Autocrine regulation of normal and malignant B lymphocytes

Expression of Interleukin-1 and Interleukin-1 Receptors Type 1 and Type 2 in Hodgkin Lymphoma

Signaling through the IL-1-receptor type 1 (IL-1R1), IL-1 is required for initiation and maintenance of diverse activities of the immune system. A second receptor, IL-1R2, blocks IL-1 signal transduction. We studied expression of IL-1beta, IL-1R1, and IL-1R2 in 17 Hodgkin lymphomas (HL) by in situ hybridization (ISH). IL-1beta expressing cells, morphologically consistent with endothelial cells and fibroblasts, occurred in all HL tissues with elevated transcript levels in areas of active fibrosis. Hodgkin and Reed-Sternberg (HRS) cells of all cases expressed low IL-1R1 transcript levels in some tumor cells, and high levels of IL-1R2 in large proportions of HRS cells. Only few bystander cells showed low levels of IL-1R1 and IL-1R2 RNA. Supernatants of 4 out of 7 HL-derived cell lines contained soluble IL-1R2 protein at high levels. HL patient sera carried variably amounts of IL-1R2 protein with significantly increased titers in patients with active disease compared to patients in complete remission and control individuals without HL. Western blots and co-immunoprecipitations showed binding of the IL-1R2 to the intracellular IL-1R-accessory protein (IL-1IRAcP). These data suggest functions of the IL-1R2 as a „decoy-receptor” sequestrating paracrine IL-1 extracellularly and intracellularly by engaging IL-1IRAcP, thus depriving IL1-R1 molecules of their extracellular and intracellular ligands. Expression of IL1-R2 by HRS cells seems to contribute to local and systemic modulation of immune function in HL.

Population depletion activates autonomous CD154-dependent survival in biopsylike Burkitt lymphoma cells

Population size is governed through cells reacting to a variety of intrinsic and extrinsic cues. Tumors, while liberated from many of the homeostatic constraints placed on physiologic counterparts, can nonetheless remain subject to both social and environmental control. Burkitt lymphoma cells faithful to the biopsy phenotype were used to model the reliance of the colony, if any, on an inbuilt population sensor. Below a normally suicidal threshold number of cells, low picomolar quantities of exogenous CD40 ligand (CD40L/CD154) were found to sustain the clone without the discernible shift in phenotype that accompanies high CD40L encounter. Although CD154 was undetectable in populous cultures, message was induced as numbers became limiting. Correspondingly, attempts to neutralize endogenous CD40L activity failed to perturb cells at optimal densities but resulted in their marked decline as the critical threshold was approached. These data reveal an auto-inducible survival mechanism seemingly regulated through the monitoring of population size, a process somewhat akin to that of "quorum sensing" among gram-negative bacteria in which diffusible molecules provide a means of communication to coordinate gene expression with population density. This process could be activated as cells discern depletions in their community or when deprived of signals otherwise furnished within an appropriate environmental niche.

Micro-environmental factors in the survival of human B-lymphoma cells

Burkitt lymphoma (BL) cells retain a high inherent propensity to undergo apoptosis indicating that net growth of the tumour population in vivo is likely to be influenced profoundly by its micro-environment. Here we investigate micro-environmental factors that affect BL-cell survival in vitro. We show that survival, and consequently net production, of tumour cells is enhanced by autocrine factors and, to a greater extent, by paracrine factors provided by relevant stromal elements of the tumour (fibroblasts and follicular dendritic cells) and by macrophages. Promotion of BL-cell survival by paracrine elements was mediated by cell/cell contact and by short-range soluble factor(s). IL-4, IL-10 and TNF-alpha promoted, whereas TGF-beta1 inhibited, tumour-cell production. Macrophages engaged in phagocytosis of apoptotic BL cells were less effective than untreated macrophages in supporting net expansion of BL populations. These results suggest that the net production of tumour cells in BL is supported by multiple micro-environmental factors that modulate apoptosis.

Enhanced apoptosis mediates inhibition of EBV-transformed lymphoblastoid cell line proliferation by curcumin

BACKGROUND

Epstein-Barr virus (EBV)-associated B-cell lymphomas occur more frequently in immunodeficient states such as organ transplantation and HIV infection. We have previously reported that B cell immortalization with EBV was promoted by cyclosporin A (CyA) and that curcumin (Cur), a natural phenol with known antioxidant and antitumor properties, blocked EBV-induced B cell immortalization. In the following experiments we show that Cur inhibits the proliferation of EBV-transformed lymphoblastoid cell lines (LCL) via enhanced apoptosis.

METHODS

LCL were generated by infecting freshly isolated human B cells with EBV (B95-8) for 12 h and coculturing with predetermined optimal concentrations of CyA (500 ng/ml) for 4 weeks. LCL were then either frozen for future use or propagated for immediate experiments. These cells were then plated in 96-well plates with 20 microM Cur or 0.1% DMSO (vehicle control). The number of immortalized colonies/well, cell count, and (3)H uptake were used as an index of immortalization. To assess apoptosis rate LCL were cultured with 0.1% DMSO or Cur (20 microM) for 0, 18, and 42 h in culture flasks and then stained with MC540 and H33342, as markers for apoptosis, and analyzed by FACS.

RESULTS

A profound inhibition of proliferation was seen in the LCL with 20 microM curcumin compared to 0.1% DMSO control. The colony count reduced from 34.5 +/- 3.4 to 0/well (P = 0.005), cell number reduced from 101,250 +/- 12,093 to 3750 +/- 1500/well (P = 0.002), and (3)H uptake reduced from 40,889 +/- 3669 to 70 +/- 5.2/well (P = 0.001). The apoptosis rate of LCL in the DMSO control at 24.07 and 16.87% increased significantly with 20 microM Cur to 76.4 and 95.1% at 18 and 42 h, respectively (P = 0.02).

CONCLUSION

Cur is a potent inhibitor of EBV-transformed LCL. This effect appears to be mediated through enhanced apoptosis. A further investigation of this effect may be useful in prevention and therapy of B-cell lymphoma in immunodeficient patients.

Common and idiosyncratic patterns of cytokine gene expression by Epstein-Barr virus transformed human B cell lines

Epstein-Barr virus (EBV) transformed human B cells proliferate indefinitely in vitro, and it has been proposed that cytokine-mediated autocrine loops contribute to the maintenance of the lymphoblastoid phenotype. We used a novel multiprobe RNase protection assay to quantify cytokine mRNA species expressed by EBV-transformed lymphoblastoid cell lines (LCL), derived either by the transformation of B cells with B95-8 or wild-type EBV or by the in vitro outgrowth of EBV-associated B cell lymphomas to identify cytokines that are commonly expressed in all LCL and thus more likely to be essential for immortalization of B cells. All 16 LCL expressed high levels of tumor necrosis factor (TNF)alpha, TNFbeta, and transforming growth factor (TGF)beta1 mRNA, while interleukin (IL)-10 transcripts were detected in most LCL but at a lower level. Expression of IL-1alpha, IL-1beta, IL-6, IL-12p35, IL-12p40, IL-13 and IFNgamma mRNA was variable among the LCL tested. Granulocyte-macrophage colony-stimulating factor (GM-CSF), IL-2, IL-4, and IL-5 mRNA were undetectable in all LCL. Furthermore, we found that IL-10, TNFalpha, and TNFbeta mRNA were induced in EBV-negative B cell lines after infection with EBV. These data define common versus idiosyncratic patterns of cytokine expression by LCL and, in the former case, such cytokines as TNFalpha, TNFbeta, and IL-10 emerge as strong candidates that are essential for the autocrine regulation of EBV-immortalized B cells.

Apoptosis and interleukin 7 gene expression in chronic B-lymphocytic leukemia cells

mRNA for interleukin 7 (IL-7) was readily detected in leukemic cells immediately upon their removal from patients with chronic B-lymphocytic leukemia (B-CLL). IL-7 mRNA expression and IL-7 gene transcription were down regulated, however, when B-CLL cells were placed in culture at 37 degrees C for 4 hr. Down regulation of the IL-7 gene was prevented in cells maintained at 4 degrees C. Continued culture of B-CLL cells at 37 degrees C resulted in programmed cell death, or apoptosis, as evidenced by DNA fragmentation. The coincident kinetics of IL-7 gene down regulation and apoptosis suggested that IL-7 gene expression may be required for maintenance of CLL viability in vivo. Signals for IL-7 gene regulation and apoptosis induction were thus examined. Activation of normal B cells through their immunoglobulin receptors did not result in upregulation of IL-7 gene expression. Reagents required for CLL cell purification and culture also did not contribute to IL-7 gene regulation and apoptosis induction. IL-7 gene expression was retained and apoptosis was prevented, however, in CLL cells cultured on a monolayer of EA.hy926 human umbilical cord endothelial hybrid cells. Signals specifically presented by EA.hy926 cells supported both CLL cell viability and IL-7 gene expression, whereas culture of CLL cells on A549/8 carcinoma cells, the fusion partner used to generate the EA.hy926 cells, did not. Cell-cell contact was required, as culture supernatants did not prevent apoptosis. Specifically, IL-7 mRNA expression was retained and apoptosis was prevented only by contact with the endothelial cell hybrids. Preliminary data indicated that integrins expressed on CLL cells affected modulation of apoptosis and IL-7 gene regulation, suggesting that integrins may play significant roles in regulating viability of CLL cells.

Differential induction of T cell cytokine mRNA in Epstein-Barr virus-transformed B cell clones: constitutive and inducible expression of interleukin-4 mRNA

Clones of human B lymphocytes, obtained after immortalization with Epstein-Barr virus (EBV) of single CD19+ B cells and expansion in the absence of human T lymphocytes, produced mRNA for the T cell cytokines interleukin(IL)-2, IL-4, and interferon (IFN)-gamma. As detected by reverse transcriptase-polymerase chain reaction, IL-2 mRNA was expressed only after stimulation with the combination of phorbol 12-myristate 13-acetate (PMA) plus ionomycin. IL-4 mRNA was constitutively detectable in all (10/10) EBV-transformed B cell clones, and the mRNA for IFN-gamma was constitutively present in half of the clones. In contrast to IL-2 mRNA, the expression of IL-4 and IFN-gamma mRNA could be increased by PMA alone. Most of the clones produced IL-2 bioactivity and immunoreactive protein, but neither IL-4 nor IFN-gamma protein secretion was detected. The intriguing question raised by these results is whether IL-2 secretion could contribute to the immune control of EBV-infected B lymphocytes by cytolytic T cells, and whether normal B lymphocytes can potentially be induced to express certain cytokines including IL-4 in response to the appropriate activation signals.

Enhancement of antigen-specific activation of CD8+ memory cytotoxic T cells by B cell-derived factors

Purified CD8+ T cells from influenza A/WSN-immune BALB/c (H-2d) mice respond with the generation of secondary A/WSN-specific Tc cells in vitro when stimulated with a synthetic peptide (NPP) with a sequence derived from influenza A virus nucleoprotein with high affinity for Kd class I MHC molecules. The process of the conversion of NPP-Kd-responding Tc cell precursors into effector Tc cells in a population of CD8+ T cells occurs with no demonstrable requirements for accessory cells or their lymphokine products. The addition of culture supernatants from several mouse and human B cell lymphomas and LPS-activated normal mouse B cells to the culture of NPP-stimulated immune CD8+ T cells enhanced the induction of secondary Ag-specific Tc cells. None of the tested supernatants in the absence of Ag (NPP) induced cytolytic Tc cells, indicating that B cell-derived secretory factors can exert their activity only on Ag-exposed CD8+ T cells. The augmentatory effect of these supernatants on Ag-specific activation of memory CD8+ T cells was attributed to the synergism between B cell-derived factors and IL-2 which is produced endogenously in cultures of NPP-stimulated D8+ T cells. The possible role of B cell-derived helper factors is discussed.

Dopamine-induced lymphoma cell death by inhibition of hormone release

Dopamine inhibits prolactin release from pituitary cells and seems to affect the release of several other hormones as well. We report here that dopamine may have similar effects on human B lymphoma cells leading to inhibition of production or release of endogenous factors required for cell viability and proliferation. Thus, addition of dopamine to serum-free cultures of Burkitt lymphoma cells (Raji, Namalwa, Daudi and Jijoye) resulted in rapid and extensive cell death while a myeloma cell line, SKO, appeared to be refractory to this treatment. The addition of FCS or supernatant from serum-free cultures of Raji or T24 bladder carcinoma cells could, to a variable degree, counteract the effect of dopamine, suggesting that dopamine acts by inhibiting the production of essential autocrine factors. When two of the hormones known to be under dopamine control, i.e. prolactin (PRL) and thyrotropin (TSH), were tested, they were able to prevent dopamine-induced cell death if combined with heparin. We further observed that the reducing agent 2-mercaptoethanol (2-ME), which is known to inhibit the binding of TSH to its receptor, displayed similar effects to those of dopamine and was strongly inhibitory for Burkitt lymphoma but not for myeloma cells. As expected from its blocking activity at the receptor level, the effect of 2-ME could not be reversed by adding exogenous factors. Contrary to its effect on B lymphoma cells, 2-ME is essential for growth of the murine T-cell lymphoma line CTLL. However, we show here that dopamine can fully compensate for 2-ME, suggesting that TSH or another factor under dopamine control is intimately involved in the regulation of T-cell growth. This study lends further support to the notion of an active interplay between the neuroendocrine and immune systems and emphasizes PRL and TSH as important regulators of lymphoid cell function. It also shows that these hormones may contribute to the autonomous growth pattern of B lymphoma cells and suggests a potential role for dopamine in the treatment of B-cell tumours.

Cytokines and Ly-1 (B1) B cells

In an attempt to elucidate the possible role of cytokines in autocrine growth of Ly-1+B cells, and the role of this subset of B cells in immune regulation, both in normal and diseased hosts, we have performed a systematic analysis of cytokine production by a series of mouse Ly-1+B lymphomas, as well as normal peritoneal Ly-1+ and conventional B cells. The lymphomas all express TGF-beta, and some express IL-3 and IL-4. We observed that both the lymphomas and the peritoneal cells produce TNF-alpha, TNF-beta and IL-6. Another cytokine, IL-10, is produced predominantly by peritoneal Ly-1+B cells from healthy mice and by Ly-1+ B lymphomas, but not by conventional B cells. As IL-10 regulates the production of monokines and a subset of T-cell derived cytokines, our results suggest a broad immunoregulatory role for Ly-1 B cells. To complement these studies we have also examined the responses of Ly-1 B cells to mitogens and cytokines previously shown to stimulate conventional B cells. In summary, Ly-1 B cells, in contrast to conventional B cells do not respond to anti-Ig antibodies, even in the presence of IL-4. They do respond to LPS, and this response is preferentially enhanced by IL-5, and marginally enhanced by IL-3. Surprisingly LPS-induced proliferation of peritoneal B cells is inhibited by IL-6 and to a greater extent by IL-10. Whether this inhibition is a result of differentiation into Ig secreting cells is currently being evaluated. We discuss our findings in terms of the potential of Ly-1 B cells to regulate their own development and the immunocompetence of other cells.