Lecture 2 - Immunity to infection Flashcards
What is immunity to infection
- A conflict between the microbe/parasite’s ability to infect and evade the host’s immune response and the ability of the immune system to detect and eliminate the pathogen without causing damage
What are the 3 different defences for immunity
- External defences
- Extra-cellular pathogens/defences
- Intra-cellular pathogens/defences
What are the two different immune systems
- Innate immunity
- Specific/adaptive immunity
Name the different types of External Defences
- Physical barriers
- Antimicrobial peptides/proteins (AMPs)
- Secretory Antibody
- Microbial antagonism
Name some physical barriers
- Skin, mucous membranes, desquamation
- Mucus, cerumen
- Muco-ciliary escalator (in bronchi)
- Fluid flow
- Skin secretions
- Non-specific mucosal secretions
How does the skin act as a physical barrier
- Has mucous membranes throughout the skin
- desquamation (peeling of the skin)
- maintaining moisture levels
- sweat which is acidic
How does pathogens gain entry through the skin
- burns and cuts
- infected needles
- arthropod bites
- mammal bites
What infection does burns and cuts causes ?
- staphylococcal, clastridial infection
What infection does infect needles cause?
- hepatitis (B & C), HIV and AIDS
What infection does arthropod bites cause?
- malaria, yellow fever, leishmaniasis
What infection does mammal bites cause?
- rabies
how does mucus and cerumen act as a physical barrier
- trapping pathogens and toxins before they can enter the lungs
How does Strep. pneumoniae and influenza virus cleave mucus?
- they both secrete neuraminidase: binds sialic acid and then cleaves mucus
How does Muco-ciliary escalator (in bronchi) act as a physical barrier
- trapping inhaled particles and debris in secreted mucus and then moving it out of the lungs via the escalator-like function of the waves created by beating cilia
Give examples of fluid flow
- tears, urine
How does fluid flow act as physical barrier to pathogens
- tears, and urine can be overcome by pathogen adhesion to mucosal cells.
- Reducing pathogenic attachment and duration of contact with bodily surfaces
Give examples for skin secretions which acts as a physical barrier
- Skin secretion such as lactic acid, hgih salt, fatty acid, lysozyme and AMPs, defects -> ringworm
What are AMPs?
- Antimicrobial peptides (AMPs)
- a class of small peptides that widely exist in nature and are an important part of the innate immune system of different organisms
what AMPs examples are used as physical barriers?
alpha-defensins
beta-defensins
cathelicidins
what secretes alpha defensins ?
- neutrophils, intestinal paneth cells
What secretes Beta-defensins ?
- epithelia (skin, trachea), neutrophils
What secretes cathelicidins?
- epithelia, keratinocytes, phagocytes
How are Anti-microbial action released rapidly when infections/tissue injury occur
- alpha and beta-defensins and cathelicidins are stored in granules such as neutrophils. (they are premade)
How does AMPs usually work?
- broad anti microbial action, cationic (+ve charge)
- AMPs can open pores in the membrane, but they can work like magnets. They can magnetise the bacteria, so they are sometimes very charged, positively
Explain the microbial evasion of defensins
- Produce inhibitory binding proteins (Streptococcus pyogenes)
- Inhibit signalling pathways for gene expression of defensins (Bordetella bronchiseptica at bronchial epithelium)
- Reduce affinity for cell wall (Staphylococcus aureus modify teichoic/lipoteichoic acids, phospholipids)
What are secretory immunoglobulins and how do they act as a physical barrier ?
- antibodies found in external fluids, such as saliva, bile and milk that are involved in mucosal immunity
How does Microbial antagonism act as a physical barrier
- Block attachment sites
- consumes nutrients
- produce inhibitors
Name the different Extracellular defences/pathogens
- Complement activation - alternative pathway
- Acute phase proteins (opsonins)
- Phagocytosis
- Antibodies & complement activation (classical)
