Cluster of differentiation 40, CD40 is a type I transmembrane protein found on antigen-presenting cells and is required for their activation. The binding of CD154 (CD40L) on TH cells to CD40 activates antigen presenting cells and induces a variety of downstream effects.
Activated CD4+ T cells primarily exhibit its ligand CD40L/CD154 to antigen-presenting cells including dendritic cells (DCs), B cells, macrophages, classical and non-classical monocytes, on a variety of non-immune cells including platelets and endothelial cells, and on several types of tumor cells.[5]
Mutations affecting this gene are the cause of autosomal recessive hyper-IgM immunodeficiency.