Expression of Toll-like receptors and antimicrobial peptides during Eimeria praecox infection in chickens

Intestinal colonization of avian species by Eimeria parasites results in the enteric disease, coccidiosis. A study was carried out to assess the immunologic effects of Eimeria praecox infection on the gut of infected chickens. In Experiment 1, birds were orally gavaged with 50,000 E. praecox oocysts; in Experiment 2, an infection dosage of 500,000 E. praecox oocysts was used. Duodenal and jejunal intestinal sections were sampled consecutively on days 1-7 post-infection. Intestinal expression of innate immune gene transcripts was analyzed by quantitative real-time polymerase chain reaction (qRT-PCR). Analysis of relative gene expression in Experiment 1 revealed an increase (P<0.05) in duodenal Toll-like receptor (TLR)3 expression on days 4 and 6 post-infection. TLR15 expression was significantly decreased in the duodenum of infected birds on day 2, and significantly increased on day 6 post-infection. In Experiment 2, TLR3 was significantly downregulated in the duodenum on day 7 post-infection; however, no significant results were observed in terms of TLR15 expression. TLR4 also exhibited decreased expression (P<0.05) on day 7 post-infection in both intestinal sections. Regarding antimicrobial peptide expression; in the first experiment, expression of liver-expressed antimicrobial peptide-2 (LEAP-2) in infected birds was significantly decreased in the duodenum on days 3 and 4, and in the jejunum on day 4. Similarly, Experiment 2 resulted in depression of LEAP-2 (P<0.05) on days 3-5 in the duodenum. In Experiment 1, cathelicidin antimicrobial peptide (CATHL3) was downregulated (P<0.05) in the jejunum of infected chickens on day 3 post-infection; however, CATHL3 results were non-significant in Experiment 2. Based on the differing results observed in each experiment, it was concluded that both TLR and antimicrobial peptide expression, and thus immunity may be dependent on infection load.