T1 L2: Innate immune defences & inflammation 1 Flashcards
(40 cards)
What is innate immunity?
The first line of defence against infection which is present from birth and is passed down genetically
It occurs within minutes of pathogen recognition
What are some receptor characteristics of innate immunity?
- Specificity is inherited
- It expressed by all cells of a particular type
- It triggers an immediate response
- It recognises a broad class of pathogens
- Interacts with a range of molecular structures of a given type
- Able to discriminate between closely related molecular structures
What are some characteristics of adaptive immunity?
- Encoded in multiple gene segments
- Requires gene rearrangement
- Clonal distribution
- Able to discriminate between closely related molecular structures
What is trained immunity?
Innate immune memory
Cells respond differently the second time because of epigenetic and metabolic reprogramming
It lasts for weeks of months because the training occurs in haemopoietic stem cells of bone marrow
What are some physical innate barriers to infection?
Skin
Respiratory tract
GI tract
What are some soluble innate barriers to infection?
Complement
Defensins
Collectins
What are some induced innate barriers to infection?
- Innate immune cells
- Pattern recognition receptors (PPR’s)
- Interferons
What is the function of lysozymes?
They disrupt bacterial cell walls by acting on peptidoglycans
Found in blood and tears
What is the function of antimicrobial peptides?
They kill pathogens by disrupting microbial membranes
Found pretty much everywhere
Which molecules bind to pathogens and target them for phagocytosis and to activate compliment?
Collectins, ficolins, and pentraxins
They act as opsonins by activating the complement pathway.
Where are lysozymes secreted?
By phagocytes and Paneth cells from the small intestine
Describe the process by which lysozymes disrupt the cell wall
They cleave the bonds between alternating sugars that make up peptidoglycan. Then phospholipase A2 comes and disrupts the phospholipids underneath
Which type of bacteria have exposed peptidoglycan layers?
Gram-positive bacteria
What are histatins?
A type of antimicrobial peptide
They are produced by the oral cavity and are active against pathogenic fungi like candida albicans
What are Cathelicidins?
A type of antimicrobial peptide
Humans only have LL-37 which has broad spectrum activity against both gram-negative and gram-positive bacteria
What are defencins?
They are amphipathic peptides that insert themselves into the cell membrane and create a pore
They have two classes: alpha and beta
What are the 3 main types of antimicrobial peptides?
Histatins, Cathelicidins, and Defensins
What are some characteristics of antimicrobial peptides?
- They are secreted by neutrophils, epithelial cells, and Paneth cells in the crypts of the intestine
- Kill bacteria in minutes
- Attack fungi and viruses and kill them by inhibiting DNA and RNA synthesis
What does amphipathic mean?
Hydrophilic on one side and hydrophobic on the other
How do collectins work?
They have globular lectin-like heads that bind to bacterial cell surface sugars
Sialic acid hides mannose antigens on host cells
How do Ficolins work?
They have a fibrinogen-like domain that recognises acylated compounds (COCH3) such as bacterial cell wall monosaccharides
How do Pentraxins work?
They are multimeric proteins in the plasma that bind to Fc gamma receptors to opsonise the pathogen
Eg. C-reactive protein (CRP). It binds to phosphocholine on bacterial surfaces. It’s used as a marker for inflammation
What are the 3 pathways to complement?
Classical, lectin, and alternative pathway
Describe the classical pathway of complement
Antigen-antibody complexes form of the pathogen surface. Molecules like C1q, C1r, C1s, C4, and C2 are created
C2 and C4 come together to cleave C3 causing amplification
