Activation of malignant B-lymphocytes: pathophysiologic and clinical importance

In vitro beta 2-microglobulin (beta 2m) secretion by normal and leukaemic B-cells: effects of recombinant cytokines and evidence for a differential response to the combined stimulus of phorbol ester and calcium ionophore

Due to the increasing therapeutic use of immunoregulatory agents and the potential effects on cellular function, we examined the modulation of in vitro beta 2-microglobulin (beta 2m) production rates by 'normal' tonsil and leukaemic B-cells in response to a number of these agents. Tonsil B-cells responded to phorbol ester (TPA) by an increased beta 2m production rate, which was further enhanced by the combined stimuli of TPA plus the calcium ionophore A23187. In marked contrast, however, lymphocytes from a majority (8/11) of B-cell malignancies showed a suppression of the TPA-induced beta 2m production rate in response to the combined TPA/A23187 stimulus. These different responses of 'normal' and malignant B-cells were not apparent when IgM production rates were examined. The recombinant cytokines IL-1, IL-2, IFN-alpha, IFN-gamma and TNF also enhanced beta 2m production rates of both normal and leukaemic B-cells, but to a considerably lesser extent than did TPA. Bryostatin-1 increased beta 2m production to a level intermediate between that obtained by TPA and the cytokines. It is suggested that beta 2m production rates may correspond to the degree of B-cell differentiation, and/or to the degree of cellular 'activation'. The results further indicate that the in vitro measurement of beta 2m production provides a different index of the cellular response than that obtained by the conventional measurement of IgM production.

Prognostic significance of immunoglobulin isotype expression in B-cell non-Hodgkin's lymphoma

Lymph node biopsies from 170 patients with untreated non-Hodgkin's lymphomas (NHL) of B-cell type were immunophenotyped and analyzed for the Ig heavy and light chain isotypes and their relation to prognosis. IgM alone was more frequently seen in high grade (53%) compared to low grade (20%) NHL. In contrast, IgM/IgD isotypes were more frequent in low grade (47%) than in high grade NHL (20%). IgG or IgA heavy chain, alone or in combination with other heavy chain isotypes, were expressed with the same frequencies in both low (32%) and high (27%) grade NHL. Clonally restricted kappa light chain expression was noted in 64% of low grade and 66% of high grade NHL patients. Only in chronic lymphocytic leukemia (CLL) and immunocytoma (IC) was a shorter survival time noted for patients with tumors expressing IgG and/or IgA heavy chains compared to those expressing IgM or IgM/IgD (P less than 0.001). This difference was not seen as being low grade follicle center cell-derived (FCC) or high grade NHL. The expression of kappa light chains on the tumor cells was associated with a significantly longer survival in CLL and IC patients only (P less than 0.01).

Triggering of neoplastic B cells via surface IgM and the cell surface antigens CD20 and CDw40. Responses differ from normal blood B cells and are restricted to certain morphologic subsets

By raising monoclonal antibodies (MAbs) against B cells, a number of cell surface molecules have recently been identified which after binding by their specific antibody can trigger B cells, either alone or in co-operation with antibodies to surface immunoglobulin (sIg). The anti-CD20 (Bp35) MAb IF5 can deliver a strong activation signal to resting normal B cells, and the anti-CDw40 (Bp50) MAb G28-5 can promote activated G1 B cells to enter S phase. These antibodies were tested for their functional effects in vitro on suspended cells from 17 follicle-center-cell (FCC) lymphomas, 5 cases of chronic lymphatic B-cell leukemia (B-CLL) and 8 cases of various histological types. Changes in cellular volume, RNA and DNA synthesis were compared with the results obtained with a polyclonal anti-mu [F(ab')2] antiserum, a MAb to surface IgM (AF6), 12-O-tetradecanoyl-phorbol-13-acetate (TPA) and B-cell growth factor (low-molecular-weight BCGF). Our data reveal differences in the requirements for triggering of various B-cell subsets: cells from CLL responded strongly to TPA but not to anti-mu, which is a potent stimulator not only of normal B cells but also of cells from individual cases of FCC lymphomas. Our observations suggest that the differentiation stage of B-CLL cells is distinct from that of small resting B cells from peripheral blood. Centrocytic lymphomas could not be activated by any of the reagents. CD20-mediated triggering was seen in neoplastic B cells from only 4 of 30 cases, indicating that most B-cell neoplasias were not responsive to this activation pathway. In contrast, the anti-CDw40 MAb consistently stimulated DNA synthesis together with anti-mu or TPA in cells from FCC lymphomas, but not from CLL. Together, these results suggest that activation in different neoplastic B-cell subsets depends on distinct signal transduction mechanisms.