Differential Expression of Immune Genes in the Rhipicephalus microplus Gut in Response to Theileria equi Infection

Abstract

Rhipicephalus microplus is the only tick species known to serve as a biological vector of Theileria equi for horses and other equids in Brazil. The protozoan T. equi is one of the causal agents of equine piroplasmosis, a major threat in horse breeding systems. Vector competence is closely linked to the pathogens' ability to evade tick defense mechanisms. However, knowledge of tick immune response against infections by hemoparasites of the Theileria genus is scarce. In the present study, the expression of genes involved in immune signaling pathways of R. microplus adults' guts when challenged with a high or low parasitic load of T. equi was evaluated. This research demonstrates divergences in the immune gene expression pattern linked to T. equi infection in R. microplus since the Toll, IMD, and JNK signaling pathways were transcriptionally repressed in the guts of adult ticks infected with T. equi. Moreover, the results showed that different infectious doses of T. equi induce differential gene expression of key components of immune signaling cascades in R. microplus gut, suggesting a link between the intensity of infection and the activation of tick immunity response. The present study adds knowledge to elucidate the gut immune signaling response of R. microplus to T. equi infection. In addition, the generated data can serve as a basis for further investigations to develop strategies for controlling and preventing equine piroplasmosis.

Keywords: horses; immunity; parasite–vector relationship; signaling pathways; tick.

Figure 1

Illustrative representation of the four main signaling pathways that regulate tick immunity: the NF-κB/Toll pathway is indicated in blue, the IMD pathway is indicated in yellow (missing components in ticks of this pathway are shown in white), the JNK pathway is marked in green, and the JAK/STAT pathway is represented in pink. The components in red are inhibitors of the signaling pathways. The figure was created with BioRender.com following the sequence of the components of the signaling route described in Fogaça et al. [10].

Figure 2

Graphic representation of the in vivo experiments performed in this study. The figure was created with BioRender.com.

Figure 3

The results shown are means and standard deviation values of gene expression levels. Results in control and Theileria equi-infected groups were analyzed by the parametric Student’s t-test or nonparametric Mann–Whitney test. (** p < 0.005, * p < 0.05; ns: not significant. (A,C,E,G) first experiment with high parasite load; (B,D,F,H) second experiment with low parasite load).

Figure 4

The results shown are means and standard deviation values of the antimicrobial peptides (microplusin, ixodidin, and defensin) gene expression levels in Rhipicephalus microplus gut infected by Theileria equi. (A) First experiment with high parasite load; (B) second experiment with low parasite load. Results in control and T. equi-infected groups were analyzed by the parametric Student’s t-test or nonparametric Mann–Whitney test.