{"id":4299,"date":"2017-03-28T20:32:14","date_gmt":"2017-03-28T20:32:14","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/wm-biology2\/?post_type=chapter&#038;p=4299"},"modified":"2024-04-26T02:30:14","modified_gmt":"2024-04-26T02:30:14","slug":"natural-killer-cells","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/wm-biology2\/chapter\/natural-killer-cells\/","title":{"raw":"Natural Killer Cells","rendered":"Natural Killer Cells"},"content":{"raw":"<div class=\"textbox learning-objectives\">\r\n<h3>Learning Outcomes<\/h3>\r\n<ul>\r\n \t<li>Discuss natural killer cells<\/li>\r\n<\/ul>\r\n<\/div>\r\n\r\n[caption id=\"attachment_3000\" align=\"alignright\" width=\"300\"]<img class=\"wp-image-3000\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/02\/09165736\/Figure_42_01_05.jpg\" alt=\"Micrograph shows a round cell with a large nucleus.\" width=\"300\" height=\"300\" \/> Figure 1.\u00a0Lymphocytes, such as NK cells, are characterized by their large nuclei that actively absorb Wright stain and therefore appear dark colored under a microscope.[\/caption]\r\n\r\n<b>Lymphocytes<\/b> are leukocytes that are histologically identifiable by their large, darkly staining nuclei; they are small cells with very little cytoplasm, as shown in Figure 1. Infected cells are identified and destroyed by <b>natural killer (NK) cells<\/b>, lymphocytes that can kill cells infected with viruses or tumor cells (abnormal cells that uncontrollably divide and invade other tissue). T cells and B cells of the adaptive immune system also are classified as lymphocytes. <b>T cells<\/b> are lymphocytes that mature in the thymus gland, and <b>B cells<\/b> are lymphocytes that mature in the bone marrow. NK cells identify intracellular infections, especially from viruses, by the altered expression of <b>major histocompatibility class (MHC) I molecules<\/b> on the surface of infected cells. MHC I molecules are proteins on the surfaces of all nucleated cells, thus they are scarce on red blood cells and platelets which are non-nucleated. The function of MHC I molecules is to display fragments of proteins from the infectious agents within the cell to T-cells; healthy cells will be ignored, while \u201cnon-self\u201d or foreign proteins will be attacked by the immune system. MHC II molecules are found mainly on cells containing antigens (\u201cnon-self proteins\u201d) and on lymphocytes. <b>MHC II molecules<\/b> interact with helper T-cells to trigger the appropriate immune response, which may include the inflammatory response.\r\n\r\nAn infected cell (or a tumor cell) is usually incapable of synthesizing and displaying MHC I molecules appropriately. The metabolic resources of cells infected by some viruses produce proteins that interfere with MHC I processing and\/or trafficking to the cell surface. The reduced MHC I on host cells varies from virus to virus and results from active inhibitors being produced by the viruses. This process can deplete host MHC I molecules on the cell surface, which NK cells detect as \u201cunhealthy\u201d or \u201cabnormal\u201d while searching for cellular MHC I molecules. Similarly, the dramatically altered gene expression of tumor cells leads to expression of extremely deformed or absent MHC I molecules that also signal \u201cunhealthy\u201d or \u201cabnormal.\u201d\r\n\r\nNK cells are always active; an interaction with normal, intact MHC I molecules on a healthy cell disables the killing sequence, and the NK cell moves on. After the NK cell detects an infected or tumor cell, its cytoplasm secretes granules comprised of <b>perforin<\/b>, a destructive protein that creates a pore in the target cell. Granzymes are released along with the perforin in the immunological synapse. A <b>granzyme<\/b> is a protease that digests cellular proteins and induces the target cell to undergo programmed cell death, or apoptosis. Phagocytic cells then digest the cell debris left behind. NK cells are constantly patrolling the body and are an effective mechanism for controlling potential infections and preventing cancer progression.\r\n<div class=\"textbox tryit\">\r\n<h3>Try It<\/h3>\r\nhttps:\/\/assess.lumenlearning.com\/practice\/1f27b0a2-3d59-4b58-8616-eb50bcda75fa\r\n<\/div>","rendered":"<div class=\"textbox learning-objectives\">\n<h3>Learning Outcomes<\/h3>\n<ul>\n<li>Discuss natural killer cells<\/li>\n<\/ul>\n<\/div>\n<div id=\"attachment_3000\" style=\"width: 310px\" class=\"wp-caption alignright\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-3000\" class=\"wp-image-3000\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/02\/09165736\/Figure_42_01_05.jpg\" alt=\"Micrograph shows a round cell with a large nucleus.\" width=\"300\" height=\"300\" \/><\/p>\n<p id=\"caption-attachment-3000\" class=\"wp-caption-text\">Figure 1.\u00a0Lymphocytes, such as NK cells, are characterized by their large nuclei that actively absorb Wright stain and therefore appear dark colored under a microscope.<\/p>\n<\/div>\n<p><b>Lymphocytes<\/b> are leukocytes that are histologically identifiable by their large, darkly staining nuclei; they are small cells with very little cytoplasm, as shown in Figure 1. Infected cells are identified and destroyed by <b>natural killer (NK) cells<\/b>, lymphocytes that can kill cells infected with viruses or tumor cells (abnormal cells that uncontrollably divide and invade other tissue). T cells and B cells of the adaptive immune system also are classified as lymphocytes. <b>T cells<\/b> are lymphocytes that mature in the thymus gland, and <b>B cells<\/b> are lymphocytes that mature in the bone marrow. NK cells identify intracellular infections, especially from viruses, by the altered expression of <b>major histocompatibility class (MHC) I molecules<\/b> on the surface of infected cells. MHC I molecules are proteins on the surfaces of all nucleated cells, thus they are scarce on red blood cells and platelets which are non-nucleated. The function of MHC I molecules is to display fragments of proteins from the infectious agents within the cell to T-cells; healthy cells will be ignored, while \u201cnon-self\u201d or foreign proteins will be attacked by the immune system. MHC II molecules are found mainly on cells containing antigens (\u201cnon-self proteins\u201d) and on lymphocytes. <b>MHC II molecules<\/b> interact with helper T-cells to trigger the appropriate immune response, which may include the inflammatory response.<\/p>\n<p>An infected cell (or a tumor cell) is usually incapable of synthesizing and displaying MHC I molecules appropriately. The metabolic resources of cells infected by some viruses produce proteins that interfere with MHC I processing and\/or trafficking to the cell surface. The reduced MHC I on host cells varies from virus to virus and results from active inhibitors being produced by the viruses. This process can deplete host MHC I molecules on the cell surface, which NK cells detect as \u201cunhealthy\u201d or \u201cabnormal\u201d while searching for cellular MHC I molecules. Similarly, the dramatically altered gene expression of tumor cells leads to expression of extremely deformed or absent MHC I molecules that also signal \u201cunhealthy\u201d or \u201cabnormal.\u201d<\/p>\n<p>NK cells are always active; an interaction with normal, intact MHC I molecules on a healthy cell disables the killing sequence, and the NK cell moves on. After the NK cell detects an infected or tumor cell, its cytoplasm secretes granules comprised of <b>perforin<\/b>, a destructive protein that creates a pore in the target cell. Granzymes are released along with the perforin in the immunological synapse. A <b>granzyme<\/b> is a protease that digests cellular proteins and induces the target cell to undergo programmed cell death, or apoptosis. Phagocytic cells then digest the cell debris left behind. NK cells are constantly patrolling the body and are an effective mechanism for controlling potential infections and preventing cancer progression.<\/p>\n<div class=\"textbox tryit\">\n<h3>Try It<\/h3>\n<p>\t<iframe id=\"assessment_practice_1f27b0a2-3d59-4b58-8616-eb50bcda75fa\" class=\"resizable\" src=\"https:\/\/assess.lumenlearning.com\/practice\/1f27b0a2-3d59-4b58-8616-eb50bcda75fa?iframe_resize_id=assessment_practice_id_1f27b0a2-3d59-4b58-8616-eb50bcda75fa\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:300px;\"><br \/>\n\t<\/iframe>\n<\/div>\n\n\t\t\t <section class=\"citations-section\" role=\"contentinfo\">\n\t\t\t <h3>Candela Citations<\/h3>\n\t\t\t\t\t <div>\n\t\t\t\t\t\t <div id=\"citation-list-4299\">\n\t\t\t\t\t\t\t <div class=\"licensing\"><div class=\"license-attribution-dropdown-subheading\">CC licensed content, Shared previously<\/div><ul class=\"citation-list\"><li>Biology 2e. <strong>Provided by<\/strong>: OpenStax. <strong>Located at<\/strong>: <a target=\"_blank\" href=\"http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8\">http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8<\/a>. <strong>License<\/strong>: <em><a target=\"_blank\" rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">CC BY: Attribution<\/a><\/em>. <strong>License Terms<\/strong>: Access for free at https:\/\/openstax.org\/books\/biology-2e\/pages\/1-introduction<\/li><\/ul><\/div>\n\t\t\t\t\t\t <\/div>\n\t\t\t\t\t <\/div>\n\t\t\t <\/section>","protected":false},"author":17,"menu_order":5,"template":"","meta":{"_candela_citation":"[{\"type\":\"cc\",\"description\":\"Biology 2e\",\"author\":\"\",\"organization\":\"OpenStax\",\"url\":\"http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8\",\"project\":\"\",\"license\":\"cc-by\",\"license_terms\":\"Access for free at https:\/\/openstax.org\/books\/biology-2e\/pages\/1-introduction\"}]","CANDELA_OUTCOMES_GUID":"8c6d4355-9c8d-495c-8e2a-2dc186099f9c, ff1435f7-a384-46c0-8b5a-c36fdcecee1e","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-4299","chapter","type-chapter","status-publish","hentry"],"part":4294,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/4299","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/users\/17"}],"version-history":[{"count":7,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/4299\/revisions"}],"predecessor-version":[{"id":8639,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/4299\/revisions\/8639"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/parts\/4294"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/4299\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/media?parent=4299"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapter-type?post=4299"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/contributor?post=4299"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/license?post=4299"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}