Indications of trained innate immunity by Escherichia coli vaccination or chitin feed supplementation assessed during Ascaridia galli infection in chickens

Infections with the gastrointestinal roundworm Ascaridia galli, cause health problems and economic losses in laying hen husbandry, particularly in organic and free-range systems. This study aimed to evaluate induction of trained innate immunity through priming with a live attenuated Escherichia coli vaccine or chitin supplementation in the feed as a novel approach to mitigate A. galli infection. The study comprised four groups of chickens: chitin-fed (day 1-7 of age), E. coli-vaccinated (day 1 of age), an untreated control group, and a naïve uninfected group. On day 7 of age, the first three groups were infected with A. galli. Immune parameters were assessed after initial treatments and post the parasite infection. Also, faecal excretion of nematode eggs and total worm burden were monitored post-infection. The chitin and E. coli treatments induced changed proportions of leukocytes in bone marrow as well as changes in cell surface receptor expression. Moreover, treatments altered the immune response to the A. galli infection, e.g. observed for numbers of heterophils and TCRγδ+CD8- T-cells in the circulation but also expression levels of cell surface receptors CD41/61, Bu-1 and MHC-II on circulating leukocyte subsets. However, neither treatment affected worm burden, faecal egg excretion or the induction of A. galli-specific IgY. The results demonstrate potential in vivo training of the avian innate immune system but further research is needed to identify strategies to explore this in relation to control of nematode infections.