Lymphatic and Immune System Lecture Notes PDF

TOPIC 8 THE LYMPHATIC AND IMMUNE SYSTEM Blood Marlina Mohd Mydin Faculty of Health Sciences UiTM Pulau Pinang Kampus Bertam 1  Functions of Lymphatic System Lymphatic System Component...

TOPIC 8 THE LYMPHATIC AND IMMUNE SYSTEM Blood Marlina Mohd Mydin Faculty of Health Sciences UiTM Pulau Pinang Kampus Bertam 1  Functions of Lymphatic System Lymphatic System Component 2 1 THE LYMPHATIC AND IMMUNE SYSTEM 5 4 3 Body Defenses Lymphoid Tissues & Organs Formation of Lymph  LESSON CONTENTS OUTCOMES By the end of the topic, student should be able to: Explain the lymphatic system structure and function. Define immune system, innate immunity and adaptive immunity. Compare and contrast cell-mediated (cellular immunity) and antibody-mediated (humoral immunity)  The Lymphatic System Functions ▪ The lymphatic system consists of several structures and organs that contain lymphatic tissue, bone marrow, and a fluid called lymph that flows within lymphatic vessel ▪ Lymphatic system functions ▪ Transports escaped fluids from the cardiovascular system back to the blood ▪ Plays essential roles in body defense and resistance to disease. ▪ Transports fats from digestive system. Transport fats from the digestive tract (lacteals) to the bloodstream Lymph that passing through lacteals appears white and known as chyle, due to presence of fat  Remember? The hydrostatic and osmotic pressures operating at capillary beds force fluid out of the blood at the arterial ends of the beds (‘upstream’) and cause most of the expelled fluid to be reabsorbed at the venous ends (‘downstream’)  Lymphatic System Component Venous Arterial system system ▪ Lymphatic system consists of Heart ▪ Lymphatic capillaries Lymph duct ▪ lymphatic vessels Lymph trunk ▪ Lymphatic organs & tissue Lymph node ▪ Lymphatic vessels transport Lymphatic fluids that have escaped from system the blood vascular system back Lymphatic to the blood. collecting vessels, ▪ Lymphoid tissues & organs with valves house phagocytic cells and Lymph lymphocytes which play capillary Tissue fluid essential roles in the body (becomes lymph) defense and resistance to disease. Blood Loose connective capillaries tissue around capillaries  Lymphatic System Component Lymphatic vessels Lymphatic capillaries Small Lymphatic vessels Lymphatic trunks Lymphatic ducts Lymphatic organ Thymus Lymph nodes Spleen Lymphatic tissue Tonsils Peyer’s patches  Lymphatic Vessels and Capillaries ▪ Lymphatic vessels begin as lymphatic capillaries, which are closed on one end. ▪ Lymphatic capillaries are located between cells of many tissues ▪ Lymphatic capillaries merge to form lymphatic vessels: ▪ Resemble veins in structure ▪ Connect to lymph nodes at various intervals ▪ Lymphatic capillaries which have thin walls and many valves. ▪ Form a one-way system Lymphatic Vessels  Lymphatic Capillaries ▪ Weave between tissue cells and blood capillaries ▪ Walls overlap to form flaplike minivalves ▪ Fluid leaks into lymphatic capillaries ▪ Capillaries are anchored to connective tissue by filaments ▪ Higher pressure on the inside closes minivalves ▪ Fluid is forced along the vessel  Lymphatic Capillaries Relationship of lymphatic capillaries to tissue cells and blood capillaries  Formation and Flow of Lymph blood capillaries (blood) ->interstitial spaces (interstitial fluid) -> lymphatic capillaries (lymph) -> lymphatic vessels (lymph) -> lymphatic ducts (lymph) -> junction of the internal jugular and subclavian veins (blood) Plasma, filtered by the blood capillaries. Passes into interstitial tissue spaces and now called as interstitial fluid. When it passes into lymph capillaries, it’s called lymph. The lymph now passes into larger lymphatics vessels.  Lymph ▪ Lymph characteristics ▪ Similar to blood plasma but less protein ▪ Usually clear and colorless ▪ Is milky if draining lipids from small intestine ▪ Contains: ▪ Lymphocytes, macrophages, and bacteria ▪ Viruses, debris, and sometimes cancer cells  Lymphatic Vessels ▪ Lymphatic vessels are similar to veins of the cardiovascular system ▪ Thin-walled ▪ Larger vessels have valves ▪ Low-pressure, pumpless system ▪ Lymph transport is aided by: ▪ Milking action of skeletal muscles ▪ Pressure changes in thorax during breathing ▪ Smooth muscle in walls of lymphatics Valves in the Lymphatic Vessels  Lymphatic Trunks and Ducts ▪ From the lymphatic vessels, lymph passes through lymph nodes and then into lymph trunks ▪ Lymph trunks include the lumbar, intestinal, bronchomediastinal, subclavian, and jugular trunks ▪ Lymph trunks then merge to form either the thoracic duct or the right lymphatic duct.  General Distribution of Lymphatic Collecting Vessels and Regional Lymph Nodes Entrance of right Regional lymphatic duct into right lymph nodes: subclavian vein Collecting ducts Cervical Internal jugular vein Right lymphatic duct nodes Thoracic duct Drains the right head, entry into left chest, and upper limb Axillary subclavian vein Empties into the right nodes Thoracic duct subclavian vein Aorta Thoracic duct Spleen Larger and longer than Cisterna chyli (receives the right lymphatic duct lymph drainage from Drains the body below Inguinal nodes digestive organs) the diaphragm, the left head, neck, chest, and upper limb Lymphatics Empties into the left subclavian vein KEY: Drained by the right lymphatic duct Drained by the thoracic duct  Lymphoid Organs & Tissues Primary lymphatic organs are the bone marrow and thymus Sites where stem cells divide and become immunocompetent (capable of mounting an immune response) Secondary lymphatic organs Sites where most immune responses occur, including the spleen and other lymphoid tissues such as the tonsils. Lymphoid Organs & Tissues Primary lymphatic organs are organs where immune cells become immunocompetent Red bone marrow Thymus Secondary lymphatic organs and tissues include: Lymph nodes Spleen Lymphatic nodules Importance House and provide a proliferation site for lymphocytes Provide surveillance points for lymphocytes and macrophages  Thymus ▪ Located at the inferior neck, extends into the superior thorax ▪ Secretes thymopoietin and thymosins – causing T lymphocytes to become mature ▪ Important at early age and recess in size at puberty and lost its structure at old age  Lymphoid Tissues & Organs ▪ Secondary lymphatic organs and tissues include: ▪ Lymph nodes ▪ Spleen ▪ Lymphatic nodules  Lymph nodes ▪ Lymph nodes filter lymph before it is returned to the blood. (Cluster along the lymphatic vessels) ▪ Harmful materials that are filtered ▪ Bacteria ▪ Viruses ▪ Cancer cells ▪ Cell debris ▪ Defense cells within lymph nodes ▪ Macrophages—engulf and destroy bacteria, viruses, and other foreign substances in lymph ▪ Lymphocytes—respond to foreign substances in lymph  Lymphatic nodes ▪ Most lymph nodes are kidney-shaped, less than 1 inch long, and buried in connective tissue ▪ Surrounded by a capsule ▪ Divided into compartments by trabeculae ▪ Cortex (outer part) ▪ Contains follicles—collections of lymphocytes ▪ Germinal centers enlarge when antibodies are released by plasma cells ▪ Medulla (inner part) ▪ Contains phagocytic macrophages Lymphatic nodes Lymph Flow ▪ Flow of lymph through nodes ▪ Lymph enters the convex side through afferent lymphatic vessels ▪ Lymph flows through a number of sinuses inside the node ▪ Lymph exits through efferent lymphatic vessels ▪ Because there are fewer efferent than afferent vessels, flow is slowed  Spleen ▪ Located on the left side of the abdomen ▪ Filters and cleans blood of bacteria, viruses, debris ▪ Provides a site for lymphocyte proliferation and immune surveillance ▪ Destroys worn-out blood cells ▪ Forms blood cells in the fetus.  Lymphatic Nodules Lymphatic nodules are masses of lymphatic tissue that are not surrounded by a capsule. ▪ They are scattered throughout the lamina propria of mucous membranes lining the gastrointestinal, urinary, and reproductive tracts and the respiratory airways. ▪ Lymphatic nodules in these areas are also referred to as mucosa-associated lymphatic tissue (MALT)  Lymphatic Nodules Tonsils ▪ Small masses of lymphoid tissue deep to the mucosa surrounding the pharynx (throat) ▪ Trap and remove bacteria and other foreign pathogens Peyer’s patches ▪ Found in the wall of the small intestine ▪ Macrophages capture and destroy bacteria in the intestine  Immune System Immunity defined – Body’s ability to protect itself by resisting or eliminating potentially harmful foreign invaders or abnormal cells Immune system functions – Defending against invading pathogens – Removing worn-out cells and damaged tissue – Immune surveillance: identifying and destroying abnormal cancer cells that have originated in the body Pathogenic bacteria and viruses are the major targets of the immune system – Virulence: disease-producing power of a pathogen Leukocytes are the effector cells of the immune system – Include neutrophils, eosinophils, basophils, monocytes, and lymphocytes Immune Responses – Innate responses nonselective defend against foreign material. – Adaptive responses selectively target particular invaders  Immune System Immune responses may be either Innate (nonspecific) immunity or adaptive (specific) immunity ▪ Innate (non-specific) defense system/responses: ▪ Consists of first and second line of defense which become body barricades against invaders. ▪ Adaptive (specific) defense system ▪ Body third line of defense mechanism Immune System  Immune System Innate immunity also called as: ▪ Non-specific immunity Provides the early line ▪ Natural immunity of defense against ▪ Native immunity microbes. Is the first and second line of defense. Most of the components exist before meet with foreign substance. It’s response is fast response (takes few hours). Prevent entry of pathogens or foreign substances. Skin: antimicrobial substances  COMPONENTS OF INNATE IMMUNITY 1. Physical barriers Skin Mucous membrane 2. Normal flora 3. Cellular barriers Leukocytes Phagocytes Cytotoxic leukocytes Inflammatory leukocytes 4. Chemical barriers Acute phase proteins Interferons Complements 5. Acute inflammatory reaction & fever  1. PHYSICAL BARRIER ▪ A cover or coat which wrap and protect the body from external environment a) Skin ▪ Layers of epithelial cells with outer layers of dead cells and waterproof keratin - stop foreign substance from entering body. ▪ Keratin not affected by weal acids and bases; resistant to bacterial enzymes and toxins. ▪ Sweat from sweat glands contains high salt concentration – can inhibit growth of many microorganisms except the normal flora of the skin. ▪ Microorganisms that live all over the skin cannot get through the skin unless it is broken. Skin - Consists of closely packed cells : keratinocyctes - Keratins: resistant to bacterial enzymes and toxins. - Outer skin cells shed continuously prevent grow of many microbs. - Low pH 3-5: discourages growth of many microbes - Dermis- Sweat glands produce sweat that contains high salt concentration.  1. PHYSICAL BARRIER b) Mucous membrane Is a moist cover lining the digestive tract, respiratory tract, urogenital tract and eyes. Epithelial cell secrete (produce) mucus (a viscous / thick fluid). Mucus trap foreign substance that attempt to entre the body. Also sites of secretion of other substances that contribute to body defenses; – Lysozyme – breaks down the cell wall of many bacteria. – Acids - secreted in stomach (pH2), kills most microorganisms that enter body via food. – Digestive enzymes and bile salts – kills microorganisms. – Lactoferrin – found in saliva, milk and seminal fluid. – Spermine – antibacterial substance found in semen. b) Mucous membrane – Fluid flow. Saliva, tear or mucous secretion wash away foreign substance. Some mucous membrane have cilia (hair like projection on epithelial cell). – Cilia sweep mucus-trapped foreign substance out. Reaction and reflex which expel mucus-trap foreign substance. – Coughing, sneezing.  Gastric juice: HCL & mucus pH 1-2 Very high acidity capable to destroying bacteria and most bacteria toxin Nose- mucus coated hair Vaginal secretion pH (3-5) Menstrual flow: clean uterus - Trapped foreign substances and vagina. Saliva: flow and washing action of saliva clean EAR away microbial colonization in mouth. Earwax is a mixture of secretion rich in fatty acid which responsible for low pH (3-5). Low pH inhibit many bacteria growth  2. NORMAL FLORA ▪ Microbes which live on our body but do not cause any complication or disease ▪ Compete with pathogenic microbes and prevent invasion by these microbes ▪ Can inhibit growth of bacteria and fungi which are potential pathogen by; ▪ By competing for nutrient ▪ By secreting toxic substances ▪ By forming bacterial layer on tissue surfaces, therefore preventing the attachment of pathogens on tissue surfaces.  2. NORMAL FLORA skin Micrococcus Staphylococcus epidermidis Staphylococcus aureus Overview of first line defense system 1. CELLULAR BARRIER  Phagocytic Leukocytes Phagocytic leucocytes – Cells which ingest (swallow) foreign substance and destroy them – Phagocytes comes from the Greek phagein, "to eat" or "devour", and "-cyte", "cell"  Phagocytic & Non-phagocytic Leukoytes Leucocytes Phagocytic Non-phagocytic leucocytes leucocytes Basophils NK cells Neutrophils Monocytes Macrophages Eosinophils (Inflammatory (Cytotoxic leucocytes leucocytes)  COMPONENTS OF INNATE IMMUNITY 1. Physical barriers Skin Mucous membrane 2. Normal flora 3. Cellular barriers Leukocytes Phagocytes Cytotoxic leukocytes Inflammatory leukocytes 4. Chemical barriers Acute phase proteins Interferons Complements 5. Acute inflammatory reaction & fever  4. Chemical barrier i. Interferons ii. Complement  ii. Interferons A family of proteins secreted by viral-infected cells Interferons produced by a viral-infected cell will protect other uninfected neighboring cells from being infected. Interferons induced uninfected neighboring cells to produce enzymes that will inhibit replication of virus. Interferons also enhanced the activity of natural killer cells. Interferons – communication molecules that prevent the spread of viruses ▪ Viruses take over cellular machinery to make viral copies. ▪ Infected cells produce and release interferons to chemically warn other cells ▪ Interferons trigger nearby cells to make antiviral proteins, thereby preventing spread.  iii. Complement system Complement is a group of serum proteins that circulate in the blood in an inactive state and are activated in the presence of pathogens. Active state of complement: Provide a major mechanism for destroying foreign substances in the body. ▪ Ability to damage the membrane of the pathogenic organisms, either destroying the pathogen or facilitate their clearance. Complement proteins are synthesized mainly by the liver and widely distribute in blood, lymph and extracellular fluid. Helps or “complements” the ability of antibodies and phagocytic cells to clear pathogens. ▪ Coating pathogens and facilitating their destruction. Function of Complement System Opsonization - enhancing phagocytosis of antigens. ▪ Neutrophils and macrophages cannot internalize ‘naked’ microorganism. Complement protein assists them by opsonization ▪ Opsonization: it coats microbial cells and serves binding site for macrophages attachment. Chemotaxis- attracting macrophages and neutrophils Cell lysis- rupturing membranes of foreign cells Clumping of antigen - bearing agents Opsonization - enhancing phagocytosis of antigens Chemotaxis - attracting macrophages and neutrophils Lysis - rupturing membranes of foreign cells  Clumping of antigen Complement can link antigen together forming a cluster that phagocytes can ingest  COMPONENTS OF INNATE IMMUNITY 1. Physical barriers Skin Mucous membrane 2. Normal flora 3. Cellular barriers Leukocytes Phagocytes Cytotoxic leukocytes Inflammatory leukocytes 4. Chemical barriers Acute phase proteins Interferons Complements 5. Acute inflammatory reaction & fever 5. ACUTE INFLAMMATORY REACTION AND FEVER The inflammatory reaction occurs when tissue is damaged by physical or chemical agents or by pathogens. E.g. tissue injury and infection Inflammation is characterized by sign: swelling, redness, heat, pain.  Functions of Inflammation i. To deliver leukocytes to the site of injury and activate them to perform normal function. ▪ To destroy the injury-causing agent and to remove it and its by-product and any cell debris. ii. To localize the microorganisms (by building a wall around them) so that they do not spread to the neighboring sites. iii. To repair & replace tissue damaged by the injurious agents and its by product.  Major events in acute inflammation 1. Vasodilation – an increase in diameter of blood vessels ▪ Happens following tissue damage. ▪ Due to vasoactive agents, histamine. ▪ Increase blood flow to damaged area. ▪ Redness (erythema) and heat ▪ Cause increase permeability 2. Increase vascular / capillary permeability ▪ Aid the influx of plasma fluid and cells from dilated capillaries to tissues ▪ The accumulation of fluid plasma in tissues causes swelling (edema), redness & pain.  Major events in acute inflammation iii. Influx of phagocytes – Due to vasodilation and increase capillaries permeability – Emigration of phagocytes involves; Adherence to endothelial wall (margination) Diapedesis – phagocytes squeezed out through spaces between endothelial cells & migrate to tissues iv. Repair – To repair damaged or injured tissue to it origin form and physiological function – Regeneration – remaining cells proliferate by mitosis – Can only be done if damage is not severe Inflammatory response  Fever ▪ The body temperature above 37°C. Systemic response to attack by microorganisms usually accompanying severe systemic inflammation. ▪ Cause by a chemical substance known as pyrogen. ▪ 2 types of pyrogens (fever causing agent); ▪ Exogenous pyrogen (exo: outside) ▪ Endotoxin (lipopolysaccharides) found on Gram negative bacteria. *Exotoxins are toxic substances secreted by bacteria and released outside the cell. Whereas Endotoxins are bacterial toxins consisting of lipids that are located within a cell) ▪ Endogenous pyrogen (endo: inside) ▪ Produce by macrophage and neutrophils during inflammation. ▪ Eg. Interleukin I, tumor necrosis factor (TNF) ▪ Pyrogens can alter the body temperature set point on the hypothalamus  Endogenous and Exogenous pyrogen ▪Fever: Pyrogenic response is caused by endotoxin Exogenous pyrogen Endogenous pyrogen Endogenous and Exogenous pyrogen  Fever High fever >40oC : dangerous Mild fever has a few advantages to the body; i. Reduce the rate of bacterial growth ii. Cause the reduction of Fe2+ & Zn2+ which are needed by bacteria for growth. The reduction is due to the intake of these ions by the liver and spleen. iii. Increase the activity of phagocytes, T-lymphocytes and the repair process.  TUTORIAL 1. What is the other name for innate immunity? 2. State the components of innate immunity. 3. How is the skin and mucous membrane can provide the physical barrier to human body? 4. How are the normal flora can inhibit the growth of pathogen? 5. List the phagocytic cells and non- phagocytic cells. 6. What is the functions of macrophage? ADAPTIVE IMMUNITY 70 INTRODUCTION  INTRODUCTION Adaptive immunity is also called as: – Specific immunity Lymphocytes express receptor that specifically recognize different antigens – Adaptive immunity (acquired immunity) Only triggered if microbes or their antigen pass through epithelial barrier. (acquired through infection) Definition of adaptive immunity – 3rd line of defense after innate immunity. – Develops in response to infection. – Made-up of variety of cells (lymphocytes, macrophages) and organs (thymus, lymph nodes). – The response is slower (takes few days). Recognize antigen, stimulation to activate the naïve lymphocytes to proliferate and differentiate inti effector cells and memory cell.  CHARACTERISTICS OF ADAPTIVE IMMUNITY 1. Self nonself recognition ▪ The ability to distinguish self from non-self ▪ Respond only to non-self molecules 2. Antigen specificity ▪ Ability to distinguish subtle differences among antigen ▪ Respond only those required, rather than making a random. ▪ Innate immune components recognize markers found on variety of ‘nonself’ invaders, adaptive immune components recognize specific markers. ▪ Antibodies can distinguish between 2 protein molecules that differ in only a single amino acid or between two isomers of the same molecule.  CHARACTERISTICS OF ADAPTIVE IMMUNITY 3. Immunological memory The ability to recall previous contact with the foreign molecule, respond with more rapid and larger response. TYPES OF ADAPTIVE IMMUNITY Adaptive Immunity Cell-mediated Humoral immunity immunity defense against extracellular microbes defense against intracellular microbes Involve B lymphocytes Involve T lymphocytes & antibodies & cytotoxin Activated T cells react directly against a B cells are activated to secrete antibodies, foreign antigen that is presented to them which are proteins called immunoglobulins. on the surface of a host cell.  DEVELOPMENT OF B LYMPHOCYTES & T LYMPHOCYTES Lymphocytes develop from precursor (stem cells) in the generative lymphoid organ (primary lymphoid organ- bone marrow and thymus). Mature lymphocytes enter peripheral lymphoid organs (secondary lymphoid organ – lymph nodes, spleen & mucosa associated lymphoid tissue) , where they respond to foreign antigens and from where they recirculate in the blood and lymph  DEVELOPMENT OF B LYMPHOCYTES B lymphocytes are produced and mature in bone marrow. Cells that produce antibody are called plasma cells (effector cell). Plasma cells are derived from B cell. B Cell → Plasma Cell → Antibody. B cells circulate through blood stream, lymph nodes, lymphoid tissue. Primary Lymphoid organ Secondary Lymphoid organ  DEVELOPMENT OF B LYMPHOCYTES Molecule of antibody (Ab) are present on the B cell. Once a naïve B cell interact with an antigen (Ag), it will proliferate in numbers and differentiate into plasma cells and memory cells. Plasma cells do not have Ab on their membrane, but they secrete the Ab. Memory cells which have Ab molecules on their membranes will enter a resting phase until the next encounter with the same Ag. Proliferation: expand number antigen-specific cells. Differentiation: converts lymphocytes into effective defenders.  ANTIBODY ▪ When a naive B cell encounters an antigen that fits or matches its membrane-bound antibody, it quickly divides in order to become either a memory B cell or an effector B cell, which is also called a plasma cell. ▪ Plasma cell produce secreted antibody ▪ Functions to bind antigen and triggers several effector mechanism to eliminate the antigen ▪ Antibody is a glycoprotein which mediates humoral immunity.  STRUCTURE OF ANTIBODY ▪ Antibody composed of 4 polypeptide: ▪ 2 identical heavy chains (H) ▪ 2 identical light chains (L) ▪ Held together by a number of disulphide (S- S) bonds. ▪ The simplest Ig molecule has a Y- shaped structure and the L and H-chains are subdivided into variable and constant regions. STRUCTURE OF ANTIBODY Variable regions – Fold together to form antigen-binding site. Constant regions – Anchor membrane bound antibody. – Interact with immune molecules and cells to mediate humoral immunity Only F(ab) involve in antigen binding Fc region tail region of an antibody that interacts with cell surface receptors. 5 types of heavy chain IgG (γ), IgA(α), IgM(µ), IgD(δ), and IgE(ε). L chains (2 types): kappa (κ) or lambda (λ) Hinge region - Forms ‘Y”, flexibility: allows Fab region to move and bind antigen epitopes that are separated from one another by varying distances.  TYPES OF ANTIBODY Base the on the differences on the heavy chain constant regions, antibody can be divided into 5 types; IgA, IgD, IgE, IgG, IgM. ▪ Each isotypes/classes of antibody may contain kappa (κ) or lambda (λ) Major Classes Of Antibodies Antibody isotypes are classified on the basis of their heavy chain, each isotype may contain either kappa (κ) or lambda (λ) light chain.  HUMORAL IMMUNE RESPONSES ▪ Antibody responses to the first and subsequent exposures to an antigen, called primary and secondary responses, differ quantitatively and qualitatively. ▪ In a primary response, naïve B cells in peripheral lymphoid tissues are activated to proliferate and differentiate into antibody-secreting cells and memory cells. ▪ In a secondary responses, memory B cells are activated to produce larger amounts of antibodies, often more heavy chain class switching and affinity maturation because this changes stimulated by helper T cells  Antibody Response Primary response Secondary response  Response when first time  Response when repeat encounter the antigen. exposure to the same  The first antibody antigen. detectable in plasma  Rapid, intense production following initial antigen exposure is IgM. of IgG, whereas IgM titer rises slower and dose not  IgM titers rise quite early, achieve a peak and then reach an impressively high. decline within weeks or months.  DEVELOPMENT OF T LYMPHOCYTES ▪ Formed in the bone marrow, T progenitor cells migrate to the thymus (hence the name “T cell”) to mature and become T cells. ▪ While in the thymus, the developing T cells start to express T cell receptors (TCRs) and other receptors called CD4 and CD8 receptors. – All T cells express T cell receptors, and either CD4 or CD8, not both. ▪ TC & TH cells by the presence either CD4 or CD8 membrane glycoprotein on their surface ▪ TC - CD8 ▪ TH - CD4  DEVELOPMENT OF T LYMPHOCYTES ▪ T cell receptors can only recognize antigens that are bound to certain receptor molecules, called Major Histocompatibility Complex class 1 (MHCI) and class 2 (MHCII). ▪ These MHC molecules are membrane-bound surface receptors can found on antigen-presenting cells, like dendritic cells and macrophages. ▪ CD4 and CD8 play a role in T cell recognition and activation by binding to either MHCI or MHCII. MHC (Major Histocompatibility Complex) ▪ MHC molecules are membrane protein on APCs that display peptide antigens for recognition by T lymphocytes. ▪ Class I and class I MHC molecules are membrane protein that each contains a peptide binding cleft. Peptide-binding cleft of MHC molecules bind peptide derived from protein antigens and display these peptide for recognition by T lymphocytes. Class I MHC expressed on all nucleated cells. Class II MHC molecules expressed mainly on professional APC (dendritic cell, macrophages) and B lymphocytes  Pathways of antigen processing ▪ The class I MHC pathway converts protein in the cytoplasm into peptides that bind to class I MHC molecules for recognition by CD8+ T cells. ▪ The class II MHC pathway convert protein antigens that endocytosed into vesicle of APC into peptide that bind to class II MHC molecules for recognition by CD4+ T lymphocytes.  Activation of Naïve T cells ▪ Three types of mature/activated T cells: ▪ Helper T cells (THcell), Cytotoxic T cells (TC cell), and T regulatory cells (TR). ▪ Naïve T cell which expresses antigen receptor CD4+ will activated into Helper T (TH)cell. ▪ to recognize and bind antigen ▪ secrete chemical substances (cytokines) which will stimulates B cells to produce Ab (IgG, IgA & IgE). ▪ Naïve T cell which expresses antigen receptor CD8+ will activated into Cytotoxic T (TC ) cell ▪ To recognize foreign and host cells that present antifen and destroy them.  COMPARISON OF ADAPTIVE IMMUNITY Adaptive immunity Humoral immunity Cell mediated immunity Provide by T lymphocytes Provide by B lymphocytes Can recognize only protein Can recognize protein, antigen polysaccharide, phospholipid and Recognize antigens presented nucleic acid antigen. by APCs with Class I and Class Can act against soluble or free II MHC molecule antigen Provides immunity to Provides immunity to extracellular intracellular bacteria, viruses bacteria, viruses and toxins. and toxins. Cause Type I, II & III hypersensitivity Cause Type IV hypersensitivity TQ & GOOD LUCK =>_