Overview. Barriers help animals defend against many dangerous pathogens they encounter.

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1 Immunity

2 Overview Barriers help animals defend against many dangerous pathogens they encounter. The immune system recognizes foreign bodies and responds with the production of immune cells and proteins. Two major types of defence have evolved: Innate immunity and acquired immunity

3 Innate immunity Present before exposure to pathogens and is effective from birth. Involves nonspecific responses to pathogens. Innate immunity consists of external barriers plus internal cellular and chemical defences.

4 Acquired immunity Acquired or adaptive immunity develops after exposure to agents such as microbes, toxins, or other foreign substances It involves a very specific response to pathogens

5 Innate immunity Recognition of traits shared by broad ranges of pathogens, using a small set of receptors Rapid response Acquired immunity Recognition of traits specific to particular pathogens, using a vast set of receptors Slower response Barrier defences: skin, mucous membranes, secretions Internal defences: Phagocytic cells, antimicrobial proteins, inflammatory response Natural killer cells Humoral response: Antibodies defend against infection in bodily fluids Cell-mediated resonse: Cytotoxic lymphocytes defend against infection in body cells

6 Barrier defences include the skin and mucus membranes of the respiratory, urinary, and reproductive tracts. Mucus traps and allows for the removal of microbes Many body fluids including saliva, mucus, and tears are hostile to microbes The low ph of skin and digestive system prevents growth of microbes

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8 White blood cells (leukocytes) engulf pathogens in the body Groups of pathogens are recognized by receptors After the WBC (white blood cell) engulfs a microbe, then it fuses with a lysosome to destroy the microbe

9 Inflammatory response occurs following an injury. Mast cells release histamine, which promotes changes in blood vessels. These changes increase local blood supply and allow more phagocytes and antimicrobial proteins to enter tissues Pus is a fluid filled with white blood cells, dead microbes, and cell debris, that builds up at the site of inflammation

10 Inflammatory response 1.Tissue injury -> release of histamine 2.Causes dilation and increased leakiness in local blood vessels and movement of phagocytes to area 3.Phagocytes consume bacteria and cell debris, and tissue heals

11 Inflammation can either be local or systemic (throughout body) Fever is a systemic inflammatory response triggered by macrophages (one type of WBC) and toxins from pathogens Septic shock is a life threatening condition caused by an overwhelming inflammatory response.

12 Natural Killer Cells Almost all cells in the body have a receptor on their surface Cancerous or infected cells no longer display this receptor, and natural killer cells attack these damaged cells Some pathogens avoid destruction by modifying their surface to prevent recognition or resisting breakdown by phagocytosis Tuberculosis is an example

13 Acquired immunity White blood cells called lymphocytes recognize and respond to antigens, or foreign molecules Lymphocytes that mature in the thymus above the heart are called T cells, and those that mature in bone marrow are called B cells.

14 Lymphocytes contribute to immunological memory, an enhanced response to a foreign molecule encountered previously B cells and T cells have receptor proteins that can bind to foreign molecules

15 Each individual lymphocyte is specialized to recognize a specific type of molecule An antigen is any foreign molecule to which a lymphocyte responds A single B or T cell has about 100,000 identical antigen receptors

16 Antigen binding site Antigen binding site Antigen receptor on a B cell Antigen receptor on a T cell

17 B cells give rise to plasma cells, which make proteins called antibodies or immunoglobulin Antibody 1 Antigen Antibody 2 Epitopes Antibody 4 Antigen binding sites Antibody 3

18 B cell receptors bind to specific, intact antigens Secreted antibodies, or immunoglobulins, are the same shape as B cell receptors

19 T cells bind to antigen fragments presented on a host cell These antigen fragments are bound to special cell-surface proteins called MHC In infected cells, MHC molecules bind and transport antigen fragments to the cell surface, called antigen presentation A nearby T cell can then detect the antigen fragment that is being displayed

20 If the MHC is presented on a normal body cell the antigen is displayed for cytotoxic T cells If the MHC is presenting on an immune system cell such as a macrophage, or B cell the antigen is displayed for cytotoxic T cells, and helper T cells

21 Normal body cell Immune cell

22 The acquired immune system has three important properties: 1. Receptor diversity (T cells and B cells can bind to any foreign particles) 2. A lack of reactivity against host cells (T cells and B cells never bind to normal cells, or proteins in the body) 3. Immunological memory (B cells remember coming in contact with a foreign particle)

23 Infected cell Antigen B cell Cytotoxic T cell Helper T cell Helper T cell Helper T cell Cytotoxic T cell Antibody production Plasma B cell Memory B cell

24 Antigen receptors are generated randomly As lymphocytes mature in bone marrow or thymus, they are tested for self reactivity Lymphocytes with receptors specific for the body's own molecules are destroyed by apoptosis

25 In the body there are a few lymphocytes with antigen receptors for any particular epitope The binding of a mature lymphocyte to an antigen induces the lymphocyte to divide rapidly This is called clonal selection Two types of clones are produced: short-lived activated plasma cells and long-lived memory cells

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27 Antigen Proliferation Memory B cell Plasma B cell

28 The first exposure to a specific antigen represents the primary immune response During this time, plasma cells are made, and T cells are activated In the secondary immune response, memory cells allow a faster, more efficient response to the same specific antigen

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30 Acquired immunity has two branches: the humoral immune response and the cell-mediated immune response Humoral immune response involves activation and clonal selection of B cells, resulting in production of secreted antibodies Cell-mediated immune response involves activation and clonal selection of cytotoxic T cells Helper T cells aid in both responses

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32 Helper T cells respond to nearly all antigen Helper T cells bind to antigen presenting cells Helper T cells secrete chemical messages that stimulate other lymphocytes

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34 Cytotoxic T cells interact the MHC on infected cells and become activated killer cells The activated cytotoxic T cell secretes proteins that destroy the infected target cell

35 Neutralization occurs when a pathogen can no longer infect a host because it is bound to an antibody Antibodies attached to antigen increase phagocytosis by macrophages

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37 Three types of immunity Innate immunity Everyone is born with a general type of protection. Many of the germs that affect other species don t harm us. For example the virus that causes leukemia in cats doesn t affect humans. Innate immunity includes the first line of defense external barriers of the body And non-specific defenses such as fever and inflammation.

38 Adaptive Immunity and Passive Immunity The second kind of defense is active immunity which develops through our lives. This involves lymphocytes and develops only as people are exposed to diseases or immunized by vaccines. Passive immunity is borrowed from another source and lasts for a short time. For example, antibodies in a mother s breast milk provide a baby with temporary immunity to diseases the mother has been exposed to.

39 Immunity Everyone s immune system is unique. Some people never seem to get infections, whereas other seem to be sick all the time. As people become older they usually become immune to more pathogens. This is why adults and teens tend to get sick less often then kids.

40 Problems of the Immune System Disorders of the immune system fall into four main categories: 1. Immunodeficiency disorders (primary or acquired) 2. Autoimmune disorder (in which the body s own immune system attacks it own tissue as foreign matter) 3. Allergic disorders (in which the immune system overreacts in response to an antigen) 4. Cancers of the immune system

41 Immunodeficiency Disorders Immunodeficiencies occur when a part of the immune system is not present or is not working properly A person can be born with an immunodeficiency, although the symptoms might not occur until later in life, or it can be acquired through infection or produced by drugs Immunodeficiencies can affect B lymphocytes, T lyphocytes, or phagocytes.

42 Innate Immunodeficiency: Severe combined immunodeficiency (SCID) also known as bubble boy disease after a boy who lived in a microbe free bubble. SCID is a serious immune system disorder that occurs because of a lack of both B and T lymphocytes, which makes it almost impossible to fight infections.

43 Acquired Immunodeficiency Usually develop after a disease, although can also be the result of malnutrition, or medical problems. Can be caused by certain medications. Example: HIV (human immunodeficiency virus)/aids a disease the steadily destroys the immune system. It is caused by HIV, a virus that wipes out T helper cells. Without these cells, the body is unable to defend against normally harmless organisms.

44 Immunodeficiency caused by medication Some medications suppress the immune system. One of the drawbacks of chemotherapy for treatment of cancer, is that it attacks many fast growing, healthy cells, including immune cells. As well people who have had organ transplants may need to take immunosuppresant medications.

45 Autoimmune Disorders In an autoimmune disorder, the immune system mistakenly attacks the body s healthy organs and tissues as though they were foreign invaders. Examples: Lupus chronic disease marked by muscle and joint pain and inflammation (may involve attacks on kidneys and other organs) Juvenile rheumatoid arthritis a disease in which the immune system attacks certain body parts ( such as joints of the knee, hand, and foot)

46 Allergic Disorders Occur when the immune system overreacts to exposure to antigens in the environment. The substances that provoke such attacks are called allergens. The immune response can cause symptoms such as swelling, inflammation, watery eyes, sneezing. Medications that are antihistamines can relieve symptoms. In some cases, allergies can be life threatening if they cause anaphylaxis which is a systemic allergic response. Allergic disorders include asthma, eczema, and allergies

47 Cancers of the immune system Cancer occurs when cells grow out of control. This can happen with cells of the immune system. Lymphoma involves the lymphoid tissue. Leukemia involves abnormal growth of leukocytes, is the most common childhood cancer. Both types of cancer in kids are curable.