Chanida Fongsaran ^1,2 Victoria I Verhoeve ^1,3 Krit Jirakanwisal ^1,2 Emma K Harris ^1,4 Kevin Macaluso ^1,5*

• ¹ Louisiana State University, Baton Rouge, Louisiana, United States
• ² University of Texas Medical Branch at Galveston, Galveston, Texas, United States
• ³ West Virginia University, Morgantown, West Virginia, United States
• ⁴ Colorado State University, Fort Collins, Colorado, United States
• ⁵ College of Medicine, University of South Alabama, Mobile, United States

Ixodid ticks serve as hosts and transmission vectors for several obligate intracellular bacteria, including members of the spotted fever group of Rickettsia. Although ticks generate an immune response to bacterial insults, many of the signaling molecules associated with the response and how they may contribute to vector competence for Rickettsia are undefined. In this study, we isolated a full-length dvrelish transcript from Dermacentor variabilis, which encoded a Relish-type NF-κB. The presence of a canonical Rel homology domain (RHD) consistent with NF-κB proteins suggested a role in tick immune response for DvRelish. The expression of DvRelish was confirmed in tick tissues and fluorescent microscopy of tick hemocytes indicated increased expression following infection with Rickettsia as compared to a non-tick borne bacterial pathogen. To further determine the effect of dvRelish gene knockdown on rickettsial infection we used RNA interference-mediated gene knockdown in D. variabilis and demonstrated that transcription of dvRelish was decreased after 24 hours post-injection of siRNA. We then assessed the response of D. variabilis when exposed to Rickettsia rickettsii and determined transcription of dvRelish was inversely associated with rickettsial loads at 48 hours post-exposure. Continued study is required to broaden the understanding of differential immune responses in ticks to SFG Rickettsia infection and elucidate the role the arthropod immune system plays in vector competence. Formatted: Left, Indent: First line: 0", Add space between paragraphs of the same style Deleted: A fitness phenotype has been associated with rickettsial 92 infection in D. variabilis and because the agents are transmitted 93 vertically, the tick likely has a mechanism to govern the infection 94 process.95 Deleted: IMD ( 96 Deleted: JAK-STAT ( 97 Deleted: In I. scapularis, the JAK-STAT pathway controls the 98 level of the obligate intracellular bacteria Anaplasma 99 phagocytophilum (Liu et al., 2012). Likewise,