The monoclonal antibody 24-31 recognizes human CD40 ligand (CD40L), also referred as CD154. CD40L is a transmembrane cell surface glycoprotein of 39 kDa expressed mainly on CD4+ T cells and platelets in an activation-dependent manner. The interaction of CD40L on activated CD4+ T cells with CD40 on antigen presenting cells is essential for the T-cell-dependent humoral immune respons. It has a role in T cell-dependent B-cell proliferation, differentiation and memory cell formation. Blocking of the CD40-CD40L interaction results in immunoglobulin isotype switch. Defects in CD40L are the cause of X-linked immunodeficiency with hyper-IgM type Ig which is characterized by elavated concentrations of serum IgMs and decreased amounts of all other types. In vivo, interruption of the CD40 signalling system limits experimental autoimmune diseases such as collagen-induced arthritis, lupus nephritis, rheumatoid arthritis, systemic lupus erythematosus (SLE) and acute or chronic graft-versus-host disease.CD40/CD40L is involved in angiogenic processes. In this process activated platelets are the source of CD40L for CD40 expressed by endothelial cells.The monoclonal antibody 24-31 cross reacts with cynomolgus CD40 ligand.