Biology subjects
Publications and source records attributed to Nielsen, H. V..
An unusually divergent Plasmodium vivax parasite was reported in a Swedish patient with recent travel. Using whole-genome sequencing, we show that the infection was caused by a strain of ape P. vivax-like, providing evidence of the zoonotic potential of these parasites that infect wild gorillas and chimpanzees in central Africa.
Although deletion of self-reactive thymocytes and their diversion into regulatory T cell (Treg) lineage are critical for immune tolerance and homeostasis, the molecular pathways that link antigen recognition to these fates are incompletely understood. The Nr4a nuclear hormone receptors are transcriptionally upregulated in response to TCR signaling in the thymus and are implicated in both deletion and diversion, but the mechanisms by which they operate are not clear. Redundancy among the family members and their requirement for Treg generation and maintenance have obscured their role in negative selection. Here we take advantage of competitive bone marrow chimeras and the OT-II/RIPmOVA model to demonstrate that Nr4a1 and Nr4a3 are essential for upregulation of Bcl2l11/BIM and negative selection by tissue-restricted model self-antigen (TRA). Moreover, we reveal that the Nr4a family is absolutely required for full induction of a broad transcriptional program triggered in self-reactive thymocytes by TRA recognition, and conserved across model systems and the natural repertoire. Importantly, both model self antigen-specific TCR Tg and polyclonal thymocytes lacking Nr4a1/3 that escape negative selection acquire an anergy-like program that persists in the periphery and is also evident among wild-type recent thymic emigrants (RTEs). We propose that the Nr4a family transduces TCR signals during thymic development to enforce the fates of highly self-reactive clones, mediating not only deletion and Treg diversion, but also contributing to a cell-intrinsic, persistent anergy-like program that may operate at the margins of canonical thymic tolerance mechanisms to restrain self-reactive T cells after thymic egress.
The NR4A family of orphan nuclear receptors (Nr4a1-3) plays redundant roles upstream of Foxp3 to establish and maintain Treg identity; deletion of multiple family members in the thymus results in Treg deficiency and a severe inflammatory disease. Consequently, it has been challenging to isolate the functions of this family in other immune cells. Here we take advantage of a competitive bone marrow chimera strategy, coupled with conditional genetic tools, to rescue Treg homeostasis and unmask such functions. Unexpectedly, chimeras harboring Nr4a1-/- Nr4a3-/- (DKO) bone marrow develop autoantibodies and a systemic inflammatory disease despite a replete Treg compartment of largely wild-type origin. This disease differs qualitatively from that seen with Treg-deficiency and is B cell-extrinsic. Negative selection of DKO thymocytes is profoundly impaired in a cell-intrinsic manner. Consistent with escape of self-reactive T cells into the periphery, DKO T cells with functional and phenotypic features of anergy accumulate in chimeric mice. Despite this, DKO T cells exhibit enhanced IL-2 production, implying a cell-intrinsic role for the NR4A family in peripheral T cell tolerance. These studies reveal roles for the NR4A family in multiple layered T cell tolerance mechanisms and demonstrate that each is essential to preserve immune homeostasis.