Immunomodulatory and morphophysiological effects of Rhipicephalus sanguineus s. l. (Acari: Ixodidae) salivary gland extracts

Depicting "arms race" of Rhipicephalus microplus and its host on a single frame platform

To improve our knowledge on host-parasite interaction, the study was undertaken on Rhipicephalus microplus infestation in cross breed cattle. This tick, being a voracious blood sucker, remains attached to the skin for prolonged period and inoculates saliva during blood feeding. Biomolecules present in the saliva have detrimental effects on host system. The present study deals with the effects of R. microplus in artificially infected nine months old cattle for a period of 21 days. There was physiological alteration during tick infestation in terms of body temperature, pulse, and respiration rate. There was drop in haemoglobin gram percentage, platelet count, total red and white blood cell count. Thrombocytopenia in infested animals was suggestive of iron deficient anaemia after artificial infestation. R. microplus infestation was found to induce stress in experimental animals. Our study on peripheral blood gene expression was suggestive of Th2 polarization since there was increased IL-4 response. Increased IL-6 response indicated skin damage due to R. microplus infestation and we further correlate eosinophilia with up-regulation of IL-6 and IL-8 responses. Increased IL-10 response and decreased IFN-γ response were suggestive of immunosuppressive and anti-inflammatory properties of tick saliva.

Rhipicephalus sanguineus salivary gland extract as a source of immunomodulatory molecules

Rhipicephalus sanguineus sensu lato (s.l.), popularly known as 'brown dog tick', is the primary vector of pathogens affecting dogs worldwide. To enter the host's organism, these pathogens utilise the anticoagulant, antiplatelet, anti-inflammatory and immunomodulatory actions of compounds present in the tick's saliva; such compounds are released by the ectoparasite in order to attach and feed on dogs. Nitric oxide (NO) is one of the regulatory factors in inflammation, apoptosis and immunomodulation. Here, we evaluated the in vitro activity of salivary gland extract of female dog ticks on the macrophage-derived J774 cell line, with and without lipopolysaccharide (LPS) stimulation. Cultures were evaluated for possible morphological alterations caused by exposure to the extract. There was no apparent in vitro cytotoxicity of the extract. Also, the NO secretory response in the non-LPS-stimulated cells was not inhibited. On the other hand, the extract presented modulatory action in the cultures of LPS-stimulated cells at a concentration of 0.1 μg/mL, possibly through macrophage activation, and induced a significant decrease in NO secretion. These results confirm the modulatory potential of bioactive molecules in the salivary glands of R. sanguineus ticks.

Tick and Host Derived Compounds Detected in the Cement Complex Substance

Ticks are obligate hematophagous arthropods and vectors of pathogens affecting human and animal health worldwide. Cement is a complex protein polymerization substance secreted by ticks with antimicrobial properties and a possible role in host attachment, sealing the feeding lesion, facilitating feeding and pathogen transmission, and protection from host immune and inflammatory responses. The biochemical properties of tick cement during feeding have not been fully characterized. In this study, we characterized the proteome of Rhipicephalus microplus salivary glands (sialome) and cement (cementome) together with their physicochemical properties at different adult female parasitic stages. The results showed the combination of tick and host derived proteins and other biomolecules such as α-Gal in cement composition, which varied during the feeding process. We propose that these compounds may synergize in cement formation, solidification and maintenance to facilitate attachment, feeding, interference with host immune response and detachment. These results advanced our knowledge of the complex tick cement composition and suggested that tick and host derived compounds modulate cement properties throughout tick feeding.

Amblyomma americanum ticks utilizes countervailing pro and anti-inflammatory proteins to evade host defense

Feeding and transmission of tick-borne disease (TBD) agents by ticks are facilitated by tick saliva proteins (TSP). Thus, defining functional roles of TSPs in tick evasion is expected to reveal potential targets in tick-antigen based vaccines to prevent TBD infections. This study describes two types of Amblyomma americanum TSPs: those that are similar to LPS activate macrophage (MΦ) to express pro-inflammation (PI) markers and another set that suppresses PI marker expression by activated MΦ. We show that similar to LPS, three recombinant (r) A. americanum insulin-like growth factor binding-related proteins (rAamIGFBP-rP1, rAamIGFBP-rP6S, and rAamIGFBP-rP6L), hereafter designated as PI-rTSPs, stimulated both PBMC -derived MΦ and mice RAW 267.4 MΦ to express PI co-stimulatory markers, CD40, CD80, and CD86 and cytokines, TNFα, IL-1, and IL-6. In contrast, two A. americanum tick saliva serine protease inhibitors (serpins), AAS27 and AAS41, hereafter designated as anti-inflammatory (AI) rTSPs, on their own did not affect MΦ function or suppress expression of PI markers, but enhanced expression of AI cytokines (IL-10 and TGFβ) in MΦ that were pre-activated by LPS or PI-rTSPs. Mice paw edema test demonstrated that in vitro validated PI- and AI-rTSPs are functional in vivo since injection of HEK293-expressed PI-rTSPs (individually or as a cocktail) induced edema comparable to carrageenan-induced edema and was characterized by upregulation of CD40, CD80, CD86, TNF-α, IL-1, IL-6, and chemokines: CXCL1, CCL2, CCL3, CCL5, and CCL11, whereas the AI-rTSPs (individually and cocktail) were suppressive. We propose that the tick may utilize countervailing PI and AI TSPs to regulate evasion of host immune defenses whereby TSPs such as rAamIGFBP-rPs activate host immune cells and proteins such as AAS27 and AAS41 suppress the activated immune cells.

Several studies have documented immuno-suppressive activities in whole tick saliva and salivary gland protein extracts. We have made contribution toward understanding the molecular basis of tick feeding, as we have described functions of defined tick saliva immuno-modulatory proteins. We have shown that A. americanum injects two groups of functionally opposed tick saliva proteins: those that could counter-intuitively be characterized as pro-host defense, and those that are expected to have anti-host immune defense functions. Based on our data, we propose that the tick evades host defense using countervailing pro- and anti- inflammatory proteins in which the pro-host defense tick saliva proteins stimulate host immune cells such as macrophages, and the anti-host defense tick saliva proteins suppress functions of the activated immune cells.

The alpha-Gal syndrome: new insights into the tick-host conflict and cooperation

This primer focuses on a recently diagnosed tick-borne allergic disease known as the alpha-Gal syndrome (AGS). Tick bites induce in humans high levels of IgE antibodies against the carbohydrate Galα1-3Galβ1-(3)4GlcNAc-R (α-Gal) present on tick salivary glycoproteins and tissues of non-catarrhine mammals, leading to the AGS in some individuals. This immune response evolved as a conflict and cooperation between ticks and human hosts including their gut microbiota. The conflict is characterized by the AGS that mediate delayed anaphylaxis to red meat consumption and certain drugs such as cetuximab, and immediate anaphylaxis to tick bites. The cooperation is supported by the capacity of anti-α-Gal IgM and IgG antibody response to protect against pathogens with α-Gal on their surface. Despite the growing diagnosis of AGS in all world continents, many questions remain to be elucidated on the tick proteins and immune mechanisms triggering this syndrome, and the protective response against pathogen infection elicited by anti-α-Gal antibodies. The answer to these questions will provide information for the evaluation of risks, diagnosis and prevention of the AGS, and the possibility of using the carbohydrate α-Gal to develop vaccines for the control of major infectious diseases.