<prompt> Leukocyte common antigen is:CD 45CD 20CD 19CD 41  <response>: Ans. a CD 45Ref: Robbins 9thpg 590; 8thpg 600; Wintrobes 12thpg 2522CD 45Found in all hematopoietic cells except erythrocytes.CD45 plays an essential role in lymphocyte activation.Peripheral blood naive T cells are CD45RA, whereas memory activated T cells are CD45RO 