Involved in the initial immune cell clustering during inflammatory response and may regulate chemotactic activity of chemokines. May play a role in melanocortin signaling pathways that regulate energy homeostasis and hair color. Low-affinity receptor for agouti (By similarity). Has a critical role in normal myelination in the central nervous system (By similarity). Monomer and homotrimer. Isoform 2 is detected in plasma (at protein level). Expressed and secreted by activated T-lymphocytes. Expressed at low to moderate levels in peripheral blood leukocytes, spleen, lymph node, tonsil, bone marrow and fetal liver. At very low levels found in thymus. Isoform 2 is the major isoform in peripheral blood leukocytes. Activation of peripheral blood leukocytes with phytohemagglutinin induces strong expression of the membrane isoform followed by the release of the secreted isoform. Heavily glycosylated. Was originally (PubMed:7539799 and PubMed:9736737) thought to have dipeptidase activity but it was shown later to lack that activity. Attractin-2