Porcine neonatal blood dendritic cells, but not monocytes, are more responsive to TLRs stimulation than their adult counterparts.

The neonatal immune system is often considered as immature or impaired compared to the adult immune system. This higher susceptibility to infections is partly due to the skewing of the neonatal immune response towards a Th2 response. Activation and maturation of dendritic cells (DCs) play an important role in shaping the immune response, therefore, DCs are a target of choice for the development of efficient and protective vaccine formulations able to redirect the neonatal immune response to a protective Th1 response. As pigs are becoming more important for vaccine development studies due to their similarity to the human immune system, we decided to compare the activation and maturation of a subpopulation of porcine DCs in adult and neonatal pigs following stimulation with different TLR ligands, which are promising candidates for adjuvants in vaccine formulations. Porcine blood derived DCs (BDCs) were directly isolated from blood and consisted of a mix of conventional and plasmacytoid DCs. Following CpG ODN (TLR9 ligand) and imiquimod (TLR7 ligand) stimulation, neonatal BDCs showed higher levels of expression of costimulatory molecules and similar (CpG ODN) or higher (imiquimod) levels of IL-12 compared to adult BDCs. Another interesting feature was that only neonatal BDCs produced IFN-α after TLR7 or TLR9 ligand stimulation. Stimulation with CpG ODN and imiquimod also induced enhanced expression of several chemokines. Moreover, in a mixed leukocyte reaction assay, neonatal BDCs displayed a greater ability to induce lymphoproliferation. These findings suggest that when stimulated via TLR7 or TLR9 porcine DCs display similar if not better response than adult porcine DCs.

Stability of expression of reference genes in porcine peripheral blood mononuclear and dendritic cells.

Real-time quantitative PCR (RT-qPCR) is a critical tool used to evaluate changes in gene expression. The precision of this tool is reliant upon the selection of reference genes whose expression remains unaltered in culture conditions and following stimulation. Stably expressed reference genes are used to normalize data so observed changes in expression are not due to artifacts but rather reflect physiological changes. In this study, we examined the expression stability of the porcine genes glyceraldehyde 3-phosphate dehydrogenase (GAPDH), succinate dehydrogenase complex subunit A (SDHA), eukaryotic elongation factor 1 gamma-like protein (eEF1), ribosomal protein L19 (RPL19), beta-actin (ACTB) and ATP synthase mitochondrial F0 complex (ATP5G1) in peripheral blood mononuclear cells (PBMCs), monocytes, monocyte-derived dendritic cells (MoDCs), blood isolated dendritic cells (BDCs) and T cells with or without stimulation with lipolysaccharide (LPS). An M value was used as a measure of gene stability as determined using geNORM software. Recommendations for the use of reference genes include using GAPDH and B-actin in PBMCs: RPL19 and SDHA in T cells; RPL19 and B-actin in monocytes; RPL-19 and SDHA in BDCs: and RPL-19 and ATP5GA in MoDCs.

Differential activation and maturation of two porcine DC populations following TLR ligand stimulation.

Dendritic cells (DCs) are at the interface of innate and adaptive immune responses. Once activated via triggering of their pattern recognition receptors (PRRs), they acquire a mature state and migrate to the lymph nodes where they activate T cells and direct the immune response. Compounds that trigger PRRs are potential vaccine adjuvants, hence in this study we stimulated two porcine DC populations, namely monocyte-derived DCs (MoDCs) and blood DCs (BDCs), with a broad range of toll-like receptors (TLRs) ligands and assessed the activation/maturation state of these porcine DCs. In order to determine if TLR ligands would have an effect on porcine DCs, we characterized the expression of TLRs and demonstrated that MoDCs and BDCs expressed the same set of TLRs but at different levels. Of the TLR ligands examined, lipopolysaccharide (LPS) and poly I:C were the most potent activators of MoDCs, inducing the up-regulation of co-stimulatory molecules CD80/86 and the chemokine receptor CCR7, and production of pro-inflammatory cytokines interleukin (IL)-6 and tumor necrosis factor (TNF)alpha. The most effective in inducing BDCs activation were LPS and class A CpG oligodeoxynucleotide (ODN), resulting in up-regulation of chemokine receptor (CCR)7 and down-regulation of CCR2 and CCR5, production of IL-12p40, and expression of a broad range of chemokines that were able to attract porcine immune cells.

A comparison between isolated blood dendritic cells and monocyte-derived dendritic cells in pigs.

Various dendritic cell (DC) populations exist that differ in phenotype and ability to present antigen to T cells. For example, plasmacytoid DCs (pDCs) are less potent T cell activators compared with conventional DCs (cDCs). Here, we compared porcine blood DCs (BDCs), containing pDCs and cDCs, and monocyte-derived DCs (MoDC), consisting of cDCs, in their phenotype, ability to uptake antigen, activation and maturation and their ability to present antigen to autologous T cells. Pigs represent an important animal model, whose immune system in many respects closely resembles that of humans. For example, the distribution of Toll-like receptors is similar to that of humans, in contrast to that of mice. Here we demonstrate that both populations endocytose foreign material. Following lipopolysaccharide stimulation, CD80/86 and chemokine receptor (CCR)7 expression was increased in both populations as was the expression of the chemokine ligands (CCL)-2, CCL-4, CCL-20 and CXCL-2. Although basal and post-stimulation protein concentrations of interleukins 6 and 8 and tumour necrosis factor-alpha were higher in MoDCs, protein concentrations showed a higher fold increase in BDCs. Antigen-specific proliferation of autologous T cells was induced by MoDCs and BDCs. Interestingly, while MoDCs induced stronger proliferation in naive T cells, no difference in proliferation was observed when primed T cells were studied. These results demonstrate that isolated porcine BDCs are highly responsive to stimulation with lipopolysaccharide and are functionally able to drive primed T-cell proliferation to the same extent as MoDCs.