Characterization of a murine monoclonal antibody specific for human early lymphohemopoietic cells

Functional insights into nucleotide-metabolizing ectoenzymes expressed by bone marrow-resident cells in patients with multiple myeloma

Human myeloma cells grow in a hypoxic acidic niche in the bone marrow. Cross talk among cellular components of this closed niche generates extracellular adenosine, which promotes tumor cell survival. This is achieved through the binding of adenosine to purinergic receptors into complexes that function as an autocrine/paracrine signal factor with immune regulatory activities that i) down-regulate the functions of most immune effector cells and ii) enhance the activity of cells that suppress anti-tumor immune responses, thus facilitating the escape of malignant myeloma cells from immune surveillance. Here we review recent findings confirming that the dominant phenotype for survival of tumor cells is that where the malignant cells have been metabolically reprogrammed for the generation of lactic acidosis in the bone marrow niche. Adenosine triphosphate and nicotinamide-adenine dinucleotide extruded from tumor cells, along with cyclic adenosine monophosphate, are the main intracellular energetic/messenger molecules that serve as leading substrates in the extracellular space for membrane-bound ectonucleotidases metabolizing purine nucleotides to signaling adenosine. Within this mechanistic framework, the adenosinergic substrate conversion can vary significantly according to the metabolic environment. Indeed, the neoplastic expansion of plasma cells exploits both enzymatic networks and hypoxic acidic conditions for migrating and homing to a protected niche and for evading the immune response. The expression of multiple specific adenosine receptors in the niche completes the profile of a complex regulatory framework whose signals modify multiple myeloma and host immune responses.

Generation and Characterization of a Murine Monoclonal Antibody Specific for the Human T1-Cd5 Molecule

Murine monoclonal antibodies (MoAbs) have found widespread applications in the characterization of the molecular and functional features of lymphocyte differentiation antigens. The present paper summarizes the results of our work dealing with the production and selection of a murine MoAb recognizing a molecule expressed during the whole differentiative life of T lymphocytes. The MoAb CB01 resulted to be specific for an apparently unique epitope of the T-cell specific membrane glycoprotein T1-CD5.

Sphingolipid Microdomains Mediate CD38 Internalization: Topography of the Endocytosis

Plasma membranes of several cell types contain specialized microdomains (or lipid rafts) enriched in sphingolipids, cholesterol, sphingomyelin, and glycosyl-phosphatidylinositol-anchored proteins. These membrane domains are characterized by detergent insolubility at low temperatures and low buoyant density. Human CD38 is the prototype of a gene family encoding surface molecules endowed with multiple functional activities. The endocytosis of the human CD38 molecule has been investigated in normal lymphocytes and in a number of leukemia- and lymphoma-derived cell lines demonstrating that internalization after CD38 ligation is a reproducible event involving only a fraction of the whole amount of the surface molecule. This study reports the results obtained by conventional, confocal, and electron microscopy on the effects induced by the engagement of the molecule with agonistic mAb, reproducing the signals mediated by its natural ligand. The results demonstrate that the endocytosis induced as consequence of CD38 ligation is preceded by a thorough rearrangement of the cell surface with formation of glycosphingolipid- and cholesterol-rich plasma membrane microdomains. These data suggest that specialized raft microdomains might be the plasma membrane structure through which CD38 translocates at intracellular level. The CD38/lipid interactions during the coated pit formation trigger a process that generate membrane curvature, considered as the first step of CD38 endocytosis. Moreover, ultrastructural studies show that early CD38+ endosomes are pleiomorphic and contain cisternal and vesicular regions. Late endosomes exhibit a complex organisation, containing uncoupled CD38-ligand multivesicular- or multilamellar-regions.

Development of an Immunochromatographic Test for Diagnosis of Visceral Leishmaniasis Based on Detection of a Circulating Antigen

Background

Visceral leishmaniasis (VL) is a life-threatening disease caused by protozoan parasites of the Leishmania donovani complex. Early case detection followed by adequate treatment is essential to the control of VL. However, the available diagnostic tests are either invasive and require considerable expertise (parasitological demonstration of the parasite in tissue smears) or unable to distinguish between past and active infection (serological methods). Therefore, we aimed to develop a lateral flow assay in the form of an immunochromatographic test (ICT) device based on the detection of a circulating Leishmania antigen using monoclonal antibodies (mAbs).

Methodology/Principal Findings

mAbs were produced by fusion of murine myeloma cells with splenocytes isolated from a mouse immunized with L. donovani soluble crude antigen. Out of 12 cloned hybridoma cell lines, two secreted mAbs recognizing the same leishmanial protein. These mAbs were used to produce an ICT as a sandwich assay for the detection of circulating antigen in serum and blood samples. The ICT was evaluated with 213 serum samples from VL patients living in VL endemic areas in China, and with 156 serum samples from patients with other diseases as well as 78 serum samples from healthy donors. Sensitivity, specificity and diagnostic efficiency of the new ICT was 95.8%, 98.7% and 97.3%, respectively. Compared with a commercially available antibody detecting ICT, our antigen-based ICT performed slightly better.

Conclusion/Significance

The newly developed ICT is an easy to use and more accurate diagnostic tool which fulfils the performance and operational characteristics required for VL case detection under field and laboratory conditions. As our ICT detects a circulating antigen, it will also be useful in monitoring treatment success and diagnosing VL in immunocompromised patients.

Visceral leishmaniasis is a neglected disease caused by different species of protozoan parasites of the genus Leishmania. The disease is endemic in 61 countries, and in many of them it poses a serious public health issue. As visceral leishmaniasis is fatal if left untreated, early diagnosis is essential for treatment and control of the disease. Current available diagnostic tests are either difficult to carry out under field conditions or insufficiently accurate. In this study we developed a new diagnostic test which detects a circulation parasite-derived antigen in serum or blood samples of patients with visceral leishmaniasis. We found that our test performed better than most other tests based on the detection of parasite-specific antibodies. In addition, as our test is a device for the detection of an acute infection, it will be useful to validate treatment and in the diagnosis of the disease in patients with deficient antibody production (as in AIDS patients).

A highly immunogenic recombinant and truncated protein of the secreted aspartic proteases family (rSap2t) of Candida albicans as a mucosal anticandidal vaccine

Sap2 (secreted aspartyl proteinase2) is a member of the Sap family of Candida albicans, a human opportunistic pathogen, which acts as a virulence factor in experimental animal models of mucosal candidiasis. The C. albicans SAP2 was subcloned into vector pDS56-RBSII-6xhis, under the control of an inducible promoter to produce a truncated 6xhis-tagged, enzymatically inactive Sap2, lacking the N-terminus 76 amino acids (rSap2t). This recombinant protein was purified to homogeneity by one-step nickel-chelate affinity chromatography and used to immunize intravaginally oophorectomized estradiol-treated rats. These animals raised local anti-rSap2t immunoglobulin G (IgG) and IgA antibodies and were protected from the challenge of a highly vaginopathic strain of the fungus. Protection was possibly due to the specific antibodies as suggested by the passive transfer of immune vaginal fluid and the protective effects of passive vaccination with anti-rSap2t IgM and IgG monoclonal antibodies. Hence, this new recombinant proteinase constitutes a novel tool to investigate mechanisms of anti-Candida protection at the vaginal level and as vaccination against vaginal candidiasis, a common, frequently recurrent and sometimes antimycotic-refractory infection in women.

NAD+-metabolizing ecto-enzymes shape tumor-host interactions: the chronic lymphocytic leukemia model

Nicotinamide adenine dinucleotide (NAD(+)) is an essential co-enzyme that can be released in the extracellular milieu. Here, it may elicit signals through binding purinergic receptors. Alternatively, NAD(+) may be dismantled to adenosine, up-taken by cells and transformed to reconstitute the intracellular nucleotide pool. An articulated ecto-enzyme network is responsible for the nucleotide-nucleoside conversion. CD38 is the main mammalian enzyme that hydrolyzes NAD(+), generating Ca(2+)-active metabolites. Evidence suggests that this extracellular network may be altered or used by tumor cells to (i) nestle in protected areas, and (ii) evade the immune response. We have exploited chronic lymphocytic leukemia as a model to test the role of the ecto-enzyme network, starting by analyzing the individual elements that make up the whole picture.

CD38 increases CXCL12-mediated signals and homing of chronic lymphocytic leukemia cells

Homing of chronic lymphocytic leukemia (CLL) cells to sites favoring growth, a critical step in disease progression, is principally coordinated by the CXCL12/CXCR4 axis. A cohort of 62 CLL patients was divided into migrating and nonmigrating subsets according to chemotaxis toward CXCL12. Migrating patients phosphorylated extracellular signal-regulated kinase 1/2 (ERK1/2) proteins more than nonmigrating patients (P<0.0002). CD38 expression was the parameter most strongly associated with heightened CXCL12 signaling (P<0.0001), confirmed by independent statistical approaches. Consistent with this observation, CD38(-) CLL cells in samples with bimodal CD38 expression responded less to CXCL12 than the intact clone (P=0.003). Furthermore, lentivirus-induced de novo expression of CD38 was paralleled by increased responses to CXCL12, as compared with cells infected with a control virus. CD38 ligation with agonistic monoclonal antibodies (mAbs) enhanced CXCL12 signaling, whereas blocking anti-CD38 mAbs inhibited chemokine effects in vitro. This is attributed to physical proximity on the membrane between CD38 and CXCR4 (the CXCL12 receptor), as shown by (i) coimmunoprecipitation and (ii) confocal microscopy experiments. Blocking anti-CD38 mAbs significantly compromised homing of CLL cells from blood to lymphoid organs in a mouse model. These results indicate that CD38 synergizes with the CXCR4 pathway and support the working hypothesis that migration is a central step in disease progression.

CD38 and CD157 ectoenzymes mark cell subsets in the human corneal limbus

Nicotinamide adenine dinucleotide (NAD(+)), a precursor of molecules involved in cell regulatory processes, is released in extra-cellular compartments after stress or inflammation.This study investigates the expression in the human cornea of CD38 and CD157, two NAD(+)-consuming ectoenzymes and surface receptors. The analysis in corneal epithelial and stromal cells was performed by means of multiple approaches, which included immunofluorescence, reverse transcriptase polymerase chain reaction (RT-PCR), Western blot, and confocal microscopy. The presence of enzymatically active NAD(+)-consumers in intact corneal cells was analyzed by high performance liquid chromatography (HPLC)-based assays. The results obtained show that CD38 and CD157 are expressed constitutively by corneal cells: CD38 appears as a 45-kDa monomer, while CD157 is a 42- to 45-kDa doublet. The molecules are enzymatically active, with features reminiscent of those observed in human leukocytes. CD38 is expressed by cells of the suprabasal limbal epithelium, whereas it is not detectable in central corneal epithelium and stroma. CD157 is expressed by basal limbal clusters, a p63(+)/cytokeratin 19(+) cell subset reported to contain corneal stem cells, and by stromal cells. The results of the work indicates that the human cornea is equipped with molecular tools capable of consuming extracellular NAD(+), and that CD157 is a potential marker of corneal limbal cells in the stem cell niche. The presence and characteristics of these ectoenzymes may be exploited to design drugs for wound repair or for applications in tissue transplantation.

Evolution and function of the ADP ribosyl cyclase/CD38 gene family in physiology and pathology

The membrane proteins CD38 and CD157 belong to an evolutionarily conserved family of enzymes that play crucial roles in human physiology. Expressed in distinct patterns in most tissues, CD38 (and CD157) cleaves NAD(+) and NADP(+), generating cyclic ADP ribose (cADPR), NAADP, and ADPR. These reaction products are essential for the regulation of intracellular Ca(2+), the most ancient and universal cell signaling system. The entire family of enzymes controls complex processes, including egg fertilization, cell activation and proliferation, muscle contraction, hormone secretion, and immune responses. Over the course of evolution, the molecules have developed the ability to interact laterally and frontally with other surface proteins and have acquired receptor-like features. As detailed in this review, the loss of CD38 function is associated with impaired immune responses, metabolic disturbances, and behavioral modifications in mice. CD38 is a powerful disease marker for human leukemias and myelomas, is directly involved in the pathogenesis and outcome of human immunodeficiency virus infection and chronic lymphocytic leukemia, and controls insulin release and the development of diabetes. Here, the data concerning diseases are examined in view of potential clinical applications in diagnosis, prognosis, and therapy. The concluding remarks try to frame all of the currently available information within a unified working model that takes into account both the enzymatic and receptorial functions of the molecules.

CD38 and ZAP-70 are functionally linked and mark CLL cells with high migratory potential

Our interest in chronic lymphocytic leukemia (CLL) derives primarily from the exploitation of human diseases as strategic models for defining the in vivo biological roles of CD38. Using this model, we showed that CD38 triggers robust proliferation/survival signals modulated through the interactions with the CD31 ligand expressed by nurse-like cells and by the stromal/endothelial components. By analyzing a cohort of 56 patients with clinically and molecularly characterized CLL, we show that (1) patients with CD38(+)/ZAP-70(+) are characterized by enhanced migration toward Stromal derived factor-1alpha (SDF-1alpha)/CXCL12; (2) CD38 ligation leads to tyrosine phosphorylation of ZAP-70, showing that these markers are functionally linked; (3) ZAP-70 represents a limiting factor for the CD38 pathway in the CLL context, as shown by studying CD38-mediated signal transduction in 26 molecularly characterized patients; and (4) the CLL subgroup of patients defined on the basis of migratory potential is marked by a specific genetic signature, with a significant number of differentially expressed genes being involved in cell-cell interactions and movement. Altogether, the results of this work provide biological evidence for why the combined analysis of CD38 and ZAP-70 expression as determined in several clinical trials results in more dependable identification of patients with CLL who have aggressive disease.

CD38/CD19: a lipid raft-dependent signaling complex in human B cells

The present work deals with the mechanisms of signal transduction mediated via CD38 in normal and neoplastic human B lymphocytes. The results indicate that CD38 is a receptor and that CD38-mediated signals are tightly regulated at 3 distinct levels. The first concerns the structural organization of CD38, which is clearly divided into monomeric and dimeric forms. The second level of regulation is based on the dynamic localization of CD38 molecules in lipid microdomains within the plasma membrane. Lateral associations with other proteins, namely with the CD19/CD81 complex, determine the third level of control. Raft localization and association with the CD19 complex are prerequisites for CD38-mediated signals in tonsillar B cells and in continuous lines. Lastly, the results indicate that lipid microdomain disruption and silencing of CD19 directly impacts on CD38's ability to mediate Ca(2+) fluxes, while leaving its surface expression unchanged. CD38 is also an enzyme capable of producing several calcium-mobilizing metabolites including cyclic adenosine diphosphate ribose (cADPR). Our inability to identify a correlation between the production of cADPR and the receptorial functions support the hypothesis that CD38 is a pleiotropic molecule whose behavior as a receptor is independent from its enzymatic activity.

The CD38/CD157 mammalian gene family: An evolutionary paradigm for other leukocyte surface enzymes

Human CD38 is the mammalian prototype of a family of phylogenetically conserved proteins which share structural similarities and enzymatic activities involved in the production of an intracellular second messenger with calcium mobilizing effects. Engagement of CD38 by agonistic monoclonal antibodies and the CD31 ligand initiates a cytoplasmic signaling cascade involving tyrosine phosphorylation of the proto-oncogene c-cbl and of the extracellular regulated kinase 1 of 2 complex. Further requirements for signal transduction include a privileged localization within the cholesterol-rich areas of the plasma membrane and physical association with specialized surface receptors. CD38-mediated signals are crucial in heterotypic cell adhesion and migration as well as in the activation of proliferation/survival programs by normal and neoplastic cells. Here we review the most recent literature on this complex topic and attempt to formulate a single model reconciling the enzymatic and receptorial activities of CD38.

CD38 autoimmunity: recent advances and relevance to human diabetes

Human CD38 is a protein which catalyzes the synthesis of nicotinic acid adenine dinucleotide (NAADP+) and the conversion of NAD+ to cADPR. Both cADPR and NAADP+ are powerful intracellular Ca2+ ([Ca2+]i) mobilizers in different cell types. Recently, the presence of CD38 autoantibodies has been found in a significant number (9-15%) of patients with Type 2 or long-standing Type 1 diabetes. These autoantibodies are biologically active, the majority of them (-60%) displaying agonistic properties, i.e., [Ca2+]i mobilization in lymphocytic cell lines and in pancreatic islets. In cultured rat pancreatic islets, the human autoantibodies inhibit glucose-induced insulin release, whereas, in human pancreatic islets CD38 autoantibodies stimulate glucose-mediated insulin secretion. The clinical phenotype of anti-CD38-positive Type 2 diabetes differs from the LADA (latent autoimmune diabetes of adults) phenotype. When accurately matched for age and obesity, only LADA patients with anti-GAD antibodies, but not GAD-negative/ CD38-positive patients, have reduced in vivo beta-cell function in comparison to antibody-negative patients. Transgenic mice overexpressing CD38 show enhanced glucose-induced insulin release, whereas, conversely, CD38 knockout mice display a severe impairment in beta-cell function. Few Japanese diabetic patients carry a missense mutation in the CD38 gene; in Caucasian patients mutations in the CD38 gene have not been found. Collectively, these findings suggest that activation of CD38 represents an alternative signaling pathway for glucose-induced insulin secretion in human beta-cells. More information, however, is necessary to gauge the role of CD38 autoimmunity in the context of the natural history of human Type 1 or Type 2 diabetes.

Glutamate-mediated overexpression of CD38 in astrocytes cultured with neurones

Recently, a new system of astrocyte-neurone glutamatergic signalling has been identified. It is started in astrocytes by ectocellular, CD38-catalysed conversion of NAD(+) to the calcium mobilizer cyclic ADP-ribose (cADPR). This is then pumped by CD38 itself into the cytosol where the resulting free intracellular Ca(2+) concentration [Ca(2+)](i) transients elicit an increased release of glutamate, which can induce an enhanced Ca(2+) response in neighbouring neurones. Here, we demonstrate that co-culture of either cortical or hippocampal astrocytes with neurones results in a significant overexpression of astrocyte CD38 both on the plasma membrane and intracellularly. The causal role of neurone-released glutamate in inducing overexpression of astrocyte CD38 is demonstrated by two observations: first, in the absence of neurones, induction of CD38 in pure astrocyte cultures can be obtained with glutamate and second, it can be prevented in co-cultures by glutamate receptor antagonists. The neuronal glutamate-mediated effect of neurones on astrocyte CD38 expression is paralleled by increased intracellular cADPR and [Ca(2+)](i) levels, both findings indicating functionality of overexpressed CD38. These results reveal a new neurone-to-astrocyte glutamatergic signalling based on the CD38/cADPR system, which affects the [Ca(2+)](i) in both cell types, adding further complexity to the bi-directional patterns of communication between astrocytes and neurones.

Human CD38 interferes with HIV-1 fusion through a sequence homologous to the V3 loop of the viral envelope glycoprotein gp120

CD38 is a progression marker in HIV-1 infection, it displays lateral association with CD4, and down-modulates gp120/CD4 binding. The aim of this study was to elucidate the mechanism behind the interplay between CD4, CD38, and HIV-1. We used mouse cell transfectants expressing human CD4 and either CD38 or other CD4-associated molecules to show that CD38 specifically inhibits gp120/CD4 binding. Human cell transfectants expressing truncated forms of CD38 and bioinformatic analysis were used to map the anti-HIV activity and show that it is concentrated in the membrane-proximal region. This region displayed significant sequence-similarity with the V3 loop of the HIV-1 gp120 glycoprotein. In line with this similarity, synthetic soluble peptides derived from this region reproduced the anti-HIV effects of full-length CD38 and inhibited HIV-1 and HIV-2 primary isolates from different subtypes and with different coreceptor use. A multiple-branched peptide construct presenting part of the sequence of the V3-like region potently and selectively inhibited HIV-1 replication in the nanomolar range. Conversely, a deletion in the V3-like region abrogated the anti-HIV-1 activity of CD38 and its lateral association with CD4. These findings may provide new insights into the early events of HIV-1 fusion and strategies to intervene.

Prolonged in vitro exposure to autoantibodies against CD38 impairs the function and survival of human pancreatic islets

Autoantibodies against CD38 (adenosine-5'-diphosphate[ADP]-ribosyl cyclase/cyclic ADP-ribose hydrolase) have been described in 10-12% of patients with type 2 diabetes. In human islets, anti-CD38 autoantibodies (CD38Abs) acutely stimulate insulin release (IR) and increase the cytosolic calcium concentration ([Ca(2+)](i)). Whether CD38Abs affect human islet cell function and survival upon prolonged in vitro exposure is not known. We cultured human islets for up to 7 days in the presence of sera from 10 patients with type 2 diabetes that had neither CD38Ab- nor [Ca(2+)](i)-mobilizing activity (-/-), sera from 6 patients with type 2 diabetes that was CD38Ab-positive and had [Ca(2+)](i)-mobilizing activity (+/+), or no sera (control). At baseline, +/+ sera caused a significant (P < 0.002) acute stimulation of IR (IR at 3.3 mmol/l glucose was 45 +/- 19, 84 +/- 24, and 34 +/- 12 micro U/ml in control, +/+, and -/- sera, respectively; the corresponding IR at 16.7 mmol/l glucose was 72 +/- 25, 204 +/- 56, and 80 +/- 32 micro U/ml). At 3 days, IR at 3.3 mmol/l glucose was 42 +/- 18, 27 +/- 11, and 43 +/- 24 micro U/ml (P = 0.0003) for control, +/+, and -/- sera, respectively, whereas at 16.7 mmol/l glucose, it was 95 +/- 76, 45 +/- 35, and 76 +/- 42 micro U/ml, respectively. After 7 days of exposure, the corresponding IR at 3.3 mmol/l glucose was 40 +/- 11, 28 +/- 12, and 35 +/- 15 micro U/ml, respectively, whereas at 16.7 mmol/l glucose it was 79 +/- 39, 39 +/- 17, and 62 +/- 39 micro U/ml. At both 3 and 7 days, IR still increased when switching from 3.3 to 16.7 mmol/l glucose (P < 0.0003), and incubation with +/+ sera induced a significant decrease in the insulin response (P < 0.002). At 7 days, the number of dead cells (as evaluated by an enzyme-linked immunosorbent assay technique) differed significantly between control (1.2 +/- 0.3 OD units) cells, islets exposed to -/- sera (1.4 +/- 0.1), and islets coincubated with +/+ sera (1.9 +/- 0.4, P < 0.01). We conclude that prolonged exposure of human islets to sera positive for the presence of CD38Abs with [Ca(2+)](i)-mobilizing activity impairs beta-cell function and viability in cultured human pancreatic islets.

CD157, the Janus of CD38 but with a unique personality

CD157 is a pleiotropic ectoenzyme which belongs to the CD38 family and to the growing number of leukocyte surface molecules known to act independently as both receptors and enzymes. A 45-kDa surface structure with a GPI anchor, the CD157 molecule displays two distinct domains in its extracellular component. The first is implicated in the enzymic activities of the molecule and the second features adhesion/signalling properties. CD157 shares several characteristics with CD38, including a similar amino acid sequence and enzymic functions. Both molecules are involved in the metabolism of NAD(+), and the CD157 gene is synthenic on 4p15 with CD38, with which it also shares a unique genomic organization. Their conservation in phylogeny is striking evidence for their relevance in the life and death cycle of the cell.

CD38 ligation plays a direct role in the induction of IL-1beta, IL-6, and IL-10 secretion in resting human monocytes

CD38 signaling, either induced by ligation with specific agonistic monoclonal antibody (mAb) or after interaction with CD31, its cognate counter-receptor, is involved in release of IL-1beta, IL-6, and IL-10 cytokines in resting human monocytes. CD38 ligation by the F(ab')(2) IB4 mAb did not induce signals relevant for cytokine secretion and the block of the Fcgamma receptor I (FcgammaRI) by anti-CD64 or FcgammaRII by anti-CD32 mAb did not inhibit CD38-mediated IL-1beta release. Dimerization or multimerization of the CD38 molecule by: (i) cross-linking of the receptor ligated by F(ab')(2) or by (ii) increasing CD38 expression by treating monocytes with IFNgamma were able to restore the truncated CD38-mediated signals involved in cytokine secretion. These data indicate that CD38 receptor-mediated signals operate directly suggesting a Fcgamma receptorial surface molecule independent activation pathway. The key element for the receptor mediated signaling is represented by surface density of CD38 on resting monocytes.

NAD-dependent inhibition of the NAD-glycohydrolase activity in A549 cells

NAD glycohydrolases are enzymes that catalyze the hydrolysis of NAD to produce ADP-ribose and nicotinamide. Regulation of these enzymes has not been fully elucidated. We have identified a NAD-glycohydrolase activity associated with the outer surface of the plasma membrane in human lung epithelial cell line A549. This activity is negatively regulated by its substrate beta-NAD but not by alpha-NAD. Partial restoration of NADase activity after incubation of the cells with arginine or histidine, known ADP-ribose acceptors, suggests that inhibition be regulated by ADP-ribosylation. A549 do not undergo to apoptosis upon NAD treatment indicating that this effect be likely mediated by a cellular component(s) lacking in epithelial cells.

Novobiocin is a novel inducer of CD38 on cells of the myelomonocytic lineage

KG-1a, HL-60 and U-937 cells, which represent different stages of myelopoiesis, showed growth retardation in response to the coumarin antibiotic novobiocin. Novobiocin was found to increase CD38 expression (in all three cell lines) and to induce differentiation along the monocytic path in HL-60 and U-937 cells but not in KG-1a cells. The increase in surface expression of CD38 was matched by NAD glycohydrolase activity and by increases in the level of specific mRNA, indicating that the gene product is active and that regulation occurs at the level of transcription or mRNA stability. Of the three cell lines tested, only the early KG-1a expressed N-cadherin, a member of Ca(2+)-dependent adhesion molecules involved in embryonic differentiation processes. In contrast to CD38, N-cadherin was slightly down-regulated pointing to a specific role of novobiocin in gene regulation.

Peripheral blood CD38 expression predicts survival in B-cell chronic lymphocytic leukemia

CD38 expression was investigated in 161 untreated patients with B-cell chronic lymphocytic leukemia (B-CLL). A score system, devised ad hoc by integrating the percentage and the mean fluorescence intensity (MFI) values of CD38(+) cells, indicated that B-CLL patients with a CD38 score < or =3 are characterized by a significantly longer survival compared to those with a CD38 score >3 (P=0.0026). Thirty-seven percent of patients with a CD38 score < or =3 and 58% of those with a score >3 were dead at 10 years. Multivariate analysis indicates that only the CD38 score successfully predicts survival (P=0.0028), with an estimated 3.8-fold greater risk of death for those cases with CD38 score >3.

Evidence of a role for cyclic ADP-ribose in calcium signalling and neurotransmitter release in cultured astrocytes

Astrocytes possess different, efficient ways to generate complex changes in intracellular calcium concentrations, which allow them to communicate with each other and to interact with adjacent neuronal cells. Here we show that cultured hippocampal astrocytes coexpress the ectoenzyme CD38, directly involved in the metabolism of the calcium mobilizer cyclic ADP-ribose, and the NAD+ transporter connexin 43. We also demonstrate that hippocampal astrocytes can release NAD+ and respond to extracellular NAD+ or cyclic ADP-ribose with intracellular calcium increases, suggesting the existence of an autocrine cyclic ADP-ribose-mediated signalling. Cyclic ADP-ribose-induced calcium changes are in turn responsible for an increased glutamate and GABA release, this effect being completely inhibited by the cyclic ADP-ribose specific antagonist 8-NH2-cADPR. Furthermore, addition of NAD+ to astrocyte-neuron co-cultures results in a delayed intracellular calcium transient in neuronal cells, which is strongly but not completely inhibited by glutamate receptor blockers. These data indicate that an astrocyte-to-neuron calcium signalling can be triggered by the CD38/cADPR system, which, through the activation of intracellular calcium responses in astrocytes, is in turn responsible for the increased release of neuromodulators from glial cells.

Expression of CD31 by cells of extensive ductal in situ and invasive carcinomas of the breast

CD31, an adhesion molecule expressed by endothelial cells, leukocytes, and platelets, is used in surgical pathology as a marker of normal and neoplastic vascularization. During the assessment of angiogenesis in breast carcinomas, CD31 expression was observed in a single case of large (5.2 cm diameter) high nuclear grade ductal carcinoma in situ (HG-DCIS) associated with poorly differentiated invasive ductal carcinoma (G3-IDC). Expression was limited to the cell membrane. This study focused on 32 HG-DCIS> or = 2 cm, either pure or associated with IDC. Cancer cells wereCD31(+) in 11 cases. Double staining using anti-CD31 monoclonal antibody (MAb) and anti-CD44 MAb, the anti-hyaluronate receptor, showed that foci of CD31(+) and CD44(-) tumour cells could be traced throughout the glandular tree, marking the intraductal diffusion of tumour up to Paget's cells at the nipple. The associated G3-IDC and their lymph node metastases were instead CD31(+) and CD44(+). CD31(+) tumours were oestrogen receptor (ER)(-), frequently p53(+) and c-erb-B2(+), and infiltrated by CD4(+) T lymphocytes. Normal and hyperplastic epithelia were constantly CD31(-). Other endothelial markers (e.g Factor VIII-RA and CD34) were not expressed by carcinoma cells, as was CD38, the CD31 ligand. In conclusion, CD31 expression is a feature acquired by breast cancer cells in the DCIS model. CD31 expression mainly correlates with tumour cells spreading within the ductal system. Finally, the invasive phenotype requires the co-expression of CD31 and CD44.

Human anti-CD38 autoantibodies raise intracellular calcium and stimulate insulin release in human pancreatic islets

CD38 is involved in transmembrane signaling in many cell types; anti-CD38 autoantibodies have been described in diabetic patients. We tested whether human anti-CD38 antibodies possess signaling properties by measuring their ability to raise intracellular calcium ([Ca2+]i) using the fluo-3-acetoxymethyl ester method in a human-derived T-cell line (Jurkat T-cells, expressing high levels of surface CD38) and in dispersed human islet cells from normal donors. In Jurkat T-cells, 11 of 19 anti-CD38-positive sera raised [Ca2+]i (by > or =20% of baseline), whereas no [Ca2+]i-mobilizing activity was found in 27 anti-CD38-negative sera (chi2 = 20.5, P < 0.0001). In dispersed human islet cells, 5 of 11 anti-CD38-positive sera (and none of three anti-CD38-negative sera) raised [Ca2+]i significantly. When preincubated with Staphylococcus aureus protein A to remove IgG, anti-CD38-positive sera showed a 70 +/- 5% reduction in [Ca2+]i-mobilizing activity. Preincubation with CD38-transfected NIH-3T3 fibroblasts, but not with mock-transfected NIH-3T3 cells, abolished [Ca2+]i mobilization. In blocking experiments, preincubation with nonagonistic anti-CD38 monoclonal antibodies also prevented [Ca2+]i mobilization. In cultured human islets, anti-CD38-positive sera exhibiting [Ca2+]i-mobilizing activity in Jurkat T-cells (n = 6) significantly stimulated insulin release at 3.3 mmol/l glucose (median [interquartile range] 738 microU/ml [234], P = 0.0001 vs. 320 [52] microU/ml of control), whereas 6 anti-CD38-positive sera without [Ca2+]i-mobilizing activity and 10 anti-CD38-negative did not. In further incubations, the five anti-CD38-positive sera displaying [Ca2+]i-mobilizing activity in dispersed islet cells significantly stimulated insulin release at both 3.3 mmol/l glucose (2.2 +/- 0.3% of insulin islet content, P < 0.002 vs. 1.2 +/- 0.1% of control) and 16.7 mmol/l glucose (3.7 +/- 0.3 vs. 2.3 +/- 0.3%, P < 0.002). We conclude that human anti-CD38 autoantibodies with agonistic properties on the CD38 effector system occur in nature; in human islets, their [Ca2+]i-mobilizing activity is coupled with the ability to stimulate insulin release.

Signaling through CD38 induces NK cell activation

Human CD38 is a signal transduction molecule, and, concurrently, an ectoenzyme catalyzing the synthesis and degradation of cyclic ADP-ribose (cADPR), a potent Ca2+ mobilizer. One facet of CD38 that has not yet been addressed is its role in NK cells. To this end, the events triggered by CD38 ligation with agonistic mAb were analyzed on freshly purified human NK cells. Ligation was followed by (i) a significant rise in the intracellular level of Ca2+, (ii) increased expression of HLA class II and CD25, and (iii) tyrosine phosphorylation of discrete cytoplasmic substrates. The phosphorylation cascade involved CD3-zeta and FcepsilonRIgamma chains, zeta-associated protein (ZAP)-70 and the proto-oncogene product c-Cbl. NK effector functions were then analyzed: CD38 signaling was able (iv) to induce release of IFN-gamma and, more prominently, of granulocyte macrophage colony stimulating factor, as assessed by measuring both mRNA and protein products; and, lastly, (v) to induce cytolytic effector functions on target cells after IL-2 activation, as shown both by cytotoxicity assays and ultrastructural changes. The tyrosine-phosphorylated substrates and all the effects mediated by CD38 were similar to those observed following triggering via CD16 (FcgammaRIIIA); moreover, Ca2+ mobilization via CD38 no longer operated in NK-derived cell lines lacking CD16. These results suggest that the activation signals transduced by CD38 in NK cells elicit relevant cellular events. The effects are similar to those elicited via CD16 and possibly rely on common signaling pathways.

Autoantibody response to CD38 in Caucasian patients with type 1 and type 2 diabetes: immunological and genetic characterization

Insulin secretion is one of the functions mediated by CD38, a nonlineage pleiotropic cell surface receptor. The molecule is the target of an autoimmune response, because serum autoantibodies (aAbs) to CD38 have been detected in diabetic patients. In the healthy Caucasian population, the CD38 gene is bi-allelic (86% CD38*B and 14% CD38*A), whereas an Arg140Trp mutation has been identified in Japanese diabetic patients. We investigated the relationship between CD38 and diabetes in Caucasian patients by characterizing anti-CD38 aAbs in terms of prevalence and function (agonistic/nonagonistic activity) and by exploring the potential influence of the CD38 genetic background. A novel enzymatic immunoassay, using recombinant soluble CD38 as the target antigen, was developed for the analysis of anti-CD38 aAb titers. Sera from 19.15% of type 1 and 16.67% of type 2 diabetic patients were positive. The majority of anti-CD38 aAbs (57.14%) displayed agonistic properties, i.e., they demonstrated the capability to trigger Ca2+ release in lymphocytic cell lines. In agreement with these functional features, the presence of anti-CD38 aAbs in type 2 diabetic patients was associated with significantly higher levels of fasting plasma C-peptide and insulin, as compared with anti-CD38-counterparts. No diabetic subject carrying the Arg140Trp mutation and no preferential association between diabetes or aAb status and the CD38*A allele was found in the study population. These results show the significance of anti-CD38 aAbs as a new diagnostic marker of beta-cell autoimmunity in diabetes. Moreover, the prevalent agonistic activity of these aAbs suggests that they could mediate relevant effects on target cells by means of Ca2+ mobilization.

Human CD38: a (r)evolutionary story of enzymes and receptors

Human CD38 is the mammalian prototype of a family of proteins which share structural similarities and an ectoenzymatic activity involved in the production of calcium mobilizing compounds. Besides the enzymatic activity, the molecule performs as a receptor, ruling adhesion and signaling in leukocytes. These functions are exerted through the interaction with surface ligands, one of which was identified as CD31. Recently, CD38 has gained attention as a prognostic marker and a pathogenetic agent in leukemias and in other diseases. Together these insights have produced a model of an as yet unique family of molecules, which act independently as receptors and enzymes.

Extracellular cyclic ADP-ribose potentiates ACh-induced contraction in bovine tracheal smooth muscle

Cyclic ADP-ribose (cADPR), a universal calcium releaser, is generated from NAD(+) by an ADP-ribosyl cyclase and is degraded to ADP-ribose by a cADPR hydrolase. In mammals, both activities are expressed as ectoenzymes by the transmembrane glycoprotein CD38. CD38 was identified in both epithelial cells and smooth myocytes isolated from bovine trachea. Intact tracheal smooth myocytes (TSMs) responded to extracellular cADPR (100 microM) with an increase in intracellular calcium concentration ([Ca(2+)](i)) both at baseline and after acetylcholine (ACh) stimulation. The nonhydrolyzable analog 3-deaza-cADPR (10 nM) elicited the same effects as cADPR, whereas the cADPR antagonist 8-NH(2)-cADPR (10 microM) inhibited both basal and ACh-stimulated [Ca(2+)](i) levels. Extracellular cADPR or 3-deaza-cADPR caused a significant increase of ACh-induced contraction in tracheal smooth muscle strips, whereas 8-NH(2)-cADPR decreased it. Tracheal mucosa strips, by releasing NAD(+), enhanced [Ca(2+)](i) in isolated TSMs, and this increase was abrogated by either NAD(+)-ase or 8-NH(2)-cADPR. These data suggest the existence of a paracrine mechanism whereby mucosa-released extracellular NAD(+) plays a hormonelike function and cADPR behaves as second messenger regulating calcium-related contractility in TSMs.

Effects of the human CD38 glycoprotein on the early stages of the HIV-1 replication cycle

CD38 displays lateral association with the HIV-1 receptor CD4. This association is potentiated by the HIV-1 envelope glycoprotein gp120. The aim of this work was to evaluate the CD38 role in T cell susceptibility to HIV-1 infection. Using laboratory X4 HIV-1 strains and X4 and X4/R5 primary isolates, we found that CD38 expression was negatively correlated to cell susceptibility to infection, evaluated as percentage of infected cells, release of HIV p24 in the supernatants, and cytopathogenicity. This correlation was at first suggested by results obtained in a panel of human CD4(+) T cell lines expressing different CD38 levels (MT-4, MT-2, C8166, CEMx174, Supt-1, and H9) and then demonstrated using CD38 transfectants of MT-4 cells (the line with the lowest CD38 expression). To address whether CD38 affected viral binding, we used mouse T cells that are non-permissive for productive infection. Gene transfection in mouse SR.D10.CD4(-).F1 T cells produced four lines expressing human CD4 and/or CD38. Ability of CD4(+)CD38(+)cells to bind HIV-1 or purified recombinant gp120 was significantly lower than that of CD4(+)CD38(-) cells. These data suggest that CD38 expression inhibits lymphocyte susceptibility to HIV infection, probably by inhibiting gp120/CD4-dependent viral binding to target cells.-Savarino, A., Bottarel, F., Calosso, L., Feito, M. J., Bensi, T., Bragardo, M., Rojo, J. M., Pugliese, A., Abbate, I., Capobianchi, M. R., Dianzani, F., Malavasi, F., and Dianzani, U. Effects of the human CD38 glycoprotein on the early stages of theHIV-1 replication cycle.

CD38/ADP-ribosyl cyclase: A new role in the regulation of osteoclastic bone resorption

The multifunctional ADP-ribosyl cyclase, CD38, catalyzes the cyclization of NAD(+) to cyclic ADP-ribose (cADPr). The latter gates Ca(2+) release through microsomal membrane-resident ryanodine receptors (RyRs). We first cloned and sequenced full-length CD38 cDNA from a rabbit osteoclast cDNA library. The predicted amino acid sequence displayed 59, 59, and 50% similarity, respectively, to the mouse, rat, and human CD38. In situ RT-PCR revealed intense cytoplasmic staining of osteoclasts, confirming CD38 mRNA expression. Both confocal microscopy and Western blotting confirmed the plasma membrane localization of the CD38 protein. The ADP-ribosyl cyclase activity of osteoclastic CD38 was next demonstrated by its ability to cyclize the NAD(+) surrogate, NGD(+), to its fluorescent derivative cGDP-ribose. We then examined the effects of CD38 on osteoclast function. CD38 activation by an agonist antibody (A10) in the presence of substrate (NAD(+)) triggered a cytosolic Ca(2+) signal. Both ryanodine receptor modulators, ryanodine, and caffeine, markedly attenuated this cytosolic Ca(2+) change. Furthermore, the anti-CD38 agonist antibody expectedly inhibited bone resorption in the pit assay and elevated interleukin-6 (IL-6) secretion. IL-6, in turn, enhanced CD38 mRNA expression. Taken together, the results provide compelling evidence for a new role for CD38/ADP-ribosyl cyclase in the control of bone resorption, most likely exerted via cADPr.

rC5a Directs the In Vitro Migration of Human Memory and Naive Tonsillar B Lymphocytes: Implications for B Cell Trafficking in Secondary Lymphoid Tissues

Human C5a is a potent chemoattractant for granulocytes, monocytes, and dendritic cells. In mice C5a has been shown to be chemotactic for germinal center (GC) B cells. To date, no information is available on the effects of C5a on human B cell locomotion. Here we demonstrate that rC5a increases polarization and migration of human tonsillar B cells. The locomotory response was due to both chemokinetic and chemotactic activities of rC5a. Moreover, memory and, at a lesser extent, naive B cell fractions from purified tonsillar populations displayed rC5a-enhanced migratory properties, whereas GC cells did not. Flow cytometry revealed C5aR (CD88) on approximately 40% memory and 10% naive cells, respectively, whereas GC cells were negative. Immunohistochemistry showed that a few CD88+ cells were of the B cell lineage and localized in tonsillar subepithelial areas, where the majority of memory B cells settle. Pretreatment of memory B cells with the CD88 mAb abolished their migratory responsiveness to rC5a. Finally, the C5 gene was found to be expressed in naive, GC, and memory B lymphocytes at both the mRNA and the protein level. This study delineates a novel role for C5a as a regulator of the trafficking of human memory and naive B lymphocytes and supports the hypothesis that the B cells themselves may serve as source of C5 in secondary lymphoid tissues.

Ligation of Cell Surface CD38 Protein with Agonistic Monoclonal Antibody Induces a Cell Growth Signal in Myeloid Leukemia Cells

CD38 is expressed during early stages of differentiation in normal and leukemic myeloid cells. Recently, CD38 has been shown to participate in intracellular signal transduction pathways following its ligation with CD38-specific mAbs. In this study we report that ligation of CD38 by one such agonistic mAb (IB4) induced proliferation of cultured leukemic cells in vitro. In HL-60, KG-1A, NB4, and OCI-AML-3 myeloid leukemia cell lines, IB4 mAb induced an increase in the proliferating cell fraction as determined by cell number, clonogenic assay, and flow cytometric analysis. The presence of Ab caused a dose-dependent increase in the number of CFU and an increase in cell divisions. HL-60-Dox cells (a HL-60-doxorubicin-resistant cell line), which have no detectable CD38 expression, failed to respond to IB4 mAb. The effect of CD38 ligation on cell growth was also evaluated in freshly isolated leukemic cells from patients with acute myelogenous leukemia (AML). A significant increase in the proliferating cell fraction (S+G2M) was observed in 50% of the patients incubated with IB4 mAb. In five of the six AML patients, anti-CD38 mAb stimulated the proliferation of AML colony-forming cells. These results suggest that ligation of CD38 can induce the proliferation of leukemic cells and may play a role in the propagation of leukemic cell clones in certain cohorts of AML patients.

The transmembrane glycoprotein CD38 is a catalytically active transporter responsible for generation and influx of the second messenger cyclic ADP-ribose across membranes

CD38 is a type II transmembrane glycoprotein expressed in many vertebrate cells. It is a bifunctional ectoenzyme that catalyzes both the synthesis of Cyclic ADP-ribose (cADPR) from NAD+ and the degradation of cADPR to ADP-ribose by means of its ADP-ribosyl cyclase and cADPR-hydrolase activities, respectively. The cyclase also converts NGD+ to cyclic GDP-ribose (cGDPR), which is refractory to cADPR-hydrolase. cADPR, but not cGDPR, is a potent calcium mobilizer from intracellular stores. It has been demonstrated to be a new second messenger involved in the regulation of calcium homeostasis in many cell types, from plants to mammals. The number of physiological processes shown to be regulated by cADPR is steadily increasing. A topological paradox exists because ectocellularly generated cADPR acts intracellularly. Here we demonstrate that the catalytic functioning of CD38 is accompanied by a cADPR (cGDPR) -transporting activity across natural and artificial membranes. In resealed membranes from CD38(+) human erythrocytes, transport of catalytically generated cADPR or cGDPR was saturation dependent and occurred against a concentration gradient. Likewise, CD38-reconstituted proteoliposomes were active in concentrating NAD+ (NGD+) -derived cADPR (cGDPR) inside the vesicle compartment. Moreover, the cADPR-transporting activity in CD38 proteoliposomes prevented the hydrolase-catalyzed degradation to ADPR that occurs conversely with detergent-solubilized CD38, resulting in selective influx of cADPR. In the CD38 proteoliposomes, catalytically active CD38 exhibited monomeric, dimeric, and tetrameric structures. In CD38 sense- but not in antisense-transfected HeLa cells, externally added NAD+ resulted in significant, transient increases in cytosolic calcium. These data suggest that transmembrane juxtaposition of two or four CD38 monomers can generate a catalytically active channel for selective formation and influx of cADPR (cGDPR) to reach cADPR-responsive intracellular calcium stores.

Dimeric and tetrameric forms of catalytically active transmembrane CD38 in transfected HeLa cells

CD38, a type II transmembrane glycoprotein, behaves as a catalytically active transporter responsible for ectocellular generation of cyclic ADP-ribose (cADPR) from NAD+ and for subsequent influx of cADPR across membranes [Franco, L., Guida, L., Bruzzone, S., Zocchi, E., Usai, C. and De Flora, A. (1998) FASEB J. in press]. cADPR regulates intracellular calcium homeostasis by releasing calcium from responsive stores. The cADPR-transporting function of CD38 requires channel-generating oligomeric forms of the protein rather than the 46 kDa monomers that have been described so far in CD38+ cells. Here we demonstrate that CD38, both in reconstituted proteoliposomes and in CD38-transfected HeLa cells, is a mixture of catalytically active monomers, homodimers and homotetramers. A soluble recombinant form of CD38 corresponding to its ectocellular region proved to be monomeric. Thus, association of native CD38 with either artificial or natural membranes seems to result in a reversible juxtaposition of monomers suitable to cADPR-transporting activity.

Characterization of a CD38-like 78-kilodalton soluble protein released from B cell lines derived from patients with X-linked agammaglobulinemia

Studies on murine B lymphocytes showed that Bruton's tyrosine kinase mediates signal transduction induced via CD38, a nonlineage-restricted 45-kD ectoenzyme. This signaling is defective in B cells from X-linked immunodeficient mice affected with the analogue of human X-linked agammaglobulinemia (XLA). We performed a structural and functional analysis of CD38 in XLA and other immunodeficiencies, using EBV-immortalized B cells derived from such patients. Membrane CD38 was not significantly different from controls in structure, epitope density, enzymatic activity, and internalization upon binding of agonistic mAbs. Meanwhile, an increased release of soluble CD38 from XLA cells was observed: immunoprecipitation from XLA culture media yielded a protein of approximately 78 kD (p78), reacting also in Western blot and displaying both enzymatic activities and a peptide map similar to membrane CD38. Soluble forms and homotypic aggregations of CD38 were documented in different cell models and by crystallographic analysis of the Aplysia ADP-ribosyl cyclase, the ancestor of human CD38. p78 might represent the product of an altered turn-over of membrane CD38, a starting point for studying its association with Bruton's tyrosine kinase and its role in XLA and other B cell immunodeficiencies.

Interleukin-15 activates proinflammatory and antimicrobial functions in polymorphonuclear cells

Interleukin-15 (IL-15) is a recently discovered cytokine produced by a wide range of different cell types including fibroblasts, keratinocytes, endothelial cells, and macrophages in response to lipopolysaccharide or microbial infection. This suggests that IL-15 may play a crucial role in the activation of phagocytic cells against pathogens. We studied polymorphonuclear leukocyte (PMN) activation by IL-15, evaluated as enhancement of PMN anti-Candida activity as well as IL-8 production, following stimulation with the cytokine. The PMN response to IL-15 depends on binding to the IL-15 receptor. Our experiments show that binding of a biotinylated human IL-15-immunoglobulin G2b IgG2b fusion protein was competed by the addition of human recombinant IL-15 (rIL-15) or of human rIL-2, suggesting that IL-15 binding to PMN might involve the IL-2Rbeta and IL-2Rgamma chains, which have been shown to be constitutively expressed by PMN. In addition, we show by reverse transcription-PCR and by flow cytometry with a specific anti-IL-15Ralpha chain monoclonal antibody that PMN express the IL-15Ralpha chain at the mRNA and protein levels. Incubation with IL-15 activated PMN to secrete the chemotactic factor IL-8, and the amount secreted was increased by costimulation with heat-inactivated Candida albicans. In addition, IL-15 primed the metabolic burst of PMN in response to formyl-methionyl-leucyl-phenylalanine but was not sufficient to trigger the respiratory burst or to increase the production of superoxide in PMN exposed to C. albicans. IL-15 also increased the ability of PMN to phagocytose heat-killed C. albicans organisms in a dose-dependent manner, without opsonization by antibodies or complement-derived products. In the same concentration range, IL-15 was as effective as gamma interferon (IFN-gamma) and IL-2 in increasing the C. albicans growth-inhibitory activity of PMN. Taken together, these results suggest that IL-15 is a potent stimulant of both proinflammatory and antifungal activities of PMN, activating several antimicrobial functions of PMN involved in the cellular response against C. albicans.

CD38 is functionally dependent on the TCR/CD3 complex in human T cells

One of the functions of surface CD38 is the induction of phosphorylation of discrete cytoplasmic substrates and mobilization of cytoplasmic calcium (Ca2+). The present work addresses the issue of whether the signaling mediated via CD38 operates through an independent pathway or, alternatively, is linked to the TCR/CD3 signaling machinery. We studied the signals elicited through CD38 by the specific agonistic IB4 monoclonal antibody (mAb) by monitoring the levels of cytoplasmic Ca2+ and the induced phenotypic and functional variations in T cell growth. IB4 mAb presented the unique ability to increase cytoplasmic Ca2+ levels, which correlated with the phosphorylation of the PLC-gamma1. These effects were blocked by phorbol 12-myristate 13-acetate (PMA) and were dependent on the presence of a functional TCR/CD3 surface complex, no effects being recorded on mutant Jurkat cells lacking part of the CD3 structures. CD38 signaling appeared to share with TCR/CD3 the ability to induce apoptotic cell death in Jurkat T cells, an event paralleled by specific up-regulation of the Fas molecule and inhibited by cyclosporin A. CD28, a costimulatory molecule, is synergized by increasing CD38-induced apoptotic cell death. The results indicate the existence of a strong functional interdependence between CD38 and TCR/CD3.

CD38 Functions Are Regulated Through an Internalization Step

The endocytosis of the human CD38 molecule has been investigated in normal lymphocytes and in a number of leukemia- and lymphoma-derived cell lines. CD38 internalization was followed using radioiodinated Abs in an acidic elution endocytosis assay to monitor the effects of cross-linking on internalization processes and to quantify the ratio of the internalized molecule. Second, conventional, confocal, and electron microscopies were used to evaluate the morphologic effects induced by ligation of the molecule with Abs mimicking the natural ligand(s). The results demonstrated that internalization is a reproducible phenomenon following CD38 ligation with both agonistic and nonagonistic specific Abs and involving only a fraction of the entire amount of the surface molecule. It is independent from signal transduction as can be inferred by the observation that 1) both agonistic and non agonistic Abs are effective and 2) the dynamic of internalization is much slower than that of cellular signaling. Morphologic studies demonstrated that endocytosis induced as a result of CD38 ligation presents a very specific pathway consisting of subcellular organelles fundamental to the processing of the complex. Our data indicate that down-regulation by endocytosis may be, in parallel with shedding, a regulatory element in activation and adhesion processes mediated by CD38. However, internalization seems not to be a key step in triggering intracellular signaling; more likely, it is a negative feedback control mechanism which interrupts signal transduction or cell-cell cross-talks mediated by membrane CD38.

Human CD38 (ADP-Ribosyl Cyclase) Is a Counter-Receptor of CD31, an Ig Superfamily Member

Human CD38 is a cell surface molecule involved in the regulation of lymphocyte adhesion to endothelial cells. This suggests that HUVEC bear a ligand(s) for CD38 on the cell surface. By means of the mAb Moon-1, which specifically inhibits CD38-mediated cell adhesion, we have identified a trans-membrane 130-kDa molecule acting as a ligand for CD38. Here, we report that the molecule recognized by the Moon-1 mAb is CD31, a member of the Ig superfamily. This conclusion is based on 1) cross-inhibition assays between Moon-1 and reference anti-CD31 mAbs; 2) sequential immunoprecipitation experiments using Moon-1 and known anti-CD31 mAbs, and 3) reactivity of the Moon-1 mAb with CD31 transfectants. Further, CD31 and CD38 cognate interactions were found to modulate heterotypic adhesion as well as to implement cytoplasmic calcium fluxes identical to those obtained by means of agonistic anti-CD38 mAbs. Other effects tested included the synthesis of messages for a panel of cytokines, markedly increased upon receptor-ligand interactions. These results suggest that the interplay between CD38 and its ligand CD31 is an important step in the regulation of cell life and of the migration of leukocytes (and CD38+ cancer cells) through the endothelial cell wall.

Ectocellular CD38-catalyzed synthesis and intracellular Ca(2+)-mobilizing activity of cyclic ADP-ribose

CD38 is a type-II transmembrane glycoprotein occurring in several hematopoietic and mature blood cells as well as in other cell types, including neurons. Although classified as an orphan receptor, CD38 is also a bifunctional ectoenzyme that catalyzes both the conversion of NAD+ to nicotinamide and cyclic ADP-ribose (cADPR), via an ADP-ribosyl cyclase reaction, and also the hydrolysis of cADPR to ADP-ribose (hydrolase). Major unresolved questions concern the correlation between receptor and catalytic properties of CD38, and also the apparent contradiction between ectocellular generation and intracellular Ca(2+)-mobilizing activity of cADPR. Results are presented that provide some explanations to this topological paradox in two different cell types. In cultured rat cerebellar granule neurons, extracellular cADPR (either generated by CD38 or directly added) elicited an enhanced intracellular Ca(2+)-response to KCl-induced depolarization, a process that can be qualified as a Ca(2+)-induced Ca2+ release (CICR) mechanism. On the other hand, in the CD38+ human Namalwa B lymphoid cells, NAD+ (and thiol compounds as well) induced a two-step process of self-aggregation followed by endocytosis of CD38, which resulted in a shift of cADPR metabolism from the cell surface to the cytosol. Both distinctive types of cellular responses to extracellular NAD+ seem to be suitable to elicit changes in the intracellular Ca2+ homeostasis.

Recombinant Tumor Necrosis Factor Enhances the Locomotion of Memory and Naive B Lymphocytes From Human Tonsils Through the Selective Engagement of the Type II Receptor

Recent studies performed in mice knocked out for the tumor necrosis factor (TNF ), the lymphotoxin-α, or the type I TNF receptor (R), genes have shown that these animals display gross defects in germinal center (GC) formation, suggesting that members of the TNF and TNFR superfamilies are involved in the control of B-cell migration. Based on these premises, we have here investigated the effects of human recombinant (r) TNF on the polarization and locomotion of tonsillar B cells. rTNF increased the spontaneous polarization and locomotion of unfractionated tonsillar B lymphocytes in a dose-dependent manner by inducing a true chemotactic response. Memory (IgD−, CD38−) and naive (IgD+, CD38−), but not GC (IgD−, CD38+) B cells purified from total tonsillar B lymphocytes, showed a significantly higher locomotion in the presence than in the absence of rTNF. Accordingly, type I and II TNF receptors (TNFRs) were detected by flow cytometry on the surface of memory and naive, but not GC, B lymphocytes. Blocking experiments with monoclonal antibodies to type I or II TNFR showed that rTNF enhanced the spontaneous chemotaxis of memory and naive B cells through the selective engagement of type II TNFR. Finally, the TNF gene was found to be expressed in memory, naive and GC B lymphocytes; the cytokine was released in culture supernatants from the three B-cell subsets after stimulation. These data may support the hypothesis that human TNF is involved in the paracrine and perhaps autocrine control of B-cell migration in secondary lymphoid tissues.

Recombinant Tumor Necrosis Factor Enhances the Locomotion of Memory and Naive B Lymphocytes From Human Tonsils Through the Selective Engagement of the Type II Receptor

Recent studies performed in mice knocked out for the tumor necrosis factor (TNF ), the lymphotoxin-α, or the type I TNF receptor (R), genes have shown that these animals display gross defects in germinal center (GC) formation, suggesting that members of the TNF and TNFR superfamilies are involved in the control of B-cell migration. Based on these premises, we have here investigated the effects of human recombinant (r) TNF on the polarization and locomotion of tonsillar B cells. rTNF increased the spontaneous polarization and locomotion of unfractionated tonsillar B lymphocytes in a dose-dependent manner by inducing a true chemotactic response. Memory (IgD−, CD38−) and naive (IgD+, CD38−), but not GC (IgD−, CD38+) B cells purified from total tonsillar B lymphocytes, showed a significantly higher locomotion in the presence than in the absence of rTNF. Accordingly, type I and II TNF receptors (TNFRs) were detected by flow cytometry on the surface of memory and naive, but not GC, B lymphocytes. Blocking experiments with monoclonal antibodies to type I or II TNFR showed that rTNF enhanced the spontaneous chemotaxis of memory and naive B cells through the selective engagement of type II TNFR. Finally, the TNF gene was found to be expressed in memory, naive and GC B lymphocytes; the cytokine was released in culture supernatants from the three B-cell subsets after stimulation. These data may support the hypothesis that human TNF is involved in the paracrine and perhaps autocrine control of B-cell migration in secondary lymphoid tissues.

The CD38/cyclic ADP-ribose system: a topological paradox

CD38 was first identified as a lymphocyte differentiation antigen that showed typical properties of an orphan receptor involved in many programs of cell proliferation and activation. However, CD38 proved also to be a bifunctional ectoenzyme that catalyzes the transient formation of cyclic ADP-ribose (cADPR) in a variety of cell types. This property raises many intriguing and so far unanswered questions, since cADPR is a new second messenger molecule directly involved in the control of calcium homeostasis by means of receptor-mediated release of calcium from ryanodine-sensitive intracellular stores. The relationship between receptor-like and enzymatic properties of CD38 is still unknown. The apparent topological paradox of ectocellular synthesis and intracellular activity of cADPR might be explained by: (a) influx of cADPR across the plasma membrane to reach its target stores, as suggested by experiments on cerebellar granule cells; and (b) NAD(+)-induced internalization, following membrane oligomerization, of CD38 with consequent partial import of cADPR metabolism to an intracellular compartment, as recently observed in lymphoid B cells. These two distinct mechanisms and other potential ones (e.g. binding of ectocellularly formed cADPR to cell surface receptors and initiation of signal-transducing pathways across the plasmamembrane) seem to be paradigmatic of processes affecting different types of cells. Although in some biological systems, such as Aplysia and sea urchin egg, cADPR metabolism is restricted to the intracellular environment, in mammalian cells the CD38/cADPR system provides new challenges in terms of subcellular compartmentation and qualifies as an unusual example of "ectobiochemistry" with potential, still unrecognized, properties of cellular regulation.

NAD+-dependent internalization of the transmembrane glycoprotein CD38 in human Namalwa B cells

CD38 is a transmembrane glycoprotein involved as an orphan receptor in many physiological processes of lymphocytes. It is also a bifunctional enzyme that catalyzes at its ectocellular domain the synthesis from NAD+ (cyclase) and the hydrolysis (hydrolase) of the calcium-mobilizing metabolite cyclic ADP-ribose (cADPR). A still unexplained paradox concerns the relationship between ectocellular localization of CD38 and intracellular calcium-releasing activity of its intermediate product cADPR. Incubation of CD38+ human Namalwa B cells with external NAD+ elicited extensive membrane down-regulation of CD38 and its internalization in non-clathrin-coated vesicles. Since the internalized CD38 was demonstrated to be enzymatically active, this NAD+-dependent process is a hitherto unrecognized means for shifting cADPR metabolism from the cell surface to the intracellular environment.

Purification and biochemical characterization of a 65-kilodalton mannoprotein (MP65), a main target of anti-Candida cell-mediated immune responses in humans

A 65 kDa-constituent (MP65) of a whole-cell mannoprotein (MP) fraction of Candida albicans was purified by immunoaffinity chromatography with monoclonal antibodies directed against periodate-insensitive, protease-sensitive MP epitopes, putatively polypeptide in nature. These antibodies were obtained by immunization of mice with concanavalin A bead-coupled, low-glycosylated MP from hyphal cells of C. albicans grown in the presence of a subinhibitory dose of tunicamycin. The immunoaffinity-purified MP65 molecule had a pI of 4.1 and a protein/polysaccharide ratio of 1.8:1. It was resistant to hydrolysis by endoglycosidase H, endoglycosidase F, or N-glycoffanases but still reactive with concanavalin A. The polysaccharide moiety of MP65 was composed exclusively of mannose and glucose at a ratio of 12.7 to 1. The protein moiety showed numerous potential O-glycosidic linkage sites as suggested by the high proportion of serine and threonine (together accounting for more than 20% of the total amino acid composition) and susceptibility to diluted alkali. This treatment and digestion with alpha-mannosidase caused a reduction in the MP65 molecular mass to around 54 kDa. The N-terminal sequence of MP65 protein moiety was rich in alanine and valine (7 of 13 amino acids) and did not show any significant homology with deposited sequences in data banks. Purified MP65, at doses of a few nanograms, induced extensive T-cell proliferation of human peripheral blood mononuclear cells. This proliferation was specifically inhibited, in a dose-response fashion, by the antigen-binding fragment of the monoclonal antibody used for immunoaffinity purification. Overall, these results highlight biochemical and molecular details of MP65, a main target of human T-cell response to C.albicans.

During HIV infection, CD4+ CD38+ T-cells are the predominant circulating CD4+ subset whose HLA-DR positivity increases with disease progression and whose V beta repertoire is similar to that of CD4+ CD38- T-cells

Three-color automated flow cytometry was carried out on peripheral blood CD4+ and CD8+ T-lymphocytes of 42 HIV-positive patients using tri-color anti-CD4 or anti-CD8, phycoerythrin-anti-CD38, and fluorescein-anti-HLA-DR, mAbs to elucidate further the T-cell activation hypothesis recently proposed to explain CD4+ T-cell abnormalities observed during HIV infection. CD4+ CD38+ T-cells constituted the major part of circulating CD4+ T-cells in HIV-infected patients and their HLA-DR molecule positivity increased as their disease progressed. The level of CD38 and HLA-DR expression on CD4+ T-cells was positively correlated to that of CD8+ T-cells and to the level of beta 2-microglobulin. Next, to determine whether CD38 expression was associated with a selective expansion or deletion of V beta gene-defined subsets, we compared the V beta gene frequencies between CD38+ and CD38- T-cells from HIV-infected CDC stage II patients using 13 mAbs specific to V beta families. While selective expansion of certain V beta families was observed in CD4+ and CD8+ T-cells the T-cell receptor V beta subset distribution was similar among CD38+ and CD38-, CD4+ and CD8+ T-cells, suggesting that CD38+ expression was either independent of an HIV-encoded antigen-driven process or rather indicative of T-cell immaturity. It is proposed that the phenotype of circulating CD4+ and CD8+ T-cells of HIV-infected patients is a feature of two different mechanisms: (i) an in vitro activation state responsible for increased DR expression and selective expansion of V beta gene-defined subsets, and (ii) T-cell immaturity due to an increased turnover of these cells and accounting for increased CD38 expression.

The clonogenic precursor cell in multiple myeloma

Multiple myeloma is characterized by the monoclonal expansion of plasma cells in the bone marrow. Although the predominant cell type is the plasma cell, the initial oncogenic transformation is considered to take place in a more immature B cell. There is still much controversy about this precursor cell type. Phenotypic analysis of bone marrow and peripheral blood revealed that in multiple myeloma a great diversity exists in the phenotype of the cells considered to be involved. Because of the lack of a myeloma specific genetic lesion it is very difficult to trace back the cell in which the transforming event, leading to multiple myeloma, took place. The only real clonal marker is the idiotype of the immunoglobulin molecule expressed by the myeloma cells. With recombinant DNA technology it is now possible to produce clonal markers for each individual myeloma patient which recognize only the immunoglobulin genes expressed by the myeloma cell and its precursors. The sequences of these myeloma immunoglobulin genes do reveal a lot of information about the stage in the B-cell differentiation pathway in which the oncogenic event might have taken place. The presence of somatic mutations in a non-random fashion without intraclonal variation leads to the conclusion that the precursor myeloma cell could not possibly be a pre-B cell or stem cell but has to be a mature B cell that has been in contact with antigen and has past through the phase of somatic mutation, like a memory B cell or plasmablast.(ABSTRACT TRUNCATED AT 250 WORDS)

CD38 ligation induces discrete cytokine mRNA expression in human cultured lymphocytes

Human CD38 is a surface glycoprotein expressed by different immuno-competent cells such as immature and activated lymphocytes, plasma cells and natural killer cells. It has recently been reported that the CD38 molecule exerts adenosine diphosphate ribosyl cyclase activity and is associated with distinct transmembrane signaling molecules. This study reports that ligation of CD38 by specific monoclonal antibodies (mAb) induces multiple cytokine mRNA expression in cultured peripheral blood mononuclear cells (PBMC). The mRNA for tumor necrosis factor-alpha, interleukin (IL)-1 beta, IL-6, granulocyte-macrophage colony-stimulating factor (GM-CSF) and IL-12 were always detected, whereas interferon-gamma and IL-10 mRNA expression were seen in most, but not all PBMC cultures. Low levels of IL-2, IL-4 and IL-5 mRNA were also found. The key observation of this work is that CD38 ligation in PBMC induces a large spectrum of cytokines, many of which overlap with those induced via CD3 activation. The main differences between CD38 and CD3 activation are the low to undetectable levels of IL-2 mRNA, and the sustained IL-1 beta and IL-6 mRNA accumulation found in PBMC cultures following treatment with anti-CD38 mAb. Furthermore, PBMC proliferation was not found to be a prerequisite for CD38-mediated cytokine induction. Together, these results suggest that human CD38 activates a signaling pathway which leads to the induction of a discrete array of cytokines, and that this pathway only partially overlaps with that controlled by T cell receptor CD3.