CD40LG protein is expressed on all B lymphocytes during various stages of development, activated T cells and monocytes, follicular dendritic cells, thymic epithelial cells, and various carcinoma cell lines. It is expressed on most mature B cell malignancies and on some early B cell acute lymphocytic leukemias. Human CD40LG has been found to be the receptor for a protein involved in an X-linked immunodeficiency syndrome. Based on its homology with other members of the TNF ligand protein superfamily, CD40LG is also referred to also as TNFSF5. The soluble form of CD40LG is generated by the intracellular proteolytic processing of the full length CD40LG. Recombinant Human CD40LG is a 17 kDa protein that represents the soluble segment of full length CD40LG and encompasses the receptor binding TNF-like domain.