Stroma-dependent development of two dendritic-like cell types with distinct antigen presenting capability

Novel antigen presenting cells (APCs) have been described in the murine spleen. Cells have a distinct CD11c^loCD11b^hiMHC-II^-CD8α^- phenotype as highly endocytic dendritic-like cells that cross-present antigen to CD8⁺ T cells but fail to activate CD4⁺ T cells. These cells are named " L-DCs" because they reflect dendritic cells (DCs) produced in long-term spleen cultures (LTC). Similar cells were produced when bone marrow progenitors were cocultured over the splenic stromal line 5G3. Cocultures continuously produced a majority of L-DCs and a transient population of cells reflecting conventional dendritic cells (cDCs). Both the L-DC and cDC-like subsets cross-present antigen to CD8⁺ T cells, inducing their activation and proliferation. However, as MHC-II^- cells, L-DCs are unable to activate CD4⁺ T cells, while MHC-II⁺ cDC-like cells present antigen for CD4⁺ T cell activation. These results distinguish two APC subsets produced in vitro: a transient population of cDC-like cells and L-DCs that are continuously produced, presumably from self-renewing progenitors. These subsets are not developmentally linked via a precursor or progeny relationship. L-DCs and cDC-like cells are also distinct in terms of cytokine expression, with 65 of 84 tested genes displaying greater than a twofold difference by quantitative reverse-transcriptase polymerase chain reaction. Splenic stroma supports production of two APC subsets reflecting different lineage origins.