HUMAN THYMIC DENDRITIC CELLS

Human thymic dendritic cells (DC) represent a member of the bone marro w-derived dendritic cell family. They have a dendritic shape and are f ound in small numbers mainly at the corticomedullary border and in med ullary regions of the thymus. Human thymic DC: were isolated by densit y gradient separation, followed by treatment with CD2, CD7, CD1, and C D11b mAb and immunobeads magnetic separation. The resulting population contains 60-75% brightly HLA-DR+ cells which present the morphologica l characteristics of DC observed in situ. Extensive phenotypic analysi s confirmed that they are of mesenchymal origin and that some express CD11a and CD54 molecules. Freshly isolated DC do not stain with a wide variety of anti-T-B and -monocyte or -macrophage mAb. However, they a cquire the CD1 molecule after a few days in culture. By using a cell s orter we obtained 90-95% of purified human thymic DC. Functional studi es have shown that human thymic DC are potent activators in mixed lymp hocyte reactions, act as accessory cells in mitogenic thymocyte prolif eration, increase the thymocyte proliferative response to a toxin sign al, and produce IL-1. They also formed spontaneous physical associatio ns with thymocytes, which raises questions about the implication of DC in differentiation and/or maturation processes of thymocytes. (C) 199 7 Wiley-Liss, Inc.