The biology of CD2: adhesion, transmembrane signal, and regulatory receptor of immunity.

Cluster of differentiation antigen-two (CD2) is a transmembrane, cell surface glycoprotein found on many lymphocyte subsets. It is a member of the immunoglobulin-gene superfamily and was originally described as an adhesion molecule, strengthening the physical interaction between responder and antigen-presenting cells and between effector and target cells. More recently, numerous studies show important receptor functions for CD2, which transmits a variety of intracellular second messages after interaction with one or more separate extracellular ligands. These second messengers modify the function of additional cell surface adhesion receptors including CD3 and LFA-1. A model is proposed which integrates several of these adhesion-receptor-messenger systems and experimental data supporting the validity of this model during cell-mediated immunity are presented. CD2 serves as a paradigm for the multitude of adhesion-receptors now being described and characterized. Detailed understanding of each molecule will allow synthesis of an integrated understanding of cellular and molecular interaction during immunity.