Cytosolic free calcium concentration in the mitogenic stimulation of T lymphocytes by anti-CD3 monoclonal antibodies

A novel single-photon counting technique applied to highly sensitive measurement of [Ca2+]i transient in human aortic smooth muscle cells

This study demonstrates that aequorin, a luminescent natural dye, is useful for vascular cell intracellular Ca2+ concentration ([Ca2+]i) determination. A new single-photon counting technique was developed to resolve the effects of fluid flow shear stress on [Ca2+]i in human aortic smooth muscle cells (HASMCs). Confluent HASMCs were grown on petri dishes loaded with aequorin. Then the dishes were placed in a luminometer chamber after the physiological level of shear stress was applied to the HASMC surfaces. The chamber was housed inside a highly sensitive photomultiplier tube. It detected ultraweak photon emission in response to the [Ca2+]i transient. In the presence of 2.0 mM extracellular Ca2+, a shear stress of 12 dyn cm2, applied for 60 s to the top surface of the HASMC monolayer, elicited a sharp increase in [Ca2+]i.

Adaptative value of a PKC-PKI55 feedback loop of inhibition that prevents the kinase's deregulation

A 168-bp amplification product was obtained in RT-PCR experiments using a degenerate oligonucleotide designed on a five-amino acid sequence of IN, a 7-kDa protein, previously characterized as a PKC inhibitor. It was included in the coding ORF of the 1530-bp-long IMAGE clone ID 38900 (accession numbers R51337 and R51448) that produces a translation product of 6.5 kDa. The translation of the ORF conceptual reading frame allowed the preparation of the synthetic protein PKI55, which was found to inhibit and degrade both untreated nPKC d isozymes and activated cPKC isozymes. The PKI55 gene is localized in chromosome 2q35. The Repeat Maskers output showed a 533-bp-long LTR32/ERVL segment that included the PKI55 coding sequence and a complete regulatory region. The coding sequence and the structure of PKI55 were detected in a brain cDNA of Macaca fascicularis (diverged from human lineages about 25 Myr ago). Three other human genes with over 60% identities with PKI55 were identified in three different loci (i.e., chromosomes 10, 15, and 20.) Synthesis of PKI55 was stimulated by PKC activation. A feedback loop of inhibition is established. When the PKCs are overactivated, PKI55 induces degradation of the enzyme and prevents the isozyme overexpression implicated in a number of important diseases including cancer, diabetes, and disorders of the immune system. The presence of the PKI55 sequence in Macaca fascicularis as well as in human chromosomes 10, 15, and 20 indicates a selective advantage for the PKI55 sequence and the adaptive value of the feedback mechanism.

Looking forward to seeing calcium

From molecules, single cells and tissues to whole organisms, our insights into Ca2+ signalling and the corresponding physiological phenomena are growing exponentially. Here, we describe the improvements that have been made in the development of the probes and instrumentation that are used for Ca2+ imaging and the expanding applications of Ca2+ imaging in basic and applied research.

The chemokine receptor CXCR3 is expressed on malignant B cells and mediates chemotaxis

B- and T-cell recirculation is crucial for the function of the immune system, with the control of cell migration being mainly mediated by several chemokines and their receptors. In this study, we investigated the expression and function of CXCR3 on normal and malignant B cells from 65 patients with chronic lymphoproliferative disorders (CLDs). Although CXCR3 is lacking on CD5(+) and CD5(-) B cells from healthy subjects, it is expressed on leukemic B lymphocytes from all (31/31) patients with chronic lymphocytic leukemia (CLL). The presence of CXCR3 was heterogeneous in other B-cell disorders, being expressed in 2 of 7 patients with mantle cell lymphoma (MCL), 4 of 12 patients with hairy cell leukemia (HCL), and 11 of 15 patients with other subtypes of non-Hodgkin's lymphomas (NHLs). Chemotaxis assay shows that normal B cells from healthy subjects do not migrate in response to IFN-inducible protein 10 (IP-10) and IFN-gamma-induced monokine (Mig). In contrast, a definite migration in response to IP-10 and Mig has been observed in all malignant B cells from patients with CLL, but not in patients with HCL or MCL (1/7 cases tested). Neoplastic B cells from other NHLs showed a heterogenous pattern. The migration elicited by IP-10 and Mig was inhibited by blocking CXCR3. No effect of IP-10 and Mig chemokines was observed on the cytosolic calcium concentration in malignant B cells. The data reported here demonstrate that CXCR3 is expressed on malignant B cells from CLDs, particularly in patients with CLL, and represents a fully functional receptor involved in chemotaxis of malignant B lymphocytes.

Differential effect on TCR:CD3 stimulation of a 90-kD glycoprotein (gp90/Mac-2BP), a member of the scavenger receptor cysteine-rich domain protein family

We studied the effects of a 90-kD glycoprotein (gp90/Mac-2BP) belonging to the scavenger receptor family, present in normal serum and at increased levels in inflammatory disease and cancer patients, on some T cell function parameters. Whereas the lymphocyte proliferative response to non-specific mitogens such as phytohaemagglutinin (PHA) and concanavalin A (Con A), but not pokeweed mitogen (PWM), was strongly reduced, probably due to the lectin-binding properties of gp90/Mac-2BP, the response to T cell receptor (TCR) agonists such as superantigens and allogeneic cells was potentiated. When lymphocytes were stimulated with different anti-TCR:CD3 MoAbs, both in soluble and solid-phase form, gp90/Mac-2BP was able to down-regulate the proliferative response to anti-CD3 MoAb, whereas the response to anti-TCR alphabeta MoAb was enhanced. A similar differential effect was observed when a MoAb against CD5 (another member of the scavenger receptor superfamily) was added to anti-CD3 or anti-TCR-stimulated cells; anti-CD5 MoAb strongly down-modulated the CD3-mediated response, whereas its presence in culture was associated with potentiation of the response to TCR alphabeta agonists. gp90/Mac-2BP was able per se to up-regulate Ca2+ levels in freshly isolated lymphocytes; moreover, its presence in culture was associated with increased Ca2+ mobilization following stimulation with anti-TCR alphabeta, but not anti-CD3 MoAb. These data indicate that gp90/Mac-2BP could be able to influence some immune responses, possibly through multiple homologous interactions with other members of the scavenger receptor family; moreover, our findings suggest that signalling through the different components of the TCR:CD3 complex may follow distinct activation pathways into the cells.

Enhancement of calcium signaling and proliferation responses in activated human T lymphocytes. Inhibitory effects of K+ channel block by charybdotoxin depend on the T cell activation state

T cell receptor (TCR) stimulation, leading to T cell activation and ultimately to cell proliferation and differentiation, evokes elevations of [Ca2+]i with a high variability between individual T lymphocytes. We have used Ca(2+)-imaging of Fura-2 loaded cells to study the origin of the variation in Ca2+ signals and its consequences for the final cellular response. We found that, compared to resting cells, the percentage of responding cells and the average amplitude of the Ca2+ signal upon TCR re-stimulation by PHA increases in the first 5 days of T cell activation and declines thereafter, with more pronounced [Ca2+]i oscillations in later stages. In parallel, an enhancement of T cell proliferation is observed. Stronger stimulation of the TCR/CD3 complex by co-crosslinking CD3 with CD4/CD8 molecules evokes oscillating Ca2+ responses irrespective of the activation state, indicating that the basic capacity for Ca2+ signaling is essentially the same in resting and activated cells. Nevertheless, also the amplitude of the CD3+CD4/8 response shows a transient additional increase during the first days of T cell activation. Experiments with the K+ channel blocker charybdotoxin (CTX) indicate that [Ca2+]i oscillations depend critically on K+ channel functioning, but suppression of these oscillations by CTX does not significantly affect the average amplitude of the Ca2+ signal nor PHA-induced proliferation. However, when applied during the first 4-5 days of activation, CTX reduces in addition the average level of the TCR evoked Ca2+ response and inhibits subsequent proliferation.

Bispecific monoclonal antibody anti-CD3 x anti-tenascin: an immunotherapeutic agent for human glioma

Besides surgery, the therapeutic possibilities for the treatment of human gliomas include adoptive cellular immunotherapy, radioimmunotherapy, immunotherapy mediated by chemoimmunoconjugates and, more recently, bispecific monoclonal antibodies (biMAbs). Anti-CD3 x anti-tenascin (TN) is the first reagent of a number of biMAbs under investigation for prospective use in vivo to maximize the cell-mediated cytolytic potential of glioma patients. This biMAb originated from the fusion of 2 parental hybridomas, made resistant by retrovirus-mediated infection to the different metabolic drugs, geneticin and methotrexate, respectively. The resulting hybrid hybridomas were selected on the basis of the double specificity for CD3 and TN, cloned several times and grown under continuous metabolic pressure. The different families of recombinant antibodies were then purified by high-pressure liquid chromatography on hydroxylapatite columns. Immunohistochemical studies on tumor specimens of different origin and histotype have shown that the selected biMAb presented a distribution pattern similar to that of the parental anti-TN MAb, maintaining the same staining homogeneity and intensity. Moreover, the mitogenic activity of anti-CD3 x anti-TN biMAb on peripheral blood mononuclear cells was similar to that featured by the parental anti-CD3 MAb. Furthermore, the hybrid molecule induced TNF-alpha gene expression in activated PBMC. Finally, the anti-CD3 x anti-TN featured the desired killer targeting ability, being able to induce a significantly increased cytotoxic activity against TN+ tumor cells.

Transfected aequorin in the measurement of cytosolic Ca2+ concentration ([Ca2+]c). A critical evaluation

Targeted recombinant aequorins represent to date the most specific means of monitoring [Ca2+] in subcellular organelles (Rizzuto, R., Simpson, A. W. M., Brini, M., and Pozzan, T. (1992) Nature 358, 325-328; Brini, M., Murgia, M., Pasti, L., Picard, D., Pozzan, T., and Rizzuto, R. (1993) EMBO J. 12, 4813-4819; Kendall, J. M., Dormer, R. L., and Campbell, A. K. (1992) Biochem. Biophys. Res. Commun. 189, 1008-1016). Up until now, however, only limited attention has been paid to the use of recombinant photoproteins for measuring, in mammalian cells, the [Ca2+] in the cytoplasm, a compartment for which effective Ca2+ probes are already available. Here we describe this approach in detail, highlighting the advantages, under various experimental conditions, of using recombinant cytosolic aequorin (cytAEQ) instead of classical fluorescent indicators. We demonstrate that cytAEQ is expressed recombinantly at high levels in transiently transfected cell lines and primary cultures as well as in stably transfected clones, and we describe a simple algorithm for converting aequorin luminescence data into [Ca2+] values. We show that although fluorescent indicators at the usual intracellular concentrations (50-100 microM) are associated with a significant buffering of the [Ca2+]c transients, this problem is negligible with recombinantly expressed aequorin. The large dynamic range of the photoprotein also allows an accurate estimate of the large [Ca2+]c increases that are observed in some cell types such as neurons. Finally, cytAEQ appears to be an invaluable tool for measuring [Ca2+]c in cotransfection experiments. In particular, we show that when cotransfected with an alpha 1-adrenergic receptor (coupled to inositol 1,4,5-trisphosphate generation), cytAEQ faithfully monitors the subpopulation of cells expressing the receptor, whereas the signal of fura-2, at the population level, is dominated largely by that of the untransfected cells.