In situ gene expression in early stage of virulent Newcastle disease in chickens

Authors: BROWN, CORRIE - University Of Georgia; ZHANG, JIAN - University Of Georgia; Pantin Jackwood, Mary; DIMITROV, KIRIL - Texas A&M Veterinary Medical Diagnostic Laboratory; FERREIRA, HELENA - Orise Fellow; Suarez, David

Submitted to: Veterinary Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/16/2021
Publication Date: 1/15/2022
Citation: Brown, C., Zhang, J., Pantin Jackwood, M.J., Dimitrov, K., Ferreira, H., Suarez, D.L. 2022. In situ gene expression in early stage of virulent Newcastle disease in chickens. Veterinary Pathology. 59(1):75-81. https://doi.org/10.1177/03009858211045945.
DOI: https://doi.org/10.1177/03009858211045945

Interpretive Summary: Newcastle disease, caused by Newcastle disease virus (NDV), represents a serious threat to the poultry industry. Infection with virulent NDV strains in chickens results in severe disease and high mortality. Previous studies indicate that an over-vigorous innate immune response in the birds may be occurring with infection with NDV. The innate immune response consists of many factors dominated by pro-inflammatory cytokines that serve to decrease infection in the early stages and initiate the development of the specific immune response. When this innate immune response is hyper-responsive, it can create severe disease in the host and has been referred to as a “cytokine storm”. In this study, selected lymphoid and reproductive tissues from three-week-old chickens and 62-week-old hens which were inoculated with a virulent NDV were examined. Immunohistochemistry for NDV, T, and B cells, as well as RNAScope assays for four cytokines revealed extensive production of interleukin 1ß and interleukin 6 in lymphoid tissues, often coinciding with similar levels of NDV antigen. In the three-week-old birds, T cell populations initially expanded but by day 3 numbers were below control levels. B cells underwent a similar expansion, but in some tissues, notably spleen, cecal tonsils, and bursa of Fabricius, remained elevated. Cytokine responses in the 62-week-old hens were overall lower than what was seen in the three-week-old birds. Also, in these older birds, there was more prolonged production of both T and B cells. This study helps in understanding the involvement of the bird immune system in the pathogenesis caused by virulent NDV.

Technical Abstract: Selected lymphoid and reproductive tissues were examined from groups of 3-week-old chickens and 62-week-old hens that were inoculated choanally and conjunctivally with 106 EID50 of a virulent Newcastle disease virus (NDV) isolate from the California 2018-2020 outbreak, and euthanized at 1, 2, and 3 days post infection. In the 3-week-old chickens, immunohistochemistry for NDV and for T and B cell lymphocytes, as well as in situ hybridization for IL-1ß, IL-6, IFN-', and TNF-a revealed extensive expression of IL-1ß and IL-6 in lymphoid tissues, often coinciding with NDV antigen. IFN-' was only expressed infrequently in the same lymphoid tissues, and TNF-a was rarely expressed. T-cell populations initially expanded but by day 3 their numbers were below control levels. B cells underwent a similar expansion but remained elevated in some tissues, notably spleen, cecal tonsils, and cloacal bursa. Cytokine expression in the 62-week-old hens was overall lower than in the 3-week-old birds, and there was more prolonged infiltration of both T and B cells in the older birds. The strong pro-inflammatory cytokine response in young chickens is proposed as the reason for more severe disease.