Human T-Cell Surface Glycoprotein CD5 (CD5) Protein

Background

The CD5 molecule is a type I transmembrane glycoprotein primarily expressed on the surface of T cells and a subset of B cells known as B1a cells. CD5 functions as an immunomodulatory receptor, playing a critical role in T-cell activation, immune tolerance, and B-cell signaling. Its primary role is in regulating immune responses by controlling the threshold of antigen receptor signaling in both T and B cells. CD5 is also involved in maintaining the delicate balance between immune activation and immune tolerance, which prevents autoimmune responses while ensuring effective immunity. CD5 belongs to the scavenger receptor cysteine-rich (SRCR) superfamily of receptors, a group of molecules known to be involved in diverse biological functions, including immunity, apoptosis, and cellular adhesion. CD5 is especially notable for its role as a negative regulator of T-cell receptor (TCR) and B-cell receptor (BCR) signaling. This regulatory capacity makes CD5 crucial in maintaining immune homeostasis.