Host cells have evolved processes by
which
they restrict the availability of intracellular permissive niches to microbes.
Microbial recognition
by PRRs,
such as NOD proteins
and TLRs,
activates
key immediate host programs
,
leading to polarized secretion of pro-inflammatory mediators (directed to either the luminal or basolateral surface).
Bacteria can either be maintained in subcellular compartments
such as microbe-containing vacuoles,
or escape into the cytoplasm,
where they can be ubiquitylated and targeted for degradation.
Both subsets can be targeted by the autophagy pathway,
which is also regulated by other host defence mechanisms
such as oxidative stress and inflammasome activation.