Abstract

Conventional dendritic cells (cDCs), are the major antigen-presenting cell type that bridges the innate and adaptive immune system. DCs are constantly replenished from myeloid bone marrow progenitors which latest stage, pre-cDC, leave the BM, seeds the peripheral tissues and further differentiates into two functionally and developmentally distinct subsets, cDC1 and cDC2. This study aimed to investigate DC development by assessing the trafficking of pre-cDCs and by analyzing the effect of a specific depletion of DC progenitors. The signals that regulate the recruitment of pre-cDCs to different peripheral organs are poorly understood. Therefore, this study aimed to identify pre-cDCs in different peripheral organs and to find differences in expression pattern of trafficking receptors. In this study 39 trafficking receptors have been identified to be expressed on pre-cDCs of the analysed tissues and showed differences in the expression patterns between peripheral organs. These receptors are interesting candidates to further study differences in the recruitment of pre-cDCs to different peripheral tissues This can provide possibilities to influence the recruitment of pre-cDCs in certain diseases, where the replenishment of cDCs is accelerated. To generate a DC deficient model, DNGR-1/ CLEC9A expressing cells and its progeny were depleted by crossing Clec9a-Cre mice to Rosa-lox-STOP-lox- diphtheria toxin (DTA) mice. Despite cDC progenitors being diminished in these mice, as expected, cells that phenotypically resemble cDC2 arise independent of conventional DC progenitors. As these cells show somatic rearrangements of the Ig-heavy gene locus, typical for lymphoid cells, they were termed lymphoid DC2. A lymphoid origin of DCs has been shown in vitro as well as in adoptive transfer studies, however, the reason for this dual origin and under which physiological settings lymphoid derived DC2 develop and replenish myeloid-derived cDCs is unknown. To test the hypothesis that lymphoid DCs represent a subset of cells with distinct functions that replace myeloid-derived DCs in certain types of diseases, functional analyses were performed. Indeed, less lymphoid DC2 showed TNFα expression after LPS stimulation compared to DC2 from control mice. Furthermore, less lymphoid DC2 showed migration towards CCR7 ligands suggesting a migration defect. Additionally, increased cell death of lymphoid DC2 compared to DC2 from control mice was found in vitro. Increased cell death, on the one hand, provides evidence that lymphoid DC2 behave different from bona fide cDC2, on the other hand it impedes the interpretation of quantitative functional analyses, such as migration assays. Taken together, depletion of myeloid DC progenitors in Clec9aCreRosaDTA mice provides an artificially induced situation in which DC2 like cells can develop in the absence of myeloid DC progenitor. Furthermore, preliminary findings indicate that lymphoid DC2 show functional differences to bona fide cDC2 which argues for the requirement of a redundant developmental pathway to create a situation adapted repertoire of cells.