Here is a very elegant story about IL-17-producing γδ T cells (γδ17 cells), from Haas and colleagues in Prinz’s lab.
They undertook very astute and clever approaches and created various original chimeras to demonstrate that there is only a narrowed window of opportunity, which occurs in the fetal thymus, for the development of γδ17 cells. Their generation appears to be TCR independent [once again adding more complexity to the long lasting debate as to the importance of TCR signaling for the emergence of IFNγ- and IL-17-producing γδ cells].
Surprisingly, they show that IL-17 itself may control the development and homeostasis of the γδ17 cells. The idea is that IL-17, which may be produced from αβ thymocytes or innate lymphoid cells (ILC), blocks de novo development of thymic γδ17 cells.
Therefore, this is the first observation that IL-17-secreting γδ cells are produced exclusively in fetal thymus (thus before birth) and that they persist as self-renewing / long lived cells.
–> However, it does not appear too clear to me, whether this first functional embryonic wave contains precursors of, or fully matured self-renewing / long lived, γδ17 cells.
Here is the pubmed link: when IL-17 is detrimental to the generation of IL-17-producing γδ cells!
Of note their study:
-a) gives evidence that commitment to IL-17 production might occur before TCR rearrangement and thereby signaling.
-b) highlights the possibility that CCR6+CD27- γδ T cells in peripheral lymphoid organs may be radioresistant. This is consistent with the existence of a recently identified population of radioresistant IL-17-producing dermal γδ T cells (Sumaria et al., 2011), although the comparison between lymphoid- and skin-derived γδ17 might be slightly far-fetched.