Langerhans Cell and Interdigitating Dendritic Cell Infection in African Swine Fever

Abstract

African swine fever (ASF) presently occurs in domestic pigs as a virulent disease, and a moderately virulent disease. The virulent form causes a necrotizing disease and high mortality in 7 to 10 days with negligible immunoglobulin production. The moderately virulent disease does not produce extensive necrosis, has low mortality, and detectable antibody to ASF is produced starting at 6 days post-inoculation (DPI).

Using avidin-biotin alkaline phosphatase (ABC-AP) immunostaining systems on paraffin sections we have identified ASF-infected interdigitating dendritic cells (IDCs) in the lymph node as early as 2 days post-infection. Infection of interdigitating cells was confirmed with anti-S-100 double staining and by finding viral factories in these cells by electron microscopy. Similar electron microscopic results were obtained in vitro with Langerhan’s cells (LCs) collected from skin expiant cultures. The infection and necrosis of these antigen-presenting cells may explain the lack of a humoral immune response in virulent ASF, despite their apparently normal lymphocyte functions.