The effect of estrogen on the early cytotoxic response to IB virus infection in hen oviduct.

The aim of this study was to determine whether the egg-laying phase and estrogen affect the induction of cytotoxic cells in response to avian infectious bronchitis (IB) virus at early stage of infection in the oviduct. Attenuated IB virus (aIBV group) or its vehicle (control group) was introduced to the oviductal magnum lumen of White Leghorn hens in the laying and molting phase, as well as molting hens injected with estradiol benzoate (M-EB hens) or corn oil (M-oil hens). Oviductal isthmus and uterus were collected 24h after injection. The frequency of CD8(+) and TCRγδ(+) T cells expression was examined by immunohistochemistry, followed by image analysis. The expression of the genes of toll-like receptor 7 (TLR7), natural killer cell receptor (BNK), cytotoxic substances (granzyme, perforin), and cytokines (CXCL12, CX3CL1, and IFNγ) were examined by real-time polymerase chain reaction analysis. The frequency of CD8(+) and TCRγδ(+) T cells in the isthmus, and CD8(+) cells in the uterus was significantly higher in the aIBV group compared to the control group of laying and M-EB hens. The expression of all the genes examined in this study in the isthmus, and CX3CL1 and IFNγ expression in the uterus was significantly higher in the aIBV group in the laying and M-EB hens. These results suggested that infection with IB virus causes an immune response involving the influx of cytotoxic cells and upregulation of cytokines in the isthmus and uterus at early stage of infection. This response was stronger during the laying phase compared to the molting phase, probably due to the effect of estrogen.