Bryostatin-1 in combination with calcium ionophore promotes the maturation of human umbilical cord-blood monocyte-derived dendritic cells capable of activating neonatal alloreactive T cells

We have investigated the effect of bryostatin-1 (Bryo-1) and calcium ionophore (CI) on maturation and functions of DCs generated from adherent cells of cord blood cultured with GM-CSF plus IL-4 (CB-DCs). The CB-DCs treated with Bryo-1+CI exhibited morphologic characteristics of mature DCs, expressed increased levels of CD1a, CD80, CD83, CD86, and MHC class II as well as enhanced ability to induce proliferation of alloreactive T cells isolated from cord blood and IFN-gamma production. Treatment of CB-DCs with TNF-alpha or PMA+CI was less effective. Thus, Bryo-1+CI promotes maturation of CB-DCs and therefore could be used to enhance the neonatal immune response.     

Evidence for the involvement of three distinct signals in the induction of IL-2 gene expression in human T lymphocytes

The regulation of IL-2 gene expression during T cell activation and proliferation has been investigated in primary cultures of purified human peripheral blood T cells. Prior results indicated that stimulation of T cells by anti-CD28 mAb plus PMA could induce IL-2 expression and T cell proliferation that was entirely resistant to cyclosporine. The present studies examined whether CD28 augments IL-2 expression by a unique pathway or merely acts at a point common to CD3-induced proliferation but distal to the effects of cyclosporine. The induction of maximal IL-2 gene expression required three signals provided by phorbol ester, calcium ionophore, and anti-CD28 mAb. Stimulation of cells by optimal amounts of calcium ionophore and PMA induced IL-2 mRNA that was completely suppressed by cyclosporine. The addition of anti-CD28 to T cells stimulated with PMA plus calcium ionophore induced a 5- to 100-fold increase in IL-2 gene expression and secretion that was resistant to cyclosporine. The CD28 signal was able to increase steady state IL-2 mRNA levels even in cells treated with maximally tolerated amounts of calcium ionophore and PMA. The three-signal requirement did not reflect differential regulation of lymphokine gene expression between the CD4 and CD8 T cell subsets or differences in the kinetics of IL-2 mRNA expression. The signal provided by CD28 is distinct from that of CD3 because although anti-CD28 plus PMA-induced proliferation is resistant to cyclosporine, anti-CD3 or anti-CD3 plus PMA-induced IL-2 expression is sensitive. Thus, these studies show that three biochemically distinct signals are required for maximal IL-2 gene expression. Furthermore, these studies suggest that lymphokine production in T cells is not controlled by an "on/off" switch, but rather, that CD28 regulates a distinct intracellular pathway which modulates the level of IL-2 production on a per cell basis. The observation that CD28 stimulation results in IL-2 concentrations that exceed 1000 U/m1 in tissue culture supernatants suggests that a role in vivo for CD28 might be to amplify immune responses initiated by the CD3/T cell receptor complex. Finally, the observation that CD28 interacts with the signals provided by PMA and calcium ionophore shows that the function of CD28 is not merely to act as a scaffold to stabilize or enhance signalling through the CD3/TCR complex.     

Effects of rhinovirus infection on histamine and cytokine production by cell lines from human mast cells and basophils

To understand the biochemical events that occur in the airways after rhinovirus (RV) infection, we developed for the first time a model in which the cell lines from human mast cells (HMC-1) and basophils (KU812) can be infected with RV14, a major group RV. Viral infection was confirmed by demonstrating that viral titers in culture supernatants, and RV RNA increased with time. RV14 infection alone and a combination of PMA plus calcium ionophore A23187, did not increase histamine production by these cells, although IgE plus anti-IgE increased the histamine production. However, histamine content in the supernatants increased in response to PMA plus A23187, or IgE plus anti-IgE after RV14 infection. PMA plus A23187 or IgE plus anti-IgE induced the production of IL-8 and GM-CSF in supernatants of HMC-1 cells and IL-4 and IL-6 in supernatants of KU812 cells. RV14 infection further increased the production of the cytokines, whereas RV14 infection alone did not alter the production of the cytokines by these cells. An Ab to ICAM-1 inhibited RV14 infection of the cells and decreased the production of cytokines and histamine after RV14 infection. RV14 infection enhanced the increases in intracellular calcium concentration and activation of NF-kappaB by PMA plus A23187 in the cells. These findings suggest that RV14 infection may prime the cytokine and histamine production from mast cells and basophils and may cause airway inflammation in asthma.     

Stimulation of AIDS lymphocytes with calcium ionophore (A23187) and phorbol ester (PMA): studies of cytoplasmic free Ca, IL-2 receptor expression, IL-2 production, and proliferation

We have studied whether the decreased lymphocyte proliferative responses of AIDS lymphocytes to stimulation by mitogens and antigens may be overcome when challenged with a combination of calcium ionophore A23187 and phorbol ester PMA. Comparison of the proliferative response of lymphocytes from nine patients with AIDS with the response of lymphocytes from nine control subjects showed that the response of AIDS lymphocytes was severely decreased when stimulated with PHA and no further response could be achieved by stimulation with A23187/PMA. On the other hand, no significant difference between the PHA-induced rise of cytoplasmic free calcium concentration ([Ca2+]1) in normal and AIDS lymphocytes was observed. The percentage of cells expressing IL-2 receptors (CD25) was also normal both after addition of PHA and after addition of A23187/PMA and the expression was normal on both CD4 and CD8 cells. The production of IL-2 in normal lymphocytes stimulated with A23187/PMA was 33 times higher than that after stimulation with PHA. In AIDS lymphocytes the production of IL-2 induced by all activators was severely decreased compared to control subjects, although the production of IL-2 after stimulation with A23187/PMA was higher than that in control lymphocytes after stimulation with PHA. The present study shows that a direct activation of protein kinase C combined with mobilization of cytoplasmic calcium does not overcome the lymphocyte proliferative deficiency of AIDS lymphocytes.     

Selective activation of helper and cytolytic T-cell functions of L3T4+ clones with either antireceptor antibody or phorbol ester and ionophore

After activation with specific antigen and antigen presenting cells (APC) L3T4+ inducer T-cell clones can lyse Ia+ APC. The present study characterizes the mechanism of activation and specificity of L3T4+ inducer cell-mediated cytolytic function. Two methods that bypass the physiological stimulus of antigen presented on Ia+ APC were used to activate L3T4+ clones. The first method utilized an antireceptor monoclonal antibody (MAb), KJ16.133, to activate KJ16.133+ clones. The activated clones expressed nonspecific cytolytic activity, killing target cells irrespective of their H-2 haplotype or their ability to express cell surface Ia molecules. The crosslinking of bound KJ16.133 antibody greatly enhanced cytolytic activity. This activation is receptor specific because KJ16.133- clones were not activated under identical conditions. The second method of activation was provided by a synergistic action of phorbol-12-myristate-13-acetate (PMA) and ionophore A23187. These agents nonspecifically activated all L3T4+ clones tested. The simultaneous presence of the two agents is required for maximal activation. Again, the activated clones expressed potent nonspecific cytolytic activity. These observations demonstrated that L3T4+ inducer T-cell-mediated killing can be separated into two stages: an activation step, which can be specifically and nonspecifically triggered and an effector phase which causes nonspecific lysis of bystander targets. The induction of nonspecific cytolytic activity by antireceptor MAb was inhibited by anti-L3T4 MAb (GK1.5). In contrast, activation of nonspecific cytolytic activity by treatment with PMA plus A23187 was not inhibited by anti-L3T4 MAb. Under the above activation conditions, antireceptor MAb selectively induced the secretion of IL-3 and expression of nonspecific cytolytic activity. However, there was little or no concomitant proliferation and production of IL-2. In contrast, activation by PMA plus A23187 coordinately induces expression of nonspecific cytolytic activity, secretion of lymphokines (IL-3 and IL-2), and cell proliferation. Thus, the anticlonotypic activation preferentially induces certain functions whereas activation with PMA plus A23187 is not selective.     

Murine lymphocytes exhibit heterogeneity in their proliferative responsiveness to calcium ionophore.

The calcium ionophore, A23187, when used alone was found to induce proliferation of murine T cells, at concentrations of 0.5-1 mM. This response required the presence of syngeneic splenic adherant cells (SAC) as a source of accessory cells. Interestingly, only CD4+ T cells but not CD8+ T cells or B cells responded to the calcium ionophore by proliferation. The inability of CD8+ T cells or B cells to respond was not related to decreased elevation in the intracellular ionized calcium [Ca2+]i concentration induced by the ionophore, because activated CD4+ T, CD8+ T and B cells all exhibited similar elevation in [Ca2+]i. The inability of CD8+ T cells to respond to calcium ionophore was probably due to insufficient production of autocrine growth factors, such as IL-2, inasmuch as the addition of exogenous IL-2 could completely restore the CD8+ T cell responsiveness. Also, exogenous rIL-1 could partially restore purified T cell response to calcium ionophore, whereas, rIL-6 failed to do so. IL-2, but not IL-4, acted as an autocrine growth factor for T cells responding to the calcium ionophore in the presence of SAC, since, antibodies against IL-2 or IL-2 receptor (IL-2R) but not against IL-4, could inhibit the T cell proliferation. Furthermore, exogenous rIL-2 but not rIL-4 supported the proliferation of T cells to calcium ionophore in the absence of accessory cells. Our results suggest that murine lymphocytes exhibit heterogeneity in their proliferative responsiveness to calcium ionophore and that this may not depend on the early activation signal such as the elevation in [Ca2+]i) induced by the ionophore but may depend on subsequent signals which regulate endogenous growth factor production.     

Stepwise activation of T cells. Role of the calcium ionophore A23187

The calcium ionophore A23187, at a concentration of 1 microgram/ml, is able to stimulate proliferation of freshly isolated peripheral blood lymphocytes, CD4+-enriched cells, or CD8+-enriched cells as measured by [3H]thymidine incorporation. This proliferation is accompanied by an increase in interleukin 2 (IL-2) receptor expression but not by a detectable up-regulation in (IL-2) production or the development of cytotoxicity. Proliferation can be blocked by anti-CD3, CD4, or CD8 monoclonal antibodies, but not by anti-Tac. If CD8+-enriched cells are activated for 3 days with A23187 and the blasts present on day 3 are sorted and returned to culture, they rapidly develop cytolytic activity in the presence of recombinant IL-2 but not recombinant interferon-gamma. CD4+ enriched cells, after activation with A23187, do not become cytotoxic in the presence of either recombinant IL-2 or recombinant interferon-gamma. These findings permit study of the stepwise maturation of T cells in this alternative pathway by using "minimal signals" that do not, by themselves and as used in these studies, stimulate precursor Tc to mature to full effector cytotoxic function. These findings are consistent with the model that A23187 drives T cells only part way along a pathway of maturation and that an additional second signal must be given to effect maturation of cytotoxic status.     

Fusion of intracellular membrane pools with cell surfaces of macrophages stimulated by phorbol esters and calcium ionophores

Mouse tumor macrophages (J774) exposed to phorbol myristate acetate (PMA) exhibited a marked increase in cell spreading. Correlated with this phenomenon was an increase in the number of cell surface transferrin (Tf) receptors and a corresponding decrease in the number of Tf receptors located intracellularly in membrane-bound endosomes. Similar effects were noted when J774 cells were exposed to the calcium ionophore A23187. Rabbit alveolar macrophages did not respond to PMA but did respond to A23187 by increasing cell spreading, which was accompanied by increases on the cell surface of four different receptors. These results demonstrate that phorbol esters and calcium ionophores can induce a redistribution of cellular receptors.     

Intracellular Ca2+ mobilization and not calcium influx promotes phorbol ester-stimulated thromboxane A2 synthesis in human platelets.

Phorbol esters, potent activators of protein kinase C (PKC), greatly enhance the release of arachidonic acid and its metabolites (TXA2, HETES, HHT) by Ca2+ ionophores in human platelets. In this paper, we report the relationship between intracellular Ca2+ mobilization and external calcium influx into platelets and the ability of PMA plus A23187 to promote thromboxane A2 (TXA2) synthesis. The enhanced levels of TXA2 due to the synergistic stimulation of the platelets with A23187 and phorbol esters are not affected significantly by the presence of external Ca2+ or the calcium-chelator EGTA. PKC inhibitors, staurosporine and sphingosine, abolished phorbol myristate acetate (PMA) potentiation of TXA2 production which strongly supports the role of PKC in the synergism. Platelet aggregation is more sensitive to PMA and external calcium than TXA2 formation. PMA increased TXA2 production as much as 4-fold at low ionophore concentrations. The A23187-induced rise in [Ca2+]i was reduced by pretreatment of human platelets with phorbol esters, both in the presence and absence of EGTA, and staurosporine reversed this inhibitory effect. These results indicate that the synergistic stimulation of TXA2 production by A23187 and phorbol esters is promoted by intracellular Ca2+ mobilization and not by external calcium influx. Our data also suggest that PKC is involved in the regulation of Ca2+ mobilization from some specific intracellular stores and that PKC may also stimulate the Ca(2+)-dependent phospholipase A2 at suboptimal Ca2+i concentrations.     

Inhibition of apoptosis by calcium ionophores in IL-3-dependent bone marrow cells is dependent upon production of IL-4+.

Calcium ionophores inhibit apoptosis in the IL-3-dependent cell line BAF3 and maintain the cells in a viable noncycling state. In this report, an identical effect of ionophore was also demonstrated on the multipotent IL-3-dependent progenitor cell line FDCP-MIX and on the primary IL-3-dependent cell population that could be cultured from murine bone marrow. Inhibition of apoptosis required extracellular calcium and could be blocked by cyclosporin A. Nuclei from IL-3-dependent cells were found to lack a calcium-activatable nuclease that degrades chromatin in the linker region between nucleosomes, unlike the nuclei of lymphoid cells. The mechanism of action of calcium ionophore could be divided into two distinct steps. First, ionophore induced the production of a survival factor that stimulated DNA synthesis and was identified as IL-4. Second, ionophore inhibited the cell cycle of the various IL-3-dependent cells. IL-4 production could be inhibited by cyclosporin A and required extracellular calcium, whereas cell cycle arrest did not. This implied that factor production was the step that was necessary for inhibition of apoptosis and maintenance of cell viability. This was confirmed by the use of an anti-IL-4R antibody, which blocked the inhibition of apoptosis induced by calcium ionophores.     

Evidence for the existence of distinct heterogeneity among the peripheral CD4-CD8- T cells from MRL-lpr/lpr mice based on the expression of the J11d marker, activation requirements, and functional properties

Autoimmune-susceptible, MRL-lpr/lpr (lpr) mice develop a profound lymphadenopathy resulting from the accumulation of CD4-CD8- (double-negative, DN) cells in peripheral lymphoid organs. The source and the mechanism of this abnormal accumulation of cells is still unknown. Recently, we reported that a significant number (approximately 35%) of the CD4-CD8- cells expressed J11d, a marker expressed by immature thymocytes but not by mature functional peripheral T cells. In the present study, we investigated the phenotype, growth requirements, and functional properties of purified J11d+ and J11d- subpopulations. Using the mAb, F23.1, which recognizes a TCR determinant encoded by the V beta 8 gene family, it was observed that approximately 30% of the J11d+ and J11d- DN cells expressed this determinant. Further studies on the thymus revealed that J11d+ DN cells from lpr thymus also contained F23.1+ cells (approximately 25%), whereas, similar cells from normal MRL(-)+/+mice were all F23.1-, consistent with earlier reports in other normal strains. Further phenotypic studies revealed that the peripheral J11d+ and J11d- cells from lpr mice were similar in expressing CD3, Ly-5 (B220), and Ly-24 (Pgp-1) determinants. When stimulated with phorbol myristic acetate (PMA) and recombinant IL-2 (rIL-2), only J11d- cells but not J11d+ cells responded by proliferation. However, in the presence of calcium ionophore (A23187) and PMA, both J11d+ and J11d- subpopulations proliferated by producing and responding to endogenous IL-2 but not IL-4. The lymph node T cells from 1-month-old MRL-lpr/lpr mice responded strongly when stimulated with PMA + rIL-4 or PMA + rIL-6. In contrast both J11d+ and J11d- subpopulations failed to respond when similarly stimulated. The J11d+ but not J11d- cells demonstrated spontaneous cytotoxic activity against the NK-sensitive YAC-1 tumor targets. The J11d- cells did not exhibit cytotoxic potential in spite of culture with PMA + rIL-2. Even after repeated culture in vitro with PMA + A23187 or PMA + rIL-2, both J11d+ and J11d- subpopulations failed to express the mature phenotype bearing CD4 and/or CD8 antigens. The present study demonstrates the expansion of unique J11d+, alpha beta-TCR+, DN T cells with cytotoxic potential in lpr mice and further suggests the existence of phenotypic and functional heterogeneity among the abnormal lpr DN cells.     

Polymorphonuclear leukocyte locomotion is insensitive to lowered cytoplasmic calcium levels

Chemotactic factors stimulate the rate of locomotion of polymorphonuclear leukocytes (PMNs). To investigate the importance of cytoplasmic calcium we have examined the ability of the chemotactic peptide N-formylnorleucyl eucylphenalanine (FNLLP) to stimulate the locomotion of PMNs whose cytoplasmic calcium levels were reduced by incubation in EGTA or in EGTA plus the calcium ionophores, ionomycin or A23187. Locomotion was assayed by migration through micropore filters and by time-lapse videomicroscopy. Cells in EGTA exhibited similar or slightly reduced rates of locomotion compared to cells in Hanks' balanced salt solution (HBSS). The peptide dose dependence for the stimulation of locomotion was similar in medium containing calcium or EGTA. The presence of 1 microM ionophore plus EGTA had no effect on the stimulation of locomotion by peptide. The presence of ionophores (1 microM) plus external calcium inhibited locomotion.     

Evidence that calcium may control neurite outgrowth by regulating the stability of actin filaments

We investigated the effects of calcium removal and calcium ionophores on the behavior and ultrastructure of cultured chick dorsal root ganglia (DRG) neurons to identify possible mechanisms by which calcium might regulate neurite outgrowth. Both calcium removal and the addition of calcium ionophores A23187 or ionomycin blocked outgrowth in previously elongating neurites, although in the case of calcium ionophores, changes in growth cone shape and retraction of neurites were also observed. Treatment with calcium ionophores significantly increased growth cone calcium. The ability of the microtubule stabilizing agent taxol to block A23187-induced neurite retraction and the ability of the actin stabilizing agent phalloidin to reverse both A23187-induced growth cone collapse and neurite retraction suggested that calcium acted on the cytoskeleton. Whole mount electron micrographs revealed an apparent disruption of actin filaments in the periphery (but not filopodia) of growth cones that were exposed to calcium ionophores in medium with normal calcium concentrations. This effect was not seen in cells treated with calcium ionophores in calcium-free medium or cells treated with the monovalent cation ionophore monensin, indicating that these effects were calcium specific. Ultrastructure of Triton X-100 extracted whole mounts further indicated that both microtubules and microfilaments may be more stable or extraction resistant after treatments which lower intracellular calcium. Taken together, the data suggest that calcium may control neurite elongation at least in part by regulating actin filament stability, and support a model for neurite outgrowth involving a balance between assembly and disassembly of the cytoskeleton.     

Pretreatment with phorbol esters abrogates mast cell adenosine responsiveness

Adenosine potentiates preformed mediator release from mouse bone marrow-derived mast cells stimulated with specific Ag or the calcium ionophore A23187. When these mast cells were cultured for 30 to 120 min with the phorbol ester PMA (10(-8) or 10(-7) M), protein kinase C activity was increased and Ag-stimulated beta-hexosaminidase release was modestly inhibited, whereas A23187-stimulated release was synergistically enhanced. However, in both cases, exogenous adenosine failed to augment beta-hexosaminidase release. Overnight PMA exposure produced a decrease in protein kinase C activity and a decrease in both Ag- and A23187-stimulated preformed mediator release, as well as a lack of responsiveness to adenosine. This hyporesponsiveness could be reversed by 24 h after washing the cells free of PMA. The generation of the arachidonic acid metabolite leukotriene C4 was not altered by mast cell PMA exposure. The ability of adenosine to increase intracellular cAMP concentrations was modestly blunted by high doses of PMA, and PMA abrogated the increase in intracellular free calcium levels usually observed in cells stimulated with Ag in the presence of 10(-5) M adenosine. PMA exposure induces a hyporesponsiveness to adenosine in mast cells, either by a direct effect on protein kinase C activity and/or by an effect on adenosine receptor expression or recycling.     

Cytokine production by mature and immature thymocytes.

We have studied the ability of subpopulations of activated thymocytes to produce four cytokines (IL-2, IL-4, IFN-gamma and TNF-alpha) which are believed to play roles in T cell development. Supernatants from various thymocyte subsets activated with calcium ionophore and PMA were tested for these cytokines. All CD3hi thymocyte subsets (CD4+8-, CD4-8- and CD4-8+) produced high titers of these four cytokines except CD3+4-8+ thymocytes, which did not produce IL-4. In contrast, CD4+8+ thymocytes did not produce any detectable cytokines. CD3-4-8- thymocytes produced IL-2, IFN-gamma, and TNF-alpha (but not IL-4) when activated by calcium ionophore + PMA and IL-1. We then separated CD3-4-8- thymocytes into IL-2R+ and IL-2R-. CD3-4-8-IL-2R+ thymocytes only produced small amounts of IL-2 when activated with calcium ionophore + PMA + IL-1, whereas CD3-4-8-IL-2R- thymocytes did not require IL-1 to produce IL-2, IFN-gamma, and TNF-alpha. Finally, CD4-8+3- thymocytes (an immature population believed to be an intermediate between CD3-4-8- and CD4+8+ thymocytes) only produced marginally detectable levels of IL-2 upon stimulation with calcium ionophore, PMA, and the addition of IL-1 did not result in increased levels of cytokine production. These observations indicate discrete patterns of cytokine production by the subsets studied and suggest specific controls of cytokine gene expression during T cell development.     

Perforin expression in human peripheral blood mononuclear cells. Definition of an IL-2-independent pathway of perforin induction in CD8+ T cells.

Perforin gene expression upon in vitro stimulation was studied at the mRNA level in normal human PBMC and in subpopulations. Freshly isolated PBMC express low levels of perforin mRNA. Increased perforin expression is rapidly induced by the calcium ionophore A23187 and by rIL-2. Phorbolesters (PMA), by comparison, are poor inducers of perforin RNA. Perforin induction by Ca-ionophore, unlike granzyme 2 and IL-2 induction, did not synergize with phorbolesters in PBMC or in purified T cells. Instead, perforin mRNA induction by A23187 in purified T cells requires the presence of adherent cells. Ca-ionophore plus adherent cell-induced perforin occurred in CD8+ T cells and was abolished by depletion of CD8+ T cells but not by depletion of CD4+ T cells. Adherent cells alone did not express perforin under any condition. Perforin mRNA induction by both A23187 and by rIL-2 is independent of de novo protein synthesis. The half-life of perforin mRNA induced by either stimulus is approximately 100 min. Cyclosporin A completely abrogates perforin induction by A23187 but only slightly inhibits the effect of rIL-2 on perforin mRNA expression. These data show that A23187 activates perforin gene expression in CD8+ cells by an IL-2-independent pathway and that the molecular mechanism of perforin expression may be different from the one induced by IL-2. Granzyme 2 (human leukocyte protease-HLP, homologous to murine granzyme B) mRNA expression was studied in comparison to perforin. Granzyme 2 in contrast to perforin responds to the synergistic action of phorbolester and Ca-ionophore in PBMC. In addition, the kinetics of the induction of granzyme and perforin mRNA, by various signals are different. Our data suggest that situations in vivo may exist that allow perforin expression in CD8+ cells in the absence of cytokines by a combination of Ca signals and accessory receptor ligation. The same signals may not be sufficient for granzyme 2 expression in any T cell subpopulation.     

Differentiation of acute and chronic myeloid leukemic blasts into the dendritic cell lineage: analysis of various differentiation-inducing signals

Purpose: Ex vivo differentiation of myeloid leukemic blasts into dendritic cells (DCs) holds significant promise for use as cellular vaccines, as they may present a constellation of endogenously expressed known and unknown leukemia antigens to the immune system. Although variety of stimuli can drive leukemiaDC differentiation in vitro, these blast-derived DCs typically have aberrant characteristics compared with DCs generated from normal progenitors by the same stimuli. It is not clear whether this is due to underlying leukemogenic mechanisms (e.g., specific oncogenes), genetic defects, stage of maturation arrest, defects in cytokine receptor expression or signal transduction pathways, or whether different stimuli themselves induce qualitatively dissimilar DC differentiation. Methods: To assess what factors may contribute to aberrant leukemic blastDC differentiation, we have examined how the same leukemic blasts (AML and CML) respond to different DC differentiation signals—including extracellular (the cytokine combination GM-CSF+TNF-+IL-4) and intracellular (the protein kinase C agonist PMA, the calcium ionophore A23187, and the combination of PMA plus A23187) stimuli. Results: We have found that the same leukemic blasts will develop qualitatively different sets of DC characteristics in response to differing stimuli, although no stimuli consistently induced all of the characteristic DC features. There were no clear differences in the responses relative to specific oncogene expression or stage of maturation arrest (AML vs CML). Signal transduction agonists that bypassed membrane receptors/proximal signaling (in particular, the combination of PMA and A23187) consistently induced the greatest capability to activate T cells. Interestingly, this ability did not clearly correlate with expression of MHC/costimulatory ligands. Conclusions: Our findings suggest that signal transduction may play an important role in the aberrant DC differentiation of leukemic blasts, and demonstrate that direct activation of PKC together with intracellular calcium signaling may be an effective method for generating immunostimulatory leukemia-derived DCs.This work was supported by NIH CA85208, CA95829, and ASCO Young Investigator Award (M.A.K-D)     

Anti-My-26: a monoclonal antibody inhibiting human phagocyte chemiluminescence

Anti-My-26, a mouse monoclonal IgG1 antibody, was raised against human granulocytes and has been shown to inhibit luminol-enhanced, glucose-independent chemiluminescence (CL) of human granulocytes (or monocytes) responding to the soluble secretagogues A23187 or ionomycin (calcium ionophores) and phorbol myristate acetate (PMA). Anti-My-26 inhibition of CL was reversible and was dependent on both secretatogue and monoclonal antibody concentration. This inhibition appeared to be directed at the component of granulocyte CL that is independent of NAD(P)H-oxidase-catalyzed formation of superoxide anion, because neither opsonized zymosan-stimulated CL nor the PMA-induced decrease in NAD (P)H-associated autofluorescence was affected by anti-My-26. In addition, ionomycin, over a wide concentration range, failed to generate any decrease in granulocyte autofluorescence. The A23187-induced CL inhibited by anti-My-26 was correlated with its depression of oxygen consumption. Furthermore, anti-My-26 was not cytotoxic and did not itself induce oxidative metabolism when used as a stimulant. Binding of anti-My-26 to phagocytic cells was not decreased by pre-exposure of cells to either A23187 or PMA. Evidence is presented to suggest that the binding of anti-My-26 to the granulocyte surface inhibits the oxidative response to calcium ionophore and PMA by blocking a common pathway(s) stimulated by these different secretagogues.