AUTHOR=Adegoke Abdulsalam , Ribeiro Jose M. C. , Smith Ryan C. , Karim Shahid 

TITLE=Tick innate immune responses to hematophagy and Ehrlichia infection at single-cell resolution

JOURNAL=Frontiers in Immunology

VOLUME=14

YEAR=2024

URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2023.1305976

DOI=10.3389/fimmu.2023.1305976

ISSN=1664-3224

ABSTRACT=<sec><title>Introduction</title><p>Ticks rely on robust cellular and humoral responses to control microbial infection. However, several aspects of the tick's innate immune system remain uncharacterized, most notably that of the immune cells (called hemocytes), which are known to play a significant role in cellular and humoral responses. Despite the importance of hemocytes in regulating microbial infection, our understanding of their basic biology and molecular mechanisms remains limited. Therefore, we believe that a more detailed understanding of the role of hemocytes in the interactions between ticks and tick-borne microbes is crucial to illuminating their function in vector competence and to help identify novel targets for developing new strategies to block tick-borne pathogen transmission.</p></sec><sec><title>Methods</title><p>This study examined hemocytes from the lone star tick (<italic>Amblyomma americanum</italic>) at the transcriptomic level using the 10X genomics single-cell RNA sequencing platform to analyze hemocyte populations from unfed, partially blood-fed, and <italic>Ehrlichia chaffeensis</italic>-infected ticks. The functional role of differentially expressed hemocyte markers in hemocyte proliferation and <italic>Ehrlichia</italic> dissemination was determined using an RNA interference approach.</p></sec><sec><title>Results and discussion</title><p>Our data exhibit the identification of fourteen distinct hemocyte populations. Our results uncover seven distinct lineages present in uninfected and <italic>Ehrlichia</italic>-infected hemocyte clusters. The functional characterization of <italic>hemocytin</italic>, <italic>cystatin</italic>, <italic>fibronectin</italic>, and <italic>lipocalin</italic> demonstrate their role in hemocyte population changes, proliferation, and <italic>Ehrlichia</italic> dissemination.</p></sec><sec><title>Conclusion</title><p>Our results uncover the tick immune responses to <italic>Ehrlichia</italic> infection and hematophagy at a single-cell resolution. This work opens a new field of tick innate immunobiology to understand the role of hemocytes, particularly in response to prolonged blood-feeding (hematophagy), and tick-microbial interactions. </p></sec>