Immunity to Microbial Infections Flashcards
describe innate immunity
the first line of defence against pathogen
- general
- non-specific
describe adaptive immunity
immunity is built up from exposure and vaccinations
what cells are present in innate immunity?
phagocytes
complement cells
NK cells
lysoszymes
what cells are present in adaptive immunity?
b lymphocytes and antibodies
t lymphocytes
what antimicrobial factors are present within the oral cavity? (5)
lysozymes
antibodies - IgA, M and G
antimicrobial peptides
- defensins
- histatins
- LL37
what are antimicrobial peptides also known as? what are their charges?
host defence peptides
- all short cationic peptides - positive charge
where are host defence peptides produced? (3)
- salivary glands
- epithelial cells
- leukocytes
4 roles of host defence peptides.
- microbial activity
- antiviral activity
- immune cell recruitment
- immune cell activation
give 3 families belonging to host defence peptides.
cathelicidins
defensins
histatins
describe defensins. the types, the composure and structure
2 types - alpha and beta
- short peptides
- 6 paired amino acid cysteine residues
- pair up to make 3 disulfide bonds
- structure = beta sheets - protects from overcleavage
how do defensins create disulfide bonds?
the r group on amino acid = sulfur
alpha defensins
- what are they produced by
- what are they known as?
- where are they stored
produced by neutrophils
known as human neutrophil peptides
stored in primary azurophil granules
how many HNP-2 are encoded by 3 alpha defensin genes?
3 genes
code
4 HNP
how can 3 genes encode 4 HNP-2?
3 genes
- DEFA 1
- DEFA 3
- DEFA 4
HNP-1 = DEFA1+3
HNP-2 = DEFA-4
HNP3 = combine DEFA1 or 3
HNP-1 and HNP-3 - if the N terminal is cleaved
= the same amino acid sequence as HNP-2
how long are HNP’s?
29-35 AA
what are HNP’s?
human neutrophil peptide
- alpha defensins
- host defence peptide
which HNPS’s are present in high abundance in the oral cavity?
HNP-1
HNP-2
HNP-3
do alpha defensins have links to periodontitis?
yes, there are increased levels in saliva and GCF when periodontitis are severe
- more neutrophil recruitment during perio
do alpha defensins have a link to edentulous patients?
- there are reduced alpha defensins
- no contact of plaque, not as much recruitment of neutrophils
what is neutropenia?
decreased levels of neutrophils
give an example of a disease caused by neutropenia and its links to alpha defensins.
Morbus Kostmann
- children born without neutrophils
- decreased levels of alpha defensins
what 4 bacteria are alpha defensins active against?
evidence was found in vitro
streptococcus mutans
p gingivalis
a actinomyocytes
candida albicans
alpha defensins regulate the immune system in three ways, explain how
- HNP-1,2,3 = chemotactic for monocytes
- draw up chemical gradient towards infection
- increase gingival IL-8 production
- increase cytokine expression
- inhibit IL-10
- increase mast cell degranulation
- histamine released
- vasodilation
= neutrophil recruitment - activate dendritic cells
- promote induction of adaptive immune response
two types of defensins
alpha and beta
how long are beta defensins? where are they usually produced?
36-45 amino acids
produced by epithelial cells
- gingival cells, salivary glands, tongue and mucosa
what colours do alpha and beta defensins stain?
alpha - azure blue
beta - brown - indicates hBD-1
describe the expression of beta defensins
hBD-1 - always expressed
hBD-2 - always only expressed in oral cavity, can be induced in other areas
- both expressed between layers: stratum spinosium and stratum granulosum
hBD-3 - can be induced
- expressed in stratified basal layer
hBD-4 - expressed in low levels
describe the antimicrobial activity of beta defensions - hBD1,2,3
- level of potency
- what bacteria they are active against
hBD1
- least potent
- active against: p gingivalis, a actinomycetes, f nucleatum
hBD-2
- active against:
- gram negative
- candida spp
hBD-3
- most potent
- active against:
- gram negative and positive
- p gingivalis, a actinomycetes, f nucleatum, s mutans, t denticola
how is the immune activity regulated by beta defensins?
hBD2,3 are activated by pro-inflam cytokines
- activate DC and T cells
- chemotaxis of monocytes, mast cells, T cells, dcs
6 steps of how defensins are antiviral
- target lipid envelope
- extracellular aggregation
- receptor blocking/downregulation
- inhibition of binding
- block
- cellular changes
describe the first step of defensins antiviral activity.
- targeting lipid envelope
- defensins bind to virus
- viral morphology changes
- associated with reduced infectivity
describe extracellular aggregation - 2/6 antiviral activity
- virus has negative charge
- defensins has positive charge
- defensins clump as a result
- can also polymerise themselves
why is aggregation important in anti-viral activity?
- body can recognise aggregated sites
- if multiple viruses are aggregated, morphology changes, can only infect one host cell
describe receptor blocking/downregulation - 3/6 antiviral activity
- defensin can block interaction between virus and host cell receptors during the infectious stage, don’t bind together
- host cell can become activated from the binding of defensin
- can activate immune response/reduce no of receptors being targeted
describe inhibition of fusion - 4/6 antiviral activity
defensins prevent fusion of viral nucleic acids and enzymes being delivered from the enveloped virus onto host cells
describe blocking/uncoating - 5/6 antiviral activity
defensins bind to unenveloped virus - bind to the capsid
- prevent capsid from releasing viral content
describe the cellular changes - 6/6 antiviral activity
- defensin can be detected by host cell
- host cell change behaviour
- viral replication requires host cell protein - PKC - protein kinase C
- stimulated host cells from defensins can reduce the no. of proteins
= inefficient replication
the 3 families belonging to host defence peptides.
cathelicidins
defensins
histatins
describe the structure of cathelicidins and how they differ from defensins
a-helical structure
- no beta sheets
- no disulfide bonds
what is the only member of the cathelicidin family which is expressed in humans? where is it present and produced by?
LL37
present in saliva, salivary glands and GCF
produced by leucocytes and epithelial cells
how does LL37 originate? How do you get it to LL37?
as a long peptide chain, in precursor form hCAP-18
- needs to be cleaved by proteases produced by neutrophils: Proteinase 3, Capethsin G and Neutrophil Elastase
- occurs outside of the cell
- into antimicrobial peptide
what is the precursor for LL37 called?
hCAP-18
how is LL37 stored?
in its precursor form - hCAP-18 in secondary granules
link between LL37 and periodontal disease?
LL37 levels in GCF and saliva increase
what bacteria is LL37 active against?
gram negative
- p intermedia, p gingivalis, a actinomycetes, f nucleatum
gram positive
- s gordonii, s sanguines
how does Haim-Munk and Papillon-Lefevre Syndrome disease link to LL37?
- patient will have large loss of secondary dentition
- patients develop periodontitis due to low levels of LL37
- due to loss of capethesin C gene
- lack of cleaved hCAP-18 into LL37
how does LL37 regulate the immune response? (4)
- reduces Candida albicans binding to epithelia
- by autoaggregation - promotes wound healing
- by inhibiting inflam responses
- neutralised gram negative - stimulates pro inflam responses
- stimulate to produce IL8
- enhance cytokines to produce wbc - chemoattractant
- move neutrophils, T cells, mast cells, monocytes up concentration gradient
3 models for how antimicrobial peptides damage bacterial cell membranes?
barrel-stave model
toroidal model - most accepted model
carpet model
describe the toroidal model
- a pore and channel made through bacterial membrane
- lined with lipid heads and antimicrobial peptide
