Measurement of the number of lymphocytes in a specified sample of blood which express both a relatively high amount of surface CD45RC antigen and surface CD4 antigen. D45RC, also known as the leukocyte common antigen, is the protein produced by the PTPRC (protein tyrosine phosphatase, receptor type, C) gene and has been shown to be an essential regulator of T- and B-cell antigen receptor signaling.