Selective antigen targeting to FcgR enhances the funtional maturation of porcine dendritic cells

Dendritic cells represent the most potent antigen presenting cells and are of pivotal importance for the initiation of adaptive immune responses to combat infections, such as enterotoxigenic Escherichia coli (ETEC). In pigs, F4+ ETEC infections are an important cause of post-weaning diarrhoea in piglets. These pathogens adhere with their F4 fimbriae to specific receptors on the intestinal epithelium. We have previously demonstrated that the oral immunisation of piglets with purified F4 fimbriae protects them from a subsequent F4+ ETEC infection. However, oral immunisation of suckling piglets is hampered due to the immature status of their immune system. Targeting of antigens to Fcγ receptors (FcγR) on human and murine dendritic cells (DC) has been shown to enhance DC maturation and both humoral and cellular immune responses. To investigate if porcine DC react to FcγR targeting in a similar manner as their human and murine counterparts, we used our F4 model antigen to target FcγR on porcine monocyte-derived DC (MoDC). We demonstrated that FcγRII and III are expressed on the cell surface and that F4-IgG immune complexes (F4-IC) are internalised by MoDC in an FcγR-dependent manner. This FcγR ligation induced a significantly enhanced expression of DC maturation markers (MHCII, CD80/86 and CD40) by MoDC. Besides this phenotypical DC maturation, the phagocytic capacity of F4-IC stimulated MoDC was reduced as evidenced by a reduced uptake of DQ-ovalbumin and FITC-dextran. Moreover, F4-IC matured MoDC showed an improved allogenic T cell stimulatory capacity, providing additional evidence that FcγR engagement by F4-IC induces a functional DC maturation. In an autologous MLR, the interaction of F4-IC with FcγR significantly augmented the efficiency of antigen presentation to lymphocytes in comparison with F4 fimbriae primed DC. The F4-IC induced DC maturation further correlated with significant higher expression levels of several proinflammatory cytokines (IL-1β, IL-6 and TNFα), the chemokine IL-8 and IL-12p40. In summary, FcγR targeting to porcine MoDC significantly enhances the Ag internalisation, DC maturation and Ag presentation to T cells, which corroborates previous experiments with both human and murine DC. Moreover, the results suggest that F4-IC could offer a promising candidate for oral vaccine formulations for the mucosal immunisation of suckling piglets. Indeed, previous studies have demonstrated that IC are transcytosed across the epithelial barrier via the neonatal Fc receptor, FcRn, which is also expressed by porcine enterocytes. In addition, porcine small intestinal DC express FcγRIII, implying that FcγR-targeted Ag delivery to porcine intestinal DC could be used in oral vaccination. However, in vivo studies are required to address if F4-IC transcytosis occurs in porcine enterocytes and if intestinal DC respond to FcγR targeting in a similar manner