Role of cytokines in regulation of porcine immune response

Questions remain about the roles of cytokine and dendritic cells (DCs) in the regulation of porcine immune responses. Biologically active recombinant porcine (rp)TNF-α, IL-6, IFN-γ and IL-10 were cloned and expressed in a baculovirus expression system. Pig monocyte-derived DCs (mDCs) were generated from blood by culturing with rpGM-CSF and IL-4 for 7 days. To evaluate variables influencing in vitro immune response induction, PAMPs, candidate antigens (Ags) and cytokines were used to treat monocytes and/or mDCs. Treatments with PAMPs were compared for effects on TLR, MHC II, B7 and/or cytokine expression while treatments with cytokines and/or Ag were compared for effects on mDC Ag presentation to autologous T-cell-enriched lymphocytes, induction of MLR and cytokine mRNA expression by the mDCs or in-contact T-cells. MHC II and/or B-7 were expressed on the surface of mDCs with some animals having high and others low expression. Treatment of mDCs with LPS, lipotechoic acid (LTA), poly IC, CpG or peptidoglycan (Pep) enhanced MHC II and B7 expression. The mRNA for IL-4 was not observed after any of the treatments. Monocytes and mDCs treated with LPS or LTA up-regulated expression of mRNA for Th-1 and Th-2-inducing cytokines. Treatment of monocytes and mDCs with poly IC or CpG tended to up-regulate mRNA for TLR 9 and Th-1-inducing cytokines. Interleukin-6, IFN-γ and TNF-α-treated mDCs induced proliferation of autologous lymphocytes and all the cytokines tested increased MLR. Interferon-γ, TNF-α, IL-6 or IL-12 tended to increase proliferation of autologous T-cell-enriched lymphocytes cultured with mDCs previously treated with killed Mycobacterium tuberculosis (Mtb) or cell wall extract of M. phlei (MCW). Interleukin-10, IFN-γ, TNF-α, or IL-6 increased proliferation of autologous T-cell-enriched lymphocytes cultured with HEWL-treated mDCs. Treatment of mDCs with HEWL increased IL-13 but not IL-12, IFN-γ or IL-10 mRNA, a DC2 phenotype which biased in-contact T-cells towards Th-2. Addition of TNF-α, IFN-γ or IL-12 to HEWL-treated mDCs increased IL-12p35, reduced IL-13 mRNA and biased mDCs towards the DC1/Th-1-inducing phenotype. Treatment of mDCs with Mtb resulted in a DC1/Th-1-inducing bias which was enhanced by the addition of TNF-α, IFN-γ or IL-12. This Th-1 bias was confirmed in in-contact T-cells. Addition of IL-10 to Mtb-treated mDCs diverted cytokine response from DC1 towards a DC2/Th-2-inducing phenotype. Results suggest that porcine mDCs and to a lesser extent monocytes, discriminate between different microorganisms via TLRs which may in turn determine cytokine expression and immune response bias. The results also provide evidence of DC1/DC2 and Th-1/Th-2-type response bias in pig cells. Cytokine environment at the time of mDC-Ag interaction alters downstream cytokine profiles of mDCs and T-cells responding to Ag-treated mDCs and cytokines may allow designed steering of porcine immune response.