CD154, also called CD40 ligand or CD40L, is a protein that is primarily expressed on activated T cells and is a member of the TNF superfamily of molecules.CD40 ligand is primarily expressed on activated CD4+ T lymphocytes but is also found in a soluble form. While CD40L was originally described on T lymphocytes, its expression has since been found on a wide variety of cells, including platelets, mast cells, macrophages, basophils, NK cells, B lymphocytes, as well as non-haematopoietic cells. Signals generated by CD40 vary depending on cell type and include activation of MAPK pathways as well as NF-κB.
