(a) Highlight the role of thymus as a lymphoid organ.
(b) Name the cells that are released from the above mentioned gland. Mention how they help in immunity.

Explanation

(a) Thymus is a primary lymphoid organ located just above the heart. It is the largest sized at puberty but atrophies with age. It secretes thymosine hormone which helps in maturation and differentiation of T-lymphocytes.
(b) T-lymphocytes are antigen-specific immune cells released from thymus gland. T-lymphocytes, when stimulated, form a clone of 3 types of cells : Helper-T cells (which stimulate B-lymphocytes to produce antibodies), Killer T-cells (which kill the pathogenic micro-organisms) and suppressor-T cells (which suppress own immune system not to attack own cells).