CD48 is a 40-47 kD GPI-anchored membrane protein, also known as Blast-1 and HuLy-m3. It is a member of the CD2 family that contains 2 IgSF domains and is widely expressed on both resting and activated hematopoietic cells with the exception of granulocytes, platelets, and erythrocytes. CD48 binds to CD2 at a considerably (>100-fold) lower affinity than CD58. It is thought to contribute to T cell activation. The cytoplasmic tail of CD48 has been shown to bind to the kinases Lck and Fyn.