Characterization of acid phosphatase from the tick Haemaphysalis longicornis

Tick Vaccines and Concealed versus Exposed Antigens

Anti-tick vaccines development mainly depends on the identification of suitable antigens, which ideally should have different features. These should be key molecules in tick biology, encoded by a single gene, expressed across life stages and tick tissues, capable of inducing B and T cells to promote an immunological response without allergenic, hemolytic, and toxic effects; and should not be homologous to the mammalian host. The discussion regarding this subject and the usefulness of “exposed” and “concealed” antigens was effectively explored in the publication by Nuttall et al. (2006). The present commentary intends to debate the relevance of such study in the field of tick immunological control.

Protein profiling of hemolymph in Haemaphysalis flava ticks

Background

Tick hemolymph bathes internal organs, acts as an exchange medium for nutrients and cellular metabolites, and offers protection against pathogens. Hemolymph is abundant in proteins. However, there has been limited integrated protein analysis in tick hemolymph thus far. Moreover, there are difficulties in differentiating tick-derived proteins from the host source. The aim of this study was to profile the tick/host protein components in the hemolymph of Haemaphysalis flava.

Methods

Hemolymph from adult engorged H. flava females was collected by leg amputation from the Erinaceus europaeus host. Hemolymph proteins were extracted by a filter-aided sample preparation protocol, digested by trypsin, and assayed by liquid chromatography–tandem mass spectrometry (LC–MS/MS). MS raw data were searched against the UniProt Erinaceidae database and H. flava protein database for host- and tick-derived protein identification. Protein abundance was further quantified by intensity-based absolute quantification (iBAQ).

Results

Proteins extracted from hemolymph unevenly varied in size with intense bands between 100 and 130 kDa. In total, 312 proteins were identified in the present study. Therein 40 proteins were identified to be host-derived proteins, of which 18 were high-confidence proteins. Top 10 abundant host-derived proteins included hemoglobin subunit-α and subunit-β, albumin, serotransferrin-like, ubiquitin-like, haptoglobin, α-1-antitrypsin-like protein, histone H2B, apolipoprotein A-I, and C3-β. In contrast, 169 were high-confidence tick-derived proteins. These proteins were classified into six categories based on reported functions in ticks, i.e., enzymes, enzyme inhibitors, transporters, immune-related proteins, muscle proteins, and heat shock proteins. The abundance of Vg, microplusin and α-2-macroglobulin was the highest among tick-derived proteins as indicated by iBAQ.

Conclusions

Numerous tick- and host-derived proteins were identified in hemolymph. The protein profile of H. flava hemolymph revealed a sophisticated protein system in the physiological processes of anticoagulation, digestion of blood meal, and innate immunity. More investigations are needed to characterize tick-derived proteins in hemolymph.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05287-7.

Fractionation of tick saliva reveals proteins associated with the development of acquired resistance to Ixodes scapularis

Tick-borne diseases pose a global medical problem. As transmission of tick-borne pathogens to their hosts occurs during tick feeding, development of vaccines thwarting this process could potentially prevent transmission of multiple tick-borne pathogens. The idea of tick vaccines is based on the phenomenon of acquired tick immunity, rejection of ticks feeding on hosts which were repeatedly infested by ticks. Recently, we demonstrated that saliva of the blacklegged tick Ixodes scapularis, which is the main vector of tick-borne pathogens in northeast USA, is sufficient for induction of tick immunity in the guinea pig model and that immunity directed against tick glycoproteins is important in this phenomenon. Nevertheless, immunity elicited against individual tick salivary antigens, which have been identified and tested so far, provided only modest tick rejection. We therefore now tested fractions of tick saliva produced by liquid chromatography for their ability to induce tick immunity in the guinea pig model. Immunization with all individual fractions elicited antibodies that reacted with tick saliva, however only some fractions displayed the ability to induce robust protective tick immunity. Mass spectrometry analysis led to identification of 24 proteins present only in saliva fractions which were able to induce tick immunity, suggesting suitable candidates for development of a tick vaccine.

Molecular cloning and transcriptional and functional analysis of glycogen synthase kinase-3β in Haemaphysalis longicornis (Acari, Ixodidae)

Glycogen synthase kinase 3 (GSK-3), which belongs to the serine/threonine kinase family, regulates glycogen metabolism, Wnt signaling, hormonal regulation, and embryonic development in many eukaryotes. Here, we cloned a complete open reading frame (ORF) of glycogen synthase kinase 3β (GSK-3β) from Haemaphysalis longicornis and characterized its transcriptional and functional status. The ORF of GSK-3β possesses 1242 nucleotides encoding a mature protein of 413 amino acid residues. GSK-3β nucleotide and protein sequences are highly conserved among different vertebrate and invertebrate animals, with identity between 47.8–100% and 63.2–88.7%, respectively. Sequence comparison showed one signature domain between the residues of 51 and 335 amino acids, which was identified as a protein kinase (serine/threonine). RT-PCR showed GSK-3β mRNA present in all developmental stages of H. longicornis. Interestingly, a higher transcript level was observed in nymph and 7-day-old eggs compared with others by real-time PCR, indicating a role of GSK-3β in the early stages of life. The functional status of GSK-3β was characterized by RNA interference (RNAi) and caused significant (p < 0.05) reduction in feeding and reproduction, as well as an abnormality in eggs and hatching. Taken together, our results suggest that GSK-3β may be an important candidate for a multiple antigen vaccine for controlling the tick population.

Proteomic analysis of saliva from partially and fully engorged adult female Rhipicephalus microplus (Acari: Ixodidae)

Rhipicephalus microplus salivary gland secretes a number of complex bioactive proteins during feeding. These components are important in feeding and affect anti-coagulation, anti-inflammation and also have anti-microbial effects. In this study, tick saliva was collected from partially engorged female (PEF) and fully engorged female (FEF) ticks. Liquid chromatography tandem-mass spectrometry (LC-MS/MS) and isobaric tags for relative and absolute quantification (iTRAQ) were used to identify and quantify R. microplus salivary proteins. A total of 322 unique peptides were detected and 151 proteins were characterized in both PEF and FEF. Of these, 41 proteins are considered as high-confidence proteins. Fifteen high-confidence proteins were upregulated and six high-confidence proteins were downregulated (p < 0.05; PEF:FEF ratio ≥ 1.2 or PEF:FEF ratio ≤ 0.83); 17 high-confidence proteins are slightly changed (PEF:FEF ratio > 0.83 and < 1.2). These high-confidence proteins are involved in several physiological roles, including egg development, transportation of proteins, immunity and anti-microorganism, anti-coagulant, and adhesion. In comparison with PEF, the number of upregulated proteins exceeded the number of proteins downregulated. Salivary protein may be induced by the blood-meal and these proteins contribute to successful feeding.

The mRNA expression and enzymatic activity of three enzymes during embryonic development of the hard tick Haemaphysalis longicornis

Background

Three main enzymes including cathepsin B, cathepsin D and acid phosphatase are involved in vitellin degradation, which is a major biochemical event of the embryonic development and can provide nutrients and metabolites for tick embryos. In the present study, the mRNA expression profiles and enzymatic activity of cathepsin B, cathepsin D and acid phosphatase were investigated during embryonic development in the tick Haemaphysalis longicornis.

Results

The results revealed that all three enzymes were expressed throughout embryonic development. Both cathepsin B and acid phosphatase transcripts were accumulated during the first four days. Cathepsin B reached its highest expression on day 5, whereas the peak expression of acid phosphatase and cathepsin D occurred on day 11. The highest activity of cathepsin B was observed on the first day of egg development, whereas cathepsin D reached its highest activity on day 13. Acid phosphatase activity increased gradually during the first five days and then remained stable until the end of egg development.

Conclusions

Three enzymes were expressed and activated in eggs, and also presented different dynamic changes with the development of embryos. The profiles of both mRNA expression and enzymatic activity of these enzymes indicate that they are controlled orderly and play multiple roles during embryonic development in ticks.

The Essential Role of Tick Salivary Glands and Saliva in Tick Feeding and Pathogen Transmission

As long-term pool feeders, ticks have developed myriad strategies to remain discreetly but solidly attached to their hosts for the duration of their blood meal. The critical biological material that dampens host defenses and facilitates the flow of blood-thus assuring adequate feeding-is tick saliva. Saliva exhibits cytolytic, vasodilator, anticoagulant, anti-inflammatory, and immunosuppressive activity. This essential fluid is secreted by the salivary glands, which also mediate several other biological functions, including secretion of cement and hygroscopic components, as well as the watery component of blood as regards hard ticks. When salivary glands are invaded by tick-borne pathogens, pathogens may be transmitted via saliva, which is injected alternately with blood uptake during the tick bite. Both salivary glands and saliva thus play a key role in transmission of pathogenic microorganisms to vertebrate hosts. During their long co-evolution with ticks and vertebrate hosts, microorganisms have indeed developed various strategies to exploit tick salivary molecules to ensure both acquisition by ticks and transmission, local infection and systemic dissemination within the vertebrate host.

Transmission-Blocking Vaccines: Focus on Anti-Vector Vaccines against Tick-Borne Diseases

Tick-borne diseases are a potential threat that account for significant morbidity and mortality in human population worldwide. Vaccines are not available to treat several of the tick-borne diseases. With the emergence and resurgence of several tick-borne diseases, emphasis on the development of transmission-blocking vaccines remains increasing. In this review, we provide a snap shot on some of the potential candidates for the development of anti-vector vaccines (a form of transmission-blocking vaccines) against wide range of hard and soft ticks that include Ixodes, Haemaphysalis, Dermacentor, Amblyomma, Rhipicephalus and Ornithodoros species.

Identification of the tropomyosin (HL-Tm) in Haemaphysalis longicornis

Haemaphysalis longicornis tropomyosin (HL-Tm) was amplified by RT-PCR. The cDNA contained a 825 bp open reading frame coding for 274 amino acids with a predicted theoretical isoelectric point (pI) of 4.55 and molecular weight of 31.7 kDa. Real-time RT-PCR analysis showed that the expression levels of the HL-Tm in the unfed-females were significantly higher than in other tested developmental stages (eggs, unfed-larvae and unfed-nymphs). Western blot analysis showed that rabbit anti-serum against H. longicornis unfed-adult ticks recognized the recombinant HL-Tm protein (rHL-Tm). Immunization of rabbits with the rHL-Tm resulted in a statistically significant reduction of female engorgement and oviposition. Silencing of HL-Tm by RNAi showed a decrease in tick engorgement and oviposition, which is consistent with the effect of recombinant protein vaccine on the adults. These results showed that tick HL-Tm might be involved in the regulation of ticks blood-feeding, growth and oviposition.

Bioinformatics and expression analyses of the Ixodes scapularis tick cystatin family

The cystatins are inhibitors of papain- and legumain-like cysteine proteinases, classified in MEROPS subfamilies I25A-I25C. This study shows that 84 % (42/50) of tick cystatins are putatively extracellular in subfamily I25B and the rest are putatively intracellular in subfamily I25A. On the neighbor joining phylogeny guide tree, subfamily I25A members cluster together, while subfamily I25B cystatins segregate among prostriata or metastriata ticks. Two Ixodes scapularis cystatins, AAY66864 and ISCW011771 that show 50-71 % amino acid identity to metastriata tick cystatins may be linked to pathways that are common to all ticks, while ISCW000447 100 % conserved in I. ricinus is important among prostriata ticks. Likewise metastriata tick cystatins, Dermacentor variabilis-ACF35512, Rhipicephalus microplus-ACX53850, A. americanum-AEO36092, R. sanguineus-ACX53922, D. variabilis-ACF35514, R. sanguineus-ACX54033 and A. maculatum-AEO35155 that show 73-86 % amino acid identity may be essential to metastriata tick physiology. RT-PCR expression analyses revealed that I. scapularis cystatins were constitutively expressed in the salivary glands, midguts and other tissues of unfed ticks and ticks that were fed for 24-120 h, except for ISCW017861 that are restricted to the 24 h feeding time point. On the basis of mRNA expression patterns, I. scapularis cystatins, ISCW017861, ISCW011771, ISCW002215 and ISCW0024528 that are highly expressed at 24 h are likely involved in regulating early stage tick feeding events such as tick attachment onto host skin and creation of the feeding lesion. Similarly, ISCW018602, ISCW018603 and ISCW000447 that show 2-3 fold transcript increase by 120 h of feeding are likely associated with blood meal up take, while those that maintain steady state expression levels (ISCW018600, ISCW018601 and ISCW018604) during feeding may not be associated with tick feeding regulation. We discuss our findings in the context of advancing our knowledge of tick molecular biology.

New insights from the oyster Crassostrea rhizophorae on bivalve circulating hemocytes

Hemocytes are the first line of defense of the immune system in invertebrates, but despite their important role and enormous potential for the study of gene-environment relationships, research has been impeded by a lack of consensus on their classification. Here we used flow cytometry combined with histological procedures, histochemical reactions and transmission electron microscopy to characterize the hemocytes from the oyster Crassostrea rhizophorae. Transmission electron microscopy revealed remarkable morphological characteristics, such as the presence of membranous cisternae in all mature cells, regardless of size and granulation. Some granular cells contained many cytoplasmic granules that communicated with each other through a network of channels, a feature never previously described for hemocytes. The positive reactions for esterase and acid phosphatase also indicated the presence of mature cells of all sizes and granule contents. Flow cytometry revealed a clear separation in complexity between agranular and granular populations, which could not be differentiated by size, with cells ranging from 2.5 to 25 µm. Based on this evidence we suggest that, at least in C. rhizophorae, the different subpopulations of hemocytes may in reality be different stages of one type of cell, which accumulates granules and loses complexity (with no reduction in size) as it degranulates in the event of an environmental challenge.

Purification and characterization of a novel acid phosphatase from the split gill mushroom Schizophyllum commune

A monomeric acid phosphatase (ACP) with a molecular mass of 72.5 kDa was purified from fresh fruiting bodies of cultured Schizophyllum commune mushroom. The isolation procedure entailed ion exchange chromatography on DEAE-cellulose, CM-cellulose, and Q-sepharose, and gel filtration by fast protein liquid chromatography on Superdex 75. It demonstrated a unique N-terminal amino acid sequence of NAPWAQIDEV, which exhibited 60% amino acid identity to that of S. commune hypothetical histidine ACP based on its genome sequence, but less than 30% amino acid identity to that of other fungal ACPs previously reported. The ACP exhibited an optimum temperature at 50 °C, an optimum pH at pH 4.6, and was considerably stable at a pH range of 4.0 to 9.0, and a temperature range of 20-40 °C. The Km of the purified enzyme for ρ-nitrophenyl phosphate (ρNPP) was 0.248 mM and the Vmax was 9.093 × 10(-3)  μM/min. ACP activity was strongly inhibited by Al(3+) and Fe(3+) , but enhanced by Co(2+) , Mg(2+) , and Ca(2+) at a concentration of 0.5 mM.