SLAM, a novel glycoprotein of 37kDa, designated SLAM (Signaling Lymphocyte Activation Molecule) or CDw150, belongs to the immunoglobulin gene superfamily and is involved in T cell stimulation. SLAM is constitutively expressed on peripheral blood memory T cells, T cell clones, immature thymocytes, and a proportion of B cells, and is rapidly induced on naive T cells after activation. Activated B cells express the membrane bound form of SLAM and the soluble and cytoplasmic isoforms of SLAM, ａ