Comparative analysis of defensin expression in Hyalomma asiaticum ticks exposed to Staphylococcus aureus and Escherichia coli.

BACKGROUND

Hyalomma asiaticum, which acts as a vector of zoonotic pathogens, relies on its innate immune system for defense.

METHODS

Unfed adult female H. asiaticum ticks were injected with Escherichia coli (Gram-negative) or Staphylococcus aureus (Gram-positive), with PBS-injected ticks as controls. After 24 h, RNA sequencing (RNA-Seq) was performed to compare transcriptomic profiles. Differential expression analysis, KEGG pathway enrichment, and phylogenetic characterization of defensin genes were conducted. RT-qPCR was used to validate selected defensin expression levels.

RESULTS

Transcriptome assembly yielded 195,132 unigenes. Principal component analysis (PCA) clearly separated the PBS control, E. coli-challenged (EC), and S. aureus-challenged (SA) groups. A total of 4,294 and 4,582 differentially expressed genes (DEGs) were identified in the EC and SA groups, respectively, compared to the PBS control. KEGG pathway enrichment analysis revealed that the MAPK signaling pathway and the Ras signaling pathway were commonly activated in both infection groups. In contrast, the lysosome pathway was significantly enriched among down-regulated DEGs in both EC and SA groups. Fifteen putative defensin genes were identified from the transcriptome, featuring conserved RVRR, CXXXC and CXC motifs. Several of these defensin isoforms were significantly up-regulated following bacterial challenge, indicating their involvement in the antibacterial response.

CONCLUSION

This comparative transcriptomic study provides a comprehensive characterization of the defensin repertoire and immune signaling responses of H. asiaticum to Gram-negative and Gram-positive bacterial challenges. The shared activation of the MAPK pathway, together with significantly enrichment of Ras signaling pathways, reveals both common and distinct antibacterial defense strategies. The strong up-regulation of defensins and the down-regulation of lysosome highlight key transcriptional events. These findings offer a valuable resource for understanding tick innate immunity and may inform future interventions for tick-borne disease control.