Immunity 🦠Flashcards
What are antigens?
- Molecules that elicit immune response via recognition by T lymphocytes or antibodies produced by B lymphocytes
- Found on the surface of pathogens or released as toxins: these are recognition sites for immune system
What are the types of antigens?
- Self antigens: used to be recognised by the immune system as its own cells
- Non-self antigens: Things other than self antigens (foreign)
How are antigens recognised?
- B lymphocytes: membrane bound antibodies that recognise free antigens or antigens on plasma membrane of pathogen
- T lymphocytes: recognise the antigens presented by antigen presenting cells.
What are MHC markers?
- Major histocompatibility complex
- Proteins on the surface of a cell that allows it to present self or non-self antigens to T lymphocytes.
What are pathogens?
- Agents that can cause disease
- Cellular or non-cellular
What are some cellular pathogens?
- Bacteria (not all are pathogenic)
- Fungi: secretes chemicals that can cause disease
- Protozoans: Reproduce within host cell or extracellular fluid
- Worms: Parasitic worms can remain in immune system suppressing its response.
- Arthropods: Mosquitoes, ticks etc have molecules within saliva that inhibit inflammation and modify immune response.
What are non- cellular pathogens?
- Viruses, viroids and prions
- They aren’t living but have the ability to cause disease
What are viruses?
- Composed of DNA or RNA enclosed in protein
- Antigenic drift: Can make changes to antigens on surface resulting in similar viruses.
- Infects host cells through insertion of viral DNA, causing host to translate more viruses.
What are prions?
- Contains no genetic material
- Mis-folded protein and causes nearby proteins to mis-fold as well
- Protease resistant and denature resistant
- causes neurodivergent disease
- Innate immune system ineffective
- Adaptive immune response unable to identify and respond to prions.
What is innate immunity?
- First line of defence against pathogens
- Physical barriers: Skin (dead intact skin), tree bark, hairs.
- Chemical barriers: lysosome in eyes, production of tears, stomach acid, urinating, citronella.
- Microbiological barriers (microflora)
Examples of physical barriers in plants? (innate)
- Cell wall
- Cutin and waxes that form plant cuticle (outer cell wall), prevents pathogens from entering
- Stomata can open and close in response to pathogens
Examples of chemical barriers in plants? (innate)
- Caffeine: toxic to insects and fungi
- Citronella: Repels insects
- Saponin: disrupts the cell membrane on fungi
Physical barriers in animals? (innate)
- Epithelial cells: form physical barrier to prevent entering of pathogens
- Mucus secretion: trap invading organisms in mucus and sweep them away through cilia on membrane.
Chemical barriers in animals? (innate)
- Lysosome: Found in eyes. tears, sweat and saliva, generalised defence, destroying bacterial cell walls.
- Stomach acid and digestive enzymes: Kill many pathogens (e.g protease)
- Surfactants in lungs: Fluid in lungs act as surfactants, coating pathogens allowing easier removal by macrophages.
Microbiological barriers in animals? (innate)
- Non-pathogenic bacteria (normal flora): Found on skin, mouth, nose, throat, gastrointestinal tract and urogenital tract.
- Outcompetes pathogenic bacteria for
resources and space, produces chemicals that
lower pH in environment.
Characteristics of the innate immune system?
- non-specific
- rapid (can occur within hours)
- present within animals
- fixed response, does not change or alter
- creates no immunological memory or pathogenic infection
What are phagocytes?
- They are leukocytes (white blood cells) that are able to break down and engulf pathogens via a process called phagocytosis.
- some phagocytes include:
- neutrophils, macrophages, monocytes and dendritic cells.
What is a MHC 1 marker?
- found on all nucleated cells
- peptides on MHC 1 markers are presented to cytotoxic T cells in adaptive immune response
What is a MHC 2 marker?
- Found on antigen presenting cells: dendritic, macrophages and B lymphocytes.
- Peptides on the MHC 2 marker get presented to helper T lymphocytes for adaptive immune response.
Neutrophils
FUNCTION:
- phagocytosis
- release antimicrobial compounds that disrupt bacterial and fungal membranes.
CHARACTERISTICS:
- Majority of leukocytes in blood stream
- First cells to arrive at site of infection (non-specific, 1st line of defence)
Macrophages
FUNCTION:
- Antigen presentation
- Phagocytosis
CHARACTERISTICS:
- Pre-curser cell: Monocyte
- Turns into macrophage when migrates into tissue
- Type of leukocyte
Monocytes
FUNCTION:
- Phagocytosis
- Can differentiate into dendritic cells or macrophages
Dendritic cells
FUNCTION:
- Antigen presentation
- Phagocytosis
CHARACTERISTICS:
- Type of leukocyte (white blood cell)
- Many grooves to increase surface area, more contact with nearby cell
Basophils
FUNCTION:
- Release histamine which contribute to inflammation and blood vessel dilation
- limited role in phagocytosis.
Eosinophils
FUNCTION:
- Antigen presentation
- Releases cytokines and cytotoxic chemicals found as granules within them
- Involved in parasitic and viral infections
- Role in inflammatory and allergy responses
CHARACTERISTICS:
- Type of leukocyte
- Found within tissues
- 2 lobes as nucleus.
Mast cells
FUNCTION:
- Key roll in inflammation through releasing of histamine
- Plays a roll in allergies
CHARACTERISTICS:
- Found distributed near blood vessels in most tissues
- Contain many granules with histamine
Natural killer cells (NK)
FUNCTION:
- Recognises virus infected and cancer cells
- Releases cytotoxic chemicals from granules (e.g protease) which makes holes in cell membrane triggering apoptosis of infected and abnormal cells.
- releases cytokines to attract active adaptive immune system cells.
- Attacks cells that do not contain self antigens.
Complement proteins
FUNCTION:
- Opsonisation: coating of microorganism so they can be recognised increasing phagocytosis.
- Activates phagocytosis.
CHARACTERISTICS:
- Produced by the liver and circulates within the blood (inactive)
- When it comes in contact with a pathogen it activates.
Interferons
FUNCTIONS:
- Inhibits viral replication
- Signals for neighbouring cell to prevent viruses from entering
- Makes cell membrane less permeable/less fluid
- Virus infected cell undergo apoptosis
- Activates immune cells.
CHARACTERISTICS:
- Subgroup of cytokines
- Sends signals to other cells
Cytokines
- Signalling molecules
- Promote proliferation of lymphocytes, induce inflammation and fever, promote antibody responses and activate macrophages
What is inflammation?
Accumulation of plasma and leukocytes that occur when a tissue is damaged or infected
- results in heat, pain, swelling,
redness and a loss of function
What triggers inflammation?
Interaction between leukocytes and pathogens triggers inflammatory response.
This results in complement proteins and cytokines being produced, activated and released.
wha are the steps involved in the inflammatory response
- Bacteria or other pathogens breach the first line of defence (barriers such as intact skin)
- Injured cells release histamine which cause blood vessel dilation and increased permeability allowing immune cells easier entrance. (dilation causes redness), exudate around cut from capillaries enter into infected region causing swelling leading to pressure on tissue hence pain. Exudate helps with clotting.
- Neutrophils migrate towards cytokines released and are activated, macrophages are brought as well. Neutrophils release defensins and hydrogen peroxide to disrupt membrane of bacteria and kill them.
- Macrophages secrete cytokines and phagocytose pathogens, leads to pus containing leukocytes, dead pathogen and cell debris. cytokines and histamine released from neutrophils and macrophages attract more phagocytic cells to infected area.
- Neutrophil and macrophages phagocytose pathogens, pus formed consists mainly of dead phagocytic cells and other immune cells, and also contains living cells and cell debris.
- Resolution stage where anti-inflammatory cytokines are released and reversal of inflammation causing processes happen, once all pathogens are eliminated.
How does the adaptive immune response differ to the innate?
- Specificity: Ability to recognise and respond exclusively to SPECIFIC ANTIGENS on pathogens, as a result defensive mechanisms are triggered.
- Immunological memory: The cells of the adaptive immune system (B lymphocytes) produce memory cells which allow specific antibodies to a specific antigen to be produced, leading to a more rapid response when exposed to the same antigen.
Lymphocytes
- Each lymphocyte has a different receptor for a particular antigen
- They’re able to proliferate (clone themselves -> clonal expansion
- Lymphocytes classified as either B lymphocyte or T lymphocyte
B lymphocytes originate and differentiate in bone marrow, complete maturation in lymphoid tissue and organs
T lymphocytes develop in bone marrow and mature in thymus - Lymphocytes travel through the lymphatic system
- Activate when they find an antigen specific to their receptor
What are the types of adaptive immunity?
- Humoral immunity: Macromolecules are secreted into extracellular fluid
- Cell-mediated immunity: Involves T lymphocytes and phagocytosis.
