Expanding tropism: Avian B cells as novel cellular target of infectious bronchitis virus

Infectious bronchitis virus (IBV) causes infectious bronchitis (IB), which is a major concern for the global poultry industry as a result of substantial economic losses. Although epithelial cells were described as the primary target cells of IBV, other susceptible cell types including macrophages and monocytes, have been identified, where productive infection impairs cellular functions. Avian B cells are central to antibody-mediated immunity in chickens against pathogens, including IBV; however, it remains unknown if IBV can infect and replicate in B cells. This study investigated whether Delmarva (DMV)/1639 IBV can infect B cells in the bursa of Fabricius (BF) in vivo and in DT-40 cells in vitro. In vivo, a significantly higher viral genome load was observed in the BF at 3 days post-infection (dpi), with similar result in sorted B cells from the BF. Viral RNA was found to be localized within B cells of the BF using an in situ hybridization combined with immunohistochemistry. In vitro, a comparable trend in viral genome load was observed in infected DT-40 cells and culture supernatants up to 72 h post-infection (hpi). Immunofluorescence assay revealed a significantly higher percentage of DT-40 cells expressing IBV nucleoprotein. Inoculation of DT-40 cells with virus-containing supernatant confirmed infectivity as did inoculation of embryonated eggs, which resulted in IBV-specific lesions including dwarfing and stunting. These findings demonstrate that IBV can infect and replicate productively in avian B cells; however further studies are warranted to elucidate the impact of IBV infection on B cell function and its role in disease pathogenesis.