Identification of adhesins for entry into tick cells using phage display.

is an obligate, intracellular, tick-borne bacterial pathogen that causes bovine anaplasmosis, an often severe, production-limiting disease of cattle found worldwide. Methods to control this disease are lacking, in large part due to major knowledge gaps in our understanding of the molecular underpinnings of basic host-pathogen interactions. For example, the surface proteins that serve as adhesins and, thus, likely play a role in pathogen entry into tick cells are largely unknown. To address this knowledge gap, we developed a phage display library and screened 66 . proteins for their ability to adhere to tick cells. From this screen, 17 candidate adhesins were identified, including OmpA and multiple members of the Msp1 family, including Msp1b, Mlp3, and Mlp4. We then measured the transcript of and all members of the gene family through time, and determined that , , and have increased transcript during tick cell infection, suggesting a possible role in host cell binding or entry. Finally, Msp1a, Msp1b, Mlp3, and OmpA were expressed as recombinant protein. When added to cultured tick cells prior to infection, all proteins except the C-terminus of Msp1a reduced entry by 2.2- to 4.7-fold. Except OmpA, these adhesins lack orthologs in related pathogens of humans and animals, including and the spp., thus limiting their utility in a universal tick transmission-blocking vaccine. However, this work greatly advances efforts toward developing methods to control bovine anaplasmosis and, thus, may help improve global food security.