Phd in IINNOVATION IN IMMUNO-MEDIATED AND HEMATOLOGICAL DISORDERS

Thesis title: Checkpoint Mechanisms Underlying ILC2 Activity

Background. Innate lymphocytes are classified into five prototypical subsets, namely NK cells, ILC1, ILC2, ILC3, and (lymphoid tissue inducer) LTi cells, based on the expression of lineage defining transcription factors (LDTF) and their functions. ILC2 are characterized for the expression of the LDTF GATA3 and production of typical type 2 cytokines such as IL-4, IL-5, IL-9, and IL-13. ILC2 are mainly activated by the alarmins IL-25 and IL-33, required for protection against helminthic infection. While the molecular processes underlying ILC2 activation have been highly investigated, how termination of effector responses occurs remains unknown. Purpose. The project aims to dissect checkpoint mechanisms triggered upon ILC2 activation. Results. To investigate the checkpoint mechanisms underlying ILC2 activity, we analyzed the transcriptome of ILC2 isolated from the lung of mice infected with N. brasiliensis. In these settings, ILC2 expressed high levels of Ctla4, as compared to resting ILC2. Induction of Ctla4 transcript occurred along with increased DNA accessibility of the Ctla4 locus. By employing in vitro and vivo models, we evaluated the contribution of distinct cytokines in regulating the expression of CTLA4 protein, including IL-25, IL-33, and TGF-b. Plate-bound B7.1/2 was able to limit ILC2 activation, as evaluated by induction of IL-33R expression. Moreover, blocking CTLA4 antibody was used to evaluate the role of this molecule on ILC2 in vivo. Conclusions. ILC2 express CTLA4 upon activation through a mechanism involving changes of DNA-accessibility and the action of multiple cytokines. Moreover, our data suggest a role for CTLA4 in regulating ILC2 activation, in vivo.