Cross-linking of membrane IgM on B CLL cells: dissociation between intracellular free Ca2+ mobilization and cell proliferation.
It has been shown previously that chronic lymphocytic leukemia (CLL) B cells are frozen at different stages of activation with unique requirements for proliferation. Although most B CLL cells express surface IgM, anti-mu antibodies are able to trigger only some of them to proliferate and/or respond to B cell growth factor (BCGF) or interleukin 2 (IL2), as normal B cells. In this report we extend these observations using three different monoclonal antibodies (mAb) to human mu chain (one mitogenic in soluble form for normal B cells, the two others mitogenic only when coupled on Sepharose 4B beads). Cells from only 3 out of 11 B CLL patients proliferated in the presence of either mitogenic anti-mu. When the early events following surface Ig cross-linking, such as calcium mobilization (by flow cytometry on indo-1-labeled cells), were studied all three mAb in soluble form were able to induce a similar increase in the intracellular free calcium concentration ([Ca2+]i); analogous to [Ca2+]i rise after the mitogenic F(ab')2 anti-mu stimulation. This response was seen only in 8 out of the 12 CLL B cells studied. All B CLL cells, however, proliferate in response to a combination of phorbol ester 12,13-dibutyrate (PBt2) and ionomycin. Therefore, three patterns of response to sIg cross-linking by anti-mu could be distinguished: cells from 4 out of 12 cases proliferate and mobilize Ca2+ upon anti-mu triggering (behaving like resting B lymphocytes); in 4 other cases anti-mu lead to Ca2+ mobilization without cell proliferation; in the last 4 cases neither Ca2+ mobilization, IP3 generation (in the one case studied) nor cell proliferation are observed although these cells do proliferate directly in response to growth factors. Moreover, anti-mu stimulation in this group leads to increased proliferation in response to BCGF and IL2 suggesting an anti-Ig signaling independent of inositol phosphate metabolism. These results are interpreted in terms of differential anti-mu signaling on B cells at different stages of activation.
Hivroz
C
C
Laboratory of Immunochemistry and Immunopathology, INSERM U 108, Hôpital Saint-Louis, Paris, France.
Grillot-Courvalin
C
C
Labaume
S
S
Miglierina
R
R
Brouet
J C
JC
D000888:Antibodies, Anti-Idiotypic / Q000276:immunology; D001402:B-Lymphocytes / Q000502:physiology*; D002118:Calcium / Q000502:physiology*; D002455:Cell Division; D003432:Cross-Linking Reagents; D004987:Ethers / Q000494:pharmacology; D006801:Humans; D007148:Immunoglobulin mu-Chains / Q000502:physiology; D007295:Inositol Phosphates / Q000502:physiology; D007376:Interleukin-2 / Q000494:pharmacology; D015847:Interleukin-4; D007378:Interleukins / Q000494:pharmacology; D015759:Ionomycin; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000503:physiopathology*; D010703:Phorbol Esters / Q000494:pharmacology; D011947:Receptors, Antigen, B-Cell / Q000502:physiology*; D014407:Tumor Cells, Cultured
D000888:Antibodies, Anti-Idiotypic; D003432:Cross-Linking Reagents; D004987:Ethers; D007148:Immunoglobulin mu-Chains; D007295:Inositol Phosphates; D007376:Interleukin-2; D007378:Interleukins; D010703:Phorbol Esters; D011947:Receptors, Antigen, B-Cell; D015847:Interleukin-4; D015759:Ionomycin; D002118:Calcium