CELLS OF THE IMMUNE SYSTEM

CELLS OF THE IMMUNE SYSTEM
The immune system is a complex network of cells and organs that work together to defend the body against foreign substances (antigens) such as bacteria, viruses or tumor cells. It is separated into two branches: humoral immunity and cellular immunity. The immune cells that make up our immune system consist of several different types of white blood cells or leukocytes that work together to keep us healthy. They circulate through the body between the organs and nodes via the lymphatic system. Most however are stored in the lymphoid organs until needed.
Immune Cells Ancestor:
All immune cells begin as immature stem cells in the bone marrow. They respond to different cytokines and other chemical signals to grow into specific immune cell types. All cells of the immune system originate from a pluripotent hematopoietic stem cell in the bone marrow, which gives rise to two major lineages, a myeloid progenitor cell and a lymphoid progenitor cell. These two progenitors give rise to the myeloid cells (monocytes, macrophages, dendritic cells, megakaryocytes and granulocytes (eosinophils, neutrophils, basophils) and lymphoid cells (T cells, B cells and natural killer (NK) cells), respectively.

PHAGOCYTES
This is a group of immune cells specialized in finding and "eating" bacteria, viruses, and dead or injured body cells. There are three main types, the granulocyte, the macrophage, and the dendritic cell. Phagocytes are called "professional" or "non-professional" depending on how effective they are at phagocytosis. The professional phagocytes include many types of white blood cells (such as neutrophils, monocytes, macrophages, mast cells, and dendritic cells). The main difference between professional and non-professional phagocytes is that the professional phagocytes have receptors on their surfaces that can detect antigens.