CIE 11 immunity topical
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Questions and Answers

What characteristic of the TB bacteria allows it to survive inside macrophages without being completely destroyed?

  • Thin cell wall
  • Presence of flagella
  • Waxy, thick cell wall (correct)
  • Low mutation rate

    • Which statement accurately describes the initial action of HIV in the immune system?

  • HIV initiates infection by targeting natural killer cells.
  • HIV directly attacks B cells to produce antibodies.
  • HIV replicates inside helper T cells to disrupt immune response. (correct)
  • HIV first targets macrophages to enhance immune response.

    • How does HIV manage to evade the body's humoral immunity over time?

  • By enhancing the production of memory cells.
  • By increasing its susceptibility to phagocytosis.
  • By rapidly changing its antigens. (correct)
  • By remaining dormant in liver cells.

    • For how long can the HIV virus remain dormant in the body after initial infection?

    <p>Up to 10 years</p> Signup and view all the answers

    What is the consequence of TB bacteria lying dormant in macrophages after phagocytosis?

    <p>They can reactivate when the immune system is compromised.</p> Signup and view all the answers

    What is the main difference between natural immunity and artificial immunity?

    <p>Natural immunity develops from infection, whereas artificial immunity comes from vaccines.</p> Signup and view all the answers

    Which statement about active immunity is correct?

    <p>Booster vaccinations are sometimes required to maintain active immunity.</p> Signup and view all the answers

    What is the role of memory cells in immunity?

    <p>Memory cells are responsible for the rapid response during secondary infections.</p> Signup and view all the answers

    How do vaccines function to provide immunity?

    <p>Vaccines contain dead or weakened viruses to simulate an infection.</p> Signup and view all the answers

    What is a characteristic feature of passive immunity?

    <p>It is acquired through the injection of antibodies from another source.</p> Signup and view all the answers

    Which of the following statements is true regarding vaccines?

    <p>Currently, vaccines are designed only against viruses.</p> Signup and view all the answers

    Why might a patient require a booster vaccination?

    <p>To reinforce an immune response that has diminished over time.</p> Signup and view all the answers

    What allows mothers to pass on natural immunity to their infants?

    <p>Transfer of antibodies through breast milk.</p> Signup and view all the answers

    What is the role of passive immunity in fighting infections?

    <p>It involves transferring antibodies from another source to an infected individual.</p> Signup and view all the answers

    What is the significance of herd immunity in a population?

    <p>It protects unvaccinated individuals by breaking the transmission chain.</p> Signup and view all the answers

    What can cause antigenic variation in pathogens?

    <p>Mutations in the pathogen's genetic material.</p> Signup and view all the answers

    Why is it important to develop new flu vaccines annually?

    <p>The influenza virus has a high mutation rate resulting in new strains.</p> Signup and view all the answers

    Which statement best explains active immunity?

    <p>It occurs when an individual is naturally or artificially exposed to an antigen.</p> Signup and view all the answers

    What are the concerns associated with the ethics of vaccination?

    <p>The potential risks of using animal testing and human volunteer testing.</p> Signup and view all the answers

    How does mass vaccination impact the spread of diseases?

    <p>It breaks the chain of infection and limits disease spread.</p> Signup and view all the answers

    What can lead to a loss of herd immunity in a population?

    <p>A decline in vaccination rates.</p> Signup and view all the answers

    What aspect of vaccines alleviates concerns about their safety?

    <p>Vaccine manufacturing is heavily regulated.</p> Signup and view all the answers

    Which of the following best describes antigenic drift?

    <p>Minor variations in antigenic structure that allow new virus strains.</p> Signup and view all the answers

    Which of the following accurately describes the primary immune response?

    <p>It takes considerable time to develop and generates memory cells.</p> Signup and view all the answers

    What can happen if individuals do not vaccinate against certain diseases?

    <p>Disease outbreaks may resurgence.</p> Signup and view all the answers

    Why do infants particularly benefit from herd immunity?

    <p>They are not able to receive all vaccinations at a young age.</p> Signup and view all the answers

    In what way does antigenic shift differ from antigenic drift?

    <p>Antigenic shift involves major antigenic changes and new types of viruses.</p> Signup and view all the answers

    What is the function of the constant region of an antibody?

    <p>To remain the same across different antibodies.</p> Signup and view all the answers

    What structural feature of antibodies allows them to bind to multiple antigens?

    <p>The flexibility provided by hinge regions.</p> Signup and view all the answers

    Which of the following statements about monoclonal antibodies is true?

    <p>They have a highly specific antigen binding site.</p> Signup and view all the answers

    How do antibodies neutralize toxins produced by pathogens?

    <p>By binding to them and preventing their binding to host cells.</p> Signup and view all the answers

    What role do antibodies play in agglutination?

    <p>They group pathogens together to facilitate removal by phagocytes.</p> Signup and view all the answers

    What distinguishes polyclonal antibodies from monoclonal antibodies?

    <p>Polyclonal antibodies have a diverse range of binding sites.</p> Signup and view all the answers

    What characteristic of the variable region in antibodies is vital for their function?

    <p>It differs among antibodies, allowing specific binding to antigens.</p> Signup and view all the answers

    Why are antibodies described as glycoproteins?

    <p>Due to the presence of carbohydrate molecules attached to their structure.</p> Signup and view all the answers

    What is the primary function of monoclonal antibodies in cancer treatment?

    <p>To attract and neutralize cancer cells by targeting tumor markers</p> Signup and view all the answers

    What key step is involved in the hybridoma method for producing monoclonal antibodies?

    <p>Fusing spleen B cells with cancerous myeloma cells</p> Signup and view all the answers

    How do monoclonal antibodies function in medical diagnosis?

    <p>By detecting specific antigens in blood or tissue samples</p> Signup and view all the answers

    Why are monoclonal antibodies particularly advantageous in treating poisoning?

    <p>They can be designed to specifically target and neutralize certain toxins</p> Signup and view all the answers

    What is a major characteristic of hybridoma cells used to produce monoclonal antibodies?

    <p>They can divide indefinitely and produce large quantities of antibodies</p> Signup and view all the answers

    In the production of monoclonal antibodies, what role do spleen cells play?

    <p>They produce the antibodies required for various treatments</p> Signup and view all the answers

    What potential use of monoclonal antibodies is employed in pregnancy testing?

    <p>Detection of human chorionic gonadotrophin (hCG)</p> Signup and view all the answers

    What is a potential downside of using monoclonal antibodies for treatment?

    <p>They can lead to the development of resistant cancer cells</p> Signup and view all the answers

    What is the term used for the process that eliminates T-cells and B-cells that react to self-antigens?

    <p>Clonal deletion</p> Signup and view all the answers

    Which cells are primarily responsible for recognizing infected cells and initiating the apoptosis process?

    <p>Cytotoxic T-cells</p> Signup and view all the answers

    What is the main role of T-helper cells (TH cells) in the immune response?

    <p>Activate other immune cells</p> Signup and view all the answers

    What do perforin proteins do during the mechanism of cytotoxic T cells?

    <p>Create pores in infected cell membranes</p> Signup and view all the answers

    Which of the following best describes the function of memory B cells?

    <p>Rapidly differentiate into plasma cells upon re-exposure to the same pathogen</p> Signup and view all the answers

    Which type of immunity is primarily mediated by antibodies produced by B cells?

    <p>Humoral immunity</p> Signup and view all the answers

    What mechanism allows cytotoxic T cells to induce apoptosis in target cells?

    <p>Fas ligand and Fas receptor interaction</p> Signup and view all the answers

    What is the major role of plasma B cells during an infection?

    <p>Produce antibodies against specific antigens</p> Signup and view all the answers

    What term describes the long-lasting immunity developed after an initial exposure to a pathogen?

    <p>Immunological memory</p> Signup and view all the answers

    What occurs during clonal expansion of B cells?

    <p>B cells differentiate into effector cells and memory cells</p> Signup and view all the answers

    What is the role of interferons released by infected cells?

    <p>To inhibit viral replication and boost anti-viral defenses</p> Signup and view all the answers

    Which cells are responsible for inhibiting the immune responses to prevent attacks on the body's own cells?

    <p>Regulatory T-cells</p> Signup and view all the answers

    Which statement describes the action of granzyme A during the cytotoxic T cell mechanism?

    <p>It catalyzes reactions leading to cell destruction.</p> Signup and view all the answers

    What type of antigens do B-cells respond to during the immune response?

    <p>Soluble antigens</p> Signup and view all the answers

    Which type of leukocyte primarily activates B cells?

    <p>T-helper cells</p> Signup and view all the answers

    What process occurs in the thymus to ensure T cells do not react to self-antigens?

    <p>Clonal deletion</p> Signup and view all the answers

    What is the primary function of antigen presenting cells (APCs)?

    <p>Present antigens to T cells</p> Signup and view all the answers

    Which of the following statements about B cells is true?

    <p>B cells primarily produce antibodies</p> Signup and view all the answers

    What type of lymphocyte is primarily responsible for cell-mediated immunity?

    <p>Cytotoxic T cells</p> Signup and view all the answers

    What occurs during central tolerance in the maturation of T and B cells?

    <p>Self-reactive cells are deleted</p> Signup and view all the answers

    Which of the following best describes the origin of T cells?

    <p>Produced in the bone marrow</p> Signup and view all the answers

    Which type of immunity involves the production of memory cells?

    <p>Adaptive immunity</p> Signup and view all the answers

    What specific role do MHC class II molecules play in the immune system?

    <p>They bind to foreign antigens to activate immune responses.</p> Signup and view all the answers

    Which of the following describes a characteristic of autoimmune disorders?

    <p>They involve the immune system attacking the body's own tissues.</p> Signup and view all the answers

    What action must be taken due to the variability of MHC genes between individuals?

    <p>Donor organs must closely match the antigen profile of the recipient.</p> Signup and view all the answers

    Which autoimmune disease is characterized by the attack on nearly any organ or joint in the body?

    <p>Systemic lupus erythematosus</p> Signup and view all the answers

    Which of the following is a consequence of the immune system's inability to distinguish self from non-self?

    <p>Autoimmune diseases may develop as the body attacks its own tissues.</p> Signup and view all the answers

    What is the primary role of neutrophils in the innate immune system response?

    <p>Breaking down pathogens via phagocytosis</p> Signup and view all the answers

    Which function do T-memory (Tm) cells serve in the adaptive immune system?

    <p>Provide long-term immunity</p> Signup and view all the answers

    What type of antigens do MHC I molecules primarily interact with?

    <p>Endogenous antigens produced by body cells</p> Signup and view all the answers

    What can result from the immune system attacking self-cells?

    <p>Development of autoimmune diseases</p> Signup and view all the answers

    What triggers the adaptive immune response once a pathogen is detected?

    <p>Activation of T-helper cells and specific T cells</p> Signup and view all the answers

    What is a defining characteristic of antigens in pathogens as compared to normal cells?

    <p>Most antigens from pathogens do not exist on normal cells</p> Signup and view all the answers

    Which type of T cells are responsible for directly destroying infected body cells?

    <p>Cytotoxic T (Tc) cells</p> Signup and view all the answers

    What is the consequence of a malfunction in MHC protein expression?

    <p>Failure to distinguish self from non-self cells</p> Signup and view all the answers

    What role does keratin play in the primary defenses of the skin?

    <p>It forms a physical barrier against pathogens.</p> Signup and view all the answers

    What is the primary function of inflammation in response to pathogens?

    <p>To increase blood flow and permeability.</p> Signup and view all the answers

    What is one consequence of skin damage that necessitates wound repair?

    <p>Entry of pathogens through the broken barrier.</p> Signup and view all the answers

    What is the role of platelets in wound repair?

    <p>To form clumps and create a blood clot.</p> Signup and view all the answers

    How do skin flora contribute to the body's primary defenses?

    <p>By taking up space and preventing colonization by harmful pathogens.</p> Signup and view all the answers

    What event occurs during wound healing that allows skin cells to proliferate?

    <p>Laying down of collagen fibers.</p> Signup and view all the answers

    What triggers the redness and heat associated with inflammation?

    <p>Vasodilation of blood vessels.</p> Signup and view all the answers

    What is the purpose of mucous membranes as a primary defense?

    <p>To trap pathogens and prevent them from entering the body.</p> Signup and view all the answers

    What is the primary mechanism by which goblet cells contribute to pathogen defense in the respiratory system?

    <p>They secrete mucous that traps pathogens.</p> Signup and view all the answers

    Which of the following actions is classified as an expulsive reflex to remove trapped pathogens?

    <p>Coughing</p> Signup and view all the answers

    What role does callose play in plant defense mechanisms?

    <p>It blocks pathogen entry between cells.</p> Signup and view all the answers

    How does the stomach serve as a primary defense against ingested pathogens?

    <p>By maintaining a low pH that destroys many pathogens.</p> Signup and view all the answers

    What is the function of the waxy cuticle in plant defense?

    <p>It acts as a barrier to pathogen entry.</p> Signup and view all the answers

    What type of chemicals can plants secrete to combat pathogens?

    <p>Antimicrobial compounds to inhibit growth.</p> Signup and view all the answers

    Which primary defense mechanism is specific to the gut's microbiota?

    <p>Antimicrobial chemicals produced by flora.</p> Signup and view all the answers

    What is one way that the plant cell walls contribute to pathogen defense?

    <p>They provide a physical barrier to entry.</p> Signup and view all the answers

    What is NOT a characteristic of the innate immune response?

    <p>Has immunologic memory</p> Signup and view all the answers

    Which cells are primarily involved in the acute inflammatory response?

    <p>Neutrophils</p> Signup and view all the answers

    What is the primary role of the complement system in the immune response?

    <p>Triggers inflammation and kills pathogens</p> Signup and view all the answers

    Which type of leukocyte is known for presenting antigens to other immune cells?

    <p>Monocytes</p> Signup and view all the answers

    What aspect distinguishes the adaptive immune response from the innate immune response?

    <p>Ability to remember past infections</p> Signup and view all the answers

    Which process involves the replication of specific immune cells following exposure to an antigen?

    <p>Clonal expansion</p> Signup and view all the answers

    What is a primary function of dendritic cells in the immune system?

    <p>Perform phagocytosis</p> Signup and view all the answers

    Which statement accurately describes eosinophils?

    <p>They are involved in fighting parasitic infections</p> Signup and view all the answers

    What distinguishes dendritic cells from macrophages in their interaction with T cells?

    <p>Dendritic cells present antigens to T cells after moving to lymph nodes.</p> Signup and view all the answers

    Which of the following statements about B cells is incorrect?

    <p>B cells present antigens on MHC I molecules.</p> Signup and view all the answers

    What role do NK cells play in the immune response?

    <p>They kill infected or cancerous cells via cytotoxic granules.</p> Signup and view all the answers

    Which process do phagocytes use to destroy pathogens once they have engulfed them?

    <p>They create phagosomes that fuse with granules to form phagolysosomes.</p> Signup and view all the answers

    Which statement about CD4+ T cells is true?

    <p>They secrete cytokines to help coordinate the immune response.</p> Signup and view all the answers

    What is a characteristic feature of granulocytes?

    <p>They contain granules in their cytoplasm.</p> Signup and view all the answers

    How do cytotoxic T cells induce apoptosis in target cells?

    <p>Using perforin proteins to create pores in the target cell membranes.</p> Signup and view all the answers

    Which cell type is primarily responsible for antigen presentation in the adaptive immune response?

    <p>Dendritic cells</p> Signup and view all the answers

    Which type of vaccine is designed to protect against specific toxins that cause illness?

    <p>Toxoid vaccines</p> Signup and view all the answers

    What type of immune response is primarily achieved through intramuscular vaccinations?

    <p>IgG production</p> Signup and view all the answers

    Which type of vaccine is generally ineffective in children under two years old due to their inability to form memory B cells?

    <p>Subunit vaccines</p> Signup and view all the answers

    What is a significant drawback of inactivated vaccines compared to live attenuated vaccines?

    <p>Reduced immune response efficacy</p> Signup and view all the answers

    Which of the following vaccines can potentially lead to contraindications in individuals with a weakened immune system?

    <p>Live attenuated vaccines</p> Signup and view all the answers

    Study Notes

    Natural Immunity

    • Develops after infection
    • Body's response to an antigen
    • Primary immune response leads to immunological memory
    • Memory cells develop during primary infection
    • Secondary infection triggers rapid response by memory cells
    • Can be passed from mother to infant through breastfeeding

    Artificial Immunity (Vaccines)

    • Priming of the immune system through vaccines
    • Vaccines contain dead or weakened viruses
    • Stimulate immune system to develop immunological memory
    • Allow body to detect and eliminate live virus quickly
    • Currently only designed against viruses

    Active Immunity

    • Body creates antibodies in response to pathogen exposure
    • Vaccination provides active immunity
    • Lasting due to memory B cells and antibodies
    • May require booster vaccinations to revitalize immunity

    Passive Immunity

    • Acquired from antibodies from another animal
    • Immediate treatment for infected individuals
    • Antibodies quickly identify and fight infection
    • Natural passive immunity: mother to baby through placenta
    • Artificial passive immunity: injection of antibodies

    Importance of Vaccination

    • Body can develop immunity upon infection, but it takes time
    • Many pathogens are too fast for the immune system to respond
    • Vaccines allow for a quicker and more effective immune response

    Herd Immunity

    • Mass vaccination breaks the chain of infection
    • Protects those who cannot be vaccinated
    • Particularly important for infants

    Ethics of Vaccination

    • Herd immunity can fall if people don't get vaccines
    • Loss leads to resurgence of disease
    • Near-eradicated diseases can return due to declining vaccination rates

    Concerns About Vaccination Safety

    • Speculative reports on autism and vaccination: No scientific evidence supports the link
    • Concerns about injecting pathogens: Vaccine production is tightly regulated
    • Animal testing concerns: Benefits outweigh risks if done ethically
    • Risk of harm to human volunteers: Risks are mitigated by thorough testing

    Antigenic Variability

    • Vaccines target specific antigens
    • Antigens can change, leading to ineffective vaccines
    • Antigenic drift: minor variations causing new strains
    • Antigenic shift: major variations leading to new virus types

    Influenza Virus Case Study

    • High mutation rate requires yearly vaccine updates
    • New strains emerge annually, requiring new vaccines
    • Unvaccinated individuals contribute to virus evolution

    Evolutionary Race Between Pathogens and Host

    • Pathogens have evolved to evade immune systems
    • Tuberculosis bacteria have a waxy cell wall, allowing them to survive in macrophages
    • HIV has a high mutation rate, making it difficult for the immune system to target
    • HIV targets and replicates in helper T cells, disrupting immune responses

    Implications of Pathogen Evolution

    • Tuberculosis can lie dormant in macrophages, reactivating when the immune system is weak
    • HIV can remain dormant for years, reactivating and causing illness

    Antibody Structure

    • Antibodies are Y-shaped glycoproteins with four polypeptide chains: two long heavy chains and two short light chains.
    • Antibodies contain a constant region, which is the same in all antibodies and binds to phagocytes.
    • Antibodies also have a variable region, which has a unique structure for each antibody and acts as the antigen binding site.
    • Antibodies have flexible hinge regions, allowing the branches of the Y to move apart, increasing their flexibility and ability to bind multiple antigens.

    Antibody Functions

    • Antibodies can neutralize pathogens by binding to and neutralizing toxins or viral attachment proteins, preventing infection.
    • Antibodies can agglutinate pathogens, clumping them together to make them easier for phagocytes to engulf.
    • Antibodies can mark pathogens, attracting phagocytes and lymphocytes to the area.
    • Antibodies can work with enzymes to break down pathogens.

    Monoclonal and Polyclonal Antibodies

    • Monoclonal antibodies have a highly specific antigen binding site, able to recognize only one specific antigenic sequence.
    • Polyclonal antibodies have diverse antigen binding sites, able to recognize different variations of the same antigen.

    Functions of Monoclonal Antibodies

    • Monoclonal antibodies are used to neutralize poisons in patients.
    • They can be used in cancer treatment by targeting tumor markers, neutralizing cancer cells, attracting cytotoxic T cells, and delivering anti-cancer drugs.
    • Monoclonal antibodies are used for medical diagnosis, detecting specific antigens in blood or tissue samples.

    Producing Monoclonal Antibodies

    • Mice are injected with an antigen to induce an immune response and antibody production by B cells.
    • Spleen cells are harvested from the mouse, containing B cells responsible for antibody production.
    • The spleen cells are fused with myeloma cells, forming hybridoma cells that can continuously divide and produce monoclonal antibodies.
    • The hybridoma cells are grown in culture and the monoclonal antibodies are harvested for further use.

    The Adaptive Immune Response

    • The adaptive immune response is a specific defense mechanism against pathogens.
    • It is activated by antigen-presenting cells (APCs), including macrophages, dendritic cells, and neutrophils.
    • APCs present antigens from foreign pathogens to the immune system, initiating the adaptive response.

    Lymphocytes

    • Lymphocytes are a type of white blood cell involved in the adaptive immune response.
    • There are two main types of lymphocytes: T cells and B cells.
    • T cells mature in the thymus and are responsible for cell-mediated immunity.
    • T cells are activated by APCs and can differentiate into cytotoxic T cells (TC), memory T cells (TM), helper T cells (TH), and regulatory T cells (TR).
    • B cells mature in the bone marrow and are responsible for humoral immunity.
    • B cells are activated by TH cells and differentiate into plasma cells and memory B cells.

    T-Lymphocytes and Cell-Mediated Immunity

    • Origin and Maturation: T cells originate in the bone marrow and undergo maturation in the thymus.
    • Clonal Deletion: T cells undergo clonal deletion to eliminate cells that recognize self-antigens.
      • Central Tolerance: Occurs during maturation in the thymus.
      • Peripheral Tolerance: Occurs after maturation in other tissues.
    • Steps of T-Cell Action:
      1. Antigen Presentation: APCs present antigens to TH cells.
      2. TH Cell Activation: Activated TH cells activate pathogen-specific TC, TM, and B cells.
      3. Cytotoxic T Cell Action (TC): TC cells kill infected cells via apoptosis.
      4. Memory T Cell Formation (TM): TM cells provide long-term immunity.
      5. Regulatory T Cell Action (TR): TR cells regulate the immune response to prevent autoimmunity.
      6. B Cell Activation: TH cells activate B cells.

    Mechanism of Cytotoxic T Cells

    • TC cells bind to infected cells through MHC molecules.
    • TC cells release perforins, which create pores in the target cell membrane.
    • TC cells release granzyme enzymes, which enter the target cell through the pores.
    • Granzyme A poisons the cell, while granzyme B destroys the cell.
    • TC cells also express Fas ligand, which binds to Fas receptors on target cells, inducing apoptosis.
    • Interferons are released by the target cell before apoptosis, inhibiting viral replication in surrounding cells.
    • Antibodies can neutralize any viruses released from the dying cell.

    B-Cells and Humoral Immunity

    • B cells are antigen-specific and activated by TH cells.
    • B cells undergo clonal expansion and differentiate into:
      • Plasma Cells: Short-lived cells that produce antibodies.
      • Memory B Cells: Responsible for the secondary immune response.
    • B cells and their antibodies contribute to humoral immunity, which is mediated by molecules in the bloodstream and lymphatic fluid.
    • Immunological memory, provided by memory B cells, allows for faster and more effective responses to subsequent infections by the same pathogen.

    Immune System Overview

    • The immune system has two main mechanisms: innate and adaptive.
    • The innate immune system is the primary response, while the adaptive immune system is the secondary response.

    Innate Immune System

    • The innate immune system is the body’s first line of defense against pathogens.
    • It is triggered by the detection of foreign antigens on the surface of pathogens.
    • Neutrophils and macrophages are key cells in the innate immune system.
    • Neutrophils carry out phagocytosis of pathogens in the blood.
    • Macrophages perform phagocytosis in lymph nodes.

    Adaptive Immune System

    • The adaptive immune system is specific to individual pathogens.
    • The adaptive immune system is activated by the innate immune system.
    • Phagocytes activate three types of T cells: T-helper, cytotoxic T, and T-memory cells.
    • T-helper cells activate B cells and T-killer cells.
    • Cytotoxic T cells destroy pathogens.
    • T-memory cells provide long-term immunity.
    • B cells produce antibodies to neutralize pathogens.
    • B cells can differentiate into plasma cells, which produce more antibodies

    Antigens

    • Antigens are molecules that trigger an immune response.
    • They are typically found on the surface of cells, including pathogens.
    • Antigens are specific to individual cells and pathogens.
    • Most antigens found in pathogens are not present in normal cells.

    Self and Non-Self

    • The immune system can distinguish between self-cells (native cells) and non-self cells (foreign cells).
    • MHC proteins help the immune system identify self-cells.
    • MHC I molecules are found on normal body cells and present endogenous antigens.
    • MHC II molecules are found on immune system cells and present foreign antigens.
    • Autoimmune disorders occur when the immune system attacks self-cells.
    • They can target any organ or joint in the body and can be acute or chronic.

    Non-Self and Rejection

    • The immune system can be counterproductive when it attacks non-self cells that are not pathogens.
    • This can lead to the rejection of organ transplants.
    • MHC genes, which determine self-recognition, vary between individuals (except identical twins).
    • As a result, the recipient’s immune system may attack the donor organ unless the donor and recipient's MHC genes are closely matched.

    Primary Defences

    • Are non-specific barriers that protect the body from any pathogen, not just a specific one.
    • Are the first line of defence against infection.

    Primary Defences in Animals:

    • Skin:

      • Forms a strong physical barrier made of dead cells.
      • Reinforced by keratin.
      • Secretes antimicrobial sebum.
      • Contains skin flora which prevent growth of harmful pathogens.

    • Inflammation:

      • Natural response to foreign stimuli or tissue damage.
      • Characterised by redness, heat, swelling, and pain.
      • Swelling is caused by vasodilation and increased vascular permeability.
      • This brings white blood cells and immune system components to fight off pathogens.

    • Wound Formation:

      • Repairs skin barrier after damage.
      • Involves blood clotting and skin barrier repair.
      • Blood clotting plugs wounds and prevents blood loss.
      • Formed through platelet aggregation and fibrin mesh formation.
      • Skin barrier repair involves fibroblasts depositing collagen fibres and skin cells migrating to the wound edge.

    • Mucous Membranes:

      • Secrete mucus which traps pathogens.
      • Ciliated cells sweep trapped pathogens away.
      • Expulsive reflexes (coughing, sneezing, vomiting) remove pathogens.

    • Gut:

      • Stomach acidity destroys ingested pathogens.
      • Gut flora prevents harmful pathogen proliferation.

    Primary Defences in Plants:

    • Physical Defences:

      • Waxy cuticle acts as a barrier to pathogens.
      • Cell walls provide a secondary barrier to pathogen entry.
      • Callose can block pathogen entry and spread between cells.

    • Chemical Defences:

      • Plants produce antimicrobial chemicals to kill pathogens.
      • Plants produce saponins that damage fungal cell membranes.
      • Phytoalexins inhibit pathogen growth.
      • Plants produce toxins poisonous to insects, reducing viral transmission via insect vectors.

    Immune System Overview

    • The immune system is a complex network of organs, tissues, cells, and molecules that protects the body from disease.
    • It has two branches: innate and adaptive immunity.

    Innate Immune Response

    • The innate immune response is the first line of defense against pathogens.
    • It is nonspecific, meaning it does not target specific pathogens.
    • It is rapid, typically responding within minutes to hours.
    • Cells:
      • Phagocytes (e.g., neutrophils, macrophages) engulf and destroy pathogens.
      • Natural killer (NK) cells kill infected or cancerous cells.
    • Noncellular Components:
      • Physical barriers (e.g., skin, mucous membranes) prevent pathogens from entering the body.
      • Chemical barriers (e.g., lysozymes in tears, cilia in airways) kill or inhibit pathogens.
      • Inflammation is a localized response to injury or infection.
        • It involves four cardinal signs: redness, heat, swelling, and pain.
        • It helps to stop the spread of infection and promote healing.
      • The complement system is a cascade of proteins that:
        • Triggers inflammation.
        • Kills pathogens by cytolysis (rupturing the cell membrane).
        • Tags cells for destruction by phagocytes.

    Adaptive Immune Response

    • The adaptive immune response is a highly specific and targeted response that develops over time.
    • It requires priming, meaning it needs to be exposed to a pathogen before it can mount a response.
    • It is slower than the innate response, typically taking weeks to develop.
    • Cells:
      • T cells and B cells are highly specific lymphocytes that recognize and destroy specific pathogens.
    • Key Characteristics:
      • Clonal expansion: Immune cells replicate to create a large army of cells that target the specific pathogen.
      • Clonal deletion: After the immune response, many immune cells die off. Some survive as memory cells, which can quickly mount an immune response if the body encounters the same pathogen again.

    Cells of the Immune System

    • Leukocytes (white blood cells) are the main cells of the immune system.
    • They are formed by hematopoiesis in the bone marrow.
      • Hematopoiesis starts with multipotent hematopoietic stem cells.
      • These stem cells develop into myeloid or lymphoid progenitor cells.
    • Myeloid Cells:
      • Neutrophils: Most numerous leukocytes. They are phagocytes, granulocytes, and polymorphonuclear cells (nucleus segmented into 3-5 lobes). They stain light pink/reddish-purple.
      • Eosinophils: Granulocytes and polymorphonuclear cells (nucleus usually bilobed). They stain pink with eosin. They are larger cells that fight parasites.
      • Basophils: They are the least numerous leukocytes. They are nonphagocytes, granulocytes, and polymorphonuclear cells (nucleus bilobed/segmented). They stain blue-purple with hematoxylin. They are involved in fighting parasites and inflammatory responses. Their granules contain histamine and heparin.
      • Mast cells: Granulocytes involved in inflammatory responses. They are not phagocytes.
      • Monocytes: Phagocytes, antigen-presenting cells. They circulate only in the blood and differentiate into macrophages or dendritic cells. They release cytokines to recruit other cells.
      • Dendritic cells: Phagocytes, antigen-presenting cells. They circulate in lymph and release cytokines to recruit other cells.

    Dendritic Cells

    • Phagocytic and antigen-presenting cells
    • Circulate in lymph, blood, and tissue
    • Consume large proteins from interstitial fluid
    • Break down bloodborne pathogens into small amino acid chains
    • Migrate to lymph nodes to present antigens to T cells
    • Release cytokines to recruit other immune cells

    Macrophages

    • Phagocytic and antigen-presenting cells
    • Remain in connective tissue and lymphoid organs, not found in blood
    • Release cytokines to recruit other immune cells

    Lymphoid Cells

    • Contribute to the adaptive immune response (except NK cells)

    Natural Killer (NK) Cells

    • Part of the innate immune response
    • Mature in bone marrow
    • Large cells with granules
    • Primarily target infected and cancerous cells
    • Kill target cells using cytotoxic granules which create holes in cell membranes by binding to phospholipids, trigger apoptosis

    B Cells

    • Participate in adaptive immunity
    • Mature in bone marrow
    • Bind to specific antigens without needing antigen presentation
    • Capable of phagocytosis and antigen presentation
    • Load antigens onto MHC II molecules and display them to T cells
    • T-cell activation leads to B cell maturation into plasma cells
    • Plasma cells secrete antibodies/immunoglobulins (B cell receptors in secreted form) to mark pathogens for destruction, "humoral immunity"

    T Cells

    • Involved in adaptive immunity
    • Mature in the thymus
    • Responsible for cell-mediated immunity
    • Bind to specific antigens, requiring antigen presentation
    • Naive T cells are primed by antigen-presenting cells (often dendritic cells)
    • Classified into CD4+ and CD8+ T cells
      • CD4+ (helper) T cells secrete cytokines to coordinate the immune response and only recognize antigens presented on MHC II
      • CD8+ (cytotoxic) T cells kill target cells that display antigens on MHC I

    Phagocytes

    • Engulf pathogens with their cytoplasm, forming a phagosome
    • Destroy some pathogens using cytoplasmic granules that fuse with phagosomes to form phagolysosomes, lowering the pH within the vesicle to kill pathogens
    • Continue to engulf pathogens before an oxidative burst, producing highly reactive oxygen species (like H2O2) that destroy proteins, nucleic acids, and kill both pathogens and the phagocyte

    Granulocytes

    • Contain granules in their cytoplasm
    • All cells (except mast cells) are polymorphonuclear

    Antigen-Presenting Cells

    • Present antigens to T cells

    Vaccines and the Adaptive Immune Response

    • Vaccines stimulate the body's adaptive immune response against non-pathogenic forms or components of microbes.
    • This is different from passive immunity, where antibodies are directly given to the body rather than being produced by the body itself.
    • Vaccines can be administered through various routes, such as intramuscularly, intradermally, intranasally, subcutaneously, and orally.
    • Vaccine types influence the specific immune response, for instance, intramuscular vaccinations induce IgG production, while oral rotavirus vaccinations lead to IgA production.
    • The four main types of vaccines include:

      Live Attenuated Vaccines

      • These vaccines contain weakened versions of the pathogen that can still replicate but are not pathogenic.
      • Examples include vaccines for measles, mumps, rubella, varicella (MMRV), rotavirus, smallpox, and yellow fever.

      Inactivated Vaccines

      • These vaccines contain pathogens killed using heat or formalin.
      • They primarily elicit a humoral/antibody-mediated response, with limited cellular immunity, leading to a weaker and shorter-lasting response.
      • Examples include vaccines for Hepatitis A, polio, rabies, and influenza.

      Subunit Vaccines

      • These vaccines include immunogenic portions of pathogens, such as polysaccharides or proteins.
      • Conjugate subunit vaccines combine proteins from different pathogens.
      • Polysaccharide vaccines are T cell-independent, meaning they only respond to protein antigens.
      • These vaccines are not effective in children under two years old because they don't stimulate memory B cell formation, requiring repeated doses.
      • Examples include vaccines for Haemophilus influenzae type B, hepatitis B, HPV, Bordetella pertussis (pertussis), Streptococcus pneumoniae, Neisseria meningitidis, and Varicella zoster.

      Toxoid Vaccines

      • These vaccines target specific toxins, often the main cause of illness by inactivating the toxin with formalin.
      • They are often combined with subunit vaccines.
      • Examples include tetanus, diphtheria, and pertussis (TdP), diphtheria, tetanus, and pertussis (DTaP) vaccines.

      Vaccine Contraindications

      • Moderate or severe infection
      • Allergies to eggs or previous vaccines
      • Guillain-Barré syndrome (particularly with influenza and DTaP vaccines)
      • Weakened immune systems
      • Pregnancy (live attenuated vaccines)

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    Test your knowledge on natural and artificial immunity, including active and passive immunity. This quiz covers key concepts such as immunological memory and the body's response to pathogens through vaccines. Assess your understanding of how different immunities are developed and their effects on health.

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