Expression of pTα mRNA in a committed dendritic cell precursor in the human thymus

We have characterized dendritic cell precursors (pre-DC) in the human thymus. These CD1a(-)CD3(-)CD4(+)CD8(-) cells express high levels of interleukin-3R alpha (IL-3R alpha) on the membrane and are able to develop into mature DC upon culture with IL-3 and CD40 ligation. The DC precursors are predominantly located in the thymic medulla. Interestingly, the pre-DC express pT alpha mRNA, which is also present in CD1a(+)CD3(-)CD4(+) CD8(-) pre-T cells. Yet, the pre-DC jack expression of recombination activating gene-1 mRNA and fail to develop into T cells in appropriate assays. The thymic pre-DC are very similar to the recently characterized pre-DC found in the T cell areas of the tonsil, and it is suggested that these pre-DC populations are of lymphoid origin. (C) 1999 by The American Society of Hematology.