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Introduction: 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. Methods: This study examined hemocytes from the lone star tick (Amblyomma americanum) at the transcriptomic level using the 10X genomics single-cell RNA sequencing platform to analyze hemocyte populations from unfed, partially blood-fed, and Ehrlichia chaffeensis -infected ticks. The functional role of differentially expressed hemocyte markers in hemocyte proliferation and Ehrlichia dissemination was determined using an RNA interference approach. Results and discussion: Our data exhibit the identification of fourteen distinct hemocyte populations. Our results uncover seven distinct lineages present in uninfected and Ehrlichia -infected hemocyte clusters. The functional characterization of hemocytin , cystatin , fibronectin , and lipocalin demonstrate their role in hemocyte population changes, proliferation, and Ehrlichia dissemination. Conclusion: Our results uncover the tick immune responses to Ehrlichia 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. [ABSTRACT FROM AUTHOR]

In tsetse flies, nutrients for intrauterine larval development are synthesized by the modified accessory gland (milk gland) and provided in mother's milk during lactation. Interference with at least two milk proteins has been shown to extend larval development and reduce fecundity. The goal of this study was to perform a comprehensive characterization of tsetse milk proteins using lactation-specific transcriptome/milk proteome analyses and to define functional role(s) for the milk proteins during lactation. Differential analysis of RNA-seq data from lactating and dry (non-lactating) females revealed enrichment of transcripts coding for protein synthesis machinery, lipid metabolism and secretory proteins during lactation. Among the genes induced during lactation were those encoding the previously identified milk proteins (milk gland proteins 1-3, transferrin and acid sphingomyelinase 1) and seven new genes (mgp4-10). The genes encoding mgp2-10 are organized on a 40 kb syntenic block in the tsetse genome, have similar exon-intron arrangements, and share regions of amino acid sequence similarity. Expression of mgp2-10 is female-specific and high during milk secretion. While knockdown of a single mgp failed to reduce fecundity, simultaneous knockdown of multiple variants reduced milk protein levels and lowered fecundity. The genomic localization, gene structure similarities, and functional redundancy of MGP2-10 suggest that they constitute a novel highly divergent protein family. Our data indicates that MGP2-10 function both as the primary amino acid resource for the developing larva and in the maintenance of milk homeostasis, similar to the function of the mammalian casein family of milk proteins. This study underscores the dynamic nature of the lactation cycle and identifies a novel family of lactation-specific proteins, unique to Glossina sp., that are essential to larval development. The specificity of MGP2-10 to tsetse and their critical role during lactation suggests that these proteins may be an excellent target for tsetse-specific population control approaches.

Leishmaniases are caused by [approximately equal to] 20 Leishmania species transmitted to humans through sand-fly bites and have been classified into 3 main forms: cutaneous leishmaniasis, mucocutaneous or mucosal leishmaniasis, [...]

This correction notice from the journal "Frontiers in Immunology" addresses an error in the Data availability statement of the article "Tick innate immune responses to hematophagy and Ehrlichia infection at single-cell resolution." The correct accession number for the raw datasets is PRJNA1017904, not PRJNA226980 as previously stated. The authors have acknowledged and rectified this mistake, emphasizing that it does not impact the scientific conclusions of the study. The article has been updated accordingly, and the publisher notes that the views expressed are solely those of the authors. [Extracted from the article]

The Gulf Coast tick, Amblyomma maculatum, is a vector of several tick-borne pathogens, including Rickettsia parkeri. The ability of R. parkeri to persist within the tick population through transovarial and transstadial transmission, without apparently harming the ticks, contributes to the pathogen's perpetuation in the tick population. Previous studies have shown that the R. parkeri load in A. maculatum is regulated by the tick tissues' oxidant/antioxidant balance and the non-pathogenic tick microbiome. To obtain further insights into the interaction between tick and pathogen, we performed a bulk RNA-Seq for differential transcriptomic analysis of ovaries and salivary glands from R. parkeri-infected and uninfected ticks over the feeding course on a host. The most differentially expressed functional category was of bacterial origin, exhibiting a massive overexpression of bacterial transcripts in response to the R. parkeri infection. Candidatus Midichloria mitochondrii and bacteria from the genus Rickettsia were mainly responsible for the overexpression of bacterial transcripts. Host genes were also modulated in R. parkeri-infected tick organs. A similar number of host transcripts from all analyzed functional categories was negatively and positively modulated, revealing a global alteration of the A. maculatum transcriptome in response to pathogen infection. R. parkeri infection led to an increase in salivary transcripts involved in blood feeding success as well as a decrease in ovarian immune transcripts. We hypothesize that these transcriptional alterations facilitate pathogen persistence and transmission within tick population. [ABSTRACT FROM AUTHOR]

Most studies of gene expression in Plasmodium have been concerned with asexual and/or sexual erythrocytic stages. Identification and cloning of genes expressed in the preerythrocytic stages lag far behind. We have constructed a high quality cDNA library of the Plasmodium sporozoite stage by using the rodent malaria parasite P. yoelii, an important model for malaria vaccine development. The technical obstacles associated with limited amounts of RNA material were overcome by PCR-amplifying the transcriptome before cloning. Contamination with mosquito RNA was negligible. Generation of 1,972 expressed sequence tags (EST) resulted in a total of 1,547 unique sequences, allowing insight into sporozoite gene expression. The circumsporozoite protein (CS) and the sporozoite surface protein 2 (SSP2) are well represented in the data set. A BLASTX search with all tags of the nonredundant protein database gave only 161 unique significant matches (P(N) [is less than or equal to] [10.sup.-4]), whereas 1,386 of the unique sequences represented novel sporozoite-expressed genes. We identified ESTs for three proteins that may be involved in host cell invasion and documented their expression in sporozoites. These data should facilitate our understanding of the preerythrocytic Plasmodium life cycle stages and the development of preerythrocytic vaccines.

The saliva of bloodsucking arthropods contains a large array of pharmacologically active compounds that assist hematophagy. Arthropod saliva is also responsible for causing uncomfortable allergic responses in its vertebrate hosts. In this article, we investigate whether the sand fly Phlebotomus papatasi, known to produce a strong delayed-type hypersensitivity (DTH) in humans, could benefit from, and possibly adaptively induce, this response in their vertebrate hosts. In this study, we show that flies fed on humans to completion nearly twice as fast in DTH sites as compared with normal skin sites. DTH sites had significantly larger blood flow as measured by the laser Doppler method. Sand flies feeding at sites in mouse ears that had a DTH response also fed faster than at normal sites. We conclude that in the case of P. papatasi, and possibly other arthropods such as fleas and bed bugs, the strong saliva-induced DTH response may reflect an adaptation of the fly to manipulate host immunity for the insect's own advantage.

The saliva of blood-sucking arthropods contains powerful pharmacologically active substances and may be a vaccine target against some vector-borne diseases. Subtractive cloning combined with biochemical approaches was used to discover activities in the salivary glands of the hematophagous fly Lutzomyia longipalpis. Sequences of nine full-length cDNA clones were obtained, five of which are possibly associated with blood-meal acquisition, each having cDNA similarity to: (i) the bed bug Cimex lectularius apyrase, (ii) a 5'-nucleotidase/phosphodiesterase, (iii) a hyaluronidase, (iv) a protein containing a carbohydrate-recognition domain (CRD), and (v) a RGD-containing peptide with no significant matches to known proteins in the BLAST databases. Following these findings, we observed that the salivary apyrase activity of L. longipalpis is indeed similar to that of Cimex apyrase in its metal requirements. The predicted isoelectric point of the putative apyrase matches the value found for Lutzomyia salivary apyrase. A 5'-nucleotidase, as well as hyaluronidase activity, was found in the salivary glands, and the CRD-containing cDNA matches the N-terminal sequence of the HPLC-purified salivary anticlotting protein. A cDNA similar to [Alpha]-amylase was discovered and salivary enzymatic activity demonstrated for the first time in a bloodsucking arthropod. Full-length clones were also found coding for three proteins of unknown function matching, respectively, the N-terminal sequence of an abundant salivary protein, having similarity to the CAP superfamily of proteins and the Drosophila yellow protein. Finally, two partial sequences are reported that match possible housekeeping genes. Subtractive cloning will considerably enhance efforts to unravel the salivary pharmacopeia of blood-sucking arthropods.