Molecular characterization and serodiagnostic potential of two serpin proteins in Psoroptes cuniculi

Background: Psoroptes cuniculi is a global common ectoparasite of wild and domestic rabbits and causes an economically devastating loss and serious welfare issues of commercial rabbit husbandry. Serine proteinase inhibitor (Serpin) is present in almost all organisms that are involved in host-pathogen interactions, inflammatory responses, and reproductive development, etc. However, the research on P. cuniculi serpins is still limited.Methods: In this study, two serpin genes of P. cuniculi (Pso c 27 and PsoSP2 cDNAs) were cloned, and the molecular characterization was analyzed. The transcriptional profiles and tissue localization of these two serpins in P. cuniculi were investigated by quantitative real-time PCR and immunohistochemistry, respectively. The potential function of recombinant Pso c 27 and PsoSP2 (rPso c 27and rPsoSP2) in the serodiagnosis of P. cuniculi infestation in rabbits were evaluated by indirect enzyme-linked immunosorbent assay (iELISA). Results: Both of the 523 residue Pso c 27 and the 240 residue PsoSP2 proteins contained typical serpin domains and signatures. Both Pso c 27and PsoSP2 cDNAs expressed throughout the life cycle, more specifically, significantly higher expression in female mites than the larva, nymph, and male mites (p < 0.001). The native Pso c 27 and PsoSP2 localized in ovary and mouthpart of adult female mites, respectively. Compared to rPsoSP2, the rPso c 27 displayed better diagnostic efficiency with higher values of sensitivity, specificity and the area under the receiver operating characteristic curve (AUC) (rPso c 27 - rPsoSP2: 96.0% - 90.0%; 90.91% - 78.18%; 0.988 - 0.964, respectively). Moreover, the rPso c 27 showed seropositive in 80% rabbits as early as the 2nd week post-infestation (p.i.), prior to visible clinical signs and microscopy-positive of skin scrapings. Conclusions: These results suggested that these two serpins may play essential roles in reproductive development, serum-feeding, and pathogenicity of P. cuniculi. Compared to PsoSP2, Pso c 27 appeared as a potential antigen for serodiagnosis of P. cuniculi infestation in rabbits, especially at the early stage of infestation.