title: Letter: When is a null cell null?
mesh_terms: D001402:B-Lymphocytes / Q000276:immunology*; D003601:Cytotoxicity Tests, Immunologic; D006801:Humans; D008218:Lymphocytosis / Q000276:immunology*; D011947:Receptors, Antigen, B-Cell / Q000032:analysis; D013601:T-Lymphocytes / Q000276:immunology*
chemical_list: D011947:Receptors, Antigen, B-Cell