Occurrence of apoptosis in lymphoid tissues from chickens acutely infected with strains of Newcastle disease of varying virulence

Abstract

Newcastle Disease Virus (NDV) poses many threats to the poultry industry. Virulence of different strains varies widely and creates a wide range of disease manifestations. Low virulence strains often circulate with minimal disease, while high virulence strains can rapidly sicken and kill an entire house of chickens. Presence of highly virulent viruses within our country will seriously damage our abilities to export chicken meat or live birds. Because apoptosis, or programmed cell death, serves as a key defense mechanism during viral infections, increased knowledge concerning apoptosis is essential in understanding host-pathogen interactions. Additionally, comparing apoptosis among strains of varying virulence generates better understanding of clinical consequences from infection with different viral strains. Immunohistochemistry (IHC) for active caspase-3, a key enzyme in apoptosis, was done on formalin-fixed, paraffin embedded sections from chickens infected with various strains of NDV. Apoptotic activity was examined in the spleen, thymus, bursa, and intestine. All tissues were harvested at two days post-infection. To confirm virus presence, IHC was done for NDV nucleoprotein. Active caspase-3 expression in lymphoid tissue infected with virulent strains was significantly increased when compared to tissue infected with milder strains. Heightened apoptosis in the virulent strains may be a key component of the severe disease manifestations seen. Because severe disease manifestation results in losses to the poultry industry, generating greater understanding of apoptosis in response to NDV infection exists as an important research initiative.