Clone ATM-2 recognizes the rat CD252 antigen, a member of the TNF ligand superfamily, also known as OX40 ligand (OX40L) or tumor necrosis factor ligand superfamily member 4 (TNSFSF4). CD252 is constitutively expressed by splenic dendritic cells and can be upregulated on splenic B cells via stimulation with LPS. Expression of the cognate receptor CD134 (OX40) is found predominantly on activated T cells. CD252/CD134 interaction promotes the proliferation and survival of effector T cells, modulates cytokine production, suppresses the activity of natural regulatory T cells, and inhibits the generation of inducible regulatory T cells.