Attenuated cytokine responses in porcine lymph node cells stimulated with CpG DNA are associated with low frequency of IFNα-producing cells and TLR9 mRNA expression

The immune stimulatory effects of synthetic CpG DNA, on porcine peripheral blood mononuclear cells (PBMC) have been reported, but little is known about CpG-induced responses in other lymphoid tissues of pigs. We investigated innate immune responses induced by CpG DNA in cells from blood, lymph nodes (LN) and spleens of pigs. Porcine PBMC and lymph node cells (LNC) were stimulated in vitro with three classes (A-, B- and C-class) of CpG oligodeoxynucleotides (ODNs), and a non-CpG control ODN. All three classes of CpG ODNs induced significant production of IFNα, TNFα, IL-1, IL-6 and IL-12 in PBMC. In contrast, in LNC, only IL-12 was stimulated by all three classes of CpG ODNs, while IFNα, and IL-6 were induced by A- and C-class ODNs. No TNFα was induced in LNC by any of the ODNs. Significant lymphocyte proliferation was induced in PBMC by all three classes of CpG ODNs and non-CpG control. However, in LNC, B- and C-class ODNs induced significant proliferation, while no proliferation was seen with A-class and non-CpG control ODN. All three classes of ODNs induced NK-like cytotoxicity in PBMC and spleen cells, but were less effective in inducing NK cytotoxicity in LNC. We then investigated the reasons for the relatively poor CpG-induced responses in LNC. Our investigations revealed that LNC had a lower frequency of IFNα-secreting cells and expressed low levels of TLR9 mRNA compared to PBMC. We conclude that the lower number of IFNα-secreting cells and receptor expression may contribute to the attenuated responses in LNC following stimulation with CpG ODN.