CLM-9, also known as TREM4, is a receptor which belongs to the TREM family. The TREM family of receptors regulates the activity of various cell types of the immune system including neutrophils, monocyte/macrophages, microglia, and dendritic cells. CLM-9 may mediate L-selectin-dependent lymphocyte rollings. It binds SELL in a calcium dependent manner. CLM-9 also binds lymphocyte which suggests that it functions in lymphocyte adhesion. The major CLM-9 transcript is expressed highly in human heart, skeletal muscle, and placenta. The mouse protein has been shown to be expressed in capillary endothelial cells. Human CLM-9 mediates the uptake of human IgA2 and mouse IgM.