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Page 2
Components of the Immune System
The soluble components consist of complement, cytokines and antibodies. Complement is a group of proteins found in blood that works with antibodies to kill bacteria. When activated, complement coats antigenic particles that identify them for ingestion by phagocytes. Complement can also break down cells by lysis (rupture of their cell membranes). Cytokines are proteins secreted by monocytes and lymphocytes in response to interaction with an antigen. Cytokines perform essential roles in communication among immune cells. Antibodies are secreted by B-cells and are an essential part of the learned response to antigen stimulus. The major histocompatability complex (MHC) is a group of molecules that are important in helping the body to distinguish self from non-self. Its synonym is human leukocyte antigen, which implies that it is a cell surface structure with antigenic properties. Each person has a unique MHC. There are two types of MHC; Class 1 molecules are found in all cells with a nucleus, while Class 2 molecules are found in antigen presenting cells, B-cells, and activated T-cells. The parts of the immune system can also be classified as to whether they are innate or acquired. Innate components are present at birth and respond to an antigenic stimulus in a similar manner; the recognition of antigens does not vary from person to person. Examples of innate components are macrophages, neutrophils and complement. Cytokines themselves are innate, but their secretion depends on a learned response. Acquired immunity is a learned response that depends upon the specific type of antigen encountered. Because of this encounter, specialized antibody (humoral) or lymphocyte (cell-mediated) responses are developed. The immune system functions within the lymphatic system that extends throughout the body. Lymph, a fluid rich in white blood cells, flows through lymphatic vessels. Lymph nodes, which contain tightly packed lymphocytes, are located at strategic places in the body. These lymph nodes serve as sentinels during periods of infection and often during cancer spread. Since they serve to filter, attack, and destroy harmful organisms, a swollen lymph node can indicate to the physician that an active infection is taking place. Other bodily organs can also play a role in the immune response. In next week's paper, I will discuss some details of the working of the immune system.
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