FC‐28 Ultrastructural markers expressed in cultured canine dendritic cells and laminated bodies found in Langerhans cells: similarities and differences

Abstract

Ultrastructural markers that consist of coated vesicles, regularly laminated bodies, pleiomorphic inclusions and paracrystalline structures have been described in canine cutaneous histiocytoma (CCH), a cutaneous tumour of Langerhans cell origin. These microstructures are also observed in congenital self‐healing histiocytosis, a human Langerhans cell tumour. We have observed for the first time ultrastructural markers in canine dendritic cells (DC) that share some of the features of the microstructures described in CCH. Canine DC were generated in vitro from adherent peripheral blood mononuclear cells. Morphological analyses and ultrastructural and functional studies showed that these cells display typical DC features. After 1 week of in vitro culture of adherent peripheral blood mononuclear cells in the presence of canine IL‐4 and human GM‐CSF, a great proportion of the cells displayed typical cytoplasmic processes (optical and electronic microscopy) and expressed CD14 and MHC class II molecules (cytometric analysis). In addition, allogeneic mixed lymphocyte reactions were performed to assess the ability of these cells to stimulate the proliferation of allogeneic lymphocytes. Compared to monocytes/macrophages, these cells were able to stimulate allogeneic lymphocyte proliferation very strongly, as is reported for DC in other species. Ultrastructural analysis of these DC revealed the presence of cytoplasmic organites, dense granules of variable sizes containing periodic microstructures. These results were obtained for the three different breeds tested. The microstructures previously described in Langerhans cells (e.g. in CCH) share some similarities with periodic microstructures (membrane, laminated aspect, cytoplasmic localization), but not the typical periodic aspect seen in DC. Funding: National Veterinary School of Nantes.