Attractin/ATRN, also known as DPPT-L, is an approximately 200 kDa transmembrane glycoprotein that shows dipeptidyl peptidase activity similar to DPPIV/CD26. Attractin is involved in a variety of processes including monocyte-T cell adhesion, axon myelination, melanocyte pigment synthesis, and energy homeostasis. Attractin is transiently upregulated during T cell activation before expression switches to the 175 kDa secreted isoform which is released into the circulation. Soluble Attractin is preferentially expressed by leukocytes and differentiating neurons. It blocks neurite formation and is elevated in the CSF of astrocytoma patients.