Pathogen-associated molecules can have both membrane-associated and intracellular receptors. Bacterial lipoproteins are recognized by Toll-like receptor 2, but it is unclear whether they can also be sensed by cytoplasmic receptors. Here we found that bacterial lipoproteins could be recognized in the cytoplasm of macrophages by cystathionine γ-lyase (CTH) and hydrolyzed into lipid chains containing sulfhydryl groups. The hydrolyzed lipid chains form molecules containing four acylated chains linked through disulfide bonds, which further cleave caspase-11 and activate the noncanonical inflammasome. Changing the redox environment in macrophages affects their recognition of bacterial lipoproteins. CTH-deficient primary and immortalized macrophages do not trigger activation of the noncanonical inflammasome in the presence of intracellular bacterial lipoproteins, while CTH-deficient mice exhibit attenuated immune responses to infection with Staphylococcus aureus and Listeria monocytogenes. Our findings elucidate the molecular mechanisms by which macrophages recognize intracellular bacterial lipoproteins, as well as the regulatory relationship between cellular redox levels and infection resistance.
Liu et al. (Thu,) studied this question.