CD40 is a coreceptor expressed on B cells and other antigen presenting cells (APCs). When engaged by its ligand CD40L, which is expressed on T cells, CD40 recruits TRAF1-6 to the membrane. These factors then initiate different signaling pathways, with several resulting in the activation of NF-κB, a transcription factor that drives inflammatory responses as well as upregulation of costimulatory molecules (i.e. CD80/86) on APCs. In B cells, these signaling pathways can induce processes like immunoglobulin (Ig) class switching and formation of plasma cells.
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