CD2

CD2 is a cell-surface glycoprotein that serves as a marker of mature T lymphocytes and natural killer (NK) cells. It belongs to the immunoglobulin superfamily and functions as an adhesion molecule that binds to its ligand CD58, also known as LFA-3, on antigen-presenting cells and other targets. CD2 plays a role in forming stable cell contacts during immune interactions and can modulate signals delivered through the T cell receptor.

The structure of CD2 includes an extracellular immunoglobulin-like domain, a single-pass transmembrane region, and a cytoplasmic tail that participates in signaling and linkages to the cytoskeleton. The extracellular domain mediates adhesion, while the cytoplasmic portion participates in intracellular signaling pathways that can influence cell activation.

Expression and function: CD2 is widely expressed on most peripheral T cells and NK cells, with lower levels on some thymocytes and limited expression on other lineages. Upon activation, CD2 expression can be upregulated in some contexts. Functionally, CD2 promotes adhesion to CD58-bearing cells, contributing to immunological synapse stability and providing costimulatory signals that can augment TCR-driven activation, calcium flux, proliferation, and cytokine production.

Clinical relevance: CD2 is used as a marker in immunophenotyping and has been investigated as a therapeutic target in transplantation and autoimmune diseases. Anti-CD2 therapies have been explored to deplete activated T cells and modulate immune responses, though no widely approved CD2-targeted drugs are in routine clinical use.

Genetics and evolution: The CD2 gene encodes the protein in humans and is conserved across jawed vertebrates, reflecting its role in adaptive immunity.