AUSTRALIAN NATUROPATHIC NETWORK
The ability of the body to defend itself against specific invading agents such as bacteria, toxins, viruses and foreign tissues is called immunity. Immunity is said to have a memory for most invading agents encountered before, because a second encounter with the same agent prompts a rapid and vigorous response. This is called immunological memory which leads to a perception that an individual is immune to a particular agent.
There are two types of immune response: cell-mediated (CMI) associated with specialised blood cells called T-cells, and antibody mediated associated with specialised blood cells called B-cells. Both immune responses act on substances called antigens.
Antigens are defined by their ability to provoke an immune response (immunogenicity). Immunogenicity causes the proliferation of specific T-cells or the production of particular antibodies by B-cells. Antigens also said to have reactivity: the ability to react specifically with T-cells, or antibodies.
T-cells are produced in the bone marrow and migrate to the thymus to mature. They then reside in lymphatic tissue until threatened by a foreign antigen when they move out on a ‘seek and destroy’ mission.
There are four main types of T-cells:
Helper T-cells – which assist in both CMI and AMI. They secrete lymphokines (cytokines) which are hormones that stimulate other cells in the body to resist invading antibodies. They display the protein CD4 on their surface;
Killer T-cells – which kill antigens directly once stimulated by agents released by the helper T-cells. They display the protein CD8 on their surface;
Suppressor T-cells – are a controversial cell that is believed to dampen or suppress the immune response; and
Memory T-cells - which recognise the original invading antigen. When the antigen returns thousands of memory cells are available to initiate a far swifter reaction than occurred during the first invasion.
B-cells are produced and mature in the bone marrow. When the body is invaded by a foreign antigen they do not migrate like T-cells rather they stay put in lymphatic tissue, the spleen, lymph nodes, and the GIT. When activated they differentiate into plasma cells that secrete antibodies into lymph and blood. Helper T-cells amplify antibody production. The antibodies circulate the cardiovascular and lymphatic systems to reach the site of infection.
B-cells that are activated but do not differentiate into plasma cells remain as memory B-cells, ready to respond more rapidly and forcefully should the same antigen reappear at a future time.
In summary of immunological memory, during the first attack by a specific invading agent, only a handful of cells have the ability to recognise the antigen. This is called the primary response. During the attack thousands of memory T-cells and memory B-cells are formed. When the same antigen launches another attack weeks, years or months later, memory cells, developed during the initial invasion, spring swiftly into action, and their sheer volume aids in the rapid elimination of the antigen. This accelerated response is called a secondary response. Antibodies produced in the secondary response have a higher affinity for the antigen than those produced in the primary response
Memory cells may last for decades, every time the same antigen is encountered there is a rapid proliferation of memory cells. The concept of Immunisation is based on immunological memory. The memory of the immune system is a key benefit of being exposed to pathogens as a child. In theory, exposure to antigens early on in life will reduce the risk of the same antigen causing illness later in life.
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