HOST DEFENCE 1 Flashcards
Give examples of viruses? (2)
- Influenza
- Polio mellitus
Give some examples of parasites? (3)
- Tapeworms
- Malaria
- Helminths
What are the benefits of the immune system? (2)
- Protection from invaders
- Eliminates altered self cells
What are the negative effects of the immune system? (2)
- Discomfort (inflammation)
- Damage to self (autoimmunity)
What are the two major elements of the immune system?
- Innate immune system
- Adaptive immune system
List 4 innate defence mechanisms
- Anatomic resisting barriers e.g skin, mucous
- Physiological barriers e.g temp, pH
- Phagocytosis
- Inflammatory defensive barriers e.g vasodilation, increase in capillary permeability, influx of phagocytes
What is the role of epithelia in innate immunity? (3)
- Physical barrier
- Antibiotics - locally produced on epithelial tissue
- Intra-epithelial lymphocytes - live on the skin
What are the four soluble factors that the innate immune system uses to provide defence against bacterial infections?
- Lysozymes
- Acute phase proteins
- Complement
- Interferons (cytokines)
What is the role of lysozymes?
Splits the peptidoglycan wall of susceptible bacteria, this ruptures the extracellular membrane
What is the role of acute phase proteins e.g. C reactive protein?
- Opsonization
- Attraction of phagocytes
- Increased blood flow - in areas where there’s a high conc. of foreign pathogens (this brings several chemicals and cells which are required to eliminate potential pathogens) = part of inflammation
- Basically activate complement
What are complements?
A group of 20 serum proteins with the role of opsonization
What are interferons?
Provide antiviral resistance (break down viral wall)
What is opsonization?
Formation of a coating surface around the pathogen, so the pathogen can be identified more easily
What cells are part of the innate immune system? (two)
- Phagocytes: engulfs particles
- Natural killer NK cells: recognises cell surface changes occurring on virally infected and tumour cells
Where do all cells of the immune system arise from?
Pluripotent hemopoietic stem cells
What can pluripotent hemopoietic stem cells differientate into?
- Myeloid stem cells
- Lympoid stem cells
What can Myeloid cells differentiate into? (2)
- Granulocytic stem cells
- Monocytic stem cells
What can granulocytic stem cells differentiate into? (3)
- Neutrophils
- Basophils
- Eosinophils
What can monocytic stem cells differentiate into? (4)
- Macrophages
- Langerhans & Kupffer cells
- Dendritic cells
What can lymphoid cells differentiate into?
- T cells (THELPER TCYTOTOXIC)
- B cells (plasma cells)
How do specialised cells develop from stem cells?
- Cytokine growth factors
- The development of a progenitor cell (committed cell, meaning that it is committed to that line of cell growth)
- e.g. an eosinophil progenitor must become an eosinophil
Describe the structure of monocytes?
- Larger than lymphocytes
- Have ONE horseshoe-shaped nucelus
- Often contain faint azurophillic granules
What’s the function of monocytes?
Precusor of Macrophages, Langerhans, Kupffer, and Dendritic cells
How do macrophages recognise microbes and give an example of a receptor?
Through different Pattern Recognition Receptors (PRR) such as Toll-like receptor.
How do macrophages present the antigens of a pathogen on it’s surface?
- The macrophage produces an MHC Class II molecules
- This binds the degraded peptides of the pathogen and transfers the peptides to the outer surface
- So the peptides can be detected by Th1 cells
What are the functions of macrophages? (4)
- Phagocytosis
- Intracellular and extra-cellular killing
- Tissue repair
- Antigen presentation
What is the structure of neutrophils? (2)
Are polymorphonuclear
- This means they have a nucleus with several lobes and a cytoplasm that contains granules (these granules are not acidic or basic)
What is the difference between macrophages and neutrophils? (5)
- Neutrophils aren’t antigen-presenting cells
- Neutrophils are found in the blood and macrophages are found in the tissue
- Neutrophils nucleus has several lobes and macrophage has a horse-shoed nucleus
- Neutrophilis has lots of granules
- Neutrophilis are at the infected site first
What are the four types of PRRs?
- Fc receptors – activate phagocytosis
- Complement receptors – bind to C3b-coated bateria and results in enhanced phagocytosis
- Scavenger receptors – Bind to polyanions on bacterial surfaces = recognition + phagocytosis
- Toll-like receptors – recognize PAMPs + phagocytosis
What are the three stages involved in killing of opsonised microbes?
- . In the innate immune response this occurs via Complement Receptors and in the adaptive immune response by Fc receptors. In both systems, pattern recognition receptors (PRR) are also needed to identify the organism.
- The microbe is ingested by the pseudopodia of the phagocyte (forms a phagosome)
- Metabolic reactions take place in phagosome, generating oxygen and nitrogen radicals which damage microbes
- formation of phagolysosomes = reduction reactions + low pH and lysosomal enzymes = death of microbe
In the killing of opsonised microbes, pseudopodia ingest the microbe. How does this differ in innate and adaptive response?
- In innate - complement receptors carry this out
- In adaptive - Fc receptors carry this out
- Both systems require PRRs
What do basophil contain? (2)
- Contain glycogen
- Contain deep violet-blue granules (contain histamine and are acidic)
Which complements do basophils bind?
C3a, C3b and C5a
How do eosinophils work?They gather at a parasitic infection or site of allergic reaction such as asthma
they release their toxins, contained in their granules
- Eosinophils gather where there is a parasite infection or an allergic reaction such as allergic asthma
- They degranulate releasing the contents of their granules (peroxidase and histaminase)
How do NK cells know which host cells are infected?
- Virally infected cells inhibit the expression of MHC Class I molecules = reduced expression of MHC class I
- Virally infected cells don’t respond to IFNα and IFNβ (MHC Class I aren’t produced)
When both receptors on NK cells are occupied, the NK cell becomes activated. True or false?
False - not activated when both receptors are occupied so doesn’t kill virally infected cells
When the activating receptor is occupied (not the inhibitory one) what happens?
The NK cells receive a signal to secrete chemicals that kill virally infected cells
What’s the complement pathway/ overview of innate immune response? (4)
- Mast cells are activated causing vasodilation and increased capillary permeability to bring immune cells to the site of infection
- Permeable capillaries allow influx of fluid and cells
- Phagocytes + neutrophils move to site of inflammation (chemotaxis)
- Phagocytes and antibacterial destroy bacteria
What are cytokines (interferons)?
Toxic to viruses
What shows resistance to phagocytosis and how does it do this?
Pneumococcus
- Capsular polysaccharide inhibits phagocytosis
What shows resistance to reactive oxygen intermediates in phagocytes and how does it do this?
- Staphylococci
- Produces catalase which breaks down oxygen intermediates
What shows resistance to complement activation (alternative pathway) and how does it do this?
- Neisseria meningitides: expresses sialic acid which inhibits C3 and C5 convertases
- Streptococcus: M protein blocks C3 binding to organism and C3b binding to complement receptors
What shows resistance to antimicrobial peptide antibiotics and how does it do this?
- Pseudomonas
- Synthesis of modified LPS that resists action of peptide AB’s
