Lymphoid organs of the body Lymphoid organs : These are the organs where origin and or maturation and proliferation of lymphocytes occur. (a) The primary lymphoid organs are bone marrow and thymus where immature lymphocytes differentiate into sensitive lymphocytes. (1) Bone marrow : Bone marrow present in bones is the main lymphoid organ where all bllod cells including lyphocytes are produced. Bone marrow provides the microenvironment for the development and maturationof B lymphocytes. (2) Thymus : Thymus is a lobeled organ located near the heart and beneath the breast bone. Thymus is quite large at the time of birth but keeps reducing withg age and by the time puberty is attained ity atrophies to a very small size. It provides microenvironment for the development and maturation of T- lymphocytes. (b) Secondary lymphoid organs : The lymphocytes after maturatio...