Lymphocyte

Video 17 White Cell Lymphocytes

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• published: 14 Jan 2014
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17) White Cell Lymphocytes Lymphocytes are a sub-group of white cells (leukocytes) that make up the core of our immune system, protecting the body from an endless stream of antigens. There are three types of lymphocytes: B-cells, T-cells and natural killer cells. Natural killer cells play a primary role in our innate immune system, but also have a role in our adaptive immune system. Natural killer cells are not antigen specific, meaning they do not rely on surface antibody receptors to activate their function. B-cells and T-cells on the other hand are antigen specific and utilize surface receptors in activating their functions. These surface receptors are protein molecules commonly know as antibodies and formally known as immunoglobulins. B-cells and T-cells are primarily associated with our adaptive immune system and work together in dynamic ways to detect and eliminate an almost endless number of antigens. B-cells are found circulating in the blood and are also stored in the lymph system. The surface of B-cells are covered with antibody receptors precisely matched to specific antigens. Consequently, there are a countless number of unique B-cells found in our blood and lymph systems, each ready to respond if it encounters an antigen that matches its own surface receptor antibodies. T-cells are found in the thymus where they are stored as immature lymphocytes. When called into action the immature lymphocyctes differentiate to match the antigen of the activing cell and are then released into the lymph fluid and bloodstream. There are two primary types of mature T-cells: cytotoxic T-cells and helper T-cells. When an antigen penetrates the body and is detected by a matching B-cell, the B-cell sets off a chain reaction in the immune system. The B-cell will ingest the antigen, break it apart and then present a piece of the antigen onto a surface marker of the B-cell. The B-cell must then be activated by a helper T-cell to begin producing antigen specific antibodies. Phagocytic white cells, such as dendritic cells are also involved as they too will bind to the antigen, ingest it, break it down and also present a piece on the surface of the dendritic cell. Meanwhile, chemical signals from the B-cell flow into the lymphatic system and to the thymus, where they trigger the release of helper T-cells, which migrate to the point of infection. When the helper T-cells come into contact with the dendritic cell it will bind to the antigen presenting marker on the dendritic cell. This activates the helper T-cell, which then divides into both a memory cell and effector cells. The memory cell remains circulating in the body and ready for any future attacks by this specific antigen. The effector cells migrate to the B-cell where they bind to the matching antigen presenting receptor. This process with the helper T-cell provides a safety check for the immune system to confirm the presence of the anitigen before triggering the alarm. Once this helper T-cell effector binds with the B-cell it activates the B-cell, which will begin dividing. When the B-cell divides it will create factory cells and memory cells. The factory B-cells produce matching antibody molecules that are released into the blood stream, searching for and binding to that specific antigen. The memory cells retain the information about the specific antigen and circulate in the blood providing defense for the future. At the point of infection, B-cells with matching surface receptors and free floating antibody molecules will bind to the antigen, helping to prevent the antigen from binding to cells in the body and thereby depriving the microbe of the food it needs to produce energy to divide and multiply. Phagocytic white cells then assist by ingesting and eliminating the antigen. Cytotoxic T-cells come into play by targeting the infected human cell. By releasing toxic protiens the cytotoxic T-cell causes the ultimate destruction and death of the infected cell. Cytotoxic T-cells also target defect human cells, such as cancer cells.