Chapter 5: Responding to Antigens and Acquiring Immunity Flashcards
Define antigen
- Antigens are molecules or parts of molecules that stimulate an immune response
Describe the difference between self and non-self antigens
- Self antigens are antigens on cells that are recognised by self-receptors as being part of the same body
- Non-self antigens are antigens that do not belong to the body’s own cells
Describe the difference between MHC-I and MHC-II self markers
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MHC-I is a type of major histocompatibility complex found on all nucleated cells
- They allow cells to be recognised as “self”
- MHC-II is a type of major histocompatibility complex found on specific white blood cells, including antigen-presenting cells, involved in the adaptive immune response
Explain what a pathogen is
- Pathogens are agents that cause disease to a host
Explain the difference between pathogens and antigens
- Antigens are substances such as pollen, bacteria and viruses that trigger an immune response
- Pathogens are harmful agents such as bacteria that can cause disease
List the 6 main types of pathogen
- Bacteria, worms, fungi, protozoa, viruses and prions
Compare infection and disease
- Infection is the invasion and growth of a pathogen in the body
- Disease is a condition that impairs the normal functioning of an organ, structure or system of an organism
Describe the difference between cellular and non-cellular pathogens
- Cellular pathogens are living organisms that are able to reproduce independently
- Non-cellular pathogens are non-living and require a host to reproduce
Compare extracellular and intracellular pathogens
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Extracellular pathogens are targeted by the humoral immune response
- Cannot survive inside the phagocyte once ingested
- In the body but have yet to enter cells
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Intracellular pathogens are targeted by the cell-mediated immune response
- Can survive inside of host cells/phagocytes
- Have entered cells
Explain how viruses damage cells
- Viruses cause disease by killing body cells (cell lysis) and uses the cell’s organelles to reproduce
- Virus adheres to a host cell, injecting its viral DNA
- Viral nucleic acid moves to nucleus where it is transcribed
- Viral mRNA is then translated and viral protein is packaged
- The infected host cell bursts as its plasma membrane disintegrates and viral particles are released into the extracellular fluid from where they can infect other cells
NOTE: Viruses have either DNA or RNA that is surrounded by a protein shell (capsid).
Explain how bacteria cause disease
- If bacteria multiplies in areas in which they are not normally found, they can cause disease
Define allergen
- Allergens are substances that cause allergic response
Outline the general process of an allergic response
- Allergic response is a reaction to normally harmless antigens
- Sensitization → initial exposure to allergen
- Allergen enters the bloodstream, B cells differentiate into plasma cells, plasma cells produce antibodies and antibodies attach to mast cells
- Mast cells become ‘primed’ with IgE/antibodies specific for the allergen (able to recognise and respond to the allergen)
- Allergic reaction → secondary exposure to the same allergen
- Allergen binds to antibodies forming cross links on mast cells, histamine is released from the mast cells and an allergic reaction occurs
- When an allergen binds to more than one antibody a cross link will form (this results in the release of histamine)
- No cross link = no histamine produced
Describe the role of mast cells, with clear reference to allergic response
- Mast cells are immune cells that release histamines via degranulation, which causes inflammation
Describe 3 different physical barriers in animals
- Intact skin → the constant shedding of surface cells is an effective barrier against the entry of pathogens
- Ear wax → reduces the access that pathogens have to the ear drum and ear canal as well as protects the ear from dust and other foreign particles
- Nasal hair and mucus → trap and prevent the entry of pathogens
Describe 3 different chemical barriers in animals
- Lysozyme → an enzyme present in sweat, tears and saliva that kills pathogens
- Sebum → an oily secretion produced by sebaceous glands that provides a protective and antimicrobial film on the skin
- Stomach acid → including digestive enzymes kill pathogens that enter the digestive tract
Explain how microbiological barriers in animals can prevent infection
- Microbiological barriers include harmless bacteria that occur naturally within the body that inhibit the growth of pathogens
- They do this by secreting antimicrobial chemicals and by outcompeting them for nutrients and adhesion site
Describe 3 different physical barriers in plants
- Waxy cuticle → the waxy coat on leaves that prevent infection
- Formation of galls → limits the spread of pathogens
- Thorns → protect plants from grazing animals such as cattle and sheep
Describe chemical barriers in plants
- Caffeine → helps to prevent fungi and insects from invading the plant
- Antimicrobial enzymes → prevent pathogens from entering the plant
- Antimicrobial chemicals → produced by plants to disrupt bacterial cell membranes and deter predators
Describe components of the first line of defence that work against viruses
- Mucous membranes make it difficult to viruses to adhere
- Nose hairs (cilia) are a physical barrier to the virus
- Acidic environment of the stomach kill viruses
Describe the innate immune response, with specific reference to the second line of defence
- The innate immune response is an inborn system that lacks specifity and memory
- The second line of defence involves cell-mediated innate immunity, humoral innate immunity, as well as inflammation and fever
- The second line of defence is in effect once the first line of defence has been breached or when pathogens have entered tissue or the bloodstream
Explain the purpose of a fever
- Increased body temperatures enhance the performance of immune cells, making them work more efficiently
- Heat can also kill bacteria and viruses as well as denature bacterial enzymes
NOTE: Fevers are part of the second line of defence.
Describe the process of phagocytosis
- A pathogen is identified by a pattern recognition receptor and is engulfed in the plasma membrane of a phagocyte (macrophages, neutrophils or dendritic cells)
- The pathogen is engulfed in a vesicle called a phagosome
- Lysosomes fuse with the phagosome
- Toxic chemicals from the lysosome digest and destroy the pathogen
- Indigestible material is released through exocytosis
List the main phagocytes in the immune response
- Macrophages, neutrophils and dendritic cells
Compare the roles of macrophages, neutrophils and dendritic cells
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Macrophages eliminate pathogens through phagocytosis
- They are also antigen presenting cells that activate the adaptive immune response
- Found in tissues
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Neutrophils eliminate pathogens through phagocytosis
- Most abundant and are the first to arrive at an infection site
- Found in blood
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Dendritic cells eliminate pathogens through phagocytosis
- They are also antigen presenting cells that activate the adaptive immune response
- Found in tissues
- Occupy and patrol the skin and mucosal surfaces
NOTE: Neutrophils are phagocytes, NOT antigen presenting cells.
Describe the role of eosinophils and how they perform this role
- Eosinophils destroy larger pathogens such as parasites that are too large to be engulfed via phagocytosis
- They attack via degranulation (releasing cytotoxic chemicals)
- Found in the respiratory, gastrointestinal and urinary tracts
- They are also involved in the allergic process
Describe the role of natural killer cells and explain how they destroy virally-infected cells
- Natural killer cells kill virus-infected cells through apoptosis, destroying both the cell and the virus it contains (kills pathogens once they have entered a cell, not the pathogen alone)
- The NK cell releases perforin and protease enzymes
- Perforin creates pores in the plasma membrane of the target cell allowing protease to enter
- Protease enzymes induce apoptosis
- The infected cell is eliminated
- Found in blood/lymph
State where mast cells are located and what they contain
- Mast cells are found in tissue beneath the surface of the skin, near vessels and in the respiratory system
- They contain histamine, cytokines and heparin
Describe the role of mast cells
- Mast cells are vital in the inflammatory response
- They release histamines causing permeability and vasodilation in blood vessels
- They release cytokines which attracts other immune cells to help destroy the pathogen
Define permeability and vasodilation in terms of blood vessels
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Permeability → causes capillaries to be leaky
- Protein-rich fluid (exudate) can escape from capillaries to the infected region
- The exudate causes swelling, putting pressure on surrounding tissues and stimulating nerve endings which causes pain
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Vasodilation → causes capillaries to be wider
- Increases blood flow to damaged area resulting in heat production and redness
Describe complement proteins
- Complement proteins are proteins that assist other innate immune cells to destroy pathogens
- They are initially inactive but are activated when they make direct contact with antigens
- Part of the innate (non-specific) immune response
NOTE: Complement proteins are effective on all pathogens, including viruses.
Describe how complement proteins can help to remove pathogens
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Lysis → complement proteins interact to form a membrane-attack complex on the plasma membrane of the pathogen
- The MAC creates a pore in the plasma membrane causing the pathogen to swell and burst
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Opsonisation → complement proteins coat the surface of pathogens allowing phagocytes to more easily bind to the pathogen
- Phagocytes have receptors that are complementary to those on the complement proteins (higher likelihood of phagocytosis)
- Chemotaxis → complement proteins diffuse from the pathogen and attracts immune cells to the site of infection
NOTE: Complement proteins can also coat bacteria to prevent binary fission (replication).
State what interferons are
- Interferons are a subgroup of cytokines (signalling proteins) that are made and released by virally infected cells or host cells
- They interfere with viral replication
- Part of the innate immune response
State 4 effects that interferons can have
- Activate immune cells such as NK cells
- Signals neighbouring infected cells to undergo apoptosis
- Signals neighbouring uninfected cells to reduce protein synthesis
- Signals change in plasma membrane to prevent further entry of the virus
Describe the 3 stages of inflammation (VCR), including the role of various cells and proteins
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Vascular stage involving blood cells
- Mast cells release histamines causing permeability and vasodilation in cappilaries (blood vessels)
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Cellular stage involving immune cells
- Cytokines released by mast cells attract phagocytes such as macrophages and dendritic cells
- Complement proteins opsonise the pathogen allowing phagocytosis to occur
- Platelets travel to the site to block the wound (clotting)
- Pus (consisting of dead tissue and pathogens) indicates that this stage is occuring
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Resolution stage when the antigen is removed
- Occurs when tissue is returned to its normal state and the infection is under control
- If the resolution stage is not reached, chronic inflammation may occur
Outline the process that leads to a sore and inflamed throat
- Upon cell destruction in the throat, chemicals are released that cause increased membrane permeability and swelling
- Vasodilation allows more immune cells to move to the site
- Mast cells release histamines, which causes inflammation
Outline how antigen presenting cells present antigens
- An antigen is enfgulfed by a dendritic cell or macrophage (antigen presenting cells)
- The antigen is destroyed and fragments are presented on MHC-II molecules
- The APC presents the antigen to specific helper T cells
State where antigen presentation occurs
- Lymph nodes
Explain the role of T helper cells
- They are activated by antigen-presenting cells that present antigens on their MHC II markers
- Once active, they clone and secrete cytokines (interleukins) which activates either the humoral adaptive immune response (B cells) or the cell-mediated adaptive immune response (cytotoxic T cells)
Explain the role of cytotoxic T cells
- Upon the release of cytokines from helper T cells, cytotoxic T cells proliferate (multiply), producing activated cytotoxic T cells and memory T cells via clonal selection and expansion
- Cytotoxic T cells destroy the target cell through apoptosis
Outline the function of the lymphatic system
- The lympathic system acts as a transport network
- Allows for antigen recognition
- Involved in the production and maturation of immune cells
- The removal of excess fluids from body tissues
- Absorption and transportation of fatty acids to the digestive system
List and state the function of the primary lymphoid organs
- Primary lymphoid organs are where immune cells are produced and mature
- Bone marrow is the site in which all immune cells originate (including red blood cells and T cells) and where B cells mature
- The thymus is where T cells mature after being released from the bone marrow
List and state the function of the secondary lymphoid organs
- Secondary lymphoid organs are where immune cells are activated by meeting antigens and where immune responses occur
- The spleen filters blood clearing it from bacteria, viruses or worn-out red blood cells
- Lymph nodes are the site for antigen recognition
Describe both the structure and function of lymph nodes
- Lymph nodes are small bean shaped structures located in the armpits, neck, groin and abdomen
- Composed of lymphoid tissue with clusters of lymphocytes residing within the lymphatic system
- They are sites where antigen presentation occurs and activates T and B cells
- Swelling due to infection occurs because the number of B and T cells in the lymph nodes increase
- Valves in lymph nodes prevent the backward flow of lymph fluid
Describe how the lympathic system acts as a transport network for immune cells
- Immune cells can travel around the body through the lymph
Describe the key features of the adaptive immune response
- T and B cells (special white blood cells known as lymphocytes)
- Antibodies, also known as immunoglobulins (special antigen-binding proteins)
- Secondary lymphoid organs where B and T cells meet foreign antigens and are activated, and where adaptive immune responses occur
Define clonal expansion and clonal selection
- Clonal expansion is when activated cells divide into many identical copies (clones)
- Clonal selection is when a cell binds with its specific antigen
Explain adaptive immunity
- Adaptive immunity involves a specific response against a specific pathogen where memory is retained for future infection
- Usually only required if an infection is not cleared by the innate response
- Specificity refers to adaptive immune cells (B and T cells) having unique receptors that recognise specific antigens
- Immunological memory refers to the ability for the immune system to remember antigens from previous infections which enables a stronger and more rapid immune response upon reinfection with the same antigen
Outline the humoral and cell-mediated parts of the adaptive immune response
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Humoral immunity is a response that occurs in body fluids
- It involves the actions of B lymphocytes and their antibodies
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Cell mediated immunity is a response that kills body cells
- Involves the actions of cytotoxic T cells
- Both produce memory
Outline how the cell-mediated response removes body cells infected by viruses (or cancerous)
- Upon antigen recognition, helper T cells clone and secrete cytokines
- Cytotoxic T cells proliferate producing activated cytotoxic T cells and memory T cells through clonal selection and expansion
- Cytotoxic T cells destroy the cells through apoptosis
Outline how cytotoxic T cells attack antigens
- Cytotoxic T cells release perforin that enters a target cell and create pores in its plasma membrane
- Cytotoxic T cells also release protease enzymes that enter the infected cell via the pore and initiate apoptosis
- The cytotoxic T cells are then free to attack other infected cells that display the same foreign antigen
NOTE: Apoptosis by cytotoxic T cells, unlike NK cells, are specific for certain antigens and form memory.
Describe the key components and functions of the humoral adaptive response
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B cells are activated by binding to pathogens or cytokines secreted by T helper cells
- Some become memory cells (stored in lymphatic system)
- Some become plasma cells (floats around the bloodstream)
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Plasma cells make antibodies
- Antibodies work against the pathogen (PIANO)
Outline how the humoral immune response removes extracellular pathogens from the body fluids
- B lymphocytes (cells) are covered in specific receptors and are activated by T helper cells
- When activated by a T helper cell, B cells replicate (clonal expansion) producing plasma cells and memory cells
- The plasma cells make antibodies which can opsonise or agglutinate pathogens
Describe the difference between memory cells and plasma cells
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Memory cells
- Inactive
- Lifelong
- Produce rapid and enhanced immune responses upon secondary exposure to a previously identified antigen
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Plasma cells
- Active
- Tend to live shorter than memory cells
- Gives protection by producing antibodies
- Each type of plasma produces one specific type of antibody
Outline the process that leads to the production of antibodies
- When a pathogen comes into contact with a B cell, the B cell divides and clones to produce memory and plasma cells
- Plasma cells produce antibodies that act against the pathogen
Draw and label the structure of an antibody
- Diagram should include
- 2 heavy and 2 light polypeptide chains
- Variable and constant region
- 2 identical specific antigen-binding sites
NOTE: Antibodies have a quaternary structure. They are composed of 4 polypeptide chains that are held together by disulphide bonds.
Explain what creates the difference in variable regions for an antibody
- Antigenic variation
- The shuffling of nucleotides that code for variable regions create different combinations
- These combinations code for varying protein structures
Describe the effects of antibodies (PIANO)
- Precipitation → antibodies bind to soluble agents making them insoluble to create a solid that is more visible to the immune system (due to cross-linking between antigens and antibodies)
- Inflammation → antibodies initiate the release of histamine by binding to mast cells
- Agglutination → antibodies bind to antigens forming antigen-antibody complexes causing them to clump together and become more visible to the immune system
- Neutralisation → antibodies bind to antigens and block their receptors so that the pathogens cannot attach to healthy body cells and infect them
- Opsinisation → antibodies bind to antigens to make them more susceptible to phagocytosis
NOTE: Antibodies do not directly eliminate pathogens.
Describe 3 ways that antibodies can neutralise pathogens
- Bind to antigens to stop them from functioning
- Coat the surface of antigens to make them more susceptible to phagocytosis (opsinisation)
- Bind to antigens to initiate lysis by complement proteins
Describe the difference between natural and artificial immunity
- Natural immunity is a form of immunity that occurs naturally without deliberate intervention
- Artificial immunity is a form of immunity that is created via deliberate intervention or exposure to an antigen
Describe the differences between active and passive immunity
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Active immunity involves antibodies being produced by an individual’s own immune system in response to exposure to a particular antigen
- Secondary response is enhanced due to memory, long lasting, more effective, immunity is developed over weeks
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Passive immunity involves antibodies being acquired from an external source
- No immunological memory, short lasting, less effective, immunity is immediate
State ways in which natural immunity can develop
- Antibodies naturally produced in response to catching a cold
- Mother-child (breastfeeding)
- Contracting chicken pox via “chickenpox parties”
State 2 ways in which artificial immunity can develop
- Vaccination (deliberate exposure to a pathogen to produce antibodies)
- Injection of antibodies
State 2 ways in which active immunity can develop
- Vaccines
- Infection
State 2 ways in which passive immunity can develop
- Mother-child
- Injection of antibodies
NOTE: No memory cells are produced due to a lack of exposure to the antigen.
State the function of ducts leading to and leading from the lymph nodes
- Ducts leading to the lymph nodes
- Carry APCs that display antigens on the MHC-II molecules
- Carry free-floating antigens
- Ducts leading from the lymph nodes
- Carry specific cytotoxic T cells
- Carry specific helper T cells
- Carry specific antibodies
NOTE: From NEAP 2023 exam.
List the changes that occur during an inflammatory response
- Increased…
- Mast cell activation
- Histamine release
- Blood flow to the area
- Swelling
- Blood vessel dilation
- Clotting factors
Distinguish between T memory and B memory cells
- T memory cells proliferate into T helper cells and cytotoxic T cells when the body is exposed to a previously identified pathogen, mounting a quicker and stronger immune response
- B memory cells will rapidly divide and form new antibody-producing plasma cells
NOTE: T memory cells are involved in cell-mediated immunity while B memory cells are involved in humoral immunity.
