Cells and Organs of the Immune System

The immune system is a system of cells, organs and their soluble products that recognises, attacks and destroys any sort of threatening entity. The cells of the immune system must be capable of distinguishing self from non-self and, furthermore, discriminating between non-self molecules which are harmful or innocuous. The cells of the innate and adaptive immune response normally circulate in the blood and lymph, and are also scattered throughout tissues and lymphoid organs. Most immune system cells arise from hematopoietic stem cells (HSCs) in the fetal liver and postnatal bone marrow. HSCs are pluripotent cells, that is, they have the potential to produce all blood cell types. Myeloid cells are the front-line attacking cells during an immune response. Lymphoid organs are scattered throughout the body and are mainly concerned with the growth and deployment of lymphocytes.