Cell Systems- Immunity PDF

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Summary

General Features of Blood  Describe the composition of blood and identify the function of blood constituents  Describe the role of platelets and wound healing and clotting  Discuss the mechanisms that permit oxygen and carbon dioxide transport in the blood  Understand blood typingBasic facts Spe...

Description

General Features of Blood  Describe the composition of blood and identify the function of blood constituents  Describe the role of platelets and wound healing and clotting  Discuss the mechanisms that permit oxygen and carbon dioxide transport in the blood  Understand blood typing Basic facts Specialised 'fluid' connective tissue  Average men- approx 5-6 litres (ca. 7% body weight) average women- approx 4-5 litres (7% body weight)  Children- approx 75-80 ml/kg  Babies- approx 85-105 ml/kg Normal pressure (systolic/diastolic) Systolic: pressure exerted on blood vessels when heart beats Diastolic: pressure exerted on vessels or arteries when heart is at rest  in adults: 120/80-140/90  In children: 95/58  In newborns: 64/40  Adults are larger therefore more pressure required to drive blood around the body pH: 7.35-7.45 at average temperature of 38°C - very tightly controlled: important for gas carrying component of system Approx 5x more viscous than water: 2.57-2.65 mm^2/sec (temperature dependent) Blood composition

Plasma proteins: Albumin  65-70 kDa- range is to do with varying different posttranslational modifications which can help modulate to function of protein in plasma e.g. glycosylation  Most abundant soluble serum protein (ca 30-55 g/l)  Main function: maintenance of intravascular colloid osmotic pressure (COP) by binding water  Pressure is created by albumin and its ability to bind water- very important to help retain water in blood- prevents water moving out of blood and into tissues along concentration gradient- critical for maintaining blood volume- physically creates pressure  Some drugs target albumin as a carrier protein  Other functions: cation transport (Ca2+, Na+, K+), fatty acids, hormones, bilirubin, thyroxin & some pharmaceuticals Plasma proteins: Globulins  Total conc in blood: ca 27 g/l  α1-globulins: important transport of lipids, thyroxine, corticosteroids, hormones  α2-globulins: important for transport of lipids and copper ions, antitrypsin  β-globulins: transport of iron (transferring: 76 kDa) and antioxidants. Some complement and some isotypes of antibodies  Y- globulins: also called immunoglobulins (antibodies) in immunity  Named based on spectral peaks shown below- way they migrate in electrical field  This type of trace is important for blood health- if some peaks differ, it could indicate disease e.g. if you have a lot of y-globulin it means you have a lot of immunoglobulins which could indicate infection

Plasma proteins: Fibrinogen

a major glycoprotein of approx. 340 kDa -crucial for blood clotting. Converted enzymatically to fibrin by thrombin and factor XIIIa  This is a complicated process with lots of factors involved in wound healing  Two pathways converge (tissue trauma pathway and blood activated by platelets) in a common pathway- Factor Xa  Fibringogen converted into monomers and then factor XIIIa converts them into polymers which function in wound healing process

Cells of the buffy coat (leukocytes)  Generally involved in immunity  Neutrophils- phagocytes that are important in first part of inflammatory response and activating various bactericidal mechanisms. They are characteristic by their multi-lobed nucleus  Basophils- promotion of allergic response and anti-parasitic immunity  Monocytes- migrate into tissue to differentiate into either macrophages or dendritic cells. Macrophages are phagocytic cells that are important for activation of bactericidal mechanisms and also for presenting antigen to alert the adaptive immune response. Dendritic cells are important for phagocytosis, processing proteins from pathogens and present those proteins as antigens on surface of cell- important for the adaptive immune response  Lymphocytes- B and T cells: B cells- antibody producing cells, T cells- part of the cell mediated immune response Platelets (blood thrombocytes)- another component of buffy coat  Found scattered in blood- derived from cell type called megakaryocyte  Megakaryocytes are huge cells that create pseudopodia (projections out from the cell) a the end of those projections, they bud off portions of the cell which are these platelets (=> not actually cells but fragments of cells)  Small (1-4µm diameter) colourless, disc-shaped, anuclear (lacks a nucleus) cell fragments  Approx- 1.5-4.5 x 10^5 ml^-1 in blood. Lifespan ca. 10 days  they do contain mitochondria and other cell organelle- they have a membrane made up a coat proteins that is heavily glycosylated which are really important for adhesion to the sites of injury and also promote more platelets to bind- important for wound healing  Inside the coat, there is a band of microtubules- important for maintaining disc shapeimportant for adhesion and also for shape for signalling to occur- mechanosensing components of membrane may induce cell signalling events  Other major components: α and dense granules  Dense granules contain ADP, serotonin, rich in calcium (important for adhesion and attraction of other platelets)  α-granules secrete molecules (important for platelet adherence) and also clotting factors

Thrombus (clot) formation  Diagram of blood vessel, upon damage- the extracellular matrix (which is largely made up of collagen) is exposed as a consequence  Platelets are very good at sensing collagen which induces them to aggregate

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As they stick, microtubules change , discs flatten out- change in shape leads to intracellular signalling pathway leading to secretion from dense granules Whole process leads to development of clot- each step of the way, there is an increase in the ability of platelets to bind to each other, aggregate and form the clot During aggregation, additional signalling occurs causing the release of fibrinogen from α particles, which is then converted to fibrin which increases recruitment of platelets and RBCs and leukocytes

Red blood cells (erythrocytes)  Most abundant cells in the blood ca. 4.5-6.0 x 10^6 µl ^-1 (higher in men than women)  20-30 trillion per person. Approx 25% of all cells in the body  Anucleated cells with bi-concave shape (Except birds and fish) and no organelles- needed for efficient gas exchange  Size: 7.5 µm diameter x 2.5 µm deep  Life span: approx 120 days  Contains the red pigment haemoglobin- important for oxygen transport Erythrocytes membrane  Asymmetric lipid distribution: lipids are charged on inner layer, uncharged on outer  Outside part is neutral- important to ensure blood flows freely and in circulation- no charge dependent binding to vessels of endothelial cells  Important molecules anchored to, or associated with, lipid bilayer  Proteins associated with membrane of RBC- Band 3 protein, glyocophorins, aqauporins, spectrins, actin, ankyrin Erythrocytes integral membrane proteins  Band 3: transports bicarbonate and chloride ions- important in gas exchange proteins  Glycophorines: sialoglyproteins that lend the cell a highly hydrophilic-charged coatensures RBC stay in suspension in blood  Aquaporins: proteins that form pores in cells to facilitate transport of water across the membrane  Spectrins: large, heterodimeric proteins that maintain stability and structure of the cell membrane  Ankyrin: anchor proteins with cytoskeleton Erythropoiesis     

Erythrocyte numbers are controlled by the cytokine called erythropoietin (EPO) EPO is produced in the kidney when O2 levels are low (hypoxia) Released into the blood and simulates RBC production in bone marrow Recombinant human erythropoietin (rhEPO) used (illegally) for blood doping to enhance athletic performance. This is detectable and is tested for in blood tests Self-transfusion of blood used for blood-doping racehorses

Haemoglobin  Oxygen carrying protein of blood  Made up of four chains of polypeptides (2 α and 2 β)  Structure of blood means it contains a haem group: part of the protein that can coordinate metal (ferratin molecule in this case)  This allows blood to bind to oxygen

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Four chains => haemoglobin can carry 4 oxygens There are 2.5 x 10^7 haem groups per RBC- oxygen carrying potential is enormous Oxygen binds reversibly and is dependent on partial pressure of oxygen When partial pressure is low- oxygen dissociates from RBC When high- it readily binds to oxygen and can dissociate tissues wherever respiration is occuring

Each haem group binds reversibly with one molecule of O2 Oxygen binding  Haemoglobin binds up to 4 oxygen molecules  Co-operative binding: O2 binding increases the affinity for more oxygen molecules due to conformational changes in Hb 

Conversely, when each O2 molecule is released, opposite change makes it easier for others to unload

Oxyhaemoglobin  Haemoglobin bound to O2 is bright red, brown when O2 is released  Binding occurs at high ppO2  Dissociation occurs at low ppO2  Haemoglobin unloads oxygen stepwise in the tissue as:  HbO8 > HbO6 > HbO4 > HbO2 > Hb  Extent and rate are work/exercise dependent  When oxygen is dissociated, it is known as reduced haemoglobin Oxygen dissociation curves  At low O2 levels (hypoxia) the % saturation is low  At high O2 levels haemoglobin is fully saturated  Rate of oxygen saturation speeds up and plataeu is observed once oxygen is saturated Dissociation curves for different O2-binding molecules  Fetal haemoglobin absorbs oxygen more efficiently as it is taking haemglobin from the placenta  Myoglobin- rapidly binds oxygen, found in skeletal and cardiac muscle and is only used in anaerobic respiration and when partial pressure is very low

Factors influencing O2 dissociation  High CO2 concentration can lead to lower oxygen binding  PH- drastic shift may alter protein structure which limits its ability to perform function  

At altitude the ppO2 is lower than at sea level, so harder to breathe. Acclimatation increases haematocrit (volume % of RBCs) levels to compensate Acclimation to weightlessness in space decrease the haematocrit levels so harder to breathe on return to earth

Carbon dioxide transport  CO2 can be carried in the blood in 3 ways: oxygen can be dissolving plasma, haemoglobin can bind small amounts of CO2- together these two methods account for about 10% of CO2 transport

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Major way CO2 is carried through the blood is bicarbonate- CO2 can diffuse into RBC's which are important for the production of bicarbonate ions When CO2 enters RBC it quickly binds H20 which forms carbonic acid (H2CO3)- this reaction is performed by carbonic anhydrase Carbonic acid is very unstable so quickly dissociated into hydrogen ions and bicarb ionsbicarb diffuses out in exchange for chloride ions and its band 3 protein (part of the membrane of RBC) is very important in regulating the bicarb-chloride exchange Increase in H+ can alter the pH of RBC's which drastically affects the gas transport system but RBC's are very efficient in buffering pH- a critical part of RBC function

Maintaining blood pH  Bicarb is carried in plasma until it reaches the lungs and reverse reaction occurs  Bicarb re-enters RBC, merges with H+ ions and reforms carbonic acid  Quickly breaks down into water and CO2  Co2 then can diffuse across the endothelial membrane and can be exhaled Human blood groups  The reason we have blood groups is not entirely resolved but is thought to be part of our arms-race against infection  People of African descent often have more O type of blood and it is known that malaria has a hard time binding to this type  O type evolutionary evolved after A type A, B or O controlled by single gene that encodes a glycosyltransferase which catalyses the final sugar (NAc or galactose) onto the end of a glycoprotein  If terminal sugar is NAc- you have A type blood providing with A antigen  Galactose= B type blood => B antigen Blood group compatability Blood type determination  Agglutination test is used to determine blood type  Can use known properties of antibodies in plasma  If you have two different tubes coated with anti-A antibodies in one and anti-B in the other and spot blood in them  Antibody will cross-react with antigens in blood causing blood to stick together  Blood group below shows AB  If has type B- blood will agglumitate to type B Blood disorders Many known: most prominent discussed include:  HDN (rhesus factor) Haemophilia  Anaemia  Polycythenia Haemolytic disease of newborn (HDN) RhD factor  Genetic disease that compromises survival of some newborn babies  Rh factors are a large (ca 45) group of transmembrane protein antigens on RBCs

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Main ones: D,C,c, E & e with D the most important D+= Rh+ individuals; D-= RhRhD-mothers produce lgG against the foetal RhD+ antigen with first RhD+ foetus

HDN: RhD factor Symptoms  Haemolysis  Anaemia  Jaundice  Enlarged liver (hepatic failure)  Hydrops felatis Prevention 

Mother given anti-RhD+ antibodies before and after birth

Treatment  

Blood transfusion pre and post birth UV exposure post birth to convert bilirubin to photobilirubin

Haemophilia  Usually an inherited condition in which blood clotting is impaired: risk of haemorrhage  Caused either by lack of clotting factor VIII (Haemophilia A), factor IX (Haemophilia B)

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A range of conditions due to abnormally low number of healthy RBCs Causes: often low iron intake, internal bleeding, cancer or inherited genetic traits Sickle cell anaemia: inherited disease due to abnormal haemoglobin (S-type)

Polycythenia  Group of afflictions due to abnormally high count of RBCs in the blood  The RBC thicken the blood, slow its flow and raise risk of stroke, blood clots or heart attack Two forms 1. Primary: polycythenia vera: rare slow growing blood cancer. Caused by faulty JAK2 gene that regulates bone marrow activity 2. Secondary: polycythenia due to over production of erythropoietin often from kidney cancer or other conditions Innate Immunity Outcomes  Explain what innate immunity is  Identify the role different innate immune cells play during the inflammatory response  Explain what PAMPs and PRRs are  Describe the important role innate immunity plays in activating the adaptive immune response Several levels of pathogen protection

Innate immune response  The innate immune responses are the first line of defence against invading pathogens  They are also required to initiate specific adaptive immune responses  Innate immune responses rely on the body's ability to recognise conserved features of pathogens that are not present in the uninfected host and respond in a way that creates an unfavorable environment for the invading pathogen Characteristics  Present from birth  Immediate  Non-specific  No enhancement with second exposure  No memory Cell types    

Neutrophils Basophils Eosinophils Natural killer cells

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Monocytes Mast cells

Cell functions  Degranulation – release of chemicals contained in granules in some types of innate immune cells, released to help kill infection  Chemotaxis- recruitment of other immune cells to site of infection  Phagocytosis- take up and break down pathogens  Killing  Trapping – preventing spread around the body

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Cells of the immune system are generated in the bone marrow by hematopoietic stem cells Myeloid progenitor cells and lymphoid cells are produced first which can give rise to a number of cell types Eosinophils, basophils and neutrophils also known as granulocytes because they have visible, dense granules in their cytoplasm which contain a lot of chemicals to combat the pathogen that will be released upon pathogen detection Also known as polymorphonuclear cells because they have a characteristic architecture to their nuclear e.g. neutrophils have multi-lobed nucleus Monocytes circulate in blood and can phagocytose foreign material as with all the other cells When monocytes traffic into tissues – they exit the blood, pass through endothelial wall and enter tissues- they differentiate into either dendritic cells or macrophages which are important for first line defence Dendritic cells are important for alerting the adaptive immune response Lymphoid progenitor cells develop into T and B cells which can create a specific response to a pathogen and provide immunological memory B cells can differentiate into plasma cells which are the cells that predominantly release antibodies and can also differentiate into memory cells ILC and NK cells are involved in our innate immune response but function more similarly to lymphocytes (T and B cells) in regards to the kinds of cytokines they produce in response to infection but they are unable to provide immunological memory

Infection and response  

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Series of steps from infection to immunological response Pathogen can adhere to epithelial cells or the cell its invading, within those cells there are tissue macrophages and tissue dendritic cells which are at strategic places in the tissue If pathogen breaches the layer of epithelial cells, it can enter tissue which induces a number of responses e.g. wound healing response, release of antimicrobial proteins, phagocytosis by macrophages and dendritic cells to prevent spread and also the complement system Once phagocytes take up pathogen, this induces release of cytokines or chemokines which further activate activity of macrophages and other responses are further augmented to limit ability of pathogen to take hold As part of the phagocytic process, dendritic cells will take in invading pathogens and break them up

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A lot of pathogen proteins that are then broken up inside the dendritic cells can be presented by dendritic cells as little bits on their surface as antigens and migrate to local lymph nodes Presentation of antigens in the lymph nodes initiates adaptive immune responseactivates T and B cells

Step-wise process of cell-mediated immunity 

Bacterial LPS found on gram –ve bacteria – induce inflammatory response and recruitment of innate immune cells

Phases of the immune response: innate and adaptive Response

Time taken to Duration induce response

Innate immune response

Inflammation, complement activation, phagocytosis, destruction of pathogen

Adaptive immune response

Interaction between antigen (Ag)- presenting dendritic hours cells and Ag- specific T cells: recognition of Ag, adhesion, co-stimulation, T-cell proliferation and differentiation

days

Activation of Ag-specific B cells

hours

days

Formation of effector and memory T cells

days

weeks

Interaction of T cells with B cells, days germinal centre formation in peripheral lymphoid tissue, formation of effector B cells (plasma cells) and memory B cells. Antibody production

weeks

Emigration of effector lymphocytes from peripheral lymphoid organs (e.g. spleen, lymph nodes)

Few days

weeks

Elimination of pathogen by effector cells and antibody

Few days

weeks

Maintenance of memory B cells and T cells and high serum or mucosal antibody levels. Protection from reinfection.

Days to weeks

Can be lifelong

Immunological memory

minutes

days

Immune cells  Cells found in buffy coat if blood is separated by centrifugation shown below  Neutrophils- phagocytic cells, most numerous, can take up a variety of pathogens by phagocytosis and efficiently destroy them in intracellular vesicles, these granules contain enzymes able to degrade bacterial or other pathogen components  Eosinophils and basophils- less abundant but like neutrophils they contain granules containing a variety of enzymes ...