Flow cytometric analysis of porcine peripheral blood leukocytes infected with pseudorabies virus

The susceptibility of fractionated porcine peripheral blood leukocytes (PBL) to pseudorabies virus (PRV) was studied by flow cytometry and defined by viral antigen expression. Viral antigens on the surface of infected cells and cell viability were evaluated by forward angle light scatter (FALS), 90-degree light scatter (90LS), green fluorescence (FITC-anti-PRV), and red fluorescence (propidium iodide). Approximately 10% of infected mononuclear cells from healthy pigs expressed cell-surface PRV antigen. Cell-surface fluorescence and cell type were confirmed by sorting live positive cells for microscopy. In sorted positive samples, the lymphocyte versus monocyte ratio was approximately 50%:50%, defined by morphology. Positive lymphocytes represent 5.75% of total mononuclear cells. When cells were stimulated with phytohemagglutinin (PHA) and lipopolysaccharide (LPS) before infection, mitogen-stimulated T-lymphoblasts showed increased susceptibility to PRV (40.7% positive) and died of infection. Monocytes, particularly adherent monocytes, were highly susceptible (40% to 71.4% positive). Granulocytes appeared to be refractory. The relative susceptibility of various PBL populations was compared by normalizing lymphocyte susceptibility to 1 as follows: resting total lymphocytes (1); B-lymphocytes (0.67); T-lymphoblasts (7.08); total monocytes (4.27); adherent cells (4.03 to 10.88); adherent monocytes (6.95 to 12.42); granulocytes (0.24). These findings suggest a possible mechanism by which PRV could have an immunosuppressive effect as well as a pathway for dissemination of PRV.