A B-cell hybridoma product inhibiting antibody secretion via 5'-nucleotidase

A mouse spleen cell/plasmacytoma fusion designed to generate hybridomas making monoclonal antibodies to human lymphocyte 5'-nucleotidase yielded three hybridomas secreting material which inhibited about 50% of human and mouse lymphocyte ecto 5'-nucleotidase activity. The inhibition proved not to be due to antibody but to material of molecular weight 44,000 +/- 7,000 which was not part of an immunoglobulin molecule, although it may be related to a B cell Fc gamma receptor. In a haemolytic plaque assay this material inhibited the production of IgG but not IgM antibody by spleen cells of mice immunized with dinitrophenylated keyhole limpit haemocyanin. By contrast, IgG production by pokeweed mitogen-stimulated human tonsillar lymphocytes (assessed by reverse haemolytic plaque assay) was partially inhibited only by ascitic fluid of one of the hybridomas. The factor was called BAN (B cell anti 5'-nucleotidase). The suppressive action of BAN on IgG production was blocked by antibodies against 5'-nucleotidase suggesting that the lymphocyte enzyme may be acting as a BAN receptor.