Susan Gilfillan

Mice Lacking Terminal Deoxynucleotidyl Transferase: Adult Mice with a Fetal Antigen Receptor Repertoire

TdT knock-out mice have established the role of this enzyme in vivo: TdT mediates the transition from the relatively limited fetal to the highly diverse adult antigen receptor repertoire by adding template independent N nucleotides and disrupting homology-directed recombination. Lacking this source of diversity, TdT degree mice harbor essentially fetal antigen receptor repertoires. In alpha beta TCRs, the TdT null mutation affects the length and diversity of the CDR3 loops thought to be important in directing MHC/peptide recognition. N- CDR3 loops appear to wield less influence than do their N+ counterparts--positive selection is more efficient in the TdT degree animals and the peripheral repertiore is more polyreactive and less peptide-oriented than is the N+ repertoire. However, this loss of specificity does not markedly diminish the response to specific peptides. Overall, mice harboring essentially fetal repertoires are robust and effectively respond to a wide variety of challenges to the immune system.

SMAD4 impedes the conversion of NK cells into ILC1-like cells by curtailing non-canonical TGF-[beta] signaling

Among the features that distinguish type 1 innate lymphoid cells (ILC1s) from natural killer (NK) cells is a gene signature indicative of imprinting by cytokines of the TGF-β family. We studied mice in which ILC1s and NK cells lacked SMAD4, a signal transducer that facilitates the canonical signaling pathway common to all cytokines of the TGF-β family. While SMAD4 deficiency did not affect ILC1 differentiation, NK cells unexpectedly acquired an ILC1-like gene signature and were unable to control tumor metastasis or viral infection. Mechanistically, SMAD4 restrained non-canonical TGF-β signaling mediated by the cytokine receptor TGFβR1 in NK cells. NK cells from a SMAD4-deficient person affected by polyposis were also hyper-responsive to TGF-β. These results identify SMAD4 as a previously unknown regulator that restricts non-canonical TGF-β signaling in NK cells.

IL-15 sustains IL-7R-independent ILC2 and ILC3 development

The signals that maintain tissue-resident innate lymphoid cells (ILC) in different microenvironments are incompletely understood. Here we show that IL-7 receptor (IL-7R) is not strictly required for the development of any ILC subset, as residual cells persist in the small intestinal lamina propria (siLP) of adult and neonatal Il7ra−/− mice. Il7ra−/− ILC2 primarily express an ST2− phenotype, but are not inflammatory ILC2. CCR6+ ILC3, which express higher Bcl-2 than other ILC3, are the most abundant subset in Il7ra−/− siLP. All ILC subsets are functionally competent in vitro, and are sufficient to provide enhanced protection to infection with C. rodentium. IL-15 equally sustains wild-type and Il7ra−/− ILC survival in vitro and compensates for IL-7R deficiency, as residual ILCs are depleted in mice lacking both molecules. Collectively, these data demonstrate that siLP ILCs are not completely IL-7R dependent, but can persist partially through IL-15 signalling.