Abstract

Small resting B lymphocytes are activated when their cell surface immuno-globulin (Ig) receptors interact with specific antigen or anti-Ig antibodies. Such a receptor-ligand interaction leads to enlargement and proliferation of B lymphocytes. These activated B cells can subsequently mature into Ig-secreting cells in the presence of appropriate accessory cell signals (1-3). However, monovalent anti-Ig antibodies cannot induce B cell activation even though they can bind to the surface Ig (4-7). It has thus been concluded that membrane Ig has to be cross-linked to induce early steps in B cell activation (membrane depolarization; 8) as well as later steps (proliferation). T h e r e are several B cell mitogens as well as antibodies to B cell m e m b r a n e components that stimulate B cell proliferation but probably interact with B cell surface moieties other than Ig (9-1 1). It is not clear if cross-linking of demonstrated or postulated receptor structures is also essential for these agents to transform resting B cells into activated cells. Recently we have described a model system in which a monoclonal antibody (MAb) to a murine B lymphocyte differentiation antigen (Lyb-2) triggers B cell activation (12). We have shown that under serum-free culture conditions, MAb to the Lyb-2 molecule transform small B cells into blast cells and induce B cell proliferation. Here we investigate the possibility that this B cell activation process requires cross-linking in addition to the binding of antibody to the Lyb-2 molecules. We have prepared divalent F(ab')z fragments and monovalent Fab' fragments and tested their ability to induce B cell-specific blast transformation and proliferation. Our results demonstrate that monovalent anti-Lyb-2 is sufficient to induce B cell enlargement and proliferation so we conclude that cross-linking of Lyb-2 molecules is unnecessary for B cell activation.

Document Type

Article

Publication Date

1984

Notes/Citation Information

© The Rockefeller University Press

Digital Object Identifier (DOI)

https://doi.org/10.1084/jem.159.6.1796

Funding Information

This work was supported by grants AI-15879 and CA-06927 from the National Institutes of Health and by the Commonwealth of Pennsylvania.Current address of B. Subbarao is the Department of Microbiology and Immunology, University of Kentucky, Lexington, KY 40536.

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