PATHOLOGY

Detailed explanation-1: -Primary lymphoid organs: These organs include the bone marrow and the thymus. They create special immune system cells called lymphocytes. Secondary lymphoid organs: These organs include the lymph nodes, the spleen, the tonsils and certain tissue in various mucous membrane layers in the body (for instance in the bowel).

Detailed explanation-2: -Since the function of the lymphoid organs is to filter and trap invading pathogens and present them to immune competent cells, the high levels of viremia seen following primary infection presumably lead to an efficient infection of the lymphoid tissue with HIV or SIV.

Detailed explanation-3: -There are three major types of lymphoid cells: B-cells, T-cells, and Natural Killer (NK) cells.

Detailed explanation-4: -Central lymphoid organs are requisite for the development of the lymphoid and, therefore, the immune system. These include the thymus, bone marrow, and bursa of Fabricus. Central lymphoid organs are also termed primary lymphoid organs. They are sites where lymphocytes are generated.