Cluster of differentiation 40 (CD40) is a cell surface receptor found on antigen-presenting cells that mediates their interaction with activated T cells. CD40 is most well known for its role in the activation of B cells, which plays an important role in the immune response. CD40 is a promising target for the development of drugs to treat a variety of diseases, including cancer, autoimmune diseases, and chronic inflammation. Signosis’ Human CD40 ELISA kit can accurately measure CD40 levels in human samples and provides a human CD40 protein standard for quantitative analysis.