title: Letter:"Null cells" in systemic lupus erythematosus.
mesh_terms: D006801:Humans; D007958:Leukocyte Count; D008180:Lupus Erythematosus, Systemic / Q000097:blood*; D008214:Lymphocytes / Q000166:cytology*; D013601:T-Lymphocytes / Q000166:cytology