Effects of anti-IgM on mitogen-induced proliferation of human B-lymphocyte malignancies

Cytokines and cross-linking of sIgM augment PMA-induced activation of human leukaemic CD5+ B cells

Purified leukaemic CD5+ B cells obtained from patients with B cell chronic lymphocytic leukaemia (B-CLL) undergo activation and differentiation following in vitro stimulation with optimal concentrations of the phorbol ester PMA. This paper examines the ability of exogenous cytokines, anti-Ig antibodies, or combinations of these, to enhance or replace the activation signal provided by PMA to different populations of leukaemic B cells. Proliferation induced by PMA was enhanced 2-20-fold when the cells were co-cultured with either anti-Ig, IL-2, IL-4, IL-13, IFN-gamma or TNF-alpha. Moreover, the combination of anti-Ig, PMA and any one of the above cytokines further enhanced proliferation. Anti-Ig and exogenous cytokines were also capable of inducing proliferation in leukaemic B cells cultured with a non-mitogenic concentration of PMA. When taken together with the finding that IL-2, IL-4, IL-13, IFN-gamma and TNF-alpha prevent in vitro apoptosis of leukaemic CD5+ B cells, the results presented here suggest that these cytokines, in conjunction with signals delivered via sIg, may play a role in the proliferation of leukaemic B cells in vivo and, consequently, the pathogenesis of B-CLL.

Phorbol ester activates CD5+ leukaemic B cells via a T cell-independent mechanism

B cell chronic lymphocytic leukaemia (B-CLL) is characterized by the proliferation and accumulation of sIgM+ CD5+ lymphocytes that fail to progress to the final stages of B cell development. Stimulation of unfractionated PBL from three patients with B-CLL with the phorbol ester PMA and the mitogens PHA and PWM resulted in significant increases in cell proliferation, RNA synthesis and IgM secretion when compared to unstimulated cell populations. PMA was the most potent inducer of IgM secretion and this occurred irrespective of the presence of residual T cells. PMA-induced proliferation and RNA synthesis was also independent of T cells. However, in the presence of T cells, these parameters of cellular activation were enhanced during in vitro culture. Thus, the inductive ability of PMA on CD5+ CLL B cells was independent of T cells. In contrast, activation and differentiation of the malignant CD5+ B cells into IgM-secreting cells following culture with mitogens did not occur in the absence of T cells.

Inefficacy of extracorporeal photochemotherapy in the treatment of B-cell chronic lymphocytic leukemia: preliminary results

Because extracorporeal photopheresis has been shown to be clinically effective in Sezary syndrome, a disease characterized by a circulating malignant clone, we initiated a pilot study of its use in B-cell chronic lymphocytic leukemia (B-CLL) to see if it could be similarly effective. We treated three patients with Rai stage III and IV B-CLL with photopheresis (3 consecutive days a week every 3 weeks) and followed serial clinical and immunologic parameters. While we noted no major toxicity, there was neither clinical response to treatment nor marked improvement in white counts or mitogen assays. We conclude that photopheresis was not effective in inducing remission in this pilot study of advanced stage B-CLL patients.

Antigen-dependent transition of IgE to a detergent-insoluble form is associated with reduced IgE receptor-dependent secretion from RBL-2H3 mast cells

In mast cells, basophils, and the RBL-2H3 tumor mast cell model, crosslinking cell surface IgE-receptor complexes by multivalent ligands activates a signal transduction pathway that leads to the secretion of histamine, serotonin, and other inflammatory mediators. Receptor crosslinking in RBL-2H3 cells also changes cell surface morphology and increases F-actin assembly. Previously, Robertson et al. demonstrated that crosslinked IgE-receptor complexes become associated with the Triton X-100-insoluble fraction (the "cytoskeleton") of RBL-2H3 cells and raised the possibility that receptor-cytoskeletal association may be a required step in the stimulation of secretion. The studies reported here confirm by flow cytometry that crosslinking cell surface IgE by antigen induces the association of the crosslinked complexes with the detergent-insoluble fraction. Dose-response studies, also reported here, indicate that the detergent insolubility of the complexes does not correlate with secretion. Thus, secretion increases with antigen concentration to a maximum beyond which more antigen causes less, not more, secretion. There is little residual detergent-insoluble IgE at the concentrations of antigen that promote optimal secretion, whereas the association of IgE with the detergent-insoluble fraction is maximal at the high antigen concentrations that result in reduced secretion. The addition of monovalent hapten to reduce the amount of crosslinking caused by high concentrations of antigen increases secretion and simultaneously reduces the association of IgE with the detergent-insoluble fraction. Dihydrocytochalasin B, an inhibitor of antigen-stimulated actin polymerization, also increases the rate and extent of secretion and simultaneously delays the association of crosslinked IgE-receptor complexes with the detergent-insoluble fraction. From these data, we propose that the association of crosslinked IgE receptors with the detergent-insoluble fraction of RBL-2H3 cells increases with increased receptor crosslinking, is enhanced by antigen-induced actin polymerization, and is more likely related to the termination than the stimulation of secretion. The ligand-induced conversion of receptors to a detergent-insoluble form is not restricted to mast cells but occurs in a variety of cell types. Its general function may be to limit the generation or transmission of transmembrane signals.