Antibacterial responses Flashcards
What are the key steps in infection?
entry,
invasion and colonisation of host tissue
evasion of immunity
tissue damage
What are the features of immunity to bacteria?
Defence mechanisms against microbes comprise both innate and adaptative system
Specialised to different types of bacteria
Pathogenicity and survival of the bacteria is influenced by the ability to evade the effector mechanism of immunity
Some bacteria establish latent or persistent infection and the immune system does not clear the microbe
What is the first line of defence in an infection?
What are anti-microbial peptides?
Are capable of killing by penetrating microbial membranes thus disrupting their integrity
They are active against bacteria, fungi and enveloped and non-enveloped viruses
2 types:
Alpha-defensins
- Secreted mainly by neutrophils and Paneth cells
Beta-defensins
- Secreted by a broad range of epithelial cells, in particular, those in the respiratory tract, the skin and the urogenital tract
Whats the 1st step if the intial barriers are broken through in a infection?
Complement
Has the ability to detect PAMPs due to containing certain molecules - so can be described as a PRR - ‘classical pathway’
Can recognise gram-positive or gram-negative bacteria carbohydrates and activate alternative pathway of complement
Bacteria that has mannose on the surface of the bacteria can active the lectin pathway of complement
What are the different complement functions?
What are the consequences of detection of PAMPs by PRRs?
Phagocytosis and cytokine production
–> this then leads to inflammation (due to chemokines and cytokines)
How does inflammation occur?
Initiates by detection of infection normally a resident cell in the tissue which will get activated
This will then start producing inflammatory cytokines (IL-1, IL-6 and TNF-a)
Chemokines will have a reaction in the endothelium and beyond - allowing for circulating leukocytes to go into the site of damage or infection (first neutrophils, then monocytes, then lymphocytes)
Mast cells release histamine and prostaglandins
What are neutrophils?
Perform phagocytosis and they degranulate granules –> intracellular killing of bacteria
Phagocytosis and oxidative burst kills the bacteria
They have a special system of NETs (neutrophils extracellular traps) - suicide system
How do antibodies neutralise bacterial toxins?
Trigger classical complement pathway by binding of IgM to bacteria
- As a consequence, bacterial cell surface is coated in C3b facilitating its phagocytosis
Opsonisation - coating of bacteria to aid phagocytosis
What is the difference between Humoral and cellular response?
What do helper T cells do?
enhance phagocytosis of extracellular pathogens by activating macrophages
