Members of the CTRP (complement C1q tumor necrosis factor-related protein) family are structurally related, although functionally diverse. CTRPs share TNF 鍠like globular domains and N-terminal glycine-X-Y repeats and also tend to form trimers that have the ability to congregate into higher order structures. Functions of this protein family range from immune homeostasis to structural and extracelluar matrix-related roles. CTRP8 (complement C1q tumor necrosis factor-related protein 8), also known as UNQ5829 or C1QTNF8 (C1q and tumor necrosis factor related protein 8), is a 252 amino acid secreted protein that is expressed predominantly in lung and testis. Containing one C1q domain and one collagen-like domain, CTRP8 exists as a homotrimer and forms heteromeric complexes with C1qL1. CTRP8 is encoded by a gene located on human chromosome 16, which encodes over 900 genes and comprises nearly 3% of the human genome.