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Updated: Aug 8, 2026

Generation of Human CD40-activated B cells
Published on: October 17, 2009
A 39-kDa protein on activated helper T cells binds CD40 and transduces the signal for cognate activation of B cells
R J Noelle1, M Roy, D M Shepherd
1Department of Micribiology, Dartmouth Medical School, Lebanon, NH 03756.
Abstract:
CD40 is a B-cell surface molecule that has been shown to induce B-cell growth upon ligation with monoclonal antibodies. This report shows that triggering via CD40 is essential for the activation of resting B cells by helper T cells (Th). A soluble fusion protein of CD40 and human immunoglobulin, CD40-Ig, inhibited the induction of B-cell cycle entry, proliferation, and differentiation by activated Th1 and Th2. The ligand for CD40 was identified as a 39-kDa membrane protein that was selectively expressed on activated Th. A monoclonal antibody specific for the 39-kDa protein inhibited CD40-Ig binding and also inhibited the activation of B cells by Th. These data indicate that the 39-kDa membrane protein expressed on activated Th is a binding protein for CD40 and functions to transduce the signal for Th-dependent B-cell activation.
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