Similar CD40 ligand expression on EL-4 thymoma cell lines with widely different helper activity for B lymphocytes.
A mutagenized subclone of the murine EL-4 thymoma (clone B5) is approximately 30 times more potent than parental EL-4 cells in stimulating proliferation and Ig secretion of murine or human B cells by direct cell contact in the presence of appropriate cytokines. In this study we found that CD40 ligand (CD40L) expression was constitutive and very similar on EL-4 B5 and parental EL-4 cells according to Northern blot and flow cytometry. Activation with phorbol 12-myristate 13-acetate (PMA) alone, PMA and ionomycin, interleukin-1 (IL-1) or human T-cell supernatant did not lead to significant CD40L up-regulation. A receptor-binding assay with soluble CD40 did not reveal different ligand affinities. However, murine and human soluble CD40-IgFc fusion proteins inhibited human B-cell stimulation by EL-4 B5 cells in the presence of human T-cell supernatant. Inhibition was 96% when soluble CD40 was added on day 0 of culture and progressively decreased when the CD40 was added subsequently. Ig secretion by cytoplasmic Ig-positive cells was no longer inhibited. These findings imply that, although CD40 ligand is necessary for B-cell activation by EL-4B5 cells, additional molecule(s) must be responsible for the increased helper activity of the EL-4 B5 clone.
Werner-Favre
C
C
Department of Medicine, Hôpital Cantonal Universitaire, Genève, Switzerland.
Gauchat
J F
JF
Mazzei
G
G
Aubry
J P
JP
Bonnefoy
J Y
JY
Zubler
R H
RH
D000818:Animals; D015703:Antigens, CD / Q000032:analysis*; D000944:Antigens, Differentiation, B-Lymphocyte / Q000032:analysis*; D001402:B-Lymphocytes / Q000276:immunology*; D015152:Blotting, Northern; D019013:CD40 Antigens; D006801:Humans; D008024:Ligands; D008213:Lymphocyte Activation / Q000276:immunology; D008211:Lymphocyte Cooperation / Q000276:immunology*; D051379:Mice; D009154:Mutation; D006377:T-Lymphocytes, Helper-Inducer / Q000276:immunology*; D013945:Thymoma / Q000276:immunology; D013953:Thymus Neoplasms / Q000276:immunology; D014407:Tumor Cells, Cultured
D015703:Antigens, CD; D000944:Antigens, Differentiation, B-Lymphocyte; D019013:CD40 Antigens; D008024:Ligands