CD45RA is a type I transmembrane glycoprotein. It is a specific splice variant of the transmembrane tyrosine phosphatase CD45. The CD45RA isoform is most highly expressed on resting/naive T cells, B cells, and monocytes. Like CD45, on these cells the intracellular domain of CD45RA is a tyrosine phosphatase that serves to regulate signal transduction event. In particular, it enhances both T cell receptor and B cell receptor signaling.