced in CD45-deficient cells relative to that in its parental cells. In comparison, hydrogen peroxide-induced inositol 1,4,5-trisphosphate production and Ca(2+) mobilization were impaired in CD45-deficient DT40 cells. However, hydrogen peroxide-induced tyrosine phosphorylation of phospholipase Cgamma2 (PLCgamma2), phosphatidylinositol 3-kinase activity precipitated by anti-phosphotyrosine antibody, and activation of Bruton's tyrosine kinase appeared intact in CD45-deficient DT40 cells. This suggests that CD45 mediates the ability of hydrogen peroxide-activated PLCgamma2 to hydrolyze its substrate via a mechanism independent of both tyrosine phosphorylation of PLCgamma2 and phosphatidylinositol 3-kinase, as well as activation of Bruton's tyrosine kinase. Taken together, our observations demonstrated that, in addition to its negative regulatory or phosphatase activity, CD45 has a positive role in oxidative stress signaling.     

Distinct patterns of chemotactic peptide-induced calcium mobilization in differentiated myeloid leukemia cells and peripheral blood neutrophils.

Flow cytometry was used to compare intracellular calcium mobilization in mature neutrophilic granulocytes (PMN) with HL-60 promyelocytic leukemia cells induced to differentiate with dibutyryl cyclic adenosine 3',5'-monophosphate (dbcAMP). Using the calcium-specific probe indo-1 acetoxymethyl ester, we found that the ability of differentiating HL-60 cells to mobilize calcium in response to N-formyl-methionyl-leucyl-phenylalanine (fMLP) developed concomitantly with expression of receptors on the cells for this peptide. Mobilization of calcium in HL-60 cells, as well as in PMN, in response to fMLP was dose dependent and was related to the presence of calcium in the culture medium. In calcium-free medium, tenfold higher concentrations of fMLP were required to induce calcium mobilization than in calcium-containing medium. In HL-60 cells, calcium mobilization occurred more rapidly than in PMN and was independent of extracellular calcium. Furthermore, the response of HL-60 cells to fMLP was more prolonged than the response of PMN and was also of greater magnitude. Calcium mobilization in both HL-60 cells and PMN was partially inhibited by the calcium channel blocker, verapamil, but completely blocked by trimethylbenzoic acid 8-(diethylamino) octyl ester, an intracellular calcium antagonist. These results indicate that although both cell types mobilize calcium in response to fMLP, the characteristics of the responses are distinct. These differences may underlie distinct functional responses of PMN and differentiated HL-60 cells to fMLP.     

Mechanisms of calcium mobilization and phosphoinositide hydrolysis in human bronchial smooth muscle cells by endothelin 1.

We have previously demonstrated that human bronchial smooth muscle cells possess a single class of high-affinity binding sites for endothelin 1. In this study, we further characterized the receptor for endothelin 1 and evaluated the signal transduction mechanisms of this peptide. Stimulation of cultured human bronchial smooth muscle cells with endothelin 1 induced mobilization of Ca2+ from both intracellular and extracellular pools with a biphasic increase in cytoplasmic free Ca2+ concentration. Endothelin 1 increased cellular levels of inositol phosphates and diacylglycerol, indicating activation of phospholipase C, but induced production of inositol phosphates in smooth muscle cell membranes only in the presence of guanosine 5'-O-(thiotriphosphate) (GTP gamma S). Treatment of smooth muscle cells with pertussis toxin failed to block the endothelin 1-induced increase in inositol phosphate production and Ca2+ mobilization. These results suggest that the receptor for endothelin 1 in bronchial smooth muscle is coupled to phospholipase C through a pertussis toxin-insensitive G protein. Affinity crosslinking experiments identified the endothelin 1 receptor as a single band with an apparent molecular weight of approximately 70,000 on sodium dodecyl sulfate polyacrylamide gel electrophoresis, further supporting the functional evidence that endothelin 1 receptor belongs to the G protein-linked rhodopsin type of receptor superfamily.     

Characterization of platelet-activating factor-induced cytosolic calcium mobilization in human eosinophils.

BACKGROUND: Activated eosinophils play an important role in the pathogenesis of bronchial asthma and other allergic diseases, and platelet-activating factor (PAF) is a potent activator of eosinophils. OBJECTIVE: To characterize the cytosolic Ca2+ ([Ca2+]i) mobilization in human eosinophils in response to PAF. METHODS: [Ca2+]i responses to PAF were examined in human eosinophils using a microscopic fura-2 fluorescence-ratio imaging system. RESULTS: PAF caused a significant and dose-dependent increase in (Ca2+)i, which consisted of an initial rapid rise followed by a sustained elevation. This PAF-induced (Ca2+)i rise was inhibited by WEB 2086, a specific PAF receptor antagonist. The addition of 5 mM EGTA or 1 mM Ni2+ to a nominally Ca2+-free solution did not appreciably reduce the initial rise but significantly inhibited the sustained rise. The application of a protein kinase C inhibitor, Ro31-8220, augmented the sustained increase by PAF. Thapsigargin, a microsomal Ca2+ ATPase inhibitor, induced no appreciable change in a nominally Ca2+-free solution but induced a marked increase in (Ca2+)i when changed to a Ca2+-containing solution. CONCLUSIONS: The initial rapid rise and the following sustained rise in (Ca2+)i by PAF depends on Ca2+ release from the intracellular Ca2+ stores and Ca2+ influx, respectively, which are regulated by protein kinase C in human eosinophils. Furthermore, the so called Ca2+-capacitative entry is possibly involved in the Ca2+ influx from the extracellular solution in human eosinophils.     

Adenosine A1 receptors mediate mobilization of calcium in human bronchial smooth muscle cells

Adenosine stimulates contraction of airway smooth muscle, but the mechanism is widely considered indirect, depending on release of contractile agonists from mast cells and nerves. The goal was to determine whether adenosine, by itself, directly regulates calcium signaling in human bronchial smooth muscle cells (HBSMC). Primary cultures of HBSMC from normal subjects were loaded with fura 2-AM, and cytosolic calcium concentrations ([Ca(2+)](i)) were determined ratiometrically by imaging single cells. The nonselective adenosine receptor agonist, 5'-N-ethylcarboxamidoadenosine (NECA), and the adenosine A(1) receptor agonist, N(6)-cyclopentyladenosine (CPA), both stimulated rapid, transient increases in [Ca(2+)](i). In contrast, there were no calcium responses to 2-p-(2-carboxyethyl)phenethylamino-5'-N-ethylcarboxamido-adenosine (100 nM) or N(6)-(3-iodobenzyl)-adenosine-5'-N-methyluronamide (100 nM), selective agonists at adenosine A(2A) receptors and adenosine A(3) receptors, respectively. Calcium responses to NECA and CPA were inhibited by 8-cyclopentyl-1,3-dipropylxanthine, an adenosine A(1) receptor antagonist, and by pertussis toxin (PTX). In other experiments, NECA stimulated calcium transients in the absence of extracellular calcium, but not when cells were preincubated in cyclopiazonic acid or thapsigargin to empty intracellular calcium stores. Calcium responses were attenuated by xestospongin C and 2-aminoethoxydiphenylborane, inhibitors of inositol trisphosphate (IP(3)) receptors, and by U73122, an inhibitor of phospholipase C. It was concluded that stimulation of adenosine A(1) receptors on HBSMC rapidly mobilizes intracellular calcium stores by a mechanism dependent on PTX-sensitive G proteins, and IP(3) signaling. These findings suggest that, in addition to its well-established indirect effects on HBSMC, adenosine also has direct effects on contractile signaling pathways.     

嵌合抗CD20Fab诱导Daudi细胞凋亡

为了研究嵌合抗CD20基因工程抗体Fab的抗肿瘤活性及其抗肿瘤机制,本研究采用竞争性免疫荧光抑制实验,证实抗CD20 Fab片段能竞争性抑制亲本鼠源性抗CD20单克隆抗体HI47和Daudi细胞CD20的结合。MTT法测定嵌合抗CD20 Fab对Daudi细胞生长的影响,结果显示嵌合抗CD20 Fab对Daudi细胞的生长具有抑制作用,抑制作用呈剂量依赖性,其IC50为69μg/ml;利用流式细胞仪测定嵌合抗CD20 Fab诱导细胞凋亡作用,结果显示嵌合抗CD20 Fab可诱导 Daudi细胞凋亡,其凋亡率是Rituxan的2倍。这些实验结果证实嵌合抗CD20 Fab通过诱导Daudi细胞凋亡的机制抑制Daudi细胞生长。     

Tumour-bound immunoglobulins. The fate of immunoglobulin disappearing from the surface of coated tumour cells

This paper confirms results showing that TA3 tumour cells coated in vivo with immunoglobulins, lose some of the coat upon transfer to in vitro conditions. By labelling IgG isolated from the ascitic fluid of TA3 tumours it was found that the immunoglobulin coating TA3 cells is dynamically exchanged with immunoglobulin in the corresponding ascitic fluid.

Some of the released immunoglobulin is in a degraded state as judged from the fact that most of the released material lost the antigenicity of intact immunoglobulin and has a lower capacity to precipitate with ammonium sulphate at 50% saturation. The degraded immunoglobulin has a higher binding efficiency to tumour cells.

In vivo experiments demonstrated that the ascitic fluid of mice bearing TA3 and MC1 M tumours contains a material which has some of the physicochemical properties of IgG but which does not precipitate with antisera directed against IgG.

     

Impaired calcium mobilization and differential tyrosine phosphorylation in intestinal intraepithelial lymphocytes.

Intestinal intraepithelial lymphocytes (iIEL) exhibit a unique activation state characterized by the expression of activation markers and effector functions, but a minimal response to mitogenic signals in vitro. To further characterize this activation status, iIEL were compared with splenic T cells for two key activation signals, calcium mobilization and tyrosine phosphorylation. Calcium mobilization was impaired in iIEL treated with the calcium ionophores ionomycin or A23187, thapsigargin, or by CD3-cross-linking. The calcium mobilization defect is shared by mature and embryonic iIEL. Anti-phosphotyrosine Western blot analysis revealed that the iIEL are able to respond to T-cell receptor (TCR)-mediated signals by tyrosine phosphorylation, although the patterns of phosphorylation differ from those seen in splenic T cells. We conclude that iIEL are unable to mobilize calcium in vitro, which may be due to modulation of TCR-mediated signal transduction pathways by the microenvironment of the intestinal epithelium and/or caused by the standard isolation procedure used to prepare iIEL, which must be considered in future in vitro studies of iIEL function.