T-cell differentiation antigen CD6 (CD6)

T-cell differentiation antigen CD6 is a single-chain type I transmembrane glycoprotein predominantly expressed on mature human T lymphocytes, some B cells, medullary thymocytes, and at lower levels on other immune cells. The extracellular region contains three scavenger receptor cysteine-rich domains that mediate binding to its primary ligand ALCAM/CD166—a key event in cell adhesion and immunological synapse formation during antigen presentation. Functionally, CD6 acts as a costimulatory molecule essential for optimal activation and proliferation of T cells following engagement of the antigen-specific receptor complex. It also serves as a pattern recognition receptor capable of binding bacterial components such as lipopolysaccharide from Gram-negative bacteria and lipoteichoic acid from Gram-positive bacteria—triggering downstream signaling cascades including MAP kinase pathways that modulate inflammatory cytokine production. Genetic variants in *CD6* are associated with altered susceptibility to autoimmune diseases like multiple sclerosis.

Other names

Cluster of Differentiation 6CD6 moleculeT12Soluble CD6

For anti-CD6 antibodies like itolizumab, the mechanism involves blocking costimulatory signals required for full T-cell activation, thereby reducing pathogenic immune responses. It may also interfere with cell adhesion by disrupting the interaction between CD6 and its ligand ALCAM/CD166.