African swine fever virus infection of skin-derived dendritic cells in vitro causes interference with subsequent foot-and-mouth disease virus infection

Foreign Animal Disease Diagnostic Laboratory, National Veterinary Services Laboratories, APHIS, USDA, Greenport, NY 11944, USA. Highly purified skin-derived dendritic cells (SDDCs) isolated from swine skin by a simple novel method were cultured for 24 hours before independent or sequential inoculation with African swine fever virus (ASFV) and foot-and-mouth disease virus (FMDV). By avidin-biotin immunohistochemical staining, ASFV antigen was detected in 50% of SDDCs as early as 1.5 hours postinfection (HPI) and in 80% by 3 HPI when cytopathic effect was noted. Cell lysis was detected with FMDV infection as early as 8 HPI; immunostaining for FMDV antigen was found in 10% of the cells. African swine fever virus replication was detected by transmission electron microscopy in a high percentage of SDDCs by 11 HPI. Sequential infection with FMDV 3 hours after ASFV inoculation blocked FMDV infection. These findings demonstrate that both ASFV and FMDV infect dendritic cells of Langerhans cell type in vitro and ASFV interferes with FMDV infection.