Interactions at the vector-host interface are likely to be most critical to transmission of 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 bloodfeeding 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 discovered 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 test our hypothesis, that an effective prevention strategy for Lyme disease, and other I. scapularis-transmitted infections, can be developed by manipulating host immune responses to components of vector saliva or saliva-induced microbial products. In continuing this project, we will identify and isolate molecules from the saliva of vector ticks and from B. burgdorferi that provide protection against Lyme disease and other infections transmitted by I. scapularis. A comprehensive protocol integrating vector salivary gland genomics and proteomics is expected to accelerate both discovery and recovery of potentially important protective molecules. Massive cDNA sequencing of an I. scapularis salivary gland cDNA library containing full-length clones has revealed nearly 1,200 sequences and at least 476 genes. We will begin cloning these into plasmids using high-throughput technology to generate candidate DNA vaccines. In addition, recent advances in B. burgdorferi genomics will allow rapid progress 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 protective molecules. 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 these studies to lead to new vaccination strategies that combine tick and bacterial elements for preventing Lyme disease, and possibly a broader range of tick-transmitted infections.
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