The Lymphoid Past of Mouse Plasmacytoid Cells and Thymic Dendritic Cells

There has been controversy over the possible lymphoid origin of certain dendritic cell (DC) subtypes. To resolve this issue, DC and plasmacytoid pre-DC isolated from normal mouse tissues were analyzed for transient (mRNA) and permanent (DNA rearrangement) markers of early stages of lymphoid development. About 27% of the DNA of CD8(+) DC from thymus, and 22-35% of the DNA of plasmacytoid pre-DC from spleen and thymus, was found to contain IgH gene D-J rearrangements, compared with 40% for T cells. However, the DC DNA did not contain IgH gene V-D-J rearrangements nor T cell Ag receptor beta gene D-J rearrangements. The same DC lineage populations containing IgH D-J rearrangements expressed mRNA for CD3 chains, and for pre-T alpha. In contrast, little of the DNA of the conventional DC derived from spleen, lymph nodes, or skin, whether CD8(+) or CD8(-), contained IgH D-J rearrangements and splenic conventional DC expressed very little CD3 epsilon or pre-T alpha mRNA. Therefore, many plasmacytoid pre-DC and thymic CD8(+) DC have shared early steps of development with the lymphoid lineages, and differ in origin from conventional peripheral DC.