Although inflammatory responses play a key role in controlling infection, dysregulated inflammation is associated with inflammatory and immune-mediated diseases. IL-1b is a cytokine that functions in host defense as an initiator of inflammation, and the pathways of IL-1b synthesis and release by myeloid cells have been described. In the classical pathway of activation, signals through Toll-like receptors (TLRs) trigger NF-kB activation and IL-1b transcription, and pro-IL-1b is proteolytically cleaved to mature, bioactive IL-1b by caspase-1 functioning in the inflammasome. This pathway is best characterized in mouse macrophages. Interestingly, however, human cells regulate the inflammasome differently than mouse cells, and the molecular basis for the functional differences in these inflammatory pathways are relatively poorly understood. The long-term goal of my research is to define molecular mechanisms of human innate immunity during infection with the intracellular protozoan parasite Toxoplasma gondii. Although T. gondii infects an estimated one-third of humans worldwide and causes fatal disease in immune-compromised individuals, relatively little is known about human innate recognition of the parasite, since the TLRs that recognize T. gondii in mice (TLR11/TLR12) are not functional in human cells. We recently reported that infection of human peripheral blood monocytes with T. gondii results in IL-1b release via Syk-CARD9-NF-kB signaling and NLRP3 inflammasome activation. In preliminary studies using genetic knockout cells and pharmacological inhibitors, we found that caspase-8 deficiency resulted in reduced IL-1b release from T. gondii-infected human monocytes. We hypothesize that caspase-8 is involved in IL-1b release downstream of inflammasome activation during T. gondii infection of human monocytes. Caspase-8 is critical for inflammation and monocyte- mediated host defense against T. gondii in mice. However, it remains unknown how caspase-8 functions in inflammatory pathways during T. gondii infection of human monocytes. The objective of this proposal is to determine the role of caspase-8 in the regulation of IL-1b release from T. gondii-infected human monocytes. This research is significant because pathways of inflammation in human immune cells are relatively poorly defined, and understanding these processes may contribute to efforts to develop therapeutics to modulate or dampen inflammation.
In Aim 1, we will determine the role of caspase-8 in IL-1b release from infected monocytes.
In Aim 2, we will define the functional requirements of caspase-8 activity, including its processing and association with cellular partners, during T. gondii infection. This proposal seeks to decipher the molecular determinants of inflammatory signaling during T. gondii infection of human monocytes and will contribute to defining innate immune pathways activated in response to infection with a human pathogen of global health importance.
Inflammatory immune responses play an important role in controlling infections, but inflammation in the body must also be tightly regulated to prevent immune-mediated diseases. This proposal focuses on defining how inflammation is triggered and regulated during infection with Toxoplasma gondii, a parasite that infects one- third of humans worldwide and causes fatal disease in immune-compromised individuals.
