TIR8/SIGIRR is expressed in tissues of adult and embryo chicken

The orphan receptor TIR8/SIGIRR, belongs to the TIR superfamily. TIR8 does not activate NF-kB and IRF3 and negatively modulates the inflammatory responses. It acts as antagonist for the TIR family members and triggers a negative pathway of the TIR receptor system, crucial for dampening inflammation. TIR8 was well characterized in mouse, humans and in other mammals, but it is poorly known in birds. We investigated TIR8 distribution in adult and embryo chicken samples. The pattern of expression of chicken TIR8 in adult was ubiquitary and similar to mammals, but it resulted unique in pancreas, female reproductive tract, heterophils. Different TIR8 isoforms were detected, suggesting the occurrence of post-translational modifications or alternative splicing. Immunohistochemistry revealed TIR8 immunolabeling in the intestine, thymus and oesophageal ganglia. These results demonstrate that TIR8, although evolutionarily conserved, show species-specific peculiarities. We analyzed TIR8 expression in embryos of layer- and broiler-chicken at different incubation time-points. TIR8 was detected since the first stages of development, but it reached a remarkable expression level at day 10. TIR8 was ubiquitously expressed, but the highest expression were found in liver and kidney. This pattern was comparable to those observed in adult chickens and in mammals examined to date. No differences were observed between the two different chicken breeds despite their immunological discrepancies. These are the first findings concerning TIR8 expression in developmental stages and they contribute to better understand the reproductive physiology and transovarian pathogen transmission, together with the recent findings of TLR expression in ovary and embryos of different species.