ANATOMY

Detailed explanation-1: -Although the brain is still seen as immunologically unique-its barriers prevent immune cells from coming and going at will-it’s clear that the brain and immune system constantly interact, he adds (see ‘The brain’s immune defences’).

Detailed explanation-2: -A brain is not involved in elicitation of immune response but regulates the function of the whole body.

Detailed explanation-3: -Microglia and perivascular macrophages are the only resident immune cells of the brain parenchyma (Goldmann et al., 2016).

Detailed explanation-4: -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).