Lecture 1: Working of Immune System Lecture Notes PDF

Introduction to immunology & Immune mechanisms AISHATH MAJIDHA HASSAN  Objectives  By the end of this session students will be able to:  Describe general terms related to immunology  Describe the general functions of the immune system  Describe the c...

Introduction to immunology & Immune mechanisms AISHATH MAJIDHA HASSAN  Objectives  By the end of this session students will be able to:  Describe general terms related to immunology  Describe the general functions of the immune system  Describe the characteristics of the immune response, giving appropriate examples  Differentiate the first line of defense, innate & acquired immunity  Describe mechanisms involved in the first line of defense, innate & acquired immunity  Briefly describe the structure and function of MHC molecule and T cell receptor and the process of antigen processing and presentation  “A human body is a conversation going on, both within the cells and between the cells” W. Daniel Hillis  The immune system  Includes the structures and processes that defends the body against potential pathogens or foreign bodies  Composed of specific and non-specific elements.  Immunity: the ability of an organism to defend the body against pathogens or foreign bodies  Immunology: study of immunity/immune mechanisms  Function of immune system Self Non-Self  Recognize self vs. non-self  Defend body against non-self  Important terms  Antigen  Anything causing an immune response, usually foreign material but may be our own tissues  Pathogen  Any disease causing microorganism  Chemotaxis  Migration of a cell in response to a chemical stimulus  Characteristics of the immune system  Specificity  Memory  Mobility  Replicability  Cooperativity  Defense mechanisms  First line of defense  Barriers to infection  Second line of defense  Innate immune mechanisms  Third line of defense  Acquired immune mechanisms First line of defense  Barriers to infection  Physical/mechanical  Skin  Cilia, hair  Movement of intestinal content  Urine flushing action  Chemical  Mucus  Tears, lysozymes  Stomach acid, bile  Sweat  pH of vagina Source: http://vcebiologyimmunityproject.weebly.com  Second line of defense  Innate:  Natural or inborn  Non- specific  Cell mediate and humoral mediated components.  Cellular: mast cells, neutrophils, macrophages  Humoral: lysozyme, interferons, complement  Protects the body from invading microbes once they gain entry  Main mechanisms include:  Phagocytosis  Inflammatory response  Complement activation  Antimicrobial normal flora  Phagocytosis  Phagocytosis is the ingestion or engulfing a microorganism by a phagocytic cell  Four steps:  Migration – ameobic movements, chemotaxis  Attachment  Ingestion & phagosome formation  Killing - O2 dependent, O2 independent mechanisms  5. Microbe in fused vesicle is killed 2. Phagocytes forms pseudopods and digested by lysosomal enzymes which eventually engulf the particle within the phagolysosome, leaving a residual body 3. Phagocytic vesicle containing antigen 1. Microbe Adheres (phagosome) 4. Phagocytic vesicle is to phagocyte fused with a lysosome (phagolysosome) 6. Indigestible and residual material is removed by exocytosis Inflammatory response  Inflammatory response  Protect body from invading microbes  Complex response system - activates the immune system, control spread, repair damage and clear infections  Characterized by a number of symptoms  Complement system  Complex chemical defense system that destroys the invading pathogens  Lytic and opsonic effect  Consists of a number of serum proteins  Three pathways  Functions by:  Lysing the invading cells  Triggering an inflammatory response  Helping in phagocytosis of microbes  Antimicrobial normal flora  Prevents establishment of pathogens by:  Occupying attachment sites  Competing for essential nutrients  Producing harmful substances to pathogenic bacteria - bacteriocins  Chemical mediators  Cytokines  Antimicrobial peptides  Non-specific mediators with antimicrobial properties  Eg: defensins, bacteriocins  Acute phase proteins  Secreted in response to inflammatory molecules  Eg: C-reactive protein (opsonin), fibrinogen, mannose-binding lectin  Fever  Pyrogens produced by bacteria/viruses  Alters body temperature homeostasis  Cytokines  Soluble proteins; signaling  Cytokines bind to molecules through which receptors on target cells; cells interact or their action may be: intercommunicate –  Autocrine “molecular messengers”  Paracrine  Endocrine  Can stimulate production of chemical mediators, cell  Can be classified as: proliferation/inhibition,  Interleukins chemotaxis etc  Chemokines  Interferons  Acquired Immunity  Allows body to recognize, remember and respond to a specific stimulus - antigen  Specificity:  Memory:  Composed of cellular and humoral components  T and B lymphocytes, plasma cells  Antibodies and cytokines  Cell mediated Acquired Immunity  Involves T lymphocytes and phagocytic cells  T lymphocytes respond to antigens associated with major histocompatibility complex (MHC) proteins presented by other cells (antigen presenting cells)  MHC: binds to peptides from pathogens and display them on the cell surface, which is recognized by T cells  MHC molecules Found on the surface of Found only on APCs - dendritic all nucleated cells, including platelets cells, phagocytes, endothelial cells, thymic epithelial cells, B cells Presents peptides from cytosolic protein digestion – endogenous pathway Ags derived from extracellular proteins  T-Cell Receptor (TcR)  Found on T-cell surface  Two polypeptide chains, α & β  variable (V) & constant (C) region  Hypervariable region:  contribute to diversity of TCR  Recognizes MHC + peptide bound in the groove Antigen processing & presentation  Humoral mediated Acquired Immunity  Mediated by antibodies formed in response to antigenic stimulation  Specific for the antigen against which it is formed  May be active or passive  Acquired Immunity Humoral mediated  Active immunity by:  Natural exposure in response to infection  By intentional injection of antigens  Passive immunity by:  Infusion of serum/plasma with high concentrations of Ab  Transplacental transfer of maternal Ab to fetus in utero  Humoral – mediated Cell – mediated Mechanism Antibody mediated Cell mediated Cell type B lymphocytes T lymphocytes Mode of action Antibody in serum Direct cell-to-cell contact or soluble products secreted by cells Purpose Primary defense against Defense against viral and bacterial infections fungal infections, intracellular organisms, tumor antigens and graft rejection https://youtu.be/PzunOgYHeyg