Analogously, Irf8 mutation only affects CD8α+ DCs in spleen, although it is now widely agreed upon that both CD8α+ DCs and CD8α− DCs are mostly derived from the same set of canonical DC precursors 1, 4. The hypothesis put forward by Luche et al. that CD8α+ tDCs develop via a canonical DC developmental pathway is consistent with a recent Maraviroc price fate mapping study of T-cell progenitors assessing the history of Il7r expression 13. In this study, Schlenner et al. showed that the vast majority of

ETPs (∼85%) has a history of Il7r expression, suggesting lymphoid commitment prior to thymus seeding. In contrast, thymic myeloid cells and DCs (except pDCs) were mostly of non-lymphoid origin. In addition, Schlenner et al. demonstrated that even ETPs lacking a history of Il7r expression were unable to generate myeloid cells upon intrathymic transfer. Thus, together with the present study of Luche et al. two independent lines of evidence now indicate that T cells and CD8α+ tDCs are of separate origins. How can these recent data be reconciled selleck screening library with earlier findings suggesting that ETPs (or earlier T-cell precursors) are the primary source of CD8α+ tDCs? Elucidation of lineage potential has been shown to be massively dependent on assay conditions.

In particular, in vitro approaches or transplantation into irradiated hosts do not necessarily reflect developmental processes occurring in the steady state 16, although such analyses are clearly of merit when assessing lineage relationships.

Furthermore, progressive subfractionation of precursor populations has revealed a striking heterogeneity of apparently homogeneous populations 11. Thymic DCs have been proposed to develop in a coordinated fashion with thymocytes, displaying similar kinetics of expansion and contraction 8, 9. Although this may be considered indirect evidence for a common origin, it is also possible that environmental cues, such as periodic opening of progenitor niches, might equally apply to independent precursor populations. In contrast tuclazepam to CD8α+ DCs from spleen, CD8α+ tDCs carry DHJH rearrangements, indicating a lymphoid history for these cells 5. However, DHJH rearrangements in CD8α+ tDCs remain to be analysed on the single-cell level and it may well be possible that only a minor fraction of CD8α+ tDCs display these rearrangements. In this context, one might speculate that DCs with a history of Il7r expression correspond to this fraction. Is a model of CD8α+ tDC generation via two pathways, a major pathway following canonical DC differentiation and a minor pathway originating from T-cell precursors (Fig. 1), compatible with the complete lack of DC potential of ETPs upon intrathymic transfer? On the one hand, developing DCs might branch off from a T-cell precursor that is more immature than ETPs, such as a yet elusive thymus seeding progenitor.