Bacteria avoid protective immunity Flashcards
Examples of ways in which bacteria avoid protective immunity
modulators on pathogen surface. Inhibit phagocytosis. Interfere with TLR signalling pathway, altering interferon and cytokine production.
Gram negative vs Gram positive
Both: capsule, cytoplasmic membrane.
Gram +ve: no LPS, thick peptidoglycan.
Gram -ve: LPS, thin peptidoglycan
Antibodies in protection
Protect by recognising epitopes of surface proteins and polysaccharides
CD4 and CD8 in protection
Protect by recognising protein epitopes presented by MHCI or MHCII
Antigenic Diversity
modulation of surface structure to avoid immune recognition
consequences of antigenic diversity
serious infection and death.
chronic, persistent or latent disease.
ability of the same bacterial species to infect a host time and time agai.
difficulties in devising vaccines.
How many serotypes of S. pneumoniae capsule
over 90
How are antibodies protective against the Streptococcus pneumoniae?
Recognise key polysaccharides within the capsule. Protective as they agglutinate, opsonise and fix complement.
Serotype 9A of S. pneumoniae
Glucose - Glucuonic acid - Galactose - N-acetyle manosamine - Glucose
Serotype 9L of S. pneumoniae
Glucose - Glucose - Galactose - Mannose - Glucose
Serotype 14 of S. pneumoniae
Galactose - Glucose - Galactose - Glucose
Salmonella enterica
different strains have different O-antigens (64 described)
Antigenic diversity at strain level
During course of infection, a particular bacterium strain changes its antigenic makeup - it’s a race against the immune system
phase variation
genes can be re-arranged or switched on/off. reversible process. enable bacteria to change the way they express protective antigens
phase variation in Neisseria gonorrhoeae
- N. gonorrhoeae attach to epithelial cell surface (with help from surface proteins, OPA proteins and type IV pili).
- Invade cells and deeper tissues.
- Undergo another cycle of infection using attachment proteins.
Type IV Pili
Encoded by pilin genes. Allow bacteria to adhere to genital tract. Attach to host cell surface as at the tip of each pilus is a particular protein that docks to the receptor on the host surface
pilin genes
mosaic of conserved sequences and variable minicasettes (mc1 - mc6).
Up to 20 pil genes.
One is expressed at any given time (pilE)
have many others within the chromosome that have a different composition of variable regions –> change these to create new versions
non-expressed are called pilS
Opa proteins
Foudn in Neisseria meniingitidis and gonorrhoeae
Opacity associated proteins.
bacteria contain multiple (up to 12) opa genes –> switched on or off
Opa proteins in a plate
Bacteria producing Opa proteins are opaque.
Bacteria which do not produce Opa proteins are transparent.
Slipped Strand Mispairing
Bacteria can switch Opa proteins on or off.
Loops out part of the encoding gene so it translates either in or out of frame. Repeated sequences in the gene - replicated then gene switched off.
