Pseudorabies virus (PRV) is a neurotropic alphaherpesvirus that produces fatal
encephalitis in newborn pigs, respiratory disorders in fattening pigs, and reproductive failure in sows. Following primary
infection of the respiratory tract, PRV can develop into a systemic
infection with dispersion of the virus via the lymphatic system that involves mononuclear cells in tracheobronchial lymph nodes (TBLNs). The objectives of the present study were to evaluate the pathogenesis and to determine the early immune
cytokine profiles in TBLNs following experimental
infection with a
feral swine PRV isolate at 1, 3, 6, and 14 days postinfection (dpi). Forty healthy pigs were purchased from a PRV-negative herd. Twenty pigs received the Florida strain isolate (FS268) of
feral swine PRV intranasally, and 20 uninfected controls received a
sham inoculum. Compared to the levels in the controls, the levels of
alpha interferon (IFN-alpha),
interleukin-1beta (IL-1beta),
IL-12, and IFN-gamma were increased in TBLN homogenates from PRV-infected pigs at 1 dpi, whereas the
IL-18 levels were decreased from 3 to 6 dpi. The
protein levels of
IL-4 and
IL-10 did not differ between the controls and the PRV-infected pigs at any time point. Flow cytometric analysis of TBLN homogenates of PRV-infected pigs and the controls revealed increases in the percentages of B cells at 6 dpi, CD4(+) cells at 14 dpi, and CD25 expression in TBLN homogenates (in the total mononuclear fraction and on B cells) in the PRV-infected pigs. Collectively, these findings demonstrate that a
feral PRV in commercial swine can modulate the host's early immune response to allow the virus to establish an
infection.