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 β gene D-J rearrangements. The same DC lineage populations containing IgH D-J rearrangements expressed mRNA for CD3 chains, and for pre-Tα. 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 CD3ε or pre-Tα 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.

The earliest lymphoid precursor population in the adult mouse thymus had previously been shown to produce not only T cells, but also dendritic cell (DC) progeny on transfer to irradiated recipients. In this study, culture of these isolated thymic precursors with a mixture of cytokines induced them to proliferate and to differentiate to DC, but not to T lineage cells. At least 70% of the individual precursors had the capacity to form DC. The resultant DC were as effective as normal thymic DC in the functional test of T cell stimulation in mixed leukocyte cultures. The cultured DC also expressed high levels of class I and class II major histocompatibility complex, together with CD11c, DEC-205, CD80, and CD86, markers characteristic of mature DC in general. However, they did not express CD8α or BP-1, markers characteristic of normal thymic DC. The optimized mixture of five to seven cytokines required for DC development from these thymic precursors did not include granulocyte/macrophage colony stimulating factor (GM-CSF), usually required for DC development in culture. The addition of anti–GM-CSF antibody or the use of precursors from GM-CSF–deficient mice did not prevent DC development. Addition of GM-CSF was without effect on DC yield when interleukin (IL) 3 and IL-7 were present, although some stimulation by GM-CSF was noted in their absence. In contrast, DC development was enhanced by addition of the Flt3/Flk2 ligand, in line with the effects of the administration of this cytokine in vivo. The results indicate that the development of a particular lineage of DC, probably those of lymphoid precursor origin, may be independent of the myeloid hormone GM-CSF.

The antigen-presenting dendritic cells (DCs) found in mouse lymphoid tissues are heterogeneous. Several types of DCs have been identified on the basis of the expression of different surface molecules, including CD4, CD8␣, and DEC-205. Previous studies by the authors showed that the mouse intrathymic lymphoidrestricted precursors (lin ؊ c-kit ؉ Thy-1 low CD4 low ) can produce DCs in the thymus and spleen upon intravenous transfer, suggesting a lymphoid origin of these DCs. In the current study, the potential for DC production by the newly identified bone marrow (BM) common lymphoid precursors (CLPs), common myeloid precursors (CMPs), and committed granulocyte and macrophage precursors was examined. It was found that both the lymphoid and the myeloid precursors had the potential to produce DCs. All the different DC populations identified in mouse thymus and spleen could be produced by all these precursor populations. However, CLPs produced predominantly the CD4 ؊ CD8␣ ؉ DCs, whereas CMPs produced similar numbers of CD4 ؊ CD8␣ ؉ and CD4 ؉ CD8␣ ؊ DCs, although at different peak times. On a per cell basis, the CLPs were more potent than the CMPs at DC production, but this may have been compensated for by an excess of CMPs over CLPs in BM. Overall, this study shows that the expression of CD8␣ does not delineate the hemopoietic precursor origin of DCs, and the nature of the early precursors may bias but does not dictate the phenotype of the DC product. (Blood. 2001;98:3376-3382)