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Barrier defence mechanisms
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Lecture detailing the barrier defence mechanisms of the immune system
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Lecture 2 -Barrier Defence Mechanism’sBarrier Defence Mechanisms-Anatomic Barrier
Skin punctured/burnt skin allows entry of pathogens.
Mucous membrane traps organisms that can be expelled afterwards. Cilia move bacteria out the
lungs and GI tract via the muco-ciliary escalator.
Other Defence Mechanisms
- pH= gastric acid (2.5), sebum or skin (3-6), vagina (<5).
- Temperature= fever impairs pathogen survival.
- Interferon (IFN)= a cytokine, there is IFN- alpha, IFN-beta which are type 1, and IFN-gamma which is
type 2.
o Type 1 interferons are released by infected cells.
o Prevents viral replication in surrounding cells.
Muco-ciliary escalator= inside conducting airway, it’s composed of mucus and cilia, the cilia move mucus up and out
the lungs.
Cytokine= small proteins important to cell signalling. It’s composed by white blood cells.
Lactoferrin
High concentration in colostrum and is present in secretions.
Sequesters iron away from bacteria and other roles microbes require iron to divide. Lactoferrin and
iron bind together to prevent this.
Lysozyme
- Cleaves peptidoglycan.
- It’s effective against gram positive but not gram-negative bacteria.
Beta Defensins
- Cationic short peptides (less than 100 residues) are found in many species.
- They can be alpha, beta or theta form. The beta form is most studied.
- Alpha and beta contain 6 cysteine residues.
Found in granules or leucocytes and is produced in the gut.
It disrupts microbe membranes by forming ion-permeable pores.
Other Anti-microbial Agents
Reactive O2 species [superoxide/hydroxyls/nitric oxide/nitrous acid].
Anionic peptides.
Surfactants in the lungs (like SP-A or SP-D).
Reactive O2 species= small and short
Anatomic living
Skin, hair,reactive molecules that contain oxygen. They act as signalling
muco-ciliary
messengers. escalator.
Chemicals Mucus, lactoferrin, lysozyme,
pH, defensins surfactant.
Other Friendly microbes.
Physical Flushing (tears, saliva, urine,
coughing), sneezing, blinking,
, earwax.
What Happens If Microbes Enter?
Army of leucocytes at the entry point.
- Specialised jobs.
- Cross communication, adaptations and organised.
Innate and Adaptive Immunity
INNATE ADAPTIVE
COMPONENTS Barrier defence, T and B lymphocytes,
phagocytic cells, memory, cell mediated.
epithelial cells,
complement,
inflammatory
response.
TIMING First response Takes days.
(seconds and
minutes).
SPECIFICITY For pathogen Very specific, short
groups, generic peptides from individual
patterns of dead species.
cells.
DIVERSITY Limited number of Lots of receptors.
receptors.
SELF AND NON-SELF Good, damage is a Good, damage is rare
DISCRIMINATION side effect. due to autoimmunity.
MEMORY Limited. Yes.
EVOLUTION Ancient. Fairly recent.
Innate Adaptive Both
- Macrophage - B cell - Natural killer
- Killer cell - Antibodies T cell
- Neutrophil - T cell [CD4+ T - Gamma delta
- Complement cell and T cell
protein CD8+T cell]
- Dendritic cell
- Mast cell
- Basophil
- Eosinophil
- Granulocyte
What is a Complement?
- 50+ proteins and glycoproteins.
- They are made in the liver and are abundant (15% of protein in serum).
Complement Proteins
C numbered, in order of discovery.
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