<P> The cells of the adaptive immune system are T and B lymphocytes ; lymphocytes are a subset of leukocyte . B cells and T cells are the major types of lymphocytes . The human body has about 2 trillion lymphocytes , constituting 20 -- 40 % of white blood cells ( WBCs ) ; their total mass is about the same as the brain or liver . The peripheral blood contains 2 % of circulating lymphocytes ; the rest move within the tissues and lymphatic system . </P>
where are the cells of the adaptive immune system found
The peripheral blood the tissues lymphatic system