Cytokine protein expression levels in tracheobronchial lymph node homogenates of pigs infected with pseudorabies virus

Abstract

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.

FIG. 1.

Clinical evaluation and gross pathology. (A) Rectal temperature for control (○) and PRV-inoculated (▪) pigs measured each day out to 14 dpi; (B) body weight measured prior to necropsy for control (○) and PRV-inoculated (▪) pigs; (C) macroscopic lesion score for lungs at necropsy for control (○) and PRV-inoculated (▪) pigs. Data are expressed as means ± standard errors (n = 5). *, P < 0.05.

FIG. 2.

Cytokine concentration in homogenates of TBLNs from pigs inoculated with PRV (▪) or controls (○) normalized to the total protein concentration per gram of TBLN. Due to differences in the concentrations of the cytokines, the graphs use different scales. Means and standard errors of the means (n = 5) are shown. *, significantly different value than that for the control (P < 0.05).

FIG. 3.

Flow cytometric analysis of homogenates of TBLNs from pigs inoculated with PRV or controls. (A) B-cell percentages; (B) CD4⁺-cell percentages; (C) mean fluorescence intensity (MFI) of CD25 for total TBLN homogenates; (D) mean fluorescence intensity of B cells in TBLN homogenates. *, significant difference (P < 0.05) from the values for the controls.