ROLE OF TICK SALIVA IN LYME DISEASE AND VACCINE STRATEGY

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DESCRIPTION (Provided by Applicant): Interactions at the vector-host interface are likely to be the most critical to transmission of many arthropod transmitted infections. Our studies have demonstrated that through the action of their saliva, black-legged ticks (Ixodes scapularis) manipulate the host immune response in a manner that both assures blood feeding success, and favors survival and transmission of Lyme disease spirochetes (Borrelia burgdorferi). We have learned that these bacteria receive cues from tick saliva to regulate their protein expression, perhaps leading to enhanced invasiveness or survival in the host. We have been successful in discovering several novel molecules, including I. scapularis' salivary anti-complement protein (Isac) and a Factor Xa-inhibiting anticoagulant (Ixolaris), and recombinant proteins are in production. Taken together, this progress now allows us to begin testing our hypothesis, that an effective prevention strategy for Lyme disease, and other I. scapularis-transmitted infections, can best be developed by manipulating host immune responses to components of vector saliva or saliva-induced microbial products. In continuing this project, we will test whether a protocol integrating vector salivary gland genomics and proteomics can accelerate both discovery and recovery of potentially important immunogenic molecules. Massive cDNA sequencing of an I. scapularis salivary gland cDNA library containing full-length clones has already revealed nearly 1,200 sequences and at least 476 genes. We will begin expressing these sequences in recombinant baculovirus expression systems or cloning them into bacterial plasmids to generate candidate protein and DNA vaccines. In addition, recent technological advances in B. burgdorferi genomics are allowing rapid progress to be made on studies examining B. burgdorferi gene and protein expression in the presence and absence of tick saliva, or under other starvation-stress conditions. We will test whether whole genome analysis by DNA arrays and 2-D gel electrophoresis can facilitate discovery of potential immunogens. Candidate vaccines will be screened for their ability to interrupt tick feeding or block pathogen transmission in a white-footed mouse (Peromyscus leucopus) model. We expect that these studies will lead us to develop vaccination strategies that combine tick and bacterial elements for preventing Lyme disease, and possibly a broader range of tick-transmitted infections.