Influence of IL-12 on interferon-gamma production by bovine leucocyte subsets in response to bovine respiratory syncytial virus.

The cytokine IL-12 is a key molecule in the regulation of CD4+ T cell development and specifically potentiates the development of T helper 1 responses in mouse and man. However the biological effects mediated by bovine IL-12 have not been defined in cattle. To produce the expression of the two mature proteins a polyprotein approach was used. This system is employed by positive strand viruses and encodes both products from a single open reading frame (ORF). The 2A region of foot-and-mouth disease virus (FMDV) encodes a site that appears to undergo auto-cleavage. Here the 2A was flanked by sequences encoding the p35 and p40 polypeptides of the heterodimeric cytokine to mediate their cleavage. Formation of the correct heterodimeric structure is an absolute requirement for IL-12 biologic activity. Using bovine respiratory syncytial virus (BRSV) and ovalbumin (OVA) we studied the effects of IL-12 on the responses of peripheral blood mononuclear cells (PBMC) to these antigens, in vitro. The presence of IL-12 markedly influenced the level of IFNg secreted by these cells, and although IL-12 induced IFNg production in the absence of antigenic stimulation, IFNg production was accelerated and augmented in response to IL-12 and antigen. Analysis of the T cell subsets by flow cytometry showed that CD4+ T cells comprised the largest contributors to IFNg production. The WC1 + gd T cells did not appear to contribute to the production of IFNg.