Where is it? --一一--一一-0-一一--一 -一---一--一一-0-一--一一--- Primary lymphoid Secondary lymphoid organs organs Tonsils and adenoids Thymus H 必 Spleen Peyer's patches Appendix Bone marrow Lymph nodes Lymphatic vesse CEC 2001 Artificial Immune SystemsCEC 2001 Artificial Immune Systems Where is it? Lymphatic vessels Lymph nodes Thymus Spleen Tonsils and adenoids Bone marrow Appendix Peyer’s patches Primary lymphoid organs Secondary lymphoid organs