The SLAM family of receptors is composed of six members named SLAM (CD150); 2B4 (CD244); Ly-9 (CD229); CD84; natural killer, T and B cell antigen (NTB-A; Ly108 in the mouse. Most, if not all,immune cell types express more than one SLAM family receptor. All six SLAM-related genes are located within a 400–500 kilobase (kb) genomic segment on chromosome 1 in humans and mice. This feature implies that the genes that encode the SLAM family were created by serial gene duplication.