Unit 4 AOS3 Flashcards
Pathogen
An agent that causes disease.
Antigen
Any molecule that triggers an immune response.
(Interacts with immune system).
Allergen
Non-pathogenic antigen that triggers an allergic reaction.
How does the immune system protect the body?
By scanning and destroying pathogens.
2 antigen types
- Self-antigens.
- Non-self antigens.
Self-antigens
Located on the surface of cells, mark the cell as ‘self’ so the immune system doesn’t attack.
MHC I markers
MHC II markers.
MHC I markers
Expressed on all nucleated cells; Identifies cells as self.
MHC II markers
Found on specialised cells of the immune system,
Allow antigen-presenting cells to show T helper cells foreign antigens which in turn kicks of the adaptive immune response.
MHC
Major Histocompatibility Complex Proteins
MHC proteins differ between individuals.
Non-self antigen
A molecule from outside the body that is recognised by the immune system and initiates an immune response attack.
Malfunctions involving antigens
The immune system results in the recognition of self-antigens as non-self. So immune system attacks self-cells; healthy cells (Autoimmune disease)
Red Blood Cells
Red blood cells have no MHC proteins.
Type A —> A antibodies.
Types of Pathogens
Cellular and Non-cellular pathogens.
Cellular pathogens
cellular structure + living organism
- Bacteria.
- Fungi.
- Worms.
- Protozoa.
Bacteria
- Unicellular prokaryotes.
- Cause disease through toxins and enzymes. Affecting the functioning of cells or causing death.
Fungi
- Eukaryotic
- Yeast, moulds containing filaments called hyphae
Thrush and Ringworm
Worms
- Multicellular invertebrate.
- Egg, larval + adult stages.
- 55m
Protozoa
- Single-cell eukaryotic.
- Free-living or parasitic.
- Inhibit nucleic acid synthesis, protein synthesis and cellular respiration.
eg. Malaria.
Non-cellular pathogens
- Viruses
- Prions.
Viruses
- Composed of genetic material inside a protein coat, sometimes covered in a lipid envelope.
- Not able to independently reproduce, so they insert genetic material into the host’s cell used for cell replication.
Prions
- Abnormally folded proteins with the ability to induce normal proteins to become misfolded.
- Only occurs in mammals and affects the brain and other neural structures.
- Contain no nucleic acids.
First Line of Defence
Physical, chemical and microbiological barriers preventing pathogenic invasion.
Innate immune system
Component of an immune system composed of generalised and non-specific defences and/or response to pathogens.
1st and 2nd line of defence.
Barriers in plants
- Physical.
- Chemical.
Physical Barriers in Plants
Prevent pathogens from physically entering.
- Thick bark.
- Thorns.
- Closing of the stomata.
- Waxy cuticles on leaves.
- Galls formation.
Chemical Barries in Plants
Production of chemicals harmful to pathogens.
- Chitinases; antifungal
- Phenols
Barriers in animals
- Physical.
- Chemical.
- Microbiological.
Physical Barriers in Animals
Block pathogens.
- Intact Skin.
- Mucous secretions // Hairs on the respiratory tract
Chemical Barriers in Animals
Chemicals make an unliveable environment.
- Low pH in Vagina.
- Lysozyme in tears.
- Acidic sweat.
- Stomach acid.
Microbiological Barriers in Animals
Non-pathogenic bacteria prevent the growth of pathogentic bacteria. “Normal flora” –> bacteria on skin etc.
Second line of Defence
Needed when pathogens slip by the first line.
Characterised by the non-specific and immediate response to injury and pathogens by cells and molecules –> destroy pathogens.
2 components : Cellular + Non-cellular.
Cellular components (2nd line)
All cells involved are leukocytes (white blood cells that protect the body from pathogens).
- Phagocytes.
- Natural Killer Cells.
- Mast Cells.
- Eosinophils.
Phagocytes
Cells that engage in phagocytosis which they consume and destroy foreign/dead material, engulfing it by endocytosis. Lysosomes then destroy the material.
- Neutrophil.
- Macrophage.
- Dendritic cell.
Neutrophil
Engages in phagocytosis of pathogens and foreign material, as well as the release of cytokines.
Macrophage
Leukocyte that engages in phagocytosis and antigen presentation. (present antigens on outside of cell from consumed)
Dendritic cell
Type of leukocyte that engages in phagocytosis and antigen presentation. (present antigens on outside of cell from consumed)
antigen-presenting cell
A subgroup of phagocytes that display antigens (MHC II) from consumed pathogens on their surface and interact with the adaptive immune system.
Process of phagocytosis + antigen presentation
- Phagocytosis of pathogen.
- Fusion with lysosome.
- Enzymes start to degrade pathogen.
- Pathogen breaks down into smaller fragments.
- Fragments of antigen are presented on cell surface.
Why are cytokines produced?
Phagocytes release them to communicate in the immune system.
What are cytokines?
Cell signalling molecules that aid in communication between immune cells and help protect against pathogens.
Natural Killer Cells
Responsible for the recognition and destruction of damaged and/or infected host cells (abnormally + virally infected).
2 Natural killer cell receptors
Killer inhibitory receptor; Exaimes cells surface for MHC I markers.
Killer activation receptor; Binds to certain molecules that appear on cells undergoing cellular stress.
Mast cells
Type of leukocyte responsible for relasing histamines (play a key role in inflammation) during allergic + inflammation responses (in result to infections)
Eosinophils
Large granulated cells contain various toxic chemical mediators that help destroy invading pathogens.
- Target pathogens too large to be phagocytosed.
Noncellular components (2nd Line)
Other key molecules/processes.
- Interferons.
- Complement proteins.
- Fever.
Interferons
Cytosine released by virally infected cells increases the viral resistance of neighbouring unaffected cells.
- Interact with receptors on neighbouring cells to make them less susceptible to viral infection. (prevent spread).
Complement proteins
Different proteins found in the blood that opsonise, cause lysis and attract phagocytes to invading pathogens. Complement cascade occurs.
Complement Cascade
Complex sequence of events where proteins react with each other after the activation of complement proteins.
3 major outcomes of the complement cascade
- Opsonisation
- Chemotaxis
- Lysis
Opsonisation
Complement proteins attach to the surface of pathogens making them easier to phagocytose (to recognise as foreign)
Chemotaxis
Complement proteins gather near pathogens and attract phagocytes.
Lysis
Complement proteins join on the surface forming a membrane attack complex (MAC) to create pores. This destroys pathogens by causing lysis via influent or fluid into pathogenic causing it to burst.