Protein based receptor ligand interactions are universally regarded as the initiating point of immune activation. However, it is questionable if it is applicable to immune recognition of solid structures. Binding of particulate antigens by antigen presenting cells (APC) is a critical step in immune activation. Previously, we demonstrated that uric acid crystals are potent adjuvants, initiating a robust adaptive immune response. However, the mechanisms of activation are unknown. Using atomic force microscopy as a tool for real time single cell activation analysis, we have collected evidence that uric acid crystals can directly engage cellular membranes, particularly the cholesterol components, with a force substantially stronger than protein based cellular contacts. Binding of particulate substances activates Syk kinase-dependent signaling in dendritic cells (DCs). These observations suggest a mechanism whereby immune cell activation can be triggered by solid structures via membrane lipid alteration without the requirement for specific cell surface receptors, and a testable hypothesis for crystal-associated arthropathies, inflammation and adjuvanticity. In this proposal, we extend our work to study how alum interacts with the immune system and to reveal if such a lipid based mechanism is applicable in alum's adjuvanticity. We will also study the association between cell surface lipid sorting and Nalp3 inflammasome activation, a critical step in uric acid crystal mediated cell activation. We will further study a set of immune activation events unrelated to inflammasome regulation in order to establish a complete picture of alum's immune regulating capacities. The outcome of this work will impact vaccine development and our understanding of crystal related diseases.
This project deals with the basic mechanism for the immune recognition of alum. It has high relevance in the vaccine development and crystal related diseases. Its outcomes will lead to better understanding of the immune system and suggest new methods for population based immunizations.
