The immune response PHYSICAL AND Non-specific (innate) CHEMICAL BARRIERS immune system • Physical barriers include the skin and the mucous membranes of the airways, guts, NATURAL KILLER Includes chemical and physical barriers and urinary and reproductive systems. (NK) CELLS (the first line of defence) and responses • Chemical barriers include hydrochloric NK cells kill pathogen- such as inflammation (the second line acid secreted by the stomach lining. infected cells and cancer of defence). Its effects are rapid, short- cells. They also release chemicals called cytokines, lived and non-specific. Found in all Mast cell which alert and attract multicellular organisms. Cells involved in allergic responses, releasing other immune cells. histamine and other inflammatory molecules. Mast cells sit within skin and mucosal tissues. INFLAMMATION IF BREACHED COMPLEMENT Invading microbes trigger A set of around 30 proteins in inflammation. This involves an the blood plasma that can be increase in blood flow to the activated by the presence of affected part of the body, which microbes or antibody–antigen leads to swelling, pain and an complexes. Complement can increase in temperature. Mast destroy pathogens and activate Basophil cells and basophils are involved phagocytic cells. Cells involved in allergic and inflammatory responses. Basophils release histamine in inflammation. like mast cells, but unlike mast cells they circulate in the blood. LEUKOCYTES PHAGOCYTOSIS READ MORE Made in the bone marrow, White blood cells including dendritic cells, macrophages Big Picture is a free post- leukocytes, or white blood cells, are and granulocytes such as eosinophils and neutrophils 16 magazine for teachers an important part of the immune engulf (or phagocytose) microbes or cells that are infected, that explores issues around system. There are two main types: damaged or dying. They enclose the particle or cell with biology. For more, go to granulocytes, which have granular a phagosome and then break down the contents with bigpictureeducation.com cytoplasm and a lobed nucleus, and hydrolytic enzymes. Some cells then become antigen- /immune agranulocytes, which have smooth presenting cells (APCs), which present the digested IMMUNE SYSTEM cytoplasm and a non-lobed nucleus. remains to other immune cells. ISSUE SPRING BRINGING CUTTINGEDGE SCIENCE INTO THE CLASSROOM Leukocytes include mast cells, Neutrophil basophils, macrophages, dendritic Fast-acting phagocytes that flock Eosinophil to the site of inflammation. cells, neutrophils, eosinophils, Phagocytes that also produce enzymes to counteract the inflammatory B cells and T cells. molecules released by mast cells. ALL SYSTEMS GO! Inside your hard-working immune system Dendritic cell Macrophage Phagocytic APCs with an important role in alerting T cells to new APCs that destroy foreign substances pathogens. by phagocytosis (engulfing them) and activate other immune cells. APC with specific antigen binds ANTIGEN PRESENTATION T cell Specific (adaptive) Named after the thymus, Antigen-presenting cells (APCs) break the organ where T cells mature. T cells have a immune system up invading or non-self particles and protein called the T cell receptor on cells and display parts of them – their surface. The third line of defence antigens – for other immune cells to against invading pathogens. In inspect. They include macrophages vertebrates, it provides long- and dendritic cells. lasting protection against specific pathogens or foreign substances. B cell Named after the bone marrow, where immature B cells are produced. B cells are both antigen- + + presenting and antigen-receiving cells. Helper T cell (CD4 ) Cytotoxic T cell (CD8 ) LYMPHOCYTES CLONAL SELECTION Agranulocyte white blood cells. The process by which a B cell and T cell Types include B cells and T cells. specific to the antigen are selected for clonal expansion by an APC. CLONAL EXPANSION After clonal selection, the selected Cytokines activate Cytokines are proteins that act as messengers B cells and T cells divide by mitosis between cells. Released by immune cells, including to produce many identical progeny, helper T cells to signal danger or damage. or clones. Memory B cell Memory B cell Plasma B cell Plasma B cell Helper T cell (CD4+) Memory T cell Memory T cell Cytotoxic T cell (CD8+) Long-lived B cells that remember past B cells that have been activated T cells that recognise antigens presented by APCs Long-lived T cells that remember past T cells that kill virus-infected cells and cancer infections by recognising antigens to to produce antibodies. Each B cell and stimulate T, B and other immune cells. Also infections to provide a secondary cells by releasing toxic chemicals. Also known as provide a secondary immune response. makes only one type of antibody. known as CD4+ cells, because of a protein that immune response. CD8+ cells, because of a protein that they express they express on their cell surface. on their cell surface, and as killer T cells. Antibodies Perforins Proteins that cause cells to lyse (burst) by making pores form in the plasma membrane of the cell. Found in the granules of cytotoxic T cells. The Wellcome Trust is a charity registered in England and Wales, no. 210183. Its sole trustee is The Wellcome Trust Limited, a company registered in England and Wales, no. 2711000 (whose registered office is at 215 Euston Road, London NW1 2BE, UK). PU-5045/12K/10–2014/BS.