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Antigens unique molecules, or parts of molecules, that initiate an immune response. Can be recognised by T lymphocytes or by antibodies produced by B lymphocytes & allow the body to recongise potentially harmful pathogens and mount an immune response against them
receptors determine if a molecule or cell they come in contact with has the appropriate structures that show it is part of the same organism
self anitgens Antigens that are produced within a person are called “self”
non- self antigens Antigens that are not produced within a person are called “non- self.”
Reacting to non- self antigens When material such as pollen, or infecting agents, such as bacteria and viruses, enter a person, the B and T cells recognise the antigens on those as “non-self” and react
B lymphocytes antigen recognition • The receptors on B lymphocytes are membrane-bound antibodies that recognise free antigens or antigens that are on the surface of a pathogen. Antibodies can also be secreted by the B lymphocytes.
T lymphocytes antigen recognition The receptors on T lymphocytes are different from the membrane-bound antibodies of B lymphocytes, and recognise antigens presented by the organism’s own cells.
major histocompatibility complex (MHC) proteins on the surface of your body’s cells that present self or non-self antigens to T lymphocytes. MHC markers or proteins are determined by the genotype of the individual, and so are unique to that individual.
Class I MHC proteins found on all healthy cells of the body communicate with cytotoxic T lymphocytes about the proteins being produced within each cell presenting self-antigens and other proteins produced intracellularly
Class II MHC proteins usually only present on specialised antigen-presenting cells (specialized white blood cells; such as dendritic cells, macrophages and B cells). MHC-II presents antigens that originated extracellularly and have been processed by phagocytosis
Diseases any change that impairs the function of an individual in some way • Inherited passed on from parents • Nutritional deficiency such as scurvy • caused by a pathogen and can be transmitted from person to person.
Pathogen organism able to cause disease in a host. Most pathogens contain unique antigens that can be recognised by the immune system. Can be: • Non-cellular agents such as prions or viruses • Cellular agents, or micro-organisms such as bacteria or fungi
Infection pathogen being present in a host, but infection does not necessarily equate with disease. A pathogen may be present in a host but cause not harm
Non-cellular Agents Non-cellular agents are not considered organisms, but they are important causes of disease in many organisms Non cellular agents include • Prions • Viruses • Viroids
Prions infectious agents consisting of only protein, and without any genetic material that causes some forms of degenerative neurological diseases. we all contain the genetic instructions to make prion protein
Viruses particles lacking cellular organisation and consisting of genetic material surrounded by a protein coat that reproduces only in a host cell Contain either DNA or RNA lack the protein-making machinery of cells so need to enter a host cell to reproduce
Bacteriophage reproduction part 1 Viruses that infect bacteria are called bacteriophages • When a bacteriophage infects a bacterial cell, its protein coat becomes attached to the bacterial wall and its DNA is injected into the bacterial cell.
Bacteriophage reproduction part 2 • The phage DNA takes over the bacterial cell and uses energy and material to make new bacteriophage protein coats and viral DNA • The new parts are then assembled into new bacteriophages • In a matter of hours, hundreds of new viruses are produced
Viroids type of self-cleaving RNA enzyme (or ribozyme) that is composed of short, circular strands of RNA that lack a protein coat. Damage plants by competing for nucleotides and forming viroid bundles, which interfere with the internal structures of plants
Cellular agents Cellular agents are micro- organisms that cause disease. Cellular agents include- • Bacteria (prokaryote) • Protozoa (eukaryote) • Funghi • Arthropods • Worms
Bacteria typically single-celled, prokaryote organisms that do not have a membrane-bound nucleus and other cell organelles Some bacterial diseases that affect humans are diphtheria, food poisoning, wound infections
Treatment of Bacteria antibiotics are naturally occurring substances that inhibit the growth of, or destroy, bacteria and other microorganisms. Broad-spectrum antibiotics are useful when the doctor is unsure of the bacteria causing infection
Protozoans Unicellular eukaryotes Absorb nutrients from their hosts Express different proteins (antigens) on the surface of their plasma membranes at different stages of their life cycle, assisting the protozoans in evading detection by the host
Fungi obtain nutrients from decomposition of dead organic matter. Many fungi are ectoparasites (live on the surface of their host.) Most fungal infections are superficial because they effect the skin, nails and hair and rarely penetrate into living tissue
Arthropods Ectoparasites that are small animals within the Arthropod group. Includes mites, body lice and the “crab”louse. They all cause extreme itching. Arthropods are also major vectors of disease in plants and animals i.e. mosquitoes
Worms Parasitic worms can infect plants and animals. They include flatworms such as tapeworms, and roundworms such as hookworms, pinworms and threadworms. Some worms live inside plant tissue; others live outside the plant and cause damage to the plant.
Controlling Pathogens • Antiseptics- used on the skin to kill pathogens • Disinfectants- used to kill pathogens on objects • Fungicides and anti-fungals treat fungi • Antivirals- treat viral infections • Antibiotics
Controlling the spread of pathogens • Quarantine affected people • Vaccinate • Sanitisation • Improved Hygienic Practices
Innate immunity non-specifically protects against a wide variety of pathogens. It consists of physical, chemical and microbiological barriers and responses to infection that occurs when these barriers are breached
Barriers to infection Organisms have a number of first-line defenses (or barriers) that provide innate resistance against pathogens. These are divided into • Physical • Chemical • Microbiological
Physical barriers - plants • Cell walls that provide strength and flexibility • Waxes create thicker cuticle • Bark
Physical barriers - animals • Intact skin acts as a continuous barrier against entry by micro-organisms • Mucous membranes forms a protective barrier and makes it difficult for micro-organisms to penetrate the cells beneath
Chemical barriers - plants • Plants have developed a vast array of chemical defenses that are toxic to fung, insects and microbes
Chemical barriers - animals • Natural secretions – tears and saliva contain lysozyme, an enzyme that causes bacteria to burst or lyse. • Stomach acid and digestive enzymes • Acidic secretions lining the vagina
Microflora (natural flora) Non-pathogenic bacteria normally found on the skin, mouth, nose & throat Competes with other bacteria for space and resources Produces chemicals that reduce the pH of the microenvironment
Innate Immune Responses If pathogens manage to breach the barriers that act as a first line of defence, they are immediately met by attacking cells and molecules
Cells of the innate response (leukocytes) • Macrophages • Neutrophils • Mast cells • Dendritic cells
Macrophages phagocytic cells; initiate acute inflammatory responses by secretion of various cytokines; also play a role as antigen-presenting cells
Neutrophils phagocytic cells; release antimicrobial compounds, such as defensins and hydrogen peroxide, that disrupt bacterial and fungal membranes; release cytokines that attract other immune cells and cause inflammation
Mast cells release of histamine and other active molecules during acute inflammation; play role in allergies
Dendritic cells phagocytic cells; characteristic star-shaped cell; migrate via lymphatic vessels to lymph glands where they act as antigen-presenting cells
Defensive molecules of the innate response • complement proteins • cytokines
Complement proteins Activation results in enzyme-triggered reaction that leads to the lysis of the invading pathogens Destroy bacteria by punching holes in their membranes, causing them to lyse Release of the bacterial contents attracts phagocytes to the site of infection
Cytokines Small signalling molecules Released by body cells in response to cell damage or the presence of pathogens Trigger a variety of responses, both non-specific and specific Interferons and chemokines are two different types of cytokines
Inflammation accumulation of fluid, plasma proteins and leukocytes that occurs when tissue is damaged or infected, and results in heat, pain, swelling, redness and loss of function.
Steps of the inflammatory response 1 Bacteria or other pathogens breach the barriers that provide a first line of defence, such as through an open cut or wound in the skin
Steps of the inflammatory response 2 Injured cells release chemokines that attract neutrophils which migrate towards the cytokines and are activated, causing the neutrophils to recruit macrophages and secrete factors, such as defensins and hydrogen peroxide, that degrade and kill pathogens.
Steps of the inflammatory response 3 Mast cells release histamine, which increases blood vessel dilation and permeability. The dilated, more permeable blood vessels allow leukocytes and fluid containing complement proteins to enter the infected tissue.
Steps of the inflammatory response 4 Platelets release clotting factors at the site of the wound
Steps of the inflammatory response 5 Macrophages in turn become activated and secrete cytokines and, along with neutrophils, phagocytose pathogens and debris at the site of infection. This may lead to pus, which is fluid containing leukocytes, dead pathogens and cell debris
Steps of the inflammatory response 6 The inflammatory response continues until the pathogen is eliminated and the wound has healed
distinguishing features of the adaptive immune response - Specificity the ability to recognise and respond exclusively to specific antigens. On recognising a specific foreign antigen on a pathogen, cells of the adaptive immune system trigger an array of defensive mechanisms that destroy the pathogen
distinguishing features of the adaptive immune response - immunological memory the ability of cells of the adaptive immune system to ‘remember’ antigens after primary exposure, and to mount a larger and more rapid response when exposed to the same antigen
Lymphocytes classified as either B lymphocytes or T lymphocytes according to their interaction with the antigen and their response to it. Lymphocytes travel through the lymphatic system and become activated when they encounter antigens specific to their receptors
mechanisms of adaptive immunity - humoral macromolecules, such as complement proteins and antibodies produced by B lymphocytes, are secreted into the extracellular fluid. B lymphocytes produce specific antibodies against foreign antigens and release them into the blood and lymph
B lymphocytes originate and commence differentiation in the bone marrow and complete their maturation in the peripheral lymphoid organs and tissues. When it meets and binds to a specific antigen its activated to differentiate and divide into two types of daughter cells
plasma cells Activation of B lymphocytes leads to the production of plasma cells, which are essentially ‘factories’ specialising in antibody production. The antibodies produced are specific to the antigen that activated the B lymphocyte
memory B lymphocytes remain in lymphoid tissues for long periods and are responsible for the immunity that often follows infection or vaccination. These cells can divide and give rise to plasma cells if secondary exposure to the antigen occurs
Antibodies (immunoglobulins Ig), produced by B lymphocytes and released into the blood and lymph. They are proteins that bind to specific antigen molecules. They do not directly destroy pathogens, but carry out several important mechanisms to interfere with the function of the pathogen
neutralisation of pathogens Antibodies bind to antigens on the surface of the pathogen, which are required for entry into host cells, thus preventing pathogen invasion of host cells
agglutination Antibodies bind to antigens on the surface of cells and form antigen–antibody complexes, which activate phagocytes and the complement cascade, leading to antigen/cell destruction
mechanisms of adaptive immunity - cell mediated cell-mediated immunity is regulated by T lymphocytes. The response is mediated by the T cell receptors (TCR). Depending on their function, T lymphocytes are classified as helper, cytotoxic or memory T lymphocytes.
Helper T lymphocytes do not directly kill pathogens, rather, as their name suggests, they ‘help’ with immune responses. To assist the immune response, helper T lymphocytes secrete cytokines that promote inflammation, and activate macrophages and B lymphocytes
Cytotoxic T lymphocytes recognise and kill foreign, infected or abnormal host cells by releasing toxic compounds. This includes virus-infected host cells, cancer cells and foreign cells such as those in transplanted tissue
Memory T lymphocytes produced after helper and cytotoxic T lymphocytes have been activated during infection Differentiate into memory T cells that are antigen-specific Persist after the infection is resolved ensuring a prompt response if same pathogen reinfect the organism.
Antigen-presenting cells (APC) part 1 specialised for presenting antigens. When an APC engulfs a pathogen, the antigens of the pathogen are broken into small peptides in the cell. These antigen fragments bind to MHC-II molecules inside the cell.
Antigen-presenting cells (APC) part 2 The antigen–MHC-II complexes then move to the cell surface to present the antigens to helper T lymphocytes. The TCRs on the helper T lymphocytes recognise the antigen–MHC-II complex.
Antigen-presenting cells (APC) part 3 Signal transduction in the T lymphocyte leads to activation of the cell, which then proliferates and releases cytokines
Immunological memory response arising from the first encounter of a T or B lymphocyte with a specific antigen is known as the primary immune response. After the initial exposure, B and T lymphocytes form B and T memory lymphocytes
secondary immune response Lymphocyte proliferation and production of antibodies occurs faster Existing memory lymphocytes, which were produced during the first encounter remain for months or years More antibodies are also produced
The lymphatic system The lymphatic system is vital to the immune response. Invading pathogens are transported in the lymph to the lymph nodes, where bacteria, viruses and cancer cells are trapped and destroyed by phagocytes and lymphocytes.
Structure of the lymphatic system The lymphatic system is made up of lymph, lymphatic vessels and primary and secondary lymphoid organs and tissues
Lymph Lymph is similar to blood plasma—it is the fluid from the circulatory system that flows into the spaces surrounding tissues. Lymph contains immune cells such as lymphocytes and phagocytes
Primary lymphoid organs The primary lymphoid organs are bone marrow and the thymus
Bone marrow contains stem cells from which B and T lymphocytes originate. B lymphocytes undergo development in the bone marrow then enter the bloodstream and travel to the spleen and other secondary lymphoid tissues, where they complete their maturation
Thymus Immature T lymphocytes travel from the bone marrow to the thymus, where they mature. The thymus is considered a primary lymphoid organ because of its role in the maturation of T lymphocytes
Secondary lymphoid organs and tissues lymph nodes, spleen, tonsils, adenoids, appendix and Peyer’s patches where adaptive immune responses begin. Lymphocytes are activated in secondary lymphoid tissues, where they recognise and respond to non-self antigens specific to their receptors
Lymph nodes composed of lymphoid tissue, and are located at regular intervals along the lymphatic system. Lymph passes through lymph nodes on its way back to the bloodstream
Function of lymph nodes part 1 • act as filters, trapping foreign particles, cellular waste, pathogens and toxins. • Some dendritic cells and macrophages are stationed in the lymph nodes, where they phagocytose pathogens, and present the foreign antigens to helper T lymphocytes.
Function of lymph nodes part 2 • Antigen-presenting cells in body tissues also migrate to the lymph nodes after phagocytising pathogens, to present foreign antigens to helper T lymphocytes.
Function of lymph nodes part 3 • B lymphocytes that identify an antigen undergo clonal expansion and differentiation to plasma cells. Antibody is released into the bloodstream to travel throughout the body.
Function of lymph nodes part 4 • Cytotoxic T lymphocytes are activated, proliferate, and travel through the bloodstream to sites where they are needed. The size of lymph nodes can expand markedly when cell proliferation is occurring in response to an infection.
Created by: emmawalton05
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