Immune signaling pathways inRhipicephalus microplus: A stage-specific response toTheileria equiinfection

Theileria equi is an etiological agent of equine piroplasmosis, a tick-borne disease that significantly affects equine health and the global equine industry. In Brazil, Rhipicephalus microplus is the only tick species with confirmed vector competence for T. equi. However, the immunological mechanisms underlying pathogen-vector interactions remain poorly understood. This study aimed to evaluate the differential expression of key genes involved in major immune signaling pathways in the larval and nymphal stages, as well as in the gut and salivary glands of engorged female ticks, following T. equi infection. Our results showed that in infected ticks, the Toll receptor and its associated transcription factor (Dorsal) were upregulated in the gut and salivary glands. The gene encoding the IMD pathway receptor (PGRP) was upregulated in the infected gut, whereas the transcription factor Relish was upregulated in the salivary glands, suggesting tissue-specific activation and alternative regulation of this pathway. Additionally, genes encoding the antimicrobial peptides Microplusin and Defensin were upregulated in both tissues in response to infection. In contrast, the JAK/STAT pathway was downregulated in the infected gut, which may explain the lack of significant differential expression of the Ixodidin gene in this tissue. In the larval and nymphal stages, the transcriptional response was more restricted, with significant downregulation of PGRP in larvae and JAK in nymphs. These findings expand current knowledge of the R. microplus-T. equi immunological interface and highlight potential molecular targets for the development of novel biotechnological strategies for the control and prevention of equine piroplasmosis.