The thymus and the precursors of antigen reactive cells.
D000818:Animals; D000941:Antigens; D001772:Blood Cell Count; D001853:Bone Marrow / Q000276:immunology*; D001854:Bone Marrow Cells; D002454:Cell Differentiation; D004912:Erythrocytes; D008214:Lymphocytes; D051379:Mice; D011830:Radiation Effects; D012756:Sheep; D013154:Spleen / Q000528:radiation effects; D013934:Thymectomy; D013950:Thymus Gland / Q000276:immunology*
D000941:Antigens