CD40 and its ligand CD40L (CD154), members of the tumor necrosis factor (TNF) super-family, have a key role in the functions of the immune system. It is well known that CD40 is widely expressed in monocytes, dendritic cells, endothelial cells, epithelial cells, platelets and fibroblasts. However, CD40 expression was observed not only in cells related to the immune system, but also in cells of several different types of carcinomas, such as in the ovary, breast, lung, renal, melanoma and colon among others. CD40 it appears to initiate the differentiation and the proliferation of certain cell types.
The CD40 ligand CD154 has been most commonly observed on activated CD4+ T lymphocytes and secondly on activated CD8+ T lymphocytes, eosinophils and B lymphocytes as well. Connection of the CD40 with its ligand CD154, results in the activation of both the humoral and cellular immune response systems via the professional antigen presenting cells (APCs) and T cells.