Complement, coagulation and NET pathway activation underlies early host response to blowfly (Lucilia cuprina)...

Blowfly strike (myiasis), caused mainly by Lucilia spp., poses a serious animal welfare concern and results in substantial economic losses to the global sheep industry. However, the early molecular and proteomic responses of sheep skin to larval infestation are not well characterised.

The early proteomic response in sheep skin following infestation by blowfly Lucilia cuprina larvae was assessed in 14 Merino ewes, 7 from a group selected for breech strike resistance and 7 from a non-selected group. Control sites were also established using mock dental plugs without blowfly eggs. After ~ 22 h post-egg implantation, larvae were removed to collect excretory-secretory (ES) products. Skin washings were also collected to recover sheep proteins secreted in response to larval activity. Using liquid chromatography-tandem mass spectrometry (LC-MS/MS), comparisons were made between (1) larval-challenged and mock control sites to identify sheep proteins induced by larval activity and (2) resistant and non-selected sheep. While this paper focuses mainly on the sheep proteins produced in response to larval activity, excretory-secretory (ES) proteins from the larvae were also detected.

In total, 105 proteins were significantly enriched at larval-challenged sites. Following challenge, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses revealed strong enrichment of the complement and coagulation cascades as well as the neutrophil extracellular trap (NET) formation pathway. Protein-protein interaction analysis identified a major cluster with alpha-2-macroglobulin (A2M) as the seed protein, while the top 10 hub proteins included A2M, serine protease inhibitors (Alfa-1 antitrypsin, Antithrombin III), fibrinogens and plasma proteins such as albumin and haptoglobin. No proteins in the skin exudate differed significantly between resistant and non-selected sheep, and larval ES products also showed no significant differences between these groups.

Early infestation by Lucilia cuprina larvae induces a strong, non-specific proteomic response in sheep skin, characterised by activation of the complement and coagulation cascades and NET formation. However, findings in this study suggests that breech strike resistance is unlikely to be associated with differences in skin protein expression during a short infestation.