Transcriptional analysis of differential immune responses to Sarcoptes scabiei infestation in a porcine model.

Scabies is one of the most prevalent skin diseases affecting over 100 million people globally. The prevailing knowledge of the disease processes and host immune response mechanisms is limited, and to identify novel vaccine and drug targets, a better understanding of the host-parasite relationship is essential. The objective of this study was to perform gene expression analysis of the skin immune response to infestation with Sarcoptes scabiei to gain a better understanding of the immune mechanisms and signaling pathways involved. A 16-week animal trial employing experimentally S. scabiei infected (n=12) and control pigs (n=6) was conducted. Scoring for clinical phenotype, monitoring of mite infestation, skin biopsies and blood samples were collected at different time points of disease progression (at baseline week 0, and at weeks 1, 2, 4 and 8 post-infestation). Transcriptomic analysis was undertaken using RNA extracted from the skin biopsies (n=60) from infested pigs with crusted scabies (n=4), ordinary scabies (n=4) and non-infested controls (n=4) at each time point. Microarrays were performed with the Agilent Porcine Gene Expression Microarray platform and differential gene expression analysed. A large number (>1000) of significantly differentially expressed genes were identified at each time point. The analysis revealed numerous genes with roles in allergy and inflammation, including pro-inflammatory cytokines and chemokines involved in immune cell activation and recruitment. In addition, the analysis demonstrated expression of transcripts of various cell surface markers, acute phase proteins, transcription factors, and signaling molecules. Key signaling pathways involved with scabies mite infestation included, “Th1 and Th2 Activation Pathway”, “JAK-STAT Signaling Pathway”, “NF-κB Signaling Pathway”, “Immune Cell Trafficking”, “Communication between Innate and Adaptive Immune Cells”, “Acute Phase Response Signaling” and “Role of IL-17F in Allergic Inflammatory Airway Disease”. In crusted scabies relative to ordinary scabies, we detected gene expression associated with pathophysiologic pathways implicated in psoriasis, atopic dermatitis, rheumatoid arthritis and Th17 (IL17A, ARG1) pronounced responses. To validate the differential gene expression, qRT- PCR confirmation was carried out for selected genes. ELISA analysis was also performed to characterise acute phase response proteins (Haptoglobin, Transferrin, Serum amyloid A and α1 Acid glycoprotein) in serum collected from pigs at selected time points. The analysis demonstrated an increased trend in SAA and significantly higher AGP levels post mite infestation in crusted scabies. In summary, transcriptional profiling revealed genes in the T helper lymphocyte (Th1), Th2 and Th17 signaling pathways, acute phase response signaling, and allergic inflammatory response are associated with scabies. For the first time, we have described key transcriptional changes associated with the development of ordinary scabies and significantly, the distinction between ordinary and crusted scabies. This work provides the basis for follow-up studies in clinical patients with crusted scabies and may provide new control strategies for this severely debilitating disease.Submitted in the fulfilment of the requirements of the degree of Doctor of Philosophy, University of the Sunshine Coast, 2018