Constitutive expression of interferons in swine leukocytes.

Interferon (IFN)-alpha and IFN-gamma positive cells were revealed by flow cytometry in peripheral blood mononuclear cells (PBMC) of Specific Pathogen Free (SPF) pigs. A low prevalence of IFN-gamma positive cells was also detected in PBMC of some Porcine Reproductive and Respiratory Syndrome virus-infected pigs and uninfected, control pigs. IFN-alpha positive cells showed phenotypes of both monocytes and plasmacytoid dendritic cells. The presence of IFN-alpha in PBMC was also confirmed by Western blotting. By immunoprecipitation, IFN-alpha was detected as 32 and 55-57 kDa bands in PBMC of healthy SPF piglets. These samples were also IFN-gamma positive; the cytokine was revealed as 24, 37 and 54 kDa bands. The unusual molecular mass values of intracellular interferons were probably due to oligomerization, as previously described for human IFN-alpha. Swine intracellular IFN-alpha displayed the expected antiviral activity on bovine MDBK cells. The results indicate that interferons are constitutively expressed in swine leukocytes with peculiar molecular features. Copyright 2009 Elsevier Ltd. All rights reserved.