The white blood cells of the immune system derive from precursors in the bone marrow

The components of the immune system.

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The cells of the immune system originate in the bone marrow, where many of them also mature. They then migrate toguard the peripheral tissues, circulating in the blood and in a specialized system of vessels called the lymphatic system.

All the cellular elements of blood, including the red blood cells that transport oxygen, the platelets that trigger blood clotting in damaged tissues, and the white blood cells of the immune system, derive ultimately from the same progenitor or precursor cells the hematopoietic stem cells in the bone marrow. As these stem cells can give rise to all of the different types of blood cells, they are often known as pluripotent hematopoietic stem cells. Initially, they give rise to stem cells of more limited potential, which are the immediate progenitors of red blood cells, platelets, and the two main categories of white blood cells. The different types of blood cell and their lineage relationships are summarized in Fig. 1.3. We shall be concerned here with all the cells derived from the common lymphoid progenitor and the myeloid progenitor, apart from the megakaryocytes and red blood cells.

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