Castanospermine (CSP) inhibits α‐glucosidase. which is involved in the initial step of N‐linked oligosaccharide processing of secretory and membrane glycoproteins. In Staphylococcus aureus Cowan I (SAC)‐stimulated human lymphocyte culture, CSP at a dose of 20 μg/ml caused a twofold increase in immunoglobulin G (IgG) release after 7 days. An initial 48‐h exposure to CSP sufficed for this enhancing effect. Plaque‐forming cell assays on the seventh day disclosed that CSP caused an increase in the number of IgG‐, IgA‐ and IgM‐secreting cells. In cross‐culture experiments, only a mixture of B cells pretreated with CSP and untreated T cells showed an increase in IgG production. Tritiated thymidine incorporation studies revealed that CSP enhanced B‐cell responses to T cell‐derived soluble factor (TSF). When incubated with CSP for 18 h. B cells showed an increased surface binding on [3H] concanavalin A (Con A). These results indicate that the alteration in B‐cell membrane oligosaccharides enhances the response to TSF at in early stage of SAC culture, leading to an increase in Ig‐secreting cell number at later stages. The present study provides evidence that cell‐surface oligosaccharides of B cells play an important role in the responses of B cells to lymphokines. Copyright © 1990, Wiley Blackwell. All rights reserved
