Expression of Fas-Ligand by T cells can induce apoptosis through interaction with Fas on the target cell. A target of Fas-mediated apoptosis is the B cell. B cells that are not activated by antigen, bystander B cells, can interact through CD40 with the CD40 ligand on T cells. The CD40-CD40L interaction induces Fas expression by bystander B cells, and the interaction of Fas with the T cell Fas-Ligand, followed by B cell apoptosis. B cells that are activated by antigen binding and that interact with the T cell receptor through the B cell MHC II appear to become resistant to Fas-mediated apoptosis, survive and proliferate. IL-4 also appears to confer B cell resistance to Fas-mediated apoptosis. The induction of apoptosis in non-antigen stimulated B cells may prevent B cells from proliferating inappropriately and failure of this mechanism may be involved in autoimmune disorders and B cell lymphomas.
Contributor: Glenn Croston, PhD.
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