CD6 (Cluster of Differentiation 6) is a transmembrane protein primarily expressed on T-lymphocytes and certain other immune cells. Structurally, it is characterized by three scavenger receptor cysteine-rich (SRCR) domains and a binding site for an activated leukocyte cell adhesion molecule (ALCAM). Functionally, CD6 is critical for the continuation of T cell activation and exhibits scavenger receptor activity. Aberrant CD6 function is associated with diseases such as Multiple Sclerosis. Its paralog is DMBT1.