Glycosidase inhibitors (castanospermine and swainsonine) and neuraminidase inhibit pokeweed mitogen‐induced B cell maturation

Castanospermine (CSP), an inhibitor of α‐glucosidase, enhanced immunoglobulin (Ig) release in a Staphylococcus aureus Cowan I (SAC)‐induced lymphocyte culture (Scand. J. Immunol. 1990. 32: 529). In a pokeweed mitogen (PWM)‐human lymphocyte culture, unlike the SAC‐stimulated system. CSP strongly decreased the number of IgG‐, IgA‐ and IgM‐secreting cells as well as that of Ig‐bearing cells. Peripheral blood lymphocytes treated with swainsonine, a mannosidase II inhibitor, or with neuraminidase also showed a reduced response to PWM. In cross‐culture experiments, only a mixture of B cells pretreated with either agent and untreated T cells showed such a suppressive effect. Adhesion was decreased between B cells treated with either agent and untreated T cells, but not between treated T cells and untreated B cells. These results demonstrate that a certain alteration in B cell membrane oligosaccharides inhibited the T cell‐B cell adhesion in the PWM culture, leading to an arrest of B cell maturation. Considering that these inhibitors eventually prevent terminal sialic acid addition, the present study provides evidence that sialic acids on B cell surface oligosaccharides play a biological role in the T cell‐B cell interaction.