(1st Place) Investigating the interplay between tick hemocytes and tick-borne rickettsiae

Blood-feeding arthropods, such as ticks rely on a robust cellular and humoral immunity to control pathogen invasion and replication. Tick immune cells, commonly known as hemocytes, produce factors that can facilitate or suppress microbial infection and replication. The control of pathogen infection and replication by tick hemocytes is an important step in determining the vectoral capacity of tick vectors. Tick cellular immunity is primarily a neglected and unexplored field of science. Our published work identified five distinct populations of hemocytes, including prohemocytes, plasmatocytes, spherulocytes, oenocytoids and granulocytes. Furthermore, bulk-RNA-Seq analysis revealed two hemocyte marker genes, nimrod b2 and eater; identified to be functional markers of hemocyte phagocytosis. In the current study, we have used the 10X genomics single-cell RNA sequencing platform (scRNA-seq) to characterize tick hemocytes from unfed, partially blood-fed, and pathogen-infected ticks. Our result demonstrates an increased complexity in the hemocyte population compared to the five previously identified hemocyte types. Using the Seurat package in R, we defined 12, 14, and 18 hemocyte clusters in unfed, partially-blood fed, and pathogen-infected ticks. Current experiments are focused on the identification of marker genes and functional validation of these genes using RNA interference, phagocytosis assay, and fluorescent antibody labeling. The completion of this study will further our understanding of tick immune cell biology and provide the basis for future work on tick innate immunity and pathogen interactions.