PROJECT 2: Microbial Detection by Ixodes scapularis Ticks Abstract: The Ixodes scapularis immune deficiency (IMD) pathway resembles the tumor necrosis factor receptor network in mammals and elicits a humoral response against the spirochete Borrelia burgdorferi and the rickettsial agent Anaplasma phagocytophilum – two distinct bacteria that cause Lyme disease and human granulocytic anaplasmosis, respectively. The Pedra laboratory recently proposed the existence of a functionally divergent IMD signaling cascade in ticks. We showed that the tick IMD network was activated in response to the lipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol (POPG), a component of bacterial inner membranes. Signaling relay in I. scapularis occurred in the absence of transmembrane peptidoglycan recognition proteins (PGRPs), Fas-associated protein with a death domain (FADD) and IMD, the adaptor molecule for which the immunological circuit was named. Interestingly, biochemical interactions proceeded between x-linked inhibitor of apoptosis protein (XIAP), an E3 ubiquitin ligase, and the E2 conjugating enzyme Bendless. For Project #2 in this P01 application, our central hypothesis states that the I. scapularis IMD pathway functions as a molecular rheostat impacting acquisition and persistence of B. burgdorferi and A. phagocytophilum. Aim#1 of this proposal will characterize the I. scapularis IMD pathway during pathogen infection. Aim#2 of this proposal will define a molecular crosstalk between the I. scapularis IMD signaling cascade and the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway, as there is increasing evidence that B. burgdorferi and A. phagocytophilum may be recognized by multiple pattern recognition receptors. Collectively, our findings will enable the detection of novel signaling hubs in tick- pathogen interactions and develop innovative scientific paradigms in microbial pathogenesis and arthropod immunity.