Cytokine and immune response-associated transcriptome profiles in cattle infected with Theileria parva vaccine stocks

Abstract

Theileria parva infections cause cattle theileriosis by seizing pathways controlling the host’s cell cycle, leading to reversible host T cell transformation. However, the role of the host immune response in varied severity of infections by different parasite stocks is not fully understood. In this study we investigated the cytokine expression and transcriptome profiles associated with host immune response in calves infected with two T. parva vaccine stocks. Three calves were experimentally infected with T. parva Katete and another three with Chitongo. Clinical manifestation was followed for 19 days, with daily blood collection. Subsequently, cytokine expression analysis, RNA sequencing and differential gene expression analysis were performed to determine differential gene expression between animals infected with the different parasite stocks and those that varied in the severity of infection. Onset of clinical signs was observed earlier in Chitongo- than in Katete-infected calves, including the enlargement of lymph nodes, which was noted three days earlier. Calves with mild and severe clinical signs were noted in both infection groups, Katete and Chitongo. Overall, the expression analysis of in vivo anti-inflammatory and pro-inflammatory cytokines showed that interleukin-4 and IL-2 genes were downregulated, while IL-10, TNF-α and IFN- were upregulated. However, significantly higher expression levels in Chitongo-infection groups compared to Katete were noted. Also notable was the marked differences in cytokine expression levels observed between animals with severe clinical signs (SCS) and mild clinical signs (MCS). To eliminate the possibility of animal-to-animal variation in response to infection, in vitro infection of PBMCs with Katete and Chitongo vaccine stocks was done. Contrary to observations in vivo, IL-2 expression was consistently upregulated (though at very low levels) in vitro. The expression analysis of the other pro- and anti-inflammatory cytokines showed similar profiles as observed in vivo, in both Katete and Chitongo infections. RNA sequencing data showed that animals with SCS had a higher number of differentially expressed genes (DEGs) compared to MCS, most of which were downregulated. This pattern was also consistent in the filtered data of DEGs associated with the immune response, indicating the negative modulation of the immune system in SCS compared to MCS. The pathways analysis of DEGs associated with T. parva infection, which included transcripts detected in both Chitongo and Katete-infected animals, confirmed the overrepresentation of immune system response. Our analysis revealed the negative modulation of Class I MHC mediated antigen processing and presentation from the adaptive immune response. The data showed that infection with T. parva results in positive modulation of the innate immune response ERK/MAPK, cytokine signalling, toll-like receptor (TLR) pathways regulated by DUSP4 and STAT2, neutrophil degranulation and DAP 12 signalling. Moreover, NFκB, TNF and STAT3, all known to play a role in inflammatory and tumour-like behaviour were upregulated in T. parva infection.