Mechanisms involved in the binding of thymocytes to rat thymic dendritic cells

An anti-DEC-205 monoclonal antibody stimulates binding of thymocytes to rat thymic dendritic cells and promotes apoptosis of thymocytes

DEC-205, a transmembrane receptor responsible for cross-presentation of apoptotic cell-derived antigens, is expressed by cortical thymic epithelial cells (TEC) and thymic dendritic cells (TDC) in humans and mice, but its function in T-cell development is still unclear. In this work we have studied for the first time the expression of DEC-205 in the rat thymus by HD83 monoclonal antibody (mAb) and immunohistochemistry, as well as the ability of this mAb to modulate thymocyte – TDC interactions in vitro. We showed the positivity of cortical TEC in situ, including thymic nurse cells (TNC) in suspension, and TDC, whereas subcapsular, perivascular and medullary TEC were negative. All examined DEC-205 positive and DEC-205 negative structures were MHC class II positive. HD83 mAb increased apoptosis of thymocytes in co-culture with TDC in vitro and the process was associated with increased binding of thymocytes to TDC in a rosette form. Since negative selection of thymocytes by clonal deletion (apoptosis) was mediated predominantly by TDC, our results suggest the possible indirect effect of the DEC-205 molecule in these mechanisms.

CD34+CD38−lin− Cord Blood Cells Develop into Dendritic Cells in Human Thymic Stromal Monolayers and Thymic Nodules

Thymic dendritic cells (DCs) appear to have distinct biologic and functional properties compared with DCs in other tissues. Currently, little is known about human thymic DCs because they have been difficult to isolate and culture in vitro. Here, we report that human thymic stroma can support the development of primitive human hemopoietic stem cells into mature DCs without cytokine or serum supplementation. Coculture of CD34+CD38−lineage (lin)− and CD34+CD38+lin− umbilical cord blood cells with thymic stromal monolayers induced 43 ± 17-fold and 32 ± 16-fold expansions, respectively, of umbilical cord blood progenitors and also generated large numbers of cells with the morphologic, phenotypic, and functional characteristics of mature DCs. These cells expressed class I and class II MHC, CD1a, CD2, CD4, CD11c, CD40, CD45, CD80, CD83, and CD86 and were potent stimulators of allogeneic T cell activation. Primitive hemopoietic progenitors also developed into mature DCs in a novel tissue culture system of thymic nodules wherein thymic epithelial cells and fibroblasts were grown in nodular aggregates in vitro. These results demonstrate that human thymic stroma efficiently supports the development of CD34+CD38−lin− cord blood cells into mature DCs. In addition, the culture conditions described in this report are useful systems for studying the ontogeny of human DCs in thymic microenvironments.