BIOL131 - Lec 2- Clinical Immunology.pdf

BIOL131 Clinical Immunology What happens after cell death following tissue damage? Possible outcomes: Restitution – if cells have proliferative capacity to regenerate Fibrous repair (e.g. collagen deposition) & formation of scar tissue – if cells cannot re-grow or tissue architecture is destroyed...

BIOL131 Clinical Immunology What happens after cell death following tissue damage? Possible outcomes: Restitution – if cells have proliferative capacity to regenerate Fibrous repair (e.g. collagen deposition) & formation of scar tissue – if cells cannot re-grow or tissue architecture is destroyed Initial response is acute inflammatory reaction If damaging agent persists = chronic inflammation Acute vs. chronic inflammation • Refers to the longevity of the immune response • Acute inflammation is a normal, healthy, temporary process; designed to eliminate damaging stimuli and heal damage • Chronic inflammation occurs when the damaging stimulus cannot be removed and the inflammatory process persists, becoming damaging to the host tissues Four cardinal effects of acute inflammation 1. Rubor (redness) - vessel dilatation/increased blood flow to site 2. Calor (heat) - vessel dilatation/increased blood flow to site 3. Dolor (pain) - pressure on nerve endings/ chemical factors 4. Tumor (swelling) described by Anders Celsius nearly 2000 years ago Molecular Cell Biology. Lodish et al. 6th Ed. p1055-1062 Acute inflammatory response • Acute injury releases chemicals mediators that stimulate the production of acute inflammatory exudate • Exudate = fluid, proteins, blood cells that mobilise local defences • Infective agents (e.g. bacteria) destroyed and eliminated by components of the exudate • Damaged tissue broken down, partly liquefied and the debris is removed from the site of damage Response controlled by mediators of acute inflammation Acute inflammatory exudate Components • Salt-containing fluids and proteins • Fibrin - high mol. wt. filamentous, insoluble protein • Neutrophils – phagocytic cells • Macrophages - phagocytes & produce cytokines, 2nd wave response • Dendritic cells – present antigen to T-cells • Lymphocytes ( T-cells: ‘cytotoxic’ & ‘helper’) • Enter tissues as a result of blood vessels becoming leaky Changes in blood vessel permeability • Slowing of flow and dilatation of blood vessels • Endothelial cells swell and partially retract • Water, salts, proteins → exudation • Neutrophil → margination → transmigration • Later monocytes (macrophages) & T-cells Transmigration of leucocytes during inflammation https://www.youtube.com/watch?v=LB9FYAo7SJU&x-ytts=1421782837&feature=player_embedded&x-yt-cl=84359240 Summary - Transmigration of leucocytes during inflammation lumen endothelial cells Intracellular 1. Mediated by selectins on endothelial cells and integrins on leukocytes 2. Leukocytes attracted by chemokines and cytokines released by tissue macrophages 3. Diapedesis/Transmigration – leukocyte forms pseudopodia and produces proteases to help move between endothelial cells of veins and migrate into the tissue Cellular mediators of acute inflammation • Neutrophils (granulocytes) - main effector cells of acute response • Monocytes in blood, upon transmigration, become macrophages in tissue • Both capable of phagocytosis • The neutrophil only lives a few days • Neutrophils far outnumber monocytes in acute inflammation Neutrophil stained with H &E Monocyte stained with H &E Cellular mediators of immune response • Monocyte/macrophage secretes cytokines (within minutes) • Cytokines attract and activate B and T-cells to trigger the adaptive immune response (within days) • Acute immune response peaks within 2 days • By 12 days, should have repair and elimination of pro-inflammatory process, so should resolve within ~2 weeks Acute inflammation histology • Neutrophil infiltration in section of lung from a 1918 influenza case with acute pneumonia Uninfected lung alveoli Acute pneumonia neutrophils x100 x200 Taubenberger et al. 2019 Sci. Transl. Med. 11 (502): eeau5484 How does acute exudate leave the tissue? • majority of cells reenter circulation via lymphatic system, stimulate adaptive immune response in lymph nodes • neutrophils do not re-circulate, they stay at site = pus buildup Chronic inflammation (disease) • Damaging stimulus persists and healing cannot occur • Results in continuing necrosis, organisation and repair occurring concurrently • Tissues infiltrated by activated lymphoid cells • Histological features: • necrotic cell debris • acute inflammatory exudate • vascular and fibrous granulation tissue • lymphoid cells & macrophages • collagenous scar persists until damaging stimulus removed Chronic high fat feeding mouse model Mice fed a low (10%) or high (45%) fat diet for 16 months High fat diet Low fat diet inflammation lipid droplets x20 x40 x10 collagen scar x40 Balancing the immune response • Continuing tissue damage Vs. removal of stimulus • Tissue-based immune response → infiltration of lymphoid cells and macrophages • Macrophage is the main effector cell • Macrophages may form discrete clusters called granulomas → granulomatous inflammation • Occurs in tuberculosis, leprosy, cryptococcosis, Crohn’s Disease, sarcoidosis, etc… Tuberculosis-infected lung • Mycobacterium tuberculosis • Invades, and replicates within macrophages • Evades acute immune response “Caseous” (cheese-like) necrosis Porcelli A Tuberculosis: Shrewd survival strategy. Nature 454, 702-703 Granuloma - Tuberculosis infected lung Granuloma (tubercle) in the lung surrounded by necrotic tissue (i.e. macrophages fuse to form multinucleate cell) Guirado and Schlesinger 2013 Front. Immunol. 4:98 Chronic intestinal inflammation Normal Crohn’s disease Crohn’s disease stricture • Inappropriate immune response to commensal microflora? • Cycles of relapse and remission • Major complications: fibrosis and stricture (prevent food movement in gut) Innate vs. Adaptive immune response • Refers to the mediators (receptor, cellular, molecular) of the response • Innate responses are (usually) more rapid, particularly if no ‘memory’ cell clones present. • Adaptive immunity involves generation of antigen-specific antibodies and T-cells (B- and T-cell clones) and confers lasting immunity • Memory clones confer ‘immunity’ • generated via natural exposure (person-person contact), artificial = active vaccination Innate immune response • initial rapid response; triggers adaptive arm • highly conserved across plant, fungi and animal kingdoms • triggered by receptors, such as Pathogen-associated molecular patterns (PAMPs) and Damageassociated molecular patterns (DAMPs) • involves phagocytes (neutrophils, macrophages), cytokine/chemokine production and complement cascade Valles et al. 2014 International Journal of Nephrology and Renovascular Disease 7:241-51 Immunodeficiency • Can either be inherited or acquired (infection), or can result from exposure to certain damaging stimuli (e.g. radiation and chemotherapy) • Inherited - Severe combined immunodeficiency (SCID) = rare genetic disorder where there is little or no function of white blood cells https://www.youtube.com/watch?v=pJa6KVLwl9U Immunodeficiency cont’d • Acquired: Human Immunodeficiency virus (HIV) = infects and destroys T-lymphocytes (lymphocytopenia) • Can lead to unusual infections (e.g. from commensal microbes) and cancer (e.g. Kaposi sarcoma) • Can you think of a situation where immunodeficiency is beneficial? Diagnosis of immunodeficiency White blood cell (WBC) count: Normal ranges • WBC 4,000 to 11,000 cells/ µL of blood • Neutrophils 2,000 to 7,500 cells/ µL of blood • Lymphocytes 1,300 to 4,000 cells/ µL of blood • Variation normally due to infection, but sustained irregularities may indicate immunodeficiency or leukaemia. Immunophenotyping • Technique used to study protein expression on cells • Can be performed on tissue sections or in cell suspensions • Detects specific proteins on cell • Enables distinction between specific immune cell populations • Expression can be detected either by microscopy (Lab 1) or flow cytometry Immunohistochemistry of blood cells Fluorescence activated cell sorting (FACS) of Tcells Microscopy vs. flow cytometry Flow cytometry Microscopy • Subjective interpretation; prone to human error • Cost of human labour • Microscopy widely available • Relatively little training to use, but training in interpretation • Can use antibodies for specific labelling • More difficult to assess multiple types of antigens at same time • Can preserve tissue structure during processing • Low throughput • Automated, reduce possible error • Cost of equipment • FACS less available (particularly in rural/low income settings) • Requires training in use & interpretation • Can use antibodies for specific labelling • Multiple cell types can be assessed at the same time • Loss of tissue structure during processing • High throughput Laboratory Practical