CD26 [also known as dipeptidyl peptidase IV (DPP IV), adenosine deaminase (ADA) binding protein]. 1 - 3 is an atypical serine protease belonging to the prolyl oligopeptidase family. It is expressed on lymphocyte cells and is upregulated during T-cell activation. CD26 is also expressed on activated B cells and natural killer cells and abundantly on epithelia. CD26 is implicated in a variety of biological functions including T-cell activation, cell adhesion with extracellular matrix such as fibronectin or collagens, and in HIV infection. Cross-linking of CD26 using this antibody dramatically enhances the anti CD3-induced IL - 2 production.