Which of the following is not true about spleen?

Immature lymphocytes differentiate into antigen-sensitive lymphocytes in primary lymphoid organs (e.g., bone marrow and thymus). The spleen is a secondary lymphoid organ in which the antigens activate antigen-sensitive lymphocytes which then become effector cells. 

The spleen is a large bean-shaped organ. It mainly contains lymphocytes and phagocytes. It acts as a filter of the blood by trapping blood-borne microorganisms. The spleen also has a large reservoir of erythrocytes. The spleen is known as blood bank because it stores blood cells for an emergency situation like hemorrhagic shock.