Keratinocytes affect biology of Langerhans cells through mRNA transfer

Abstract

Abstract Dendritic cell (DC) subsets might acquire specific immune functions based on their tissue of residence. Langerhans cells (LCs), a specific DC population located in the epidermis, are in close contact with epidermal keratinocytes (KCs), providing us with an easily accessible model to dissect the effect of epithelial cells on infiltrating DCs. Using microarray analysis, RT-qPCR, histology and flow cytometry, we showed that many of the KC-specific molecules, such as keratins and adhesion molecules, can be detected in LCs at mRNA and protein levels. To determine whether these KC-specific genes are accessible for transcription in LCs, we performed ATAC-seq on flow-purified LCs. We found that chromatin loci of these genes were in the closed conformation in LCs. Therefore, these data support the active transport of mRNAs from the KCs to LCs. Furthermore, we also showed that KC-specific expression of Cre, driven by the KRT14 promoter, can lead to genetic recombination and expression of YFP in the LCs. Additionally, YFP+ LCs could be readily identified in LC-depleted KRT14-YFP mice reconstituted with WT bone marrow, which further supports the material transfer from KCs to LCs. Of note, we found that tunneling nanotubes could be one of the potential mechanisms mediating the material transfer. The transfer of material between epithelial cells and epithelia-associated DCs was not limited to mice or to KC-to-LC transfer. Taken together, these data suggest that the epithelial environment might have a long-term effect on DC biology and that genetic tools specifically targeting epithelial cells also affect tissue-resident immune cells, which adds another layer of complexity to data interpretation.