Spread of Pathogens- Host Flashcards
(24 cards)
Where does Salmonella primarily infect?
Gastrointestinal tract (in particular the small intenstine)
What cells does Salmonella invade?
Non-phagocytic epithelial cells
How does Salmonella enter host cells?
Via Type 3 Secretion System (T3SS)
How does a T3SS work?
Acts as a molecular syringe, injecting effectors that modulate host cytoskeleton and signaling, promoting Salmonella uptake.
Enables transcytosis across interstinal barrier
After reaching the epithelium, where does Salmonella go?
It access Peyer’s patches (in the small intestine) and spreads via lymphatic system
What is the key to Salmonella survival?
It can invade and replicate inside macrophages, shielding it from humoral immunity?
What is the role of Salmonella Pathogenicity Island 1 and 2 (SPI-1/2)?
SPI-1 = Facilitates invasion into epithelial cells
SPI-2 = Facilitates survival and replication inside macrophages
How does SPI-2 work?
Inhibits phago-lysosomal fusion and allows Salmonella to avoid degradation
What can Salmonella that reaches the lymphatic vessels cause?
Bacteremia, with dissemination to the liver, spleen, kidneys.
Can result in typhoid fever
What is the chronic infection site for Salmonella?
The gallblader- this can lead to asymptomatic carriage and faecal shedding
What facilitates epithelial invasion in the gallbladder?
SPI-1 again
What must Salmonella resist in the gallbladder to survive?
Bile, which is a potent antimicrobial
How does Salmonella resist bile?
Through upregulation of efflux pumps and cell membrane alterations
What cells does HIV target?
Primarily CD4+ T cells, but also macrophages and dendritic cells
How does HIV enter cells?
Uses its envelope glycoproteins gp120 and gp41
What is the role of gp120 in HIV entry?
gp120 binds CD4 and coreceptor CCR5/CXCR4
What is the role of gp41?
Facilitates membrane fusion, delivering viral contents into the host cell
How does HIV spread in the body?
Via infected immune cells traveling through the lymphatic system & bloodstream.
It can also spread cell to cell using virological synapses
Compare antigenic variation in Salmonella and HIV
Salmonella = limited antigenic variation
HIV = high; rapid mutation of gp120
Compare shielding from immune system in Salmonella and HIV
Both survive and hide intracellularly.
Glycan shield of HIV also masks epitopes on target glycoproteins (like gp120)
Compare disruption of immune recognition in Salmonella and HIV
Salmonella = subverts phagosome maturation in phagocytes
HIV = downregulates MHC-1; prevents CD8+ T cell killing
Compare persistence in Salmonella and HIV
Salmonella= chronic carriage in gallbladder
HIV= latency in resting CD4+ T cells
What is the clinical significance of each type of persistence in Salmonella and HIV?
Salmonella = chronic (often asymptomatic carriage) can serve as reservoir for outbreaks
HIV = latent resevoir makes it impossible to irradicate HIV from host
What is the systemic spread in HIV?
Infection of immune cells in blood, lymph nodes, brain.
Leads to systemic immunodeficiency (AIDS)
