Expressed on thymocytes, T cells, natural killer cells (NK), B cells, dendritic cells (DCs), macrophages, and hematopoietic stem cells (HSCs) and is involved in lymphocyte activation. In Crohn’s disease, an upregulation of SLAMF1 has been detected in monocytes and macrophages, and upregulation of SLAMF1 on T-cells was detected in rheumatoid arthritis. In contrast, in Chronic Lymphocytic Leukemia, it was found to be downregulated. The gene discussed is SLAMF1; the disease is B-cell chronic lymphocytic leukemia.