The innate immunity receptor TIR8/SIGIRR is expressed in the early developmental stages of chicken embryos

The orphan receptor TIR8, also known as SIGIRR (Single Immunoglobulin IL-1R-Related molecule), belongs to the IL-1R/TLR (TIR) superfamily and plays an important role in the inflammatory responses. The signaling pathways of the receptors belonging to the TIR family are tightly regulated by both extracellular and intracellular mechanisms. TIR8 does not activate the transcription factors NFkB (nuclear factor kB) and IRF3 (interferon regulatory factor 3), although it negatively modulates the inflammatory responses. It acts as an antagonist for the IL-1 receptor family and triggers a negative pathway of the Toll-like/IL-1 receptor system, crucial for dampening inflammation stimuli in the gastrointestinal (GI) tract and in other organs (e.g. lung and kidney). The recent findings of TLRs expression in ovary and embryos of different species (mammals and chickens) are very important for an understanding of reproductive physiology and transovarian pathogen transmission. TIR8 was well characterized in mouse, humans and in other mammalian species, but it is still poorly characterized in the chicken. When TIR8 expression was measured in selected organs of chicken embryos of both broiler and layer types at different time points a unique pattern of expression was observed. Interestingly, TIR8 was detected during the first stages of chicken development (day 1 of incubation), and reached a remarkable level of expression by day 10. We observed this receptor to be ubiquitously expressed in the kidney, GI tract, Bursa of Fabricius, with the highest expression levels in liver and kidney. This pattern was comparable to those observed in post-hatching chickens and in mammals examined to date. No expression differences were observed between the two different chicken breeds (layer- and broiler-type) in the first incubation period (8 days). Whereas in some organs starting from day 10, higher TIR8 expression was observed in broiler-type compared to layer-type. These are the first findings concerning TIR8 expression in developmental stages and therefore they are of comparative value.