The 24-31 monoclonal antibody specifically binds to CD40 Ligand (CD40L) which is also known as CD154, gp39, T-B cell-activating molecule (T-BAM), Tumor necrosis factor ligand superfamily member 5 (TNFSF5), and TNF-related activation protein (TRAP). CD40L (CD154) is an ~39 kDa type II membrane glycoprotein that is encoded by CD40LG. It is expressed on a variety of cell types including activated CD4+ T cells and some CD8+ T cells, NK cells, mast cells and basophils. CD40L (CD154) serves as a ligand for CD40 that is expressed on B cells, macrophages, and dendritic cells. The expression of CD40L (CD154) by activated T-helper cells costimulates B-cell activation and proliferation through binding to CD40 expressed on B cells. In response to T-dependent antigens, the CD40L (CD154) and CD40 interaction is required for B-lymphocyte differentiation, including immunoglobulin production and isotype switching and memory B cell generation. The 24-31 antibody can reportedly block T cell-B cell interaction and inhibit the subsequent proliferation, differentiation, and memory formation of B cells. It has been reported that patients with X-linked hyper-IgM syndrome have defective expression of functional CD40L (CD154) due to mutations in the CD40LG gene.