Immune system Flashcards

Question

Second line of defence: Cytokines

Answer 1

Small protein hormones (chemical messengers) that stimulate or inhibit normal cell functions. * A group of non-antibody proteins secreted by leukocytes * Act on cells involved in immunity (mediate immune response) * (Analogy = email /text to communicate between different types of cells) Cytokines include: * Interleukins; These act as mediators between leukocytes. Mostly produced by T-helper cells. (Different numbers do different things e.g. Interleukin 1 releases macrophages and triggers fever response) * Interferons; Involved in anti-viral responses * Tumour necrosis factor (TNF); Promotes the accumulation of neutrophils and macrophages and causes cell death

Answer 2

Interferons comprise a group of proteins produced by virus-infected cells. * Interferons diffuse to uninfected neighbouring cells, where they induce synthesis of anti-viral proteins that interfere with viral replication * Interferons do not stop a virus attaching to and penetrating a host cell, but they prevent it replicating * Viruses can only cause disease if they replicate within body cells Interferon = interferes.

Answer 3

Phagocytes perform phagocytosis (cell digestion). * Phagocytic cells are attracted to sites of inflammation by ‘chemotaxis’ * Two major types (which migrate to an infected area) are; - Macrophages (monocytes in blood) - Neutrophils * Monocytes migrate to the site of infection and enlarge to form ‘wandering macrophages’. Other macrophages are ‘fixed macrophages’ and stand guard in specific tissues * Phagocytes are non-selective in their targets; they engulf and digest foreign materials * Macrophages are ‘antigen presenting cells’ Chemo = chemical, taxis = order, Chemotaxis = chemical attraction

Answer 4

Some macrophages are ‘fixed macrophages’ and stand guard in specific tissues. These include: * Histiocytes (connective tissue macrophages) * Kupffer cells (liver) * Alveolar macrophages (lungs) * Microglia (nervous tissue) * Langerhans cell (skin) * Tissue macrophages (spleen, bone marrow, lymph nodes)

Answer 5

Phagocytosis occurs in 5 stages: 1. Chemotaxis; release of chemicals by microbes, leukocytes, damaged tissue and by activated complement that attract phagocytes 2. Adherence; attachment of phagocyte to target (aided by complement) 3. Ingestion; the cell membrane extends projections that engulf the microbe 4. Digestion; The ingested structure merges with lysozymes to form a phagolysosome. Lysozymes and digestive enzymes ‘digest’ 5. Excretion; indigestible material is excreted (some is presented on cell)

Answer 6

Natural Killer (NK) cells account for 5-10% of lymphocytes. They are ‘non-specific lymphocytes’. * Present in blood, lymph nodes, spleen and bone marrow * NK cells attack anything that they do not recognise, inc. abnormal body cells (abnormal cell membrane proteins) e.g. cancerous cells * NK cells bind to a target cell and release granules containing the protein ‘perforin’ * Perforin inserts into the cell membrane and creates a channel for tissue to flow into the cell → cytolysis

Answer 7

Inflammation is a non-specific defensive response to tissue damage. * It can be caused by pathogens, abrasions, chemicals, cell distortion or disturbance and extreme temperatures. * The response is non-specific, meaning the response to different insults is the same The cardinal signs of inflammation include: * Redness * Heat * Pain * Swelling * Loss of function

Answer 8

Inflammation occurs in three basic stages; 1. Vasodilation and increased permeability 2. Emigration of phagocytes 3. Tissue repair

Answer 9

Stage 1; Vasodilation and increased permeability: * Vasodilation allows additional blood to the area, bringing oxygen, nutrients, immune cells and repair substances and removal of toxins and dead cells * Increased permeability permits the movement of immune cells, defensive proteins such as antibodies and clotting factors into the tissue * Together these create redness, swelling and heat. Pain results from injury to neurons and toxic chemicals released by microbes.

Answer 10

Stage 2; Emigration of phagocytes * Within an hour of the process beginning, phagocytes migrate to the scene (via chemotaxis) * Neutrophils stick to the endothelium during vasodilation and squeeze through the vessel wall to reach the damaged area (leukocytosis) * Monocytes quickly follow and transform into wandering macrophages * Dead phagocytes accumulate as pus Stage 3; Tissue repair

Answer 11

Benefits: . Promotes phagocytosis (via chemotaxis); the increase in temperature promotes activity . Promotes immune response; vasodilation and increased permeability mean that cells and proteins (e.g. antibodies) can leave the blood and enter the affected site . Dilutes toxins . Fibrin formation; isolates the affected area and helps to bind wound edges Harmful effects: . Swelling; dangerous if in the cranium . Pain; which can become chronic . Adhesions and scar tissue . Atherosclerosis; inflammation is a key feature of this process

Answer 12

Resolution; The cause is successfully overcome (complete restoration) Chronic inflammation; If injury-causing agent persists. Can cause chronic pain. Macrophages, plasma cells and lymphocytes become prevalent Granuloma; Cellular attempt to contain foreign body. Aggregation of macrophages surrounded by lymphocytes Fibrosis; Scar tissue formation. Formed by the secretion of collagen by fibroblasts. Occurs often as a result of chronic inflammation

Answer 13

A fever is an abnormally high body temperature * Occurs because the hypothalamus thermostat is reset * Commonly occurs in infection and inflammation * Many bacterial toxins elevate body temperature, which trigger the release of fever-causing cytokines from macrophages, such as interleukin-1 * One of the key functions of interleukin-1 is to induce fever Elevated body temperature: * Makes interferon’s more effective * Inhibits growth of some microbes * Speeds up reactions that aid repair

Answer 14

Lymphocytes developed in the bone marrow. There are two types of lymphocytes; 1. T-lymphocytes 2. B-lymphocytes

Answer 15

T- Lymphocytes (T-cells) (mature in Thymus): * Cytotoxic T-cells (CD8); break down / destroy foreign cells (analogy = FBI) * Helper T-cells (CD4); mediates immune response (analogy = coordinator) * Memory T cell; created after exposure to active disease * Regulatory T-cells; turn off immune reaction when immune response should be finished. Cyto = cell, toxic = toxic

Answer 16

B-lymphocytes (B-cells) (mature in red bone marrow): * Plasma cells (produce anti-bodies); B-cells produce plasma cells, which produce anti-bodies. They are specific. (analogy another department within FBI) * memory B-cells

Answer 17

T- and B- lymphocytes function in adaptive (specific) immunity, whereby they learn to respond to foreign antigens * T- and B- Lymphocytes possess specificity for antigens. They (usually) recognize self from non-self antigens. Each T- and B- lymphcyte is specific for a particular antigen * T- and B- lymphocytes produce immune memory for previously encountered antigens. * Immune memory allows them to produce a quicker and more effective attack with the next encounter with the antigen

Answer 18

T-Lymphocytes (or T-cells) play a central role in cell-mediated immunity * Millions of different T-lymphocytes exist, each with a unique T-cell receptor (TCR) that only recognizes a specific antigen * Produced in bone marrow and mature in the thymus (hence name) * Most T-cells arise before puberty but continue to mature and leave the thymus throughout life * T-cells are divided into; T helper cells and Cytotoxic cells * T- helper cells are also known as CD4 cells because they express CD4 protein on their surface (as are macrophages) * Cytotoxic T-cells are CD8 cells

Answer 19

To function properly, T-cells must have two traits: 1. Must be able to recognize self antigens (self recognition) 2. Must lack reactivity to fragments of self-antigens (self tolerance) * A loss of self-tolerance leads to autoimmunity * T-cells are ‘tested’ against thymus epithelial cells. T-cells should be able to recognize self-antigens. If they do not, these cells undergo apoptosis. * Only 1-5% of T-cells make it through the process * B-cells undergo a similar screening process in the bone marrow.

Answer 20

The innate immune system is often sufficient to destroy invading microbes. If it fails to adequately destroy the pathogen, the third line of defence is activated. * Cytokines (messenger molecules) mediate the connection between the innate immune system and the adaptive immune system * The effector cells of the adaptive immune system are T- and B- lymphocytes * T- and B- lymphocytes are normally at rest, but become activated on encountering a foreign antigen (or what they perceive to be foreign) * A key feature of the adaptive immune system is acting specifically to target certain antigens in the immune response.

Answer 21

Adaptive immunity is the ability of the body to defend itself against specific agents * Characterised by specificity for particular foreign antigens and the production of immune memory There are two types of adaptive immunity; 1. Cell mediated immunity (T-lymphocytes) 2. Antibody adapted immunity (B-lymphocytes)

Answer 22

Cell mediated immunity; * By T-lymphocytes * Cytotoxic T-cells directly attack invading antigens * Defense mostly against intra-cellular pathogens

Answer 23

Antibody mediated immunity; * By B-lymphocytes * B-cells transform into plasma cells, which synthesise and secrete specific antibodies (Ig’s) * Defense mostly against extra-cellular pathogens

Answer 24

For an immune response to occur, T-cells must recognise that a foreign antigen is present. * T-cells only recognise protein fragments (antigens) that are processed and presented in a certain way * A class of cells called antigen-presenting cells (macrophages and B-cells) are strategically located in places where antigens are likely to penetrate the body * Antigen-presenting cells combine the foreign antigen with MHC-II complexes on their cell membrane * Antigen-presenting cells migrate into lymphatic tissue, where they ‘present’ the antigen to T-helper cells. This is known as antigen presentation.

Answer 25

For the T-lymphocytes to get ‘sensitised’ to their antigen, the antigen must be presented to the cell, usually a macrophage * Through the action of phagocytosis, macrophages use lysozymes (enzymes) to break down the antigen into fragments. Some fragments will be combined with MHC molecules * When the antigen fragment binds with the T-helper cell, the T-helper cell secretes a cytokine called interleukin-2 (Il-2) * Interleukin-2 causes the T-helper cell to undergo ‘clonal selection’ Interleukin-2 is the prime trigger for T-lymphocyte proliferation and also stimulates clonal selection of B-lymphocytes

Answer 26

Interleukin-2 binds to receptors on the cell membrane of the T- helper cell that secreted it. Interleukin-2 stimulates the division and proliferation of activated T-cells. This process, called clonal selection produces; 1. Cytotoxic T-lymphocytes: Bind to target cell and destroy it using protein digesting enzymes called granzymes, and perforin 2. Memory T-lymphcytes: Inactive. Recognise the antigen with any future contact, ready to mount an immune response 3. Helper T-lymphocytes: Release cytokines which increase the acivity of immune cells such as T-, B- and NK cells

Answer 27

B-lymphocytes form and mature in bone marrow and are fixed in lymphoid tissue, where they do not leave. * An antigen binds to specific B-cells receptors, where it is taken into the cell and broken down into fragments. These are then expressed on the MHC-II * Helper T-cells recognize the antigen complex on the B-cell membrane and stimulate it by releasing interleukin-2, which triggers B-cell clonal selection. * Clonal selection produces 2 types of cells: 1. Plasma cells (secrete antibodies) 2. Memory B-cells

Answer 28

Plasma cells: * Secrete antibodies into the blood * Only produce one type of antibody * A few days after antigen exposure, secrete hundreds of millions of antibodies each day until cells die. * Short lived.

Answer 29

Memory B-cells * Long lived * Remember antigen for nect time, ready to proliferate and produce more plasma cells for a second immune reaction

Answer 30

Antibodies belong to a group of glycoproteins called globulins, and are hence also known as immunoglobulin’s * Antibodies contain 4 polypeptide chains (two heavy and two light chains). There is a variable region that is different for each kind of antibody * Antibodies generally have two antigen-binding sites * Antibodies bond specifically with the antigen that triggered their production (lock and key). They form antibody-antigen immune complexes.

Answer 31

Antibodies inactivate antigens in different ways: 1. Neutralising; Neutralise bacterial toxins or prevent viral attachment to cells. 2. Immobilising; bind to antigens on bacterial cilia or flagellae 3. Agglutinating and precipitating; antibodies use both their binding sites to cause clumping of cells 4. Activating complement; antigen-antibody complexes activate the complement cascade 5. Enhancing phagocytosis; the antibody acts as a flag to attract phagocytes and aids phagocytosis via agglutination and complement.

Answer 32

There are 4 different types of antibody (IMMUNOGLOBLINS) 1. IgG 2. IgA 3. IgM 4. IgE

Answer 33

Immunogloblin G (IgG): Location: Blood, lymph and intestines How common? Most abundant (80% of blood antibodies) Function: Protects against bacteria and viruses, only class of antibody that crosses the placenta

Answer 34

Immunogloblin A (IgA): Location: Sweat, tears, saliva, breast milk How common? 10% antibodies in blood, mainly found in mucus membranes Function: Localised protection of mucus membranes, decreases with stress

Answer 35

Immunogloblin M (IgM): Location: Blood and lymph How common? 10% blood antibodies Function: Main class of antibody in early immune response

Answer 36

Immunogloblin E (IgE): Location: Blood How common? 0.1% antibodies in blood Function: Involved in akkergic reactions. Binds to mast cells N/B; Food intolerance creates IgG response rather than IgE (true allergy reposnse)

Answer 37

Regulatory T-cells were formally ‘suppressor T-cells’. * A specialised sub-population of T-cells which deactivate immune cells (T-helper, B-cells and macrophages) when an immune response is no longer required. * Thereby maintain immune system homeostasis and tolerance to self-antigens * Without the regulatory T-cells, the body would continue trying to fight of a disease that no longer exists (and would eventually end up fighting its own cells) * Regulatory T-cells prevent excessive reactions

Answer 38

Based on the presence of long-lasting antibodies and very long lasting memory B- and memory T-cells. There are 2 types of response; 1. Primary (first exposure) 2. Secondary (subsequent exposure)

Answer 39

Primary response (first exposure); * A slow response. Antibodies do not appear for several days, then a slow rise in IgM, followed by IgG

Answer 40

Secondary response (subsequent exposure); * Memory cells can last for decades * Much faster response because a full immune response has been developed with thousands of memory cells * Often the secondary response is so effective, it kills off the microbes before you exhibit any signs or symptoms

Answer 41

Immunological memory is the basis for vaccination against certain diseases. * Vaccines contained weakened (attenuated) whole or partially-killed portions of microbes – microbes are immunogenic but are not supposed to be pathogenic * B- and T- cells are activated – primary response. Not many cells have the correct specificity to respond to the antigen, so a response can take several days. * Subsequent exposure to the living pathogen initiates a far more effective secondary response

Answer 42

Ways to acquire immunity: 1. Naturally-acquired active immunity; Natural exposure to a disease 2. Naturally-acquired passive immunity; Transfer of IgG antibodies across the placenta from mother to child, transfer of IgA form mother to child via the breast milk 3. Artificially-acquired active immunity; vaccination 4. Artificially-acquired passive immunity; injection with immunoglobulin’s, e.g. snake anti-venom

Answer 43

70% of body’s immune system is found in the GIT * GALT (gut associated lymphoid tissue) contains immune cells (e.g. macrophages, B- and T- lymphocytes) * GALT is in the tonsils, oesophagus, small intestine and large intestine * The health of the digestive system plays a critical role in a healthy immune system. Leukocytes learn from the microflora * Poor function affects immunity, nutritional status and toxic load

Answer 44

Pathogens can enter the body and cause disease through openings such as: * Breaks in the skin * The respiratory system * The digestive system * Male / female reproductive systems * Eyes