Genetic modification regulates pathogenicity of a fowl adenovirus 4 strain after cell line adaptation (genetic mutation in FAdV-4 lowered pathogenicity).

Fowl adenovirus 4 (FAdV-4) is a major avian virus that induces fatal diseases in chicken such as, hydropericardium and hepatitis. The viral structure consists of hexon, penton, fiber-1, and fiber-2 which are associated with immunopathogenesis. In this study, we investigated the genetic modification of a FAdV-4 strain after continuous passages in a cell line and evaluated the pathogenicity associated with mutations. We used the FadV-4 KNU14061 strain, which was isolated from layers in 2014. The virus went through 80 passages in the Leghorn male hepatoma (LMH) cell line. The full genetic sequence was identified, and we found a frameshift in the fiber-2 amino acid sequence after the initial thirty passages. To examine whether the frameshift in the fiber-2 gene affects the pathogenicity in chicken, we inoculated LMH80 (80 times passaged) and LMH10 (10 times passaged) into 3-day-old chickens and examined the pathogenesis. LMH10 infection via intramuscular route induced fatal pathology, but LMH80 did not. Furthermore, LHM80 pre-treatment protected hosts from the LMH10 challenge. Thus, the genetic modification isolated by serial passage lowered pathogenicity and the resulting virus acted as an attenuated vaccine that can be a FAdV-4 vaccine strain candidate.

Transcriptome analysis of primary chicken cells infected with infectious bronchitis virus strain K047-12 isolated in Korea.

Infectious bronchitis virus (IBV), an avian coronavirus, is highly contagious. Chickens with IBV infection develop acute pathogenesis in multiple organs, including the respiratory and urogenital tracts. Frequent recombination in the spike (S) glycoprotein gene has made vaccine strategies ineffective. To understand IBV pathogenesis, we analyzed the genetic distance between Korean IBV isolates and other coronaviruses, including SARS-CoV-2. To obtain comprehensive information about early immune responses such as innate cytokine production and associated immune regulation during IBV infection, we infected primary chicken embryonic kidney cells and performed transcriptome analysis. We observed that the functional pathways of innate immunity are regulated and confirmed expression of genes that coordinate early immune responses. Understanding the immune profile of the host cell may assist in vaccine development.