CD154, also called CD40 ligand or CD40L, is a protein that is primarily expressed on activated T cells[5] and is a member of the TNF superfamily of molecules. It binds to CD40 on antigen-presenting cells (APC), which leads to many effects depending on the target cell type. In total CD40L has three binding partners: CD40, α5β1 integrin and integrin αIIbβ3. CD154 acts as a costimulatory molecule and is particularly important on a subset of T cells called T follicular helper cells (TFH cells).[6] On TFH cells, CD154 promotes B cell maturation and function by engaging CD40 on the B cell surface and therefore facilitating cell-cell communication.[7] A defect in this gene results in an inability to undergo immunoglobulin class switching and is associated with hyper IgM syndrome.[8] Absence of CD154 also stops the formation of germinal centers and therefore prohibiting antibody affinity maturation, an important process in the adaptive immune system.
^Lederman S, Yellin MJ, Cleary AM, Pernis A, Inghirami G, Cohn LE, et al. (March 1994). "T-BAM/CD40-L on helper T lymphocytes augments lymphokine-induced B cell Ig isotype switch recombination and rescues B cells from programmed cell death". Journal of Immunology. 152 (5): 2163–2171. doi:10.4049/jimmunol.152.5.2163. PMID7907632. S2CID42460521.