Bovine and ovine blood mononuclear leukocytes differ markedly in innate immune responses induced by Class A and Class B CpG-oligodeoxynucleotide

Cytosine-phosphate-guanosine (CpG)-DNA can induce an impressive array of innate immune responses that may directly or indirectly contribute to the clearance of infectious agents. Assays, such as lymphocyte proliferative responses, have been used to demonstrate that the immunostimulatory activity of CpG-DNA is conserved among a broad range of vertebrate species, but no studies have been completed to determine if qualitative differences exist among species for CpG-oligodeoxynucleotide (ODN)-induced innate immune responses. In this study, we assessed the capacity of a Class A (ODN 2216) and a Class B (ODN 2007) CpG-ODN to induce innate immune responses in two closely related species, ovine (n = 28) and bovine (n = 29). The secretion of interferon (IFN)-alpha and IFN-gamma and non-major histocompatability complex (MHC)-restricted cytotoxic activity were assayed with CpG-ODN-stimulated peripheral blood mononuclear cells (PBMC). These investigations revealed significant interspecies and intraspecies variation in the responses. As expected, ODN 2216 was a potent inducer of IFN-alpha secretion by both bovine and ovine PBMC, but ODN 2007 also induced dose-dependent, CpG-specific IFN-alpha secretion by ovine PBMC. In contrast, a significant dose-dependent, CpG-specific IFN-gamma secretion response was only observed following ODN 2216 stimulation of bovine PBMC. Furthermore, both ODN 2216 and ODN 2007 induced CpG-specific non-MHC-restricted cytotoxicity with ovine but not bovine PBMC. Finally, there was not a single assay in which PBMC from all sheep or cattle responded at a detectable level. A striking aspect of these results is that such marked differences in CpG-ODN induced innate responses existed both between and within two closely related species.