Major Organs of the Immune System;
A. Thymus: The thymus is an organ located in the upper chest. Immature lymphocytes leave the bone marrow and find their way to the thymus where they are “educated” to become mature T-lymphocytes.
B. Liver: The liver is the major organ responsible for synthesizing proteins of the complement system. In addition, it contains large numbers of phagocytic cells which ingest bacteria in the blood as it passes through the liver.
C. Bone Marrow: The bone marrow is the location where all cells of the immune system begin their development from primitive stem cells.
D. Tonsils: Tonsils are collections of lymphocytes in the throat.
E. Lymph Nodes: Lymph nodes are collections of B-lymphocytes and T-lymphocytes throughout the body. Cells congregate in lymph nodes to communicate with each other.
F. Spleen: The spleen is a collection of T-lymphocytes, B-lymphocytes and monocytes. It serves to filter the blood and provides a site for organisms and cells of the immune system to interact.
G. Blood: Blood is the circulatory system that carries cells and proteins of the immune system from one part of the body to another.
Cells of the Immune System
A. Bone marrow: The site in the body where most of the cells of the immune system are produced as immature or stem cells.
B. Stem cells: These cells have the potential to differentiate and mature into the different cells of the immune system.
C. Thymus: An organ located in the chest which instructs immature lymphocytes to become mature T-lymphocytes.
D. B-Cells: These lymphocytes arise in the bone marrow and differentiate into plasma cells which in turn produce immunoglobulins (antibodies).
E. Cytotoxic T-cells: These lymphocytes mature in the thymus and are responsible for killing infected cells.
F. Helper T-cells: These specialized lymphocytes “help” other T-cells and B-cells to perform their functions.
G. Plasma Cells: These cells develop from B-cells and are the cells that make immunoglobulin for the serum and the secretions.
H. Immunoglobulins: These highly specialized protein molecules, also known as antibodies, fit foreign antigens, such as polio, like a lock and key. Their variety is so extensive that they can be produced to match all possible microorganisms in our environment.
I. Neutrophils (Polymorphonuclear PMN Cell): A type of cell found in the blood stream that rapidly ingests microorganisms and kills them.
J. Monocytes: A type of phagocytic cell found in the blood stream which develops into a macrophage when it migrates to tissues.
K. Red Blood Cells: The cells in the blood stream which carry oxygen from the lungs to the tissues.
L. Platelets: Small cells in the blood stream which are important in blood clotting.
M. Dendritic Cells: Important cells in presenting antigen to immune system cells.
Components of the Immune System
Each major component of the immune system will be discussed separately below. Immune deficiencies can affect a single component or multiple components. The manifestations of immune deficiencies can be a single type of infection or a more global susceptibility to infection. Because of the many interactions between the cells and proteins of the immune system, some immune deficiencies can be associated with a very limited range of infections. For these immune deficiencies, there are other elements that “take up the slack” and can compensate at least partly for the missing piece. In other cases, the ability to defend against infection is very weak over all and the person may have significant problems with infections.
The cells of the immune system can be categorized as lymphocytes (T-cells, B-cells and NK cells), neutrophils, and monocytes/macrophages. These are all types of white blood cells. The major proteins of the immune system are predominantly signaling proteins (often called cytokines), antibodies, and complement proteins.
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