Transcriptomic analysis of the temporal host response to skin infestation with the ectoparasitic mite Psoroptes ovis

Abstract

Background: Infestation of ovine skin with the ectoparasitic mite Psoroptes ovis results in a rapid cutaneous immune response, leading to the crusted skin lesions characteristic of sheep scab. Little is known regarding the mechanisms by which such a profound inflammatory response is instigated and to identify novel vaccine and drug targets a better understanding of the host-parasite relationship is essential. The main objective of this study was to perform a combined network and pathway analysis of the in vivo skin response to infestation with P. ovis to gain a clearer understanding of the mechanisms and signalling pathways involved.

Results: Infestation with P. ovis resulted in differential expression of 1,552 genes over a 24 hour time course. Clustering by peak gene expression enabled classification of genes into temporally related groupings. Network and pathway analysis of clusters identified key signalling pathways involved in the host response to infestation. The analysis implicated a number of genes with roles in allergy and inflammation, including pro-inflammatory cytokines (IL1A, IL1B, IL6, IL8 and TNF) and factors involved in immune cell activation and recruitment (SELE, SELL, SELP, ICAM1, CSF2, CSF3, CCL2 and CXCL2). The analysis also highlighted the influence of the transcription factors NF-kB and AP-1 in the early pro-inflammatory response, and demonstrated a bias towards a Th2 type immune response.

Conclusions: This study has provided novel insights into the signalling mechanisms leading to the development of a pro-inflammatory response in sheep scab, whilst providing crucial information regarding the nature of mite factors that may trigger this response. It has enabled the elucidation of the temporal patterns by which the immune system is regulated following exposure to P. ovis, providing novel insights into the mechanisms underlying lesion development. This study has improved our existing knowledge of the host response to P. ovis, including the identification of key parallels between sheep scab and other inflammatory skin disorders and the identification of potential targets for disease control.

Figure 1

Profile plot of 1,552 genes significantly differentially expressed during time course of infestation with P. ovis. Gene expression profiles for differentially expressed genes over the time course of infestation with P. ovis. Control (Time = 0), 1 hour, 3 hours, 6 hours and 24 hours post-infestation. Each line represents a single gene, colour coded by log normalised intensity values

Figure 2

Clustered mean temporal gene expression profiles following infestation with P. ovis. Mean gene expression profiles for gene expression clusters 1-8. Time (hours) post infestation highlighted on X-axis and the mean fold change compared to time zero sample on the Y-axis. Baseline = non-infected, IE = immediate early, E = early, IM = intermediate and L = late

Figure 3

IPA network depicting relationships among transcription factor encoding genes in cluster 1, 1 hour post-infestation with P. ovis. Merged representation of the two highest scoring networks. Individual nodes represent protein functions with relationships represented by edges. Nodes coloured by gene expression, red indicating up-regulation and white indicating gene/factor not differentially expressed but with defined relationship to other genes in network. Arrows indicate directional relationships. Red circles highlight roles for JUN, NF-kB and TNF. Only direct interactions selected

Figure 4

IPA network depicting relationships among pro-inflammatory genes in cluster 2, 3 hours post-infestation with P. ovis. Merged representation of the four highest scoring networks. Individual nodes represent protein functions with relationships represented by edges. Nodes coloured by gene expression, red indicating up-regulation and white indicating gene/factor not differentially expressed but with defined relationship to other genes in network. Arrows indicate directional relationships. Red circles highlight roles for IL1A, IL1B, IL6, NF-kB, TLR2 and TLR4. Only direct interactions selected

Figure 5

IPA network depicting relationships among pro-inflammatory genes in cluster 3, 6 hours post-infestation with P. ovis. Individual nodes represent protein functions with relationships represented by edges. Nodes coloured by gene expression, red indicating up-regulation and white indicating gene/factor not differentially expressed but with defined relationship to other genes in network. Arrows indicate directional relationships. Red circles highlight roles for NF-kB, IFNGR1 and IFNGR2. Network score = 38.

Figure 6

IPA network depicting relationships among genes in cluster 3, 6 hours post-infestation with P. ovis. Individual nodes represent protein functions with relationships represented by edges. Nodes coloured by gene expression, red indicating up-regulation and white indicating gene/factor not differentially expressed but with defined relationship to other genes in network. Arrows indicate directional relationships. Red circles highlight roles for MT1E, MT2A and SOD. Network score = 31.

Figure 7

IPA representation of the canonical pathway for leukocyte extravasation signalling in cluster 4, 24 hours post-infestation with P. ovis. Individual nodes represent protein functions with relationships represented by edges. Nodes coloured by gene expression, red indicating up-regulation and white indicating gene/factor not differentially expressed but with defined relationship to other genes in network. Arrows indicate directional relationships

Figure 8

IPA representation of IgE and pro-Th2 genes in network 3 from cluster 4, 24 hours post-infestation with P. ovis. Individual nodes represent protein functions with relationships represented by edges. Nodes coloured by gene expression, red indicating up-regulation and white indicating gene/factor not differentially expressed but with defined relationship to other genes in network. Arrows indicate directional relationships. Red circles highlight roles for FCER1A, FCER1G, FCGR3A, FCGR1A and selected MHC complex genes. Network score = 31.

Figure 9

IPA representation of the complement system pathway enriched in cluster 6, 3 hours post-infestation with P. ovis. Individual nodes represent protein functions with relationships represented by edges. Nodes coloured by gene expression, green indicating down-regulation and white indicating gene/factor not differentially expressed but with defined relationship to other genes in network. Arrows indicate directional relationships