Intercellular adhesion molecule 3 (ICAM3) also known as CD50 (Cluster of Differentiation 50) is a member of the intercellular adhesion molecule (ICAM) family. All ICAM proteins are type I transmembrane glycoproteins that bind to the leukocyte adhesion LFA-1 protein. This protein is constitutively and abundantly expressed by all leucocytes and may be the most important ligand for LFA-1 in the initiation of the immune response. It functions not only as an adhesion molecule, but also as a potent signaling molecule.
ICAM-3 is potentially the most important ligand for LFA-1 in the initiation of the immune response because the expression of ICAM-1 on resting leukocytes is low.¹ ICAM-3 is closely related to ICAM-1. ¹ ICAM-3 is essentially restricted to the haemopoietic system and is reciprocal in its expression to ICAM-1, in that it is present on resting cells and its level falls as a result of cell activation.²

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