Gene discovery and differential expression analysis of humoral immune response elements in female Culicoides sonorensis (Diptera: Ceratopogonidae)

Female Culicoides sonorensis midges (Diptera: Ceratopogonidae) are important vectors of pathogens impacting livestock and wildlife in the U.S. We recently sequenced, annotated, and determined the responding transcriptomes of female midges under several feeding states including teneral/unfed and early and late time points after blood and sucrose. Here, those transcriptomes were further analyzed to identify insect innate immune orthologs, particularly humoral immune response elements. Because the immune response participates in important processes like gut microbial-ecology and vector competence, we also examined immune gene expression profiles in response to diet across time, on both a transcriptome-wide, whole-midge level and more specifically via qRTPCR of effector expression in the alimentary canal. We identified functional components of immune deficiency (Imd), Toll and JAK/STAT pathways, including humoral factors, transmembrane receptors, signaling components, transcription factors/regulators and effectors (e.g. antimicrobial peptides, AMPs). Feeding altered the expression of receptors, regulators, effectors (AMPs, PPO and TEPs), and blood had a greater effect than sucrose on the expression profiles of most innate immune components. All five CsAMPs were significantly upregulated in the alimentary canal after blood feeding, possibly in response to proliferating populations of gut bacteria. Functional insight into C. sonorensis humoral/innate immune components updates our knowledge of the molecular functioning of this important vector. Future manipulation (e.g., RNAi) of immune gene expression will help in uncovering genetic components of vector competence, including midgut barriers to infection. The results of such studies would serve as a platform for designing novel transmission-blocking strategies.