The Signaling Lymphocytic Activation Molecule (SLAM) family of receptor molecules is a subset of the CD2 family of receptors. SLAM proteins function as co-receptors for lymphocyte activation and/or adhesion and mediate tyrosine phosphorylation signals. SLAM receptor expression is mainly restricted to immune cells. SLAM, also known as CD150, is a transmembrane glycoprotein that is upregulated on activated B cells and T cells but downregulated on Th2 polarized cells. SLAM ligation promotes the activation of Th0/Th1 cells, B cells, eosinophils, mast cell, and macrophages. SLAM also functions as a cellular entry receptor for measles virus.