SLAMF1 belongs to the immunoglobulin gene superfamily and is involved in T-cell stimulation. This protein 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. High-affinity for self-ligand is important in bidirectional T-cell to B-cell stimulation. SLAM-induced signal-transduction events in T-lymphocytes are different from those in B-cells. Two modes of SLAM signaling are likely to exist: one in which the inhibitor SH2D1A acts as a negative regulator and another in which protein-tyrosine phosphatase 2C (PTPN11)-dependent signal transduction operates. Recombinant human SLAMF1 protein, fused to His-tag at N-terminus, was expressed in E.coli.