All are peripheral lymphoid organs except-

The immune system is organized into several special tissues, which are collectively termed lymphoid or immune tissues. The tissues that have evolved to a high degree of specificity of function are termed lymphoid organs. The lymphoid organs, based on their function, are classified into central (primary) and peripheral (secondary) lymphoid organs. - Central / Primary organs- The primary lymphoid organs include thymus and bone marrow. These are the organs in which precursor lymphocytes proliferate, develop, and differentiate from lymphoid stem cells to become immunologically competent cells. In mammals, T cells mature in thymus and B cells in fetal liver and bone marrow. - Peripheral/Secondary organs- Spleen, Lymph Node, MALT (GIT & Resp), Liver: These organs serve as the sites for interaction of mature lymphocytes with antigens.