From innate to adaptive immunity: Abomasal transcriptomic responses of merino sheep to Haemonchus contortus infection

Although many important mediators and critical pathways are found to be involved in host immune responses to Haemonchus contortus infection, the initial responses to infection in the naïve and in the previously exposed state have not been compared at the transcriptional level. To further understand the development of adaptive immunity to H. contortus infection, we compared the early abomasal gene expression patterns between a primary and a tertiary challenge for four lines of sheep to discover differentially expressed genes (DEGs). The sheep were from the resistant (R) and susceptible (S) lines of two flocks of sheep selected for divergent responses to gastro-intestinal parasites (HSF and TSF). The flocks have separate origins and were initiated using two different strains of Merino sheep. One of the DEGs, mast cell proteinase 1, had significantly lower expression in tertiary compared to primary infections for all four lines of sheep. This gene was not identified in previous studies where resistant and susceptible sheep samples were compared within infection time points. Comparing the differentially expressed genes (DEGs) for the two R lines reveals that responses differed very little between the primary and tertiary challenges for HSFR and only two genes were identified, in contrast to the TSFR where there were 134 genes identified including the two identified using the HSFR animals. Similarly, comparing the primary and tertiary challenges for HSFS identified 15 DEGs, whilst for TSFS there were 128 DEGs identified. It is surprising that so few genes respond similarly between the two challenge regimes across the four lines of sheep, and suggests significant differences in immune mechanisms between the two flocks (across the lines) and also between the lines within flocks. Our results offer a quantitative snapshot comparing the transcriptome in the ovine abomasum between primary and tertiary infections with H. contortus in both genetically resistant and susceptible sheep.