Naturally Acquired Resistance to Ixodes scapularis Elicits Partial Immunity against Other Tick Vectors in a Laboratory Host

Metabolomic changes associated with acquired resistance to Ixodes scapularis

Guinea pigs repeatedly exposed to Ixodes scapularis develop acquired resistance to the ticks (ATR). The molecular mechanisms of ATR have not been fully elucidated, and partially involves immune responses to proteins in tick saliva. In this study, we examined the metabolome of sera of guinea pigs during the development of ATR. Induction of components of the tyrosine metabolic pathway, including hydroxyphenyllactic acid (HPLA), were associated with ATR. We therefore administered HPLA to mice, an animal that does not develop ATR, and exposed the animals to I. scapularis. We also administered nitisinone, a known inhibitor of tyrosine degradation, to another group of mice. The mortality of I. scapularis that fed on mice given HPLA or nitisinone was 26 % and 72 % respectively, compared with 2 % mortality among ticks that fed on control animals. These data indicate that tick bites alter the guinea pig metabolome, and that the tyrosine metabolism pathway can potentially be targeted for I. scapularis control.

Metabolomic changes associated with acquired resistance to Ixodes scapularis

Guinea pigs repeatedly exposed to Ixodes scapularis develop acquired resistance to the ticks (ATR). The molecular mechanisms of ATR have not been fully elucidated, and partially involve immune responses to proteins in tick saliva. In this study, we examined the metabolome of sera of guinea pigs during the development of ATR. Induction of components of the tyrosine metabolic pathway, including hydroxyphenyllactic acid (HPLA), were associated with ATR. We therefore administered HPLA to mice, an animal that does not develop ATR, and exposed the animals to I. scapularis . We also administered nitisinone, a known inhibitor of tyrosine degradation, to another group of mice. The mortality of I. scapularis that fed on mice given HPLA or nitisinone was 26% and 72% respectively, compared with 2% mortality among ticks that fed on control animals. These data indicate that metabolic changes that occur after tick bites contribute to ATR.

Immunization of guinea pigs with cement extract induces resistance against Ixodes scapularis ticks

As hematophagous parasites, many tick species are important vectors of medical and veterinary disease agents. Proteins found in tick saliva and midgut have been used with some success in immunizations of animal hosts against feeding ticks, and whole saliva has been used effectively in this capacity against Ixodes scapularis, the primary vector of tickborne pathogens in the United States. Tick saliva is a complex substance containing hundreds of proteins, and the identification of specific protective antigens is ongoing. We performed a series of experiments immunizing guinea pigs with extracts prepared from midgut or attachment cement collected from adult female I. scapularis followed by challenge with nymphs of the same species. Midgut extract did not induce protective immunity, while immunization with cement extract resulted in partial protection of hosts as evidenced by premature tick detachment and 34-41% reduction in tick engorgement weights. Proteomic characterization of I. scapularis cement was performed, demonstrating that the cement extract was compositionally different from tick saliva, and vitellogenin-like lipoproteins were the most abundant proteins in cement extract (>40%). Cement was also heavily enriched with lysozymes and defensins, including those originating from both the mammalian host as well as ticks. These results demonstrate that I. scapularis cement contains immunogenic components capable of stimulating host resistance against tick feeding. Because the cement is present at the tick-host interface for an extended period of time during the feeding process, these antigens present auspicious candidates for further evaluation and potential inclusion in an anti-tick vaccine.

Past, present, and future of Lyme disease vaccines: antigen engineering approaches and mechanistic insights

Introduction: Transmitted by ticks, Lyme disease is the most common vector-borne disease in the Northern hemisphere. Despite the geographical expansion of human Lyme disease cases, no effective preventive strategies are currently available. Developing an efficacious and safe vaccine is therefore urgently needed. Efforts have previously been taken to identify vaccine targets in the causative pathogen (Borrelia burgdorferi sensu lato) and arthropod vector (Ixodes spp.). However, progress was impeded due to a lack of consumer confidence caused by the myth of undesired off-target responses, low immune responses, a limited breadth of immune reactivity, as well as by the complexities of the vaccine process development.Area covered: In this review, we summarize the antigen engineering approaches that have been applied to overcome those challenges and the underlying mechanisms that can be exploited to improve both safety and efficacy of future Lyme disease vaccines.Expert opinion: Over the past two decades, several new genetically redesigned Lyme disease vaccine candidates have shown success in both preclinical and clinical settings and built a solid foundation for further development. These studies have greatly informed the protective mechanisms of reducing Lyme disease burdens and ending the endemic of this disease.

Oral vaccine formulation combining tick Subolesin with heat inactivated mycobacteria provides control of cross-species cattle tick infestations

Tick vaccines are necessary as part of a One Health approach for the control of tick infestations and tick-borne diseases. Subolesin (SUB, also known as 4D8) is a tick protective antigen that has shown efficacy in vaccine formulations for the control of ectoparasite infestations and pathogen infection/transmission. A recent proof-of-concept study reported oral vaccination combining Rhipicephalus microplus SUB with heat inactivated Mycobacterium bovis (IV) as an immunostimulant for the control of cattle tick infestations. Based on the efficacy of Rhipicephalus decoloratus SUB for the control of multiple cattle tick species in Uganda, herein we design a controlled pen trial using an oral formulation combining R. decoloratus SUB with IV for the control of R. decoloratus and Rhipicephalus appendiculatus cattle tick infestations. Vaccine efficacy (E) of SUB + IV on tick life cycle was compared with IV and SUB alone and with PBS as control. The IgG antibody titers against SUB and M. bovis P22 and the serum levels of selected protein immune biomarkers (IL-1beta, TNF-alpha, C3) were determined and analyzed as possible correlates of protection. Oral immunization with IV and SUB alone and in SUB + IV combination were effective for the control of tick infestations (E = 71-96% for R. decoloratus and 87-99% for R. appendiculatus) with highest E (higher than 95%) for SUB + IV. The results demonstrated that oral immunization with the SUB + IV formulation resulted in effective control of cattle tick infestations through the activation of multiple immune mechanisms. These results support the application of oral vaccine formulations with SUB + IV for the control of cattle infestations with Rhipicephalus species towards improving animal health.

Tick immunity using mRNA, DNA and protein-based Salp14 delivery strategies

Guinea pigs exposed to multiple infestations with Ixodes scapularis ticks develop acquired resistance to ticks, which is also known as tick immunity. The I. scapularis salivary components that contribute to tick immunity are likely multifactorial. An anticoagulant that inhibits factor Xa, named Salp14, is present in tick saliva and is associated with partial tick immunity. A tick bite naturally releases tick saliva proteins into the vertebrate host for several days, which suggests that the mode of antigen delivery may influence the genesis of tick immunity. We therefore utilized Salp14 as a model antigen to examine tick immunity using mRNA lipid nanoparticles (LNPs), plasmid DNA, or recombinant protein platforms. salp14 containing mRNA-LNPs vaccination elicited erythema at the tick bite site after tick challenge that occurred earlier, and that was more pronounced, compared with DNA or protein immunizations. Humoral and cellular responses associated with tick immunity were directed towards a 25 amino acid region of Salp14 at the carboxy terminus of the protein, as determined by antibody responses and skin-testing assays. This study demonstrates that the model of antigen delivery, also known as the vaccine platform, can influence the genesis of tick immunity in guinea pigs. mRNA-LNPs may be useful in helping to elicit erythema at the tick bite site, one of the most important early hallmarks of acquired tick resistance. mRNA-LNPs containing tick genes is a useful platform for the development of vaccines that can potentially prevent selected tick-borne diseases.

Changing the Recipe: Pathogen Directed Changes in Tick Saliva Components

Ticks are obligate hematophagous parasites and are important vectors of a wide variety of pathogens. These pathogens include spirochetes in the genus Borrelia that cause Lyme disease, rickettsial pathogens, and tick-borne encephalitis virus, among others. Due to their prolonged feeding period of up to two weeks, hard ticks must counteract vertebrate host defense reactions in order to survive and reproduce. To overcome host defense mechanisms, ticks have evolved a large number of pharmacologically active molecules that are secreted in their saliva, which inhibits or modulates host immune defenses and wound healing responses upon injection into the bite site. These bioactive molecules in tick saliva can create a privileged environment in the host’s skin that tick-borne pathogens take advantage of. In fact, evidence is accumulating that tick-transmitted pathogens manipulate tick saliva composition to enhance their own survival, transmission, and evasion of host defenses. We review what is known about specific and functionally characterized tick saliva molecules in the context of tick infection with the genus Borrelia, the intracellular pathogen Anaplasma phagocytophilum, and tick-borne encephalitis virus. Additionally, we review studies analyzing sialome-level responses to pathogen challenge.