The Fcγ receptor expression profile on porcine dendritic cells depends on the nature of the stimulus

Research Progress of Dendritic Cell Surface Receptors and Targeting

Dendritic cells are the only antigen-presenting cells capable of activating naive T cells in humans and mammals and are the most effective antigen-presenting cells. With deepening research, it has been found that dendritic cells have many subsets, and the surface receptors of each subset are different. Specific receptors targeting different subsets of DCs will cause different immune responses. At present, DC-targeted research plays an important role in the treatment and prevention of dozens of related diseases in the clinic. This article focuses on the current status of DC surface receptors and targeted applications.

The genomic organization and expression pattern of the low-affinity Fc gamma receptors (FcγR) in the Göttingen minipig

Safety and efficacy of therapeutic antibodies are often dependent on their interaction with Fc receptors for IgG (FcγRs). The Göttingen minipig represents a valuable species for biomedical research but its use in preclinical studies with therapeutic antibodies is hampered by the lack of knowledge about the porcine FcγRs. Genome analysis and sequencing now enabled the localization of the previously described FcγRIIIa in the orthologous location to human FCGR3A. In addition, we identified nearby the gene coding for the hitherto undescribed putative porcine FcγRIIa. The 1′241 bp long FCGR2A cDNA translates to a 274aa transmembrane protein containing an extracellular region with high similarity to human and cattle FcγRIIa. Like in cattle, the intracellular part does not contain an immunoreceptor tyrosine-based activation motif (ITAM) as in human FcγRIIa. Flow cytometry of the whole blood and single-cell RNA sequencing of peripheral blood mononuclear cells (PBMCs) of Göttingen minipigs revealed the expression profile of all porcine FcγRs which is compared to human and mouse. The new FcγRIIa is mainly expressed on platelets making the minipig a good model to study IgG-mediated platelet activation and aggregation. In contrast to humans, minipig blood monocytes were found to express inhibitory FcγRIIb that could lead to the underestimation of FcγR-mediated effects of monocytes observed in minipig studies with therapeutic antibodies.

Effects of arsenic on porcine dendritic cells in vitro

Exposure to arsenic (As) is an ongoing, and in some places increasing, health problem. Still, however, the effects of As exposure on the immune system are not well understood. Dendritic cells (DC) are a critical immune cell that bridges the innate and adaptive immune systems. To determine the impact of inorganic (i)As exposure on DC, the effects of (geo)anthropogenically relevant levels of NaAsO₂ on the function of porcine monocyte-derived DC (MoDC) were evaluated in an in vitro model. The results showed a low dose of iAs reduced the phagocytic capacity of MoDC. Furthermore, although surface expression of DC activation markers, such as major histocompatibility complex (MHC)-II, CD80/86, CD40 and CD25, were only slightly changed, MoDC T-cell proliferation-inducing capacity was remarkably diminished by iAs treatment. Additionally, iAs induced significant interleukin (IL)-6 secretion by MoDC after 12- or 24-h incubation, whereas IL-1β secretion was only significantly up-regulated after 12 h. The secretion patterns of IL-8, tumor necrosis factor α (TNFα and IL-10 by iAs-treated MoDC were almost similar to that by mock-treated MoDC. Considering the broad roles of DC in immunobiology, this finding deepens the understanding of molecular mechanisms/functional consequences underpinning the immunopathology, inflammation, and increases in infection arising from As exposure.

The role of Fc-receptors in the uptake and transport of therapeutic antibodies in the retinal pigment epithelium

In the ophthalmological clinic, intravitreally applied antibodies or Fc-containing fusion proteins are frequently used, but the biology and pharmacokinetics of these therapeutics in the retina are not well understood. We have previously shown intracellular uptake of Fc-containing molecules in RPE cells. In this study, we investigated the involvement of Fc-receptors, both Fcγ-receptors and the neonatal Fc-receptor (FcRn) in the uptake and intracellular trafficking of the VEGF-antagonists bevacizumab, aflibercept and the anti-CD20 antibody rituximab in three different model systems, primary porcine RPE cells, ARPE-19 cells and porcine RPE/choroid explants. The expression of Fcγ-receptors was tested in primary porcine RPE cells, and the expression of Fcγ-receptors I and II could be shown in RT-PCR and qRT-PCR, while the expression of FcRn was additionally confirmed in Western blot and immunocytochemistry. All three compounds, bevacizumab, rituximab and aflibercept, were taken up into the cells and displayed a characteristic time-dependent pattern, as shown in Western blot and immunohistochemistry. The uptake was not altered by the inhibition of Fcγ-receptors using different inhibitors (TruStain FcX, genistein, R406). However, the inhibition of FcRn with an antagonistic antibody reduced intracellular IgG in porcine RPE cells (rituximab) and ARPE-19 cells (bevacizumab, rituximab). Colocalisations between the tested compounds and myosin7a could be found. In addition, limited colocalization with FcRn and the tested compounds, as well as triple localization between compound, FcRn and myosin7a could be detected, indicating a role of myosin7a in FcRn mediated transport. However, the colocalizations are restricted to small fractions of the Fc-containing compounds. Furthermore, the FcRn is mainly found in the membrane section, where only minute amounts of the Fc-containing compounds are seen, suggesting a limited interaction. An apical to choroidal transport of IgG through the RPE/choroid can be found in RPE/choroid explants. Inhibition of FcRn increases the amount of bevacizumab found on the choroidal side, suggesting a role of FcRn in the recycling of bevacizumab. In conclusion, our data indicate a role for FcRn, but not Fcγ-receptors, in the uptake and transport of Fc-containing molecules in the RPE and indicate a recycling function of FcRn in the retina.