Final answer:
Cells of the immune system originate from hematopoietic stem cells in the bone marrow, which differentiate into various immune cells such as B cells, T cells, and macrophages.
Step-by-step explanation:
Cells of the immune system derive from hematopoietic precursors in the bone marrow. Hematopoietic stem cells within the bone marrow are stimulated by cytokines to differentiate into diverse immune cells. Notably, B cell maturation takes place within the bone marrow itself, whereas immature T cells are transported to the thymus for their maturation. The thymus plays a crucial role in ensuring that T cells which recognize self-antigens are eliminated, thus preventing autoimmune responses.
Moreover, cells like dendritic cells, macrophages, and lymphocytes (which include T cells, B cells, and natural killer cells) are all derived from hematopoietic stem cells through different pathways. Hematopoietic stem cells are not only responsible for immune cells but also for all the cellular components of the blood, like red blood cells and platelets.