Fig. 6. Mechanisms of innate immune recognition of bacterial secretion systems.

In order to distinguish between pathogenic and commensal bacteria, the mammalian innate immune system has developed methods to directly recognize patterns unique to bacterial pathogens, such as the use of protein secretion apparatuses. The immune system can sense several facets of bacterial protein secretion. These include the pore formation by secretion systems or secreted proteins, aberrant translocation of bacterial molecules into the cytosol, presence of effector proteins and/or their activities, as well as the components of the secretion systems themselves.