CD273 / PD-L2 (programmed death ligand-1), also known as B7-DC, is a member of the B7 family of regulatory proteins. It costimulates the proliferation of T cells, and mediates IFN gamma production. Ligation of CD273 on dendritic cells enhances dendritic cell activation and T cell responses. When interacting with CD279, it can act as a coinhibitor of the T cell function. CD273 expression is a useful marker to distinguish primary mediastinal B cell lymphoma from other diffuse large B cell lymphomas.