Tick hemocytes have pleiotropic roles in microbial infection and arthropod fitness

Abstract

Uncovering the complexity of systems in non-model organisms is critical for understanding arthropod immunology. Prior efforts have mostly focused on Dipteran insects, which only account for a subset of existing arthropod species in nature. Here, we describe immune cells or hemocytes from the clinically relevant tickIxodes scapularisusing bulk and single cell RNA sequencing combined with depletion via clodronate liposomes, RNA interference, Clustered Regularly Interspaced Short Palindromic Repeats activation (CRISPRa) and RNA-fluorescencein situhybridization (FISH). We observe molecular alterations in hemocytes upon tick infestation of mammals and infection with either the Lyme disease spirocheteBorrelia burgdorferior the rickettsial agentAnaplasma phagocytophilum. We predict distinct hemocyte lineages and reveal clusters exhibiting defined signatures for immunity, metabolism, and proliferation during hematophagy. Furthermore, we perform a mechanistic characterization of twoI. scapularishemocyte markers:hemocytinandastakine. Depletion of phagocytic hemocytes affectshemocytinandastakinelevels, which impacts blood feeding and molting behavior of ticks. Hemocytin specifically affects the c-Jun N-terminal kinase (JNK) signaling pathway, whereas astakine alters hemocyte proliferation inI. scapularis. Altogether, we uncover the heterogeneity and pleiotropic roles of hemocytes in ticks and provide a valuable resource for comparative biology in arthropods.

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

“…Hemocytin is differentially expressed in R. parkeri- infected A. maculatum hemocytes ( 9 ). A recent study also showed an increased Anaplasma phagocytophilum load in hemocytin-silenced tick ( 23 ), further supporting our observation. These results support that hemocytin is an essential component of the tick cellular immune response and is required for regulating intracellular pathogen infection within the tick vector.…”

“…Nevertheless, these techniques often fail to capture the full spectrum of cellular diversity and functional heterogeneity at the single-cell level, limiting our understanding of the intricate cellular immune responses accompany blood feeding or infection. Single-cell RNA sequencing (scRNA-seq) has redefined our understanding of hemocyte populations in invertebrate models such as Drosophila ( 15 – 17 ), mosquito ( 18 – 20 ), silkworm and moth ( 21 , 22 ), ticks ( 23 ) and aquatic invertebrates ( 24 – 26 ). Applying scRNA-seq in these organisms has led to identifying additional hemocyte complexity and cell types when compared to previous classifications ( 19 , 20 ).…”

Tick Innate Immune Responses to Hematophagy andEhrlichiaInfection at Single-Cell Resolution

“…Transcriptional studies of tick hemocytes (Kotsyfakis et al, 2015; Adegoke et al, 2023) have revealed important information regarding the molecular regulation of tick hemocytes during physiological processes such as blood feeding or microbial infection. Nevertheless, these techniques often fail to capture the full spectrum of cellular diversity and functional heterogeneity at the single-cell level, limiting our understanding of the intricate cellular immune responses accompany blood feeding or infection.. Single-cell RNA sequencing (scRNA-seq) has redefined our understanding of hemocyte populations in invertebrate models such as Drosophila (Cattenoz et al, 2020; Cho et al, 2020; Tattikota et al, 2020), mosquito (Severo et al, 2018; Raddi et al, 2020; Kwon et al, 2021), silkworm and moth (Feng et al, 2021; Feng et al, 2022), ticks (Rolandelli et al, 2023) and aquatic invertebrates (Koiwai et al, 2021; Pichon et al, 2022; Cui et al, 2022). Applying scRNA-seq in these organisms has led to identifying additional hemocyte complexity and cell types when compared to previous classifications (Raddi et al, 2020; Kwon et al, 2021).…”