Correct Option: D

Lymphocytes constitute 20- 40% of the body’s white blood cells and 99% of the cells in the lymph. Lymphocytes continually circulate in the blood and lymph and are capable of migrating into the tissue spaces and lymphoid organs, thereby integrating the immune system to a high degree. Lymphocytes interact with foreign antigens in lymph nodes. Lymph nodes are the sites where immune responses are mounted to antigens in lymph. They are encapsulated bean shaped structures containing a reticular network packed with lymphocytes, macrophages, dendritic cells. Lymph nodes are the first organized lymphoid structure to encounter antigens that enter the tissue spaces.