Mining a differential sialotranscriptome of Rhipicephalus microplus guides antigen discovery to formulate a vaccine that reduces tick infestations

Abstract

BackgroundTicks cause massive damage to livestock and vaccines are one sustainable substitute for the acaricides currently heavily used to control infestations. To guide antigen discovery for a vaccine that targets the gamut of parasitic strategies mediated by tick saliva and enables immunological memory, we exploited a transcriptome constructed from salivary glands from all stages of Rhipicephalus microplus ticks feeding on genetically tick-resistant and susceptible bovines.ResultsDifferent levels of host anti-tick immunity affected gene expression in tick salivary glands; we thus selected four proteins encoded by genes weakly expressed in ticks attempting to feed on resistant hosts or otherwise abundantly expressed in ticks fed on susceptible hosts; these sialoproteins mediate four functions of parasitism deployed by male ticks and that do not induce antibodies in naturally infected, susceptible bovines. We then evaluated in tick-susceptible heifers an alum-adjuvanted vaccine formulated with recombinant proteins. Parasite performance (i.e. weight and numbers of females finishing their parasitic cycle) and titres of antigen-specific antibodies were significantly reduced or increased, respectively, in vaccinated versus control heifers, conferring an efficacy of 73.2%; two of the antigens were strong immunogens, rich in predicted T-cell epitopes and challenge infestations boosted antibody responses against them.ConclusionMining sialotranscriptomes guided by the immunity of tick-resistant hosts selected important targets and infestations boosted immune memory against salivary antigens.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-017-2136-2) contains supplementary material, which is available to authorized users.

Gene Expression in the Salivary Gland of Rhipicephalus (Boophilus) microplus Fed on Tick-Susceptible and Tick-Resistant Hosts

“…(B.) microplus (Maruyama et al, 2017) and the sialotranscriptomes of other tick species (Karim et al, 2011;Díaz-Martín et al, 2013;Radulović et al, 2014;Tan et al, 2015;Ong et al, 2016;Antunes et al, 2018), and they may function in tick feeding by coating the chitinous feeding mouthparts or the feeding lesion (Francischetti, 2010). In 1998, an antigen purified from R.…”

“…This family comprises chymotrypsin, elastase and trypsin inhibitors (Sasaki et al, 2008), although many extracellular proteins also contain multiple TIL domains (Wang et al, 2015). TIL domain-containing protein family members have been found ubiquitously in blood-feeding insect and tick sialomes (Karim and Adamson, 2012;Maruyama et al, 2017), and in fungalpathogen interactions, members of this family are frequently associated with host adaptation or specialization (Schulze-Lefert and Panstruga, 2011).…”

“…Among the salivary gland transcripts predicted to code for secreted proteins, the following genes may be observed: innexins, transmembrane proteins (Richards et al, 2015) that form gap junction channels and hemichannels in invertebrates, including arthropods (Güiza et al, 2018); Na + /dicarboxylate, Na + /tricarboxylate and phosphate transporter, which may play a role in osmoregulation with ion transport function (Hui et al, 2014); the phosphoinositol 4-phosphate adaptor protein, a component of a molecule complex that recruits proteins to the cell membrane (Choudhury et al, 2005), a transduction pathway in tick salivary glands (McSwain et al, 1989); monocarboxylate transporters that catalyze rapid transport of many monocarboxylates (Lew-Tabor et al, 2011), cysteinerich proteins containing trypsin inhibitor-like (TIL) domain, belonging to the family that comprises chymotrypsin, elastase and trypsin inhibitors (Sasaki et al, 2008), which has been found ubiquitously in blood-feeding insect and tick sialomes (Karim and Adamson, 2012;Maruyama et al, 2017); BmSI-7, a trypsin inhibitor-like cysteine-rich domain family, which is involved in the inflammatory response and in injury caused by tick fixation on the bovines (Sasaki et al, 2008); defense proteins, such as defense protein 3 (Zhao et al, 2019), and ixodidin, a antimicrobial peptide (Fogaça et al, 2006), which are probably involved in the immune response in the tick; PIXR, a protein with a reeler domain, favoring the colonization of Borrelia burgdorferi in Ixodes scapularis gut (Narasimhan et al, 2017); and proteins involved in actin metabolism, such as the F-actin-uncapping protein LRRC16A isoform X2.…”

The Enigma of Identifying New Cattle Tick Vaccine Antigens

“…A Bmi-MP4 metalloprotease vaccination study in Brazil yielded 60% efficacy as reported in 2015 [29], with no patent published ( Table 2). A different Brazil-based study identified an unrelated metalloprotease Rm239/Sequence 82 (31% identity with Bmi-MP4, data not shown) as a component of a cocktail vaccine of four proteins achieving 73% protection in a tick challenge trial [30]. These proteins were identified through a salivary gland transcriptome study; thus in this instance the researchers were targeting secreted salivary proteins.…”

Vacina multicomponente recombinante baseada em antígenos secretados por Rhipicephalus microplus induz imunidade protetora contra carrapatos em bovinos e cães

“…Neste trabalho, nós utilizamos dados de sialotranscriptomas de carrapatos R. Para definir quais proteínas seriam utilizadas a partir de cada grupo funcional, foram considerados os seguintes fatores: (1) nível de expressão gênica, visto que proteínas mais expressas devem estar mais ativas no processo de alimentação; (2) expressão gênica para as diferentes fases do carrapato (adultos, larvas ou ninfas), a fim de selecionar ao menos um antígeno de cada fase; (3) presença de resultados preliminares de proteção e indução de resposta imunológica humoral 63,64 ; (4) antigenicidade predita in silico utilizando-se ranqueamento combinado pela ferramentas TEPITOPE e BebiPred 63 , tendo sido selecionadas as sequências com ranqueamento de antigenicidade mais alto dentro de seu grupo funcional. Por fim, nós selecionamos 18 antígenos, dentre os quais seis já foram avaliados de forma preliminar por nosso grupo como vacinas recombinantes anti-carrapatos em bovinos 63 e/ou cães 64 , e 12 serão abordados pela primeira vez ao longo deste trabalho.…”