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This activity provides brief descriptions of cells derived from lymphoid progenitor cells in bone marrow.

Tab Title: Natural Killer Cells

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Natural killer (NK) cells are lymphocytes attack cells that have defective markers of "self." Each of us has a unique set of major histocompatibility complex (MHC) antigens on all of our cells that identify us as unique individuals (except identical twins, who have the same set of MHC antigens). If the MHC antigens on some of our cells are absent because of transformation to cancer or infection by certain virsuses, NK cells will attack those cells and destroy them. NK cells are armed with secretory granules with potent chemicals that can destroy cells. Both NK cells and cytotoxic T-cells and attack and kill abnormal cells, but NK cells attack cells that are missing the appropriate MHC identification, while cytotoxic T-lymphocytes attack cells displaying fragments of a specific antigen.

Tab Title: Helper T-cells

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Helper T cells, or Th cells, coordinate immune responses by communicating with other cells. Helper T-lymphocytes play a key role in orchestrating the adaptive immune response to a foreign agent. Keep in mind that there are many helper T-cells, each with a receptor for a specific epitope (foreign molecular shape). If a T-helper cell comes into contact with a dendritic cell that is displaying (presenting) an antigen or epitope that it recognizes, the helper T-cell will become activated, and it will replicate to create clones of itself, and these will secrete cytokines that activate cytotoxic T-lymphocytes and/or B-lymphocytes. There are two types of helper T-cells -

• Th1 helper cells promote an inflammatory response and activate cytotoxic T-lymphoyctes that will attack foreign cells with the foreign antigen
• Th2 helper cells actibvate B-lymphocytes, which transform into plasma cells that produce antibodies againt the foreign antigen

Tab Title: Cytotoxic T-cells

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Cytotoxic T-cells look for antigen fragments bound to MHC molecules, and if the MHC molecule is displaying fragments that match the receptors for a given cytotoxic T-cell, the T-cell will attack that cell.

Tab Title: Plasma Cell

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When activated, B-lymphocytes transform into plasma cells, which synthesize antibodies specific for the antigen identified on the foreign agent.