Worksheet 3 Mic 660 PDF

**Question :1- Briefly describe the phagocytic barrier function by adding cell types evolved and their function.** **Answer:** - Phagocytic barrier is referring to as first line of body's defense system. - Its primary function is to ingest and destroy microbes and remove damage tissue...

**Question :1- Briefly describe the phagocytic barrier function by adding cell types evolved and their function.** **Answer:** - Phagocytic barrier is referring to as first line of body's defense system. - Its primary function is to ingest and destroy microbes and remove damage tissues. - This barrier contains variety of phagocytic cells which are involved in destruction of harmful microbes by engulfing them. 1. **MACROPHAGE:** - It derived from enlargement of monocyte. - Its main function is to ingest microbes by phagocytosis process with the help of surface receptor and then kill ingested microbes. - Macrophage contain surface receptors such as toll like receptors help to recognize antigen which leads to adaptive immune response and inflammation. - In phagocytic, they absorb the microbes and then this microbe known as phagosome and special type of enzyme called lysosome destroy the pathogen and convert into harmless product - The interaction of pathogen and macrophage release signaling protein such as chemokines which attract other immune cells to site of infection and also induce inflammation. - Inflammation induces production of cytokine such as interleukin 2. **NUETROPHILL:** - They are most abundant immune cells which are type of white blood cells. - Neutrophils recognize pathogen with the help of surface receptors and adhere to endothelial cells, migrate to sites of inflammation. - They release granules containing antimicrobial peptides, enzyme and reactive oxygen species to kill pathogen. - They employ both oxygen dependent and independent pathways to generate antimicrobial substance. - Neutrophils exhibit larger respiratory burst than macrophages. 3. **EOSINOPHILS:** - They are motile phagocytic cells which are migrate into tissue spaces from blood. - The cytoplasmic granules of eosinophils contain enzyme that specifically harmful for parasites cell wall. - Engulf and kill the parasites and other foreign particle and play a crucial role in allergic reactions. 4. **BASOPHILS:** - Basophils release pharmacologically active substances from their cytoplasmic granules which play major role in certain allergic response. - They use receptors like FCR and complement receptors to bind with Ige antibody. 5. **MAST CELL:** - They present in abundant amount in skin and mucosal epithelial. - They bind with Ige and initiate allergic response by realizing histamine and other mediators that promote changes in blood vessels which cause inflammation. 6. **DENDTRITIC CELL:** - They act as messenger between innate and adaptive immune system, Due to their ability to promote T lymphocyte response after innate immune activation. - They have location on tissues and their expression for pattern recognition receptors for PMPs and DAMPS, that result into rapidly and efficiently detect invading microbes. 7. **NATURAL KILLER (NK) CELL:** - they play a crucial role in innate immune response mainly against viruses and intracellular bacteria as a cytotoxic cell. - The granule protein of NK cell called perforin, that facilitates the entry of granzymes into cytosol of target cells and leads to cell death. - They recognize ligands on infected cells and kill the host cells. - NK cells respond to interlukin-12 which produce by macrophages and secret IFN-γ which activates microphages to kill phagocytosed microbes. **QUESTION 2: briefly describe the phagocytosis and how it leads to microbe death.** **ANSWER:** - It is crucial feature of cellular innate immunity performed by phagocytic cells which have ability to engulf and ingest or kill pathogens. - **This process complete with 4 major STEPS:** a. **Recognition of invading microbes:** - Macrophage has pattern recognition receptor on their plasma membrane which recognize specific molecular pattern on the pathogen, it known as pathogen-associated molecular patterns. - This step completes with interaction of specific patter receptor and PMPs. b. **Ingestion and formation of phagosome:** - Plasma membrane of the phagocyte extends surrounds the bound pathogen which result into interline microbes by forming phagosome. - This phagosome binds with lysosome inside the cytoplasm of the phagocyte, as lysosome contain digestive enzyme and other microbicidal substances. c. **Formation of phagolysosome:** - The fusion of phagosome and lysosome result into largest structure known as phagolysosome. - Phagolysosome has acidic environment that inhibits microbial growth. - The lysosome contains digestive enzyme which work as degrade microbial components which result into kill the infectious material. - This indigestible material knows as residual body. - This residual body moves towards the cell boundary and discharge outside the cell, this process known as exocytosis. - The complement cascade is important part of innate immunity. - It is made up of 20 protein which synthesized in liver. - It has ability of antibody and phagocytic cell which clear pathogen. - It has completed with 3 main pathways: 1. Classical pathways - The complement cascade depends on 4 main effector function: A. **Cell lysis:** - The membrane attack complex (MAC) inserts into target cell membrane that leads to ruptures bacterial cell wall which result into cell death. - The components of MAC are C5b, C6, C7, C8 and multiple copies of C9. - The large amount of bacterial component destroys during cell lysis. B. **Opsonization:** - This process increases phagocytosis of pathogen with help of coating pathogen with soluble proteins such as C3b. - The factor C3b activates neutrophil and macrophages which further process phagocytosis in which they engulf pathogen and destroy the infectious material. - Antibodies and complement factor are coated on dangerous antigens that then be recognized by Fc receptors on phagocytic cells. - This interconnection complements coated antigen by phagocytic cells result in phagocytosis and antigen destruction. C. **Activation of inflammatory response:** - The complement factor C3a, C4a and C5a act as inducers of inflammation. - This three complement bind with receptors on mast and basophils leads to degranulation that release histamines. - Histamines increased vascular permeability by inducing smooth muscle contraction. - Also, neutrophils and macrophages are migrated in are where antigens are present and release chemotaxis substance which leads to activate inflammation. D. **Clearence of immune complexes:** - Immune complex formed activates the complement that leads to generation of C3b which coats immune complexes and CR1 on erythrocytes bind C3b. - Red blood cells connect with these immune complexes and take them to liver and spleen where phagocytic cells destroy immune complex from the RBC. **Question:4: What is the C3 and C5 convertase for each of the complement pathways?** - C3 and C5 convertase act as enzyme complex that are essential for the complement cascade's effector function including opsonization, inflammation and membrane attack. - For classical pathway: - Classical C3 convertase: - Activated C1 leads to activation of C2 and C4. - C2 cleaved into C2a and C2b. - C4 is cleave into C4a and C4b. - C2a and C4b bind to surface of pathogen, make a complex C4b2a which known as C3 convertase. - C2b and C4a diffuse away from the bacterial cell. - Classical C5 convertase: - C3 convertasa produce more C3 molécula. - C3 is divide into C3a and C3b. - Some c3b bind with c4a2b which leads to formation of C4b2a3b that act as C5 convertase. - Then C3a diffuse away. - For alternative pathway: - - Alternative C3 convertase: - The binding of C3b with factor B allows a protein enzyme called factor D that cleave factor B and form Ba and Bb. - Factor Bb remains bound to C3b to form C3bBb which known as C3 convertase. - Alternative C5 convertase: - Amplification loop help in C3b production for bind to C3bBb to form C3Bb3b that active C5 convertase which cleaves C5 into C5a and C5b. - For lectin pathway: - Lectin C3 convertase: - Mannose binding lectin is bind to mannose on bacterial cell. - This binding activates 2 MBL associated serine proteases which is involved in cavemen and activation of C4 and C2. - As per to classical pathway, cleaved C4 and C2 generate C3 which further produce C4b2a. - Lectin C5 convertase: - Same as to classical pathway, C4b2a bind with C3b and produce C5 convertase. 1. **Question:5- Briefly describe the major points in the complement pathway where the complement activation/effector functions can be regulated.** - The complement system consists of several plasma proteins that work together to opsonize microbes, which leads to promote the recruitment of phagocytes to the site of infection, in some cases to directly kill the microbes. - Complement is heating labile component of plasma, around \> 20 proteins circulating in tissue fluid, blood and on surface. - It is mainly synthesized in liver and other tissue. - **Complement cascade:** - it normally circulating as pro-protein which work as enzyme cascade in response to recognition of microorganism. - recognition is the first step in this system which is done with three main pathways: **1. Classical pathway** **2.alternative pathway** **3.lactin pathway** **1. classical pathway:** - This pathway involves with C1, C2, C4 complement and triggered by the binding of antigen antibody complex to C1. - The formation of C3 convertase and C4b2a occurs in this pathway then they split C3 into two large fragment C3b, which covalently attach to the surface of microbial pathogen and **opsonize them**. - **Effector function:** - this pathway produces C3b which involve in opsonization. - C3b produce more neutrophils and macrophages which enhance process of phagocytosis, result into death of microbes by engulfing them. **2. alternative pathway:** - This is antibody independent pathway which involved four serum protein C3, factor B, factor D and properdin. - C3 produce C3a and C3b by spontaneous hydrolysis, in which C3b binds with factor B in presence of Mg2+ which leads to production of C3 convertase and C5 convertase. - **Effector function:** - From the C5 convertase, C5b leads to initiation of MAC-membrane attack complex which bind to bacterial cell wall and rupture it. - This is the effector function as cell lysis in which large amount of bacterial cell destroyed. **3. lectin pathway:** - Lectin is protein that binds with carbohydrate and produce MBL- mannose -binding lectin by liver in acute inflammation. - This pathway activates with binding of MBL to mannose residue with bacterial cell surface. - This binding leads to activate 2 MBL associated serine protease that cleave C4 and C2. - C4 and C2 generate C3 and C5 Convertase.