Science

  • Issue 107 / September - October 2015



    Immunological Memory

    Omer Arifagaoglu

    When we hear the word "memory," brain cells generally come to mind. However, our lymph cells, which are generated from the immune system, also possess memories. Our brain is blessed with the ability to store everything it hears, sees, or touches in its memory. Just like the brain stores everything and this storage is not wiped out until death, our immune system's memory also lasts a lifetime.

    The most striking example of immune system memory is that we only catch certain microbial diseases once in our lives. For instance, in the past, a commonly observed skin disease called "Oriental sore" would heal by leaving a pit on the skin. When this infected the face, it would cause a permanent ugly mark. People aware of the situation would let the disease occur somewhere out of sight on a child's body. So, they would take a droplet of fluid from the infected tissue of a patient and apply it to a child's back. The sore would develop on the back of child and then heal. The reason this was effective is because the immune system would permanently store the Oriental sore microbes in its memory and would build up an immunity to the microbe.

    The elements of the immune system are created to recognize microbes, and the tissues of foreign plants, animals and even humans. The immune system is created to respond to these foreign substances. However, due to the immaturity of the system's recognition, the risk of developing a disease upon the initial entry of microbes to the body is very high.

    This is because the system does not sufficiently know the microbe. The way the immune system fights microbes is with blood cells called lymphocytes. Once lymphocytes are produced inside lymph nodes, they enter the blood stream, and then into the body's tissues. This way, they reach all over the body to scan for potentially harmful foreign cells. When a microbe enters the body, lymphocytes proliferate in higher numbers to join the fight against these microbes.

    There are two types of lymphocytes: T lymphocytes and B lymphocytes. T lymphocytes are white blood cells in charge of direct encounters with microbes. B lymphocytes, however, kill microbes, via antibodies they synthesize. In other terms, while T lymphocytes kill the enemy via face-to-face combat, B lymphocytes resemble artillery soldiers, striking from afar.

    When a microbe enters the body, the lymphocytes specific to that kind of microbe enter the arena and start battling with the microbes. During this battle, strange things happen: certain T and B lymphocytes travel to the battle but return without participating in the fight. This is not an escape from war; these lymphocytes are tasked with gathering information and preparing the immune system for the future. These are called memory-B and memory-T lymphocytes.

    Memory cells reorganize their tools against microbes they recognize. For example, when they recognize a microbe, they generate a genetic "handcuff" that keeps the microbe from being effective. Lymphocytes that have never encountered a germ also produce "handcuffs"; however, there can be slight mismatches between the microbe parts and the handcuff. Memory cells are created solely to generate weapons to capture, disable, and destroy a specific microbe. These weapons are deadly enzymes and antibodies. Thus, the body regains immunity against a special microbe via a key-lock fit, which is called acquired immunity.

    Again, the difference between memory cells and normal cells is noticeable. B lymphocyte cells that have never met a microbe are in charge of producing antibodies called immunoglobulin M (IgM); because these antibodies are not tailored to the microbe, they are usually slow and ineffective. Memory B lymphocyte cells, however, synthesize special immunoglobulin G (IgG) antibodies that are suited to the dimensions (size and shape) of the germ; this makes it impossible for the microbes to develop a disease.

    These mechanisms are also utilized in vaccinations. Acquiring personal immunity happens through two ways. The first is the identification of a microbe during a disease, which is a risky method. If the body's resistance is low, the patient can endure great suffering ÔÇô or even die. If the body's cells defeats the microbe during the first fight, immunity is gained. Memory cells do not let the disease develop again. Certain illnesses like measles, smallpox, and mumps can only occur once.

    The second method of acquiring immunity is to provide the body with the microbe without permitting it to cause an illness. This is a vaccination. There are vaccinations for diseases like measles, typhoid fever, whooping cough, diphtheria, tetanus, tuberculosis, and hepatitis B. In vaccinations, the microbe is first treated chemically and this way its ability to infect is eliminated. Then, the disabled microbes are injected into the body; in other terms, the shapes and sizes of the germs are made available to the memory of the immune system.

    These mechanisms show us that humans do not only memorize with their brains. Lymphocyte cells are created in a fashion to memorize things permanently.

    Another feature of the immune system is the ability to distinguish friends from foes. Lymphocytes cells go through training when babies are approaching their birth and during the first few months after birth. In this training, the cells are introduced to every tissue in the body. This operation takes place in the thymus and other organs related to the immune system. The thymus is an organ located at the upper region of lungs, on the trachea, and T lymphocytes obtain their diplomas from here. Other immune system organs like bone marrow and the liver are also in charge of B lymphocyte training. During this training, they learn two things:

    1 . To kill foreign microbes and defend the body

    2. Not to attack their own body and organs

    Humans sometimes can obtain diplomas without sufficient literacy from schools; however, no diploma can be obtained in these organs without properly learning how to fight germs. Our immune system functions perfectly.

    The immune system rejects blood, tissues, and organs of foreign origin by causing reactions and thus removes them. However, no reaction is developed against our own tissue or organs. With aging, the immune system becomes more sensitive towards our own tissues, thus increasing the risk of autoimmune diseases developing as we get older. Autoimmune diseases form as the result of our immune system targeting our own tissues and organs.

    Of course, we're more frequently damaged by outside microbes. Each encounter with a microbe means a war. In a war, both sides may suffer damage. Therefore, our immune system is equipped with suppressive T lymphocytes which prevent extensive fighting. Suppressive T lymphocytes prevent the overreaction of our immune system and are in charge of stopping any damage to the body.

    Here we might need to mention the relationship between cancer and the immune system. In fact, cancerous cells also form in healthy people. Members of the immune system, especially T lymphocytes, scan the body from head to toe to detect and eliminate cancer cells. A person constantly wins the fight against cancer without even realizing it. However, in persons of low body resistance, cancer may form by crossing the immune system's barriers. Aging reduces the ability to fight against cancer. Grief, sadness and similar psychological stresses are also significant factors in cancer development. All these intricate mechanisms show us that these systems are not just lucky incidents occurring on their own. These systems have been created to function perfectly. We are still living in an infantile age of understanding the wonders of our body's systems and organs. It ought to be hard to claim that such an amazing body formed itself, after random collisions of atoms and molecules.

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