Kinetics of the Cellular and Transcriptomic Response to Eimeria maxima in Relatively Resistant and Susceptible Chicken Lines

Abstract

Eimeria maxima is a common cause of coccidiosis in chickens, a disease that has a huge economic impact on poultry production. Knowledge of immunity to E. maxima and the specific mechanisms that contribute to differing levels of resistance observed between chicken breeds and between congenic lines derived from a single breed of chickens is required. This study aimed to define differences in the kinetics of the immune response of two inbred lines of White Leghorn chickens that exhibit differential resistance (line C.B12) or susceptibility (line 15I) to infection by E. maxima. Line C.B12 and 15I chickens were infected with E. maxima and transcriptome analysis of jejunal tissue was performed at 2, 4, 6 and 8 days post-infection (dpi). RNA-Seq analysis revealed differences in the rapidity and magnitude of cytokine transcription responses post-infection between the two lines. In particular, IFN-γ and IL-10 transcript expression increased in the jejunum earlier in line C.B12 (at 4 dpi) compared to line 15I (at 6 dpi). Line C.B12 chickens exhibited increases of IFNG and IL10 mRNA in the jejunum at 4 dpi, whereas in line 15I transcription was delayed but increased to a greater extent. RT-qPCR and ELISAs confirmed the results of the transcriptomic study. Higher serum IL-10 correlated strongly with higher E. maxima replication in line 15I compared to line C.B12 chickens. Overall, the findings suggest early induction of the IFN-γ and IL-10 responses, as well as immune-related genes including IL21 at 4 dpi identified by RNA-Seq, may be key to resistance to E. maxima.

Dual RNA-seq transcriptome analysis of caecal tissue during primary Eimeria tenella infection in chickens

“…Among these, IFN-γ is regarded as a cytokine of central importance in chicken immunity to Eimeria -infection both as an effector cytokine inhibiting parasite intracellular development and as a key regulator of Th1-type responses (reviewed in [ 19 ]. In line with the present results, early IFN-γ responses in intestinal tissues/cells upon primary Eimeria -infection of chickens have been reported previously [ 21 , 23 , 37 , 45 , 47 , 48 , 50 , 51 ]. Moreover, in the present results some of the differentially expressed IFN-induced genes, i.e.…”

“…Since Th1-type responses are considered essential for protection against Eimeria -infection [ 19 ] our results suggest that the chain of events leading to development of protective immunity already was initiated at this time point. This was also supported by a recent report showing that the Th1 pathway was among top up-regulated GO-categories in jejeunal tissue from E. maxima infected chickens 4–6 dpi [ 37 ]. Beside this, the most striking observation in the general analysis of immune related genes in our data was the up-regulated expression of a large number of genes at 10 dpi.…”

“…GBP , IRF1 and RSAD2 , were significantly up-regulated at 4 dpi, which may be a result of IFN-γ stimulation. Expression of IFN-induced genes were also reported in caecal epithelial cells 4.5 days after E. tenella infection [ 23 ] and in jejeunal tissue 4–6 days after E. maxima infection [ 37 ] and in the latter study IFN signalling was the top enriched GO pathway at 4 dpi for chickens relatively resistant to the infection. For related Apicomplexan parasites T. gondii and Neospora caninum it has been shown that IFN-γ induced members of the murine guanylate-binding protein (GBP) family can restrict the intracellular growth of the parasites [ 52 ], which for T. gondii has been suggested essential for survival of infected mice [ 53 ].…”

“…Interleukin-10 (IL-10) is a pleiotropic cytokine well known for its immunoregulatory effects and in the context of protozoan infections IL-10 is suggested to have a role in controlling the potentially host-damaging effects of parasite-eliminating immune responses [ 57 , 58 ]. Induction of IL-10 has earlier been observed upon Eimeria infections of chickens [ 37 , 45 , 48 , 50 , 59 – 61 ] and increased IL-10 expression has been associated with increased susceptibility to Eimeria -infection [ 37 , 50 , 59 , 61 ]. Chicken macrophages have also been shown to up-regulate IL10 expression upon in vitro stimulation with recombinant E. tenella surface antigens, SAG4, SAG5 and SAG12, [ 18 ].…”

“…In previous studies using this infection model we did not detect altered expression of CTL associated genes [ 33 ] or signs of activation of CD8β-expressing cell populations [ 35 ] in caecal mucosa during this phase of infection of naïve chickens, which is in line with the present observations. Among earlier RT-PCR or RNA-seq based studies of Eimeria -infected chickens that include samples collected at 1 and 2 dpi, those using intestinal tissue samples reports no or very low changes in mRNA expression at these time points [ 37 , 46 , 47 ] while those using purified intestinal mononuclear leukocytes report genes with altered expression [ 45 , 51 ]. In addition, RNA-microarray based studies of Eimeria -infected chickens using purified intestinal mononuclear leukocytes report some altered gene expression at 1 and 2 dpi [ 20 – 22 ].…”