adaptive and innate immunity.pptx
- 1. Adaptive and innate immunity Pramila adhikari CIST College 1
- 2. Innate immunity or nonspecific, immunity is the natural resistance with which a person is born. It provides resistance through several physical, chemical, and cellular approaches. Microbes first encounter the epithelial layers, physical barriers that line our skin and mucous membranes. 2
- 3. Immunity Immunity is defined as the state of resistance or in susceptibility exhibited by the host to toxic molecules,micro organisms and foreign cells. Types of immunity: two types of immunity 1. Non-specific immunity or innate or natural immunity 2. Specific, acquired or adaptive immunity. 3
- 4. Types of immunity: 1.Species immunity 2.Racial immunity 3.Individual immunity Host factors in innate immunity a.Age b.Hormonal influence c.Nutrition 4
- 5. Species immunity • Resistance to infection varies with the species of animals. • Animals of same species exhibited uniform pattern of susceptibility to infections. • For eg;disease of mammals do not effect fish or reptiles and vice versa,Birds are immune to tetanus. 5
- 6. Racial immunity • Various animal and plant races show marked differences in their resistance to certain infectious disease. • For eg:Algerian race of sheep are immune to anthrax eventhough which is more common disease among other races of sheep;Blacks show high resistance to yellow fever and malaria than white. 6
- 7. Individual immunity • Factors affecting in individual immunity • AGE:is an important indicator ,foetus and old person are more susceptible to any diseases.In foetus immune cells are immature and in old age there is gradual wanning of immune cells. • Hormonal influence:Hormonal imbalance are also responsible for the susceptibility of an individual to any disease.For eg;diabetes,hypothyroidism and adrenal dysfunction influence the individuals susceptibility to infection. 7
- 8. • Nutrition:Immune response is suppressed in protein malnutrition and is deficiency of some essential amino acids.Besides this other factors such as personal hygiene,the nature of work place and its hazards,the oppurtunity for contacts with infected individual can also ply an imp role in innate immunity. 8
- 9. Adaptive immunity is often sub-divided into two major types depending on how the immunity was introduced. Naturally acquired immunity occurs through contact with a disease causing agent, when the contact was not deliberate, whereas artificially acquired immunity develops only through deliberate actions such as vaccination. Both naturally and artificially acquired immunity can be further subdivided depending on whether immunity is induced in the host or passively transferred from a immune host. Passive immunity is acquired through transfer of antibodies or activated T-cells from an immune host, and is short lived -- usually lasting only a few months -- whereas active immunity is induced in the host itself by antigen, and lasts much longer, sometimes life- long. The diagram below summarizes these divisions of immunity. 9
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- 11. Adaptive and innate immunity • The immune system is typically divided into two categories--innate and adaptive--although these distinctions are not mutually exclusive. • Innate immunity – Innate immunity refers to nonspecific defense mechanisms that come into play immediately or within hours of an antigen's appearance in the body – These mechanisms include physical barriers such as skin, chemicals in the blood, and immune system cells that attack foreign cells in the body – The innate immune response is activated by chemical properties of the antigen 11
- 12. Adaptive and innate immunity • Adaptive immunity – Adaptive immunity refers to antigen-specific immune response – The adaptive immune response is more complex than the innate – The antigen first must be processed and recognized. Once an antigen has been recognized, the adaptive immune system creates an army of immune cells specifically designed to attack that antigen – Adaptive immunity also includes a "memory" that makes future responses against a specific antigen more efficient. 12
- 13. Types of Acquired Immunity I. Naturally Acquired Immunity: Obtained in the course of daily life. A. Naturally Acquired Active Immunity: – Antigens or pathogens enter body naturally. – Body generates an immune response to antigens. – Immunity may be lifelong (chickenpox or mumps) or temporary (influenza or intestinal infections). B. Naturally Acquired Passive Immunity: – Antibodies pass from mother to fetus via placenta or breast feeding (colostrum). – No immune response to antigens. – Immunity is usually short-lived (weeks to months). – Protection until child’s immune system develops. 13
- 14. Types of Acquired Immunity (Continued) II. Artificially Acquired Immunity: Obtained by receiving a vaccine or immune serum. 1. Artificially Acquired Active Immunity: – Antigens are introduced in vaccines (immunization). – Body generates an immune response to antigens. – Immunity can be lifelong (oral polio vaccine) or temporary (tetanus toxoid). 2. Artificially Acquired Passive Immunity: – Preformed antibodies (antiserum) are introduced into body by injection. • Snake antivenom injection from horses or rabbits. – Immunity is short lived (half life three weeks). – Host immune system does not respond to antigens. 14
- 15. Adaptive and innate immunity Components of the immune system Innate immune system Adaptive immune system Response is non-specific Pathogen and antigen specific response Exposure leads to immediate maximal response Lag time between exposure and maximal response Cell-mediated and humoral components Cell-mediated and humoral components No immunological memory Exposure leads to immunological memory Found in nearly all forms of life Found only in jawed vertebrates 15
- 16. Anatomical barrier Additional defense mechanisms Skin Sweat, desquamation, flushing, organic acids Gastrointestinal tract Peristalsis, gastric acid, bile acids, digestive enzyme, flushing, thiocyanate, defensins , gut flora Respiratory airways and lungs Mucociliary elevator, surfactant,defensins Nasopharynx Mucus, saliva, lysozyme Eyes Tears 16
- 17. The Immune System is the Third Line of Defense Against Infection 17
- 18. Innate immunity • This prevents entry of micro-organisms into tissues or, once they have gained entry, eliminates them prior to the occurrence of disease • Characteristics – Present from birth. – Non-specific - acts on many organisms and does not show specificity. – Does not become more efficient on subsequent exposure to same organisms. • Prevention of entry of organisms – Mechanical barriers at body surfaces, skin, mucous membranes - disruption leads to infection. – Antibacterial substances in secretions, lysozyme, lactoferrin, low pH of stomach contents – Prevention of stasis. • Peristalsis/flow of urine/upward movement of secretions in bronchial tree. • Coughing • Vomiting 18
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- 20. Innate immunity • Non-specific elimination of micro-organisms 1. Phagocytosis - ingestion and killing of micro-organisms by specialised cells (phagocytes) Phagocytes - polymorphonuclear leukocytes (neutrophils), mononuclear phagocytes (monocytes, macrophages) 2. Opsonisation - the process of coating micro-organisms with some of the proteins found in plasma, to make them more easily phagocytosable 1. An OPSONIN is a plasma protein binding to bacteria. This promotes adhesion between the opsonised bacteria and macrophages because the opsonin binds to receptors on phagocyte membrane e.g. complement with complement receptors and phagocytes. Opsonisation and phagocytosis are more efficient in immune individuals. 20
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- 22. Adaptive immunity • It has been observed that the immune system responds to micro-organisms but not to its own cells and that the system knows that the body has been infected previously with a particular organism. This implies: – Immunological recognition – Self/non-self discrimination – Immunological specificity – Immunological memory • Immunity is mediated by the IMMUNE SYSTEM, which responds to infection by mounting an IMMUNE RESPONSE. An immune response must: – RECOGNISE a micro-organism as foreign (non-self) as distinct from self – RESPOND to a micro-organism by production of specific antibodies and specific lymphocytes – MEDIATE the elimination of micro-organisms – An agent which evokes an immune response is called an IMMUNOGEN. The term ANTIGEN is applied to a substance which reacts with antibody. 22
- 23. Key mediators of immunity • A specialized group of cells termed as antigen- presenting cells (APCs) link the innate and adaptive immune systems by producing cytokines, which: – Enhance innate immune cell function; and – Contribute to lymphocyte function • Phagocytes and lymphocytes are key mediators of immunity • Phagocytes are first line of defense against infection • Lymphocytes have specialized function and mediate adaptive immune response 23
- 24. Antigens • Antigens are molecule recognized by receptors in lymphocytes • Originally the term antigen was used for any molecule that induced B cells to produce a specific antibody (antibody generator) • This term now more widely used to indicate molecules that are specifically recognized by antigen receptors of either B cells or T cells • So now broadly defined as molecules that initiate adaptive immune responses (e.g. components of pathogenic organisms); can also be called immunogen • A large variety of self molecules can serve as antigen molecule as well, provoking autoimmune responses that can be highly damaging, and even lethal 24
- 25. Antigens • Antigens are the initiators and driving forces of all adaptive immune responses • When antigen is eliminated, immune responses switch off • Both T cell receptors and immunoglobulin molecules (antibody) bind to their respective antigens with a high degree of specificity • They have similar structural relationships and are closely related in their evolution, but bind to very different types of antigens and carry out different biological functions 25
- 26. Antigens Epitope: Small part of an antigen that interacts with an antibody. Any given antigen may have several epitopes. Each epitope is recognized by a different antibody. 26
- 27. Epitopes: Antigen Regions that Interact with Antibodies 27
- 28. Antibody • Soluble antibodies (immunoglobulins) are a group of serum molecules closely related to and derived from antigen receptors and B cells • Basic Y-shaped structure with two regions (variable region) at tip of Y that binds with antigen • Stem of Y is called constant region and is not involved in antigen binding • The two variable region contains identical antigen binding sites that are specific to only one type of antigen • However the amino acid sequence in variable region of different antibodies are extremely variable, therefore provide an extremely large stock of antigen-binding sites 28
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- 30. Antibody • Pathogens typically have many different antigens on their surface • Each antibody binds to an epitope, which is a restricted part of an antigen • A particular antigen can have several different epitopes or repeated epitopes • Antibodies are specific to epitopes rather than the whole antigen molecule • The constant region of antibody (Fc region) acts as adapters to link phagocytes to pathogens 30
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- 32. Immune responses • There are two phases of immune response – antigen recognition and antigen eradication • Most immune responses to infectious organisms are made up of a variety of innate and adaptive components: – In the earliest stages of infection, innate responses predominate – Later the lymphocytes start to generate adaptive immune responses; – After recovery, immunological memory remains within the population of lymphocytes, which can then mount a more effective and rapid responses if there is a reinfection from same pathogen later 32
- 33. Antigen recognition • Lymphocytes are responsible for antigen recognition, and this is achieved by clonal selection • Each lymphocyte is genetically programmed to be capable of recognizing just one particular antigen but as a whole immune system can recognize many thousands of antigens collectively (collective proportion of specific lymphocytes) • When an antigen binds to few lymphocytes that can recognize it , they are induced to proliferate rapidly which results in sufficient number of lymphocytes to mount an adequate immune response • Clonal selection – antigen selects and activates the specific clones to which it binds; this operates for both B and T cells 33
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- 35. Antigen recognition • Lymphocytes that have been stimulated by binding to their specific antigen, take the first step towards cell division – They express new receptors that allow them to respond to cytokines from other cells, which signal proliferation – May start to secrete cytokines themselves – Will usually go through a number of cycles of division before differentiating into mature cells under the influence of cytokines • Memory cells – even when infection has been overcome, some of the newly produced lymphocytes remain, available for restimulation if antigen is ever encountered again; these cells are called memory cells and can provide immunity to the infection later when needed 35
- 36. Antigen eradication • The defense mechanisms by which immune system can destroy pathogens, each being suited to given type of infection at a particular stage of its lifecycle, are often referred to as effector systems 1. Antibody binding 2. Phagocytosis 3. Cytotoxic reactions 36
- 37. Effector system • Antibody binding – One of the simplest effector systems – Antibodies can combat certain pathogens just by binding to them – E.g. antibody to the outer coat proteins of some rhinovirus (which causes colds) can prevent the viral particles from binding to and infecting host cells 37
- 38. Effector system • Phagocytosis – Antibodies activates complement or acts as an opsonin to promote ingestion by phagocytes – Phagocytes that have bound to an opsonized microbe engulf it by extending pseudopodia around it – These fuse and internalize microorganism (endocytosed)in a phagosome – Granules and lysosomes fuse with the phagosone, pouring enzyme into resulting phagolysosome, to digest the contents 38
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- 40. Effector systems • Cytotoxic reactions – These are directed against whole cells which are too large for phagocytosis – The target cell may be recognized either by • specific antibody bound to the cell surface • T cells using their specific TCRs – The attacking cells direct their granules towards the target cell which are discharged into extracellular space close to the target cells – These granules contain perforin molecules which can punch holes in outer membrane of the target – Some cytotoxic cells can signal to the target cell to initiate programmed cell death or cell suicide – a process called apoptosis 40
- 41. Electron microscope picture of Neutrophil engulfing Anthrax virus 41
- 42. Immune responses to extracellular and intracellular pathogens • In dealing with extracellular pathogens, the immune system aims to destroy the pathogen itself and neutralize its products • In dealing with intracellular pathogens, the immune system has two functions – T cells can destroy the infected cells (i.e. cytotoxicity) – T cells can activate the infected cells to deal with the pathogen itself (e.g. helper T cells release cytokines, which activate macrophages to destroy the organisms they have internalized) • Many pathogens have both intracellular and extracellular phases of infection, so different mechanisms are usually effective at different times 42
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- 44. Immune responses to extracellular and intracellular pathogens • For example, the polio virus travels from the gut, through the blood stream to infect nerve cells in the spinal cord • Antibodies and complement can block the extracellular phase of the life cycle and promote phagocytosis of the virus • Interferons produced by infected cells signal uninfected cells to induce state of antiviral resistance • Virus can multiply only within living cells; CTLs (cytotoxic T lymphocytes) recognize and destroy the infected cells 44
- 45. Reference • Roitt, I., Brostoff, J., Male, D. Immunology. 1993. Mosby-Year Book Europe Limited, London. 3rd Ed. 45