Description: The 53-7.3 monoclonal antibody reacts with mouse CD5, a 67 kDa protein expressed by a majority of thymocytes, mature T cells and a subset of B cells. The expression of CD5 by a small subset of B cells characterizes a developmentally and functionally distinct lineage of B cells called B-1 cells. CD5 is a counter-receptor for CD72 and plays a role in the T-B cell interaction.