I Immune organs center immune organs Concept places where immunocytes genesis, develop, differentiate and mature Composition: bone marrow, thymus and bursa of Fabricius(which is one of Avian character) peripheral immune organs Concept: places where mature T, b lymphocytes resident and contact with antigens and carry out Immune response composition: lymph node, spleen, mucosal-associated lymphoid tissue1 Immune organs center immune organs concept：places where immunocytes genesis, develop, differentiate and mature composition ： bone marrow, thymus and bursa of Fabricius (which is one of Avian character) peripheral immune organs concept ： places where mature T, B lymphocytes resident and contact with antigens and carry out immune response composition：lymph node, spleen, mucosal-associated lymphoid tissue