Autophagy is a key regulator of cellular homeostasis that can be activated by pathogen-associated molecules and has recently been shown to influence IL-1b secretion by macrophages. However, the mechanisms behind this are unclear. Here, we describe a novel role for autophagy in regulating the production of IL-1b in antigen-presenting cells. After treatment of macrophages with Toll-like receptor (TLR) ligands, pro-IL-1b was specifically sequestered into autophagosomes, while further activation of autophagy with rapamycin induced the degradation of pro-IL-1b and blocked secretion of the mature cytokine. Inhibition of autophagy promoted the processing and secretion of IL-1b by antigen-presenting cells in a NLRP3- and TRIF-dependent manner. This effect was reduced by inhibition of reactive oxygen species (ROS), but was independent of NOX2. Induction of autophagy in mice in vivo with rapamycin reduced serum levels of IL-1b in response to challenge with LPS. These data demonstrate that autophagy controls the production of IL-1b through at least two separate mechanisms; by targeting pro-IL-1 for lysosomal degradation and by regulating activation of the NLRP3 inflammasome.

At mammalian body temperature, the plague bacillus Yersinia pestis synthesizes lipopolysaccharide (LPS)-lipid A with poor Toll-like receptor 4 (TLR4)-stimulating activity. To address the effect of weak TLR4 stimulation on virulence, we modified Y. pestis to produce a potent TLR4-stimulating LPS. Modified Y. pestis was completely avirulent after subcutaneous infection even at high challenge doses. Resistance to disease required TLR4, the adaptor protein MyD88 and coreceptor MD-2 and was considerably enhanced by CD14 and the adaptor Mal. Both innate and adaptive responses were required for sterilizing immunity against the modified strain, and convalescent mice were protected from both subcutaneous and respiratory challenge with wild-type Y. pestis. Despite the presence of other established immune evasion mechanisms, the modified Y. pestis was unable to cause systemic disease, demonstrating that the ability to evade the LPS-induced inflammatory response is critical for Y. pestis virulence. Evading TLR4 activation by lipid A alteration may contribute to the virulence of various Gram-negative bacteria.