candidate: ( Revise in light of new research ) This is now an open question ; also , the different dendritic cell lineages may have different ‘ tasks ’ and stay in different ‘ locations . ’ T and B lymphocytes are indistinguishable histologically（that is , under a light microscope they can not be told apart.）Indeed , the inactive B and T cells are so featureless with few cytoplasmic organelles and mostly inactive chromatin that until the 1960s textbooks could describe these cells , now the central focus of immunology , as having no known function !